».H I II,!,!,■•!:.,It <::lF :i .* 1 Ml' f Li! ^M •, / ; sii ik* if!! II 'H^' ?*,. Tir,*'', t ROOT' ci ?, ^Q-c-Qe^go ^agQCQc^agQGCQ'Q'Gcg^ Surgeon General's Office . ju ± m M A ae£ m ft «? &HNEX PRESENTED BY (J [! ■^ B 2TjC,'0 OTju^DOOClfO C'j Dt)Qt) l■ j ^'/'J lJ'uu/iauC'O'u> t; 1 i I £/ as ^ ^4v c px. s t,K K/t-i ^ '{'* If 2- t/ W X/ +<- f(i ^f MORFIT'S CHEMICAL AND PHARMACEUTICAL MANIPULATIONS, WITH FOUR HUNDRED AND TWENTY-THREE ILLUSTRATIONS. LINDSAY & BLAKISTON, PHILADELPHIA, PUBLISH A MANUAL OF THE MECHANICAL AND CHEMICO-MECHANICAL OPERATIONS OF THE LABORATORY! CONTAINING A COMPLETE DESCRIPTION OF THE MOST APPROVED APPARATUS, WITH INSTRUC- TIONS AS TO THEIR APPLICATION AND MANAGEMENT, BOTH IN THE MANUFAC- TURING PROCESS AND IN THE MORE EXACT DETAILS OF ANALYSIS AND ACCURATE RESEARCH J BY CAMPBELL MORFIT, Practical and Analytical Chemist, author of "Applied Chemistry," tic. ic., ASSISTED BY ALEXANDER MUCKLE, Chemical Assistant in Professor Booth's Laboratory. IN ONE VOLUME, OCTAVO. Publisher s Advertisement.—This work, entirely new in its matter and arrangements, is designed for the thorough instruction of chemical and pharmaceutical students in every branch of their respective arts, from the veriest rudiments to the most delicate manipu- lations. The author gives, in a familiar but clear style, the details of all the manipulations of the laboratory, including the improvements of the present day, and illustrates his descriptions with numerous beautifully-executed and expressive wood-cuts, or drawings. No expense has been spared in endeavouring to make this book the substitute for all others on the same subject. Extract of a Letter from Prof. J. C. Booth, Practical and Analytic Chemist. " I regard it as a very valuable addition to a Chemical Library, whether to that of an experimental or manufacturing chemist, for while the business of the former is wholly experimental research, the latter is frequently forced to enter into the same field in order to improve his processes. Although I have been a witness of the author's untiring industry in preparing this work, yet, upon examining it in its present state am surprised to find it so complete in all its parts. I know that there is a large amount of original matter contained in it, the result of the author's observation and experience; and that which has been derived from other sources, has been judiciously and harmoniously culled from a very extensive Chemical Library I therefore think that every one connected with chemistry, in any of its numerous depart- ments, should have a copy of this work in his library. I intend using it freely in my course of instruction in Experimental Chemistry, and shall recommend it to my students." •' Mr Morfit's reputation as a scientific chemist has been established here by his association with Pro- fessor Booth in the authorship of the ' Encyclopaedia of Chemistry,'-and his practical ability was before well known from his work on ' Soap and Candles.' To such a work as the above, therefore, he brings those qualifications which alone can render it valuable. No man without both theoretical and practical knowledge and especially the latter, can properly teach the economy of a laboratory. He must himself have encountered and overcome difficulties. This the author has done; and the student of chemistry, whether apothecary, manufacturer, or the amateur, will find his labours and comprehension very much assisted by such a manual. The characteristic of Mr. Morfit's public labours is practical common sense; and too much value can hardly be set on what so thoroughly obviates the mysteries and technicalities of chemical text-books."—Saturday Evening Post. " We are always gratified bv the issue of practical works from the press, as they tend to advance the art, of civilized life, and with them, the people who are engaged in them. It is, however, comparatively are that we meet with an original work of this character issuing from the American press; and. there- fnre we hail the appearance of the present one with peculiar pleasure. It is a book of nearly five nun- dred Da«es illustrated with four hundred and twenty-three wood-cuts, and while its typography does dit to the publishers, we find that the manner in which the author has treated the subject is no less H^ervine of praise It handles the subject of manipulations in experimental and manufacturing hemistrv in a very elaborate and yet clear and perspicuous manner, giving a large amount of original matter showing that the author must have had considerable practical experience in the subjects of which he treats We feel confident that it will be extensively used as a guide by those who are entering upon "hemical'study or practice, and will be frequently resorted to by the more experienced practical chemist." —The Ledger. SPECIMEN OF THE ENGRAVINGS IN MORFIT'S CHEMICAL MANIPULATIONS. Fig. 214. CHEMICAL ANALYSIS, ClUALITATIVE AND QUANTITATIVE. / HENRY M g$fi:i?!F&*~ fTJRER ON* CHE-vnSTSTTE'rOT.^KOSGE'S HOSPITAL; AUTHOR OF "LECTURES ON ELECTRICITY," "LECTURES ON CHEMISTRY," ETC. ETC. WITH NUMEROUS ADDITIONS. iA BY CAMPBELL MORFIT WITH ILLUSTRATIONS. rfSWT7F/^s PHILADELPHIA: LINDSAY AND BLAKISTON. 1849. Entered according to the Act of Congress, in the year 1849, by LINDSAY AND BLAKISTON, in the Clerk's Office of the District Court for the Eastern District of Pennsylvania. % PHILADELPHIA : T. K. AND P. G. COLLINS, PRINTERS. PREFACE. The present work was prepared by the Author as one of a series of Chemical treatises for the " London Library of Use- ful Knowledge." The care and fidelity with which he per- formed his laborious task, left little more to be done by the Editor than to make such additions as are called for by the latest investigations in Chemical Analysis. These have been supplied, and the work is now presented as a complete manual both of Qualitative and Quantitative Analysis, in organic and inorganic chemistry, in all their details. In the original work there are some pages upon Chemical Manipulation, but as this subject, in order to be serviceable to the student, should have been more extensively elucidated, the Editor has taken the liberty of substituting other matter, and has preferred referring the reader, for such information, to uMorfit's Chemical and Pharmaceutical Manipulations." CONTENTS. INTRODUCTION, PAGE Explanatory of the important Doctrine of Equivalent Propor- tions ; of Chemical Notation and the Construction and Use of Formulae; and of the General Principles of Chemical Nomenclature . . . . . . .17 PART I.—QUALITATIVE. CHAPTER I. General Remarks on Chemical Analysis . . .35 CHAPTER II. On Reagents . . . . . . .37 CHAPTER III. On the Comportment of Substances with Reagents . . 56 1. Metallic Oxides. Group 1. Potassa, Soda, Lithia, Ammonia . . 57 —:— 2. Baryta, Strontia, Lime, Magnesia . . 60 —■— 3. Alumina, Yttria, Glucina, Thorina, Zirconia, Oxide, of Chromium, Oxides of Cerium, Ti- tanic Acid, Tantalic Acid . . .65 —— 4. Zinc, Nickel, Cobalt, Manganese, Iron, Ura- nium . . . . .72 -----5. Lead, Silver, Mercury, Bismuth, Cadmium, Copper, Palladium, Rhodium, Osmium . 82 —— 6. Antimony, Arsenic, Tin, Platinum, Iridium, Gold, Selenium, Tellurium, Tungsten, Vana- dium, Molybdenum . . . .94 2. Acids.—Inorganic. Carbonic Sulphur Selenic Phosphorus Boracic . 121 123, 143 . 126 . 127 . 128 vi CONTENTS. Acids.—Inorganic. Silicic Hydrofluoric Chromic Chlorine Bromine Iodine Cyanogen Nitrogen Chloric Organic. Oxalic Tartaric Racemic Citric Malic Succinic Benzoic Tannic Gallic Acetic Formic Uric Meconic CHAPTER IV On Systematic Qualitative Analysis 1. Examination for Bases—Principles on which the method depends 2. Examination for Acids Examples for Illustration Qualitative Analysis of Natural Silicates -------------------Mineral Waters Qualitative Detection of Poisons The Poisonous Acids 1. Sulphuric Acid 2. Nitric Acid 3. Hydrochloric Acid 4. Oxalic Acid 5. Hydrocyanic Acid The Poisonous Metals : 6. Arsenic 7. Mercury 8. Copper 9. Lead 10. Antimony 11. Zinc . 130 . 131 . 133 . 134 135, 139 137, 139 140 144 147 CONTENTS. vii PAGE TABLES. 1. Course of Analysis for the Detection of Bases. 2. ----------------------------of Bases—continued. 3. -----------------------------of Inorganic Acids. 4. ----------------------------of Organic Acids. PART II.—QUANTITATIVE. CHAPTER I. Ox the Quantitative Estimation of Substances, and their Separation from each other . . . ' . 233 Group 1. Metals of the Alkalies proper . . . 235 ----2. ----------Alkaline Earths . . .253 ----3. Aluminum, Glucinum, Yttrium, Thorium, Zirco- nium, Chromium .... 259 ----4. Zinc, Nickel, Cobalt, Manganese, Iron, Uranium 267 ----5. Lead, Silver, Mercury, Bismuth, Cadmium, Cop- per, Palladium, Rhodium, Osmium, Ruthenium 302 ----6. Antimony, Arsenic, Tin, Platinum, Iridium, Gold, Selenium, Tellurium, Tungsten, Vanadium, Mo- lybdeum.....342 Acids : Acids of Sulphur ------ Phosphorus Boracic Acid Silicic Acid Carbonic Acid Oxalic Acid Hydrofluoric Acid Hydrochloric Acid Hydrobromic Acid Hydriodic Acid Hydrocyanic Acid Nitric Acid Chloric Acid CHAPTER II. On the Elementary Analysis of Organic Bodies CHAPTER III. On the Quantitative Analysis of Mineral Waters CHAPTER IV. Ox the Analysis of Soils .... . 380 . 388 . 390 . 398 . 407 . 408 . 411 . 421 . 423 . 425 . 427 . 437 . 438 . 475 . 490 vin CONTENTS. page CHAPTER V. On the Analysis of Compounds containing the Oxides of Iron and Manganese, Alumina and Alkaline Earths, in Combina- tion with Phosphoric, Arsenic and Silicic Acids . . 510 CHAPTER VI. On the Analysis of Ashes of Plants .... 519 CHAPTER VII. On the Analysis of Urine and Urinary Calculi . . 537 TABLES. 1. For the Conversion of Degrees on the Centigrade Thermo- meter into Degrees of Fahrenheit's Scale . . 553 2. Degrees of Tension of Aqueous Vapor for different Tem- peratures ....... 554 3. Quantity of Oil of Vitriol of Specific Gravity 1.8485, and of Anhydrous Acid, in 100 parts of dilute Sulphuric Acid of different Densities ..... 555 4. Quantity of Real or Anhydrous Nitric Acid in 100 parts of Liquid Acid at different Densities . . . 556 5. Quantity of absolute Alcohol in Spirits of different Specific Gravities ....... 557 6. Quantity of absolute Alcohol by weight in Mixtures of Al- cohol and Water of different Specific Gravities . . 558 7. Tables for Calculations in Analysis . . . 561 APPENDIX. New Applications of Sulphuretted Hydrogen in Chemical Ana- lysis . . • . . . . .569 INTRODUCTION EXPLANATORY or the important doctrine of equivalent proportions ; Of Chemical Notation and the Construction and Use of Formulae; and Of the general Principles of Chemical Nomenclature. In the course of this Work will be found a Table contain- ing the names of all those substances which are at present regarded by Chemists as Elementary. There are sixty-three of these bodies, all of which have resisted every effort to resolve them into simpler forms of matter. Among them are found bodies of the most diverse characters, both physical and chemical; and out of them, as far as we yet know, everything solid, liquid, and gaseous, in and about the globe which we inhabit, is composed. The names of these sixty-three substances have not been assigned to them in accordance with any prescribed rule, the discoverer of each particular body following his own fancy in this respect, and being generally guided in his selection either by some marked peculiarity in the new substance, or by some circumstance connected with its discovery. Thus Mosander, having found in oxide of cerium a large proportion of the oxide of a hitherto unnoticed metal, named the newly discov- ered body Lantanium or Lanthanum, from the Greek word jLarflarw, I lurk, it having lain concealed in the ores of cerium; and the name osmium was given to a peculiar metal found in the ores of platinum, from oa/xyj, smell, having reference to the disagreeable and pungent character of its vapor. 9 18 the theory of equivalent proportions. The names selected by their discoverers for some substances are indeed sufficiently eccentric; thus Berzelius derived the title of Selenium, which he conferred on a certain brittle opaque solid discovered by him in the sulphur of Fahlun, from Ss^t^, the Moon, in consequence of his having at first mistaken it for Tellurium, which derived its name from tellus, the Earth. But, whatever may be thought of the propriety of such names, they can lead neither to mistakes nor to confusion, and are in this respect far better than words more significantly chosen, and bearing reference to certain characteristic properties pos- sessed, or supposed to be possessed by the substance. This method has rarely been successful: thus the name oxygen, proposed by Lavoisier for the Dephlogisticated air of Priestley, though at the time well chosen, has not stood the test of time. In Lavoisier s day this substance was supposed to be the sole cause of acidity, hence its name, from 6%v$, acid, and yewasiv. to generate; we now know, however, that this property of generating acidity is not peculiar solely to oxygen. Again, the same celebrated French Chemist proposed the name azote for that gas first noticed by Rutherford, and which we now call nitrogen—the word "azote" is derived from a, privative, and ?«oj}, life, and was suggested by the inability of the gas to support respiration; the term, however, was very unfortunate, there being several other gases in the same predicament, and equally fatal to animal life. The name azote is now abolished, that of oxygen is still retained, not because a better might not probably be found, but because it is inexpedient to mal^ any change whatever in an old-established nomenclature, without cogent and well-considered reasons. These sixty-three elementary substances have been differ- ently classified by different chemists; some divide them into two great classes, viz: Electro-positive, including all those bodies which, by their union with oxygen, form compounds the electro-chemical relations of which are decidedly positive: and Electro-negative, including those bodies which, by their union with oxygen, form compounds, the electrical characters of which are either decidedly not positive, or which may be regarded either as positive or negative. Other chemists arrange the elements into certain small groups or natural families, the members of each group being connected together by certain analogies, and the several groups shading into each other through the medium of certain links, like the classes THE THEORY OF EQUIVALENT PROPORTIONS. 19 created by the naturalist for the objects of the organic world: for a full exposition of this system of classification the reader may consult Mr. G-rahams "Elements of Chemistry." Ano- ther division, sometimes adopted, is that into combustibles and supporters of combustion; but the most convenient is that founded on the physical properties of the elements in a free state—the division into metalloids and metals; the former comprising oxygen, hydrogen, nitrogen, chlorine, bromine, iodine, fluorine, sulphur, selenium, tellurium, phosphorus, arsenic, carbon, boron, and silicon, are, without exception, electro-negative; the metals, on the other hand, are nearly all electro-positive; those that are not so ought, according to Ber- zelius, to be ranked among the metalloids. In the table above referred to there will be seen, opposite to each element, certain letters and figures; these constitute its symbol and its chemical equivalent: the former is a very convenient method of representing a substance, and the con- stitution of the compound into which it enters; it is formed from the first letter or letters of the Latin name of the body; thus the metal Tin is written Sn, an abbreviation of the Latin word Stannum; Mercury, Hg, from the Latin Hydrargyrum ; Antimony, Sb, from Stibium. When there is only one ele- mentary substance with the same initial letter, that letter usually serves as its symbol, thus F suffices for Fluorine, and .fffor Hydrogen; but where there are several elements, the name of each of which commences with the same letter, then other letters are added to the initial letter in order to keep each substance distinct; thus there are no less than eight sub- stances commencing with the letter C, viz: Carbon, Cadmium, Chlorine, Cerium, Chromium, Cobalt, Copper, and Calcium, the respective symbols for which are C, Cd, CI, Ce, Cr, Co, Cu (Cuprum), and Ca. The meaning of the term "equivalent," as applied to the numbers in the third and fourth columns of the Table, may be illustrated by the following:—Common culinary salt, wher- ever or however procured, whether by evaporation from the waters of the ocean or excavated from the mines of Salzburg, or formed artificially in the laboratory by pouring hydrochlo- ric acid on carbonate of soda, has always the same composi- tion viz: 35.5 parts of chlorine and 22.97 parts of the metal sodium; and a substance not having this precise composition, however similar it may be to common salt in other respects, 20 THE THEORY OF EQUIVALENT PROPORTIONS. is not that substance, but some other. Now, if we pour not less than 49 parts of the strongest oil of vitriol over 58.47 parts of common salt, and heat the mixture till all action has ceased, we shall obtain as the result of the decomposition, 70.97 parts of sulphate of soda or Glauber salts, and 36.5 parts of hydrochloric acid; and, if we analyze this sulphate of soda and this hydrochloric acid, we shall find that the former is composed of 30.97 parts of soda and 40 parts of sulphuric acid, and the latter of 35.5 parts of chlorine and 1 of hydro- gen ; lastly, if we compare the composition of the sulphate of soda as thus obtained with that formed by pouring sulphuric acid on carbonate of soda, we shall find that they have both precisely the same composition; and, if we explode in a strong glass vessel a mixture of hydrogen and chlorine, we shall ob- tain a highly acid gas, the composition of which is 35.5 parts of chlorine and 1 of hydrogen, the same with that of the acid obtained by the decomposition of common salt by oil of vitriol. If we look a little more closely at the facts of this decom- position, we shall get a clear idea of what is meant by the term "equivalent." We have seen that 58.47 parts of common salt, when treated with 49 parts of oil of vitriol, yield 70.97 parts of sulphate of soda, a perfectly neutral substance, containing 40 parts of sulphuric acid, but not a trace of chlorine; it is easy, therefore, to understand that in this reaction 40 parts of sulphuric acid must have removed 35.5 parts of chlorine, and the term equivalents, as applied to these two numbers, cannot be misunderstood: 40 parts of sulphuric acid are equi- valent to 35.5 parts of chlorine, and whenever chlorine re- places sulphuric acid, or sulphuric acid chlorine, in a com- pound, it is always in proportions indicated by these numbers. Again, the oil of vitriol which we have employed in effecting the above decomposition of common salt contained a certain quantity of water; none of this compound is, however, found in dry sulphate of soda. What, then, has become of it? The sulphate of soda, though it contains no water, contains an ele- ment which is not found in common salt, viz: oxygen; and the acid gas which is evolved during the decomposition contains also an element which is not found in common salt, viz: hy- drogen; but these two substances, when chemically combined constitute water, and the analysis of this fluid shows its com- position to be 8 parts by weight of oxygen to 1 part by weight of hydrogen; but these are the very proportions in which the THE THEORY OF EQUIVALENT PROPORTIONS. 21 former is found in the sulphate of soda combined with the 22.97 parts of sodium, and the latter in the hydrochloric acid gas combined with the 35.5 of chlorine. What do we deduce from these facts? Obviously this:—that, as 8 parts of oxygen are equally required by 22.97 parts of sodium, and by 1 part of hydrogen, 22.97 parts of sodium must be equivalent to 1 part of hydrogen; and, whenever sodium replaces hydrogen, or hydrogen sodium, the change must be effected in accordance with these proportions. Similarly as 22.97 parts of sodium and 1 part of hydrogen are equally saturated by 35.5 parts of chlorine, so 35.5 must be the proportion in which chlorine replaces 22.97 of sodium and 1 of hydrogen; in other words, 35.5 must be the "equivalent" of chlorine, and, on the same principles, 8 must be the "combining equivalent" of oxygen, that being the proportion in which it equally satisfies 22.97 of sodium and 1 of hydrogen; and whenever, in any compound, oxygen replaces hydrogen, it must do so in the proportion of 8 to 1: when chlorine, in the proportion of 8 to 35.5; and when sodium, in the proportion of 8 to 22.97. This reaction between common salt and oil of vitriol may, perhaps, be more clearly shown by means of the following dia- gram. Hydrochloric Acid 36.5 Common Salt or Chloride of Sodium 58.47 Sulphate of Soda 70.97 The two compounds which react on each other are placed outside the two side brackets—their composition is shown in- side the same; the products of the decomposition are placed at the top and bottom of the diagram, and the nature of the reaction is shown by the lines between the four brackets, con- necting together the different constituents of the new com- pounds. On referring to the Table of Elements, the figures in the third column, opposite chlorine, sodium, hydrogen and Chlorine 35.5___ I Sodium 22.97- ( Hydrogen ^) j Oxygen ( Sulphuric Acid Water 9 .40 Oil of Vitriol or Hydrate of Sulphuric Acid 49 22 THE THEORY OF EQUIVALENT PROPORTIONS. oxygen, will be found the same with those attached to these elements in the diagram: in this list, sulphuric acid, being a compound body, will not be found. The composition of this important acid has, however, been correctly ascertained; it is known to be composed of 16 parts, by weight, of sulphur, and 24 of oxygen; but opposite the element sulphur we find the number 16 as its equivalent, and from this we easily deduce the equivalent of sulphuric acid, thus: 16 + 24 (8 X 3) = 40. But why these particular numbers in preference to any other? Why select 22.97 as the equivalent for sodium, and 35.5 as that for chlorine ? It will be evident, on a little reflection, that any other set of numbers will do equally well, provided they bear to each other the same proportion as 22.97 does to 35.5. The real experimental import of the equivalent num- bers is the expression of the proportional and relative weights of bodies, in which they produce analogous effects in chemical combinations, and the selection of these numbers is, therefore, a matter of indifference, provided they all bear to each other the true relations. The numbers selected in the above illus- tration are those which are now pretty generally adopted by chemists in all parts of Europe. The principle on which they are constructed assumes as its starting point the composition of ivater. This fluid is found on analysis to be composed of 8 parts, by weight, of oxygen, and 1 part, by weight, of hydrogen; hence 8 is employed to express the equivalent of oxygen, and 1 that of hydrogen. The other system of numbers, forming the fourth column of the Table referred to, and which, till lately, seems to have had the preference at least in Germany and France, was con- structed on the assumption of 100 as the equivalent of oxygen. The numbers in this series are obtained by multiplying those in the former by 12|, which gives us 12.5 for hydrogen and 100 for oxygen, and the equivalent proportions of all the other substances represent the quantities of those substances which combine with 100 parts of oxygen to form a protoxide; thus 395.70 parts of copper, 350 parts of iron, 406.59 parts of zinc, and 735.29 parts of tin, each combine with 100 parts of oxygen to form the first stage of oxygenation of those metals: hence these numbers are taken as their respective equivalents, and dividing each by 12h we obtain the numbers 31.66, 28, 32.52, and 58.52, which represent the equivalents of copper, iron, zinc, and tin, on that scale which assumes hydrogen as THE THEORY OF EQUIVALENT PROPORTIONS. 23 unity. There can be no doubt as to which series of numbers deserves the preference on the ground of convenience, par- ticularly since the progress of discovery is continually adding to the list of those elements, the equivalents of which, being exact multiples of that of hydrogen, may be expressed by whole numbers, and thus far more readily retained in the memory than numbers with the appendages of fractions, or than those longer ones found in the list on the oxygen scale. Every elementary substance is thus provided with its che- mical equivalent—with a number indicating the proportion in which it enters into combination with the equivalent of any other substance with which it is capable of combining, and in which it replaces the equivalent of every other substance in cases of decomposition. Do we wish to know, for example, how much iron is required to decompose thoroughly a certain quantity of cinnabar or sulphuret of mercury? We simply refer to the Table of Equivalents, where we find opposite the metals mercury and iron the numbers 100.07 and 28. Now cinnabar is known to be a compound of 100.07 of mercury and 16 of sulphur; it is known also that iron is capable of forming a definite compound with sulphur, and the law of equivalents teaches us, that as 28 and 100.07 are respectively the equivalents of iron and mercury, so the same quantity of sulphur that will satisfy 28 parts of the first will likewise satisfy 100.07 parts of the last, and that, therefore, to remove the whole of the sulphur from 116.07 (100.07 + 16) parts of cinnabar, we require at least 28 parts of iron, the reaction by which the decomposition is brought about being simply a sub- stitution of 28 of iron for 100.07 of mercury: thus— Mercury 100.07 Mercury 100.07 Sulphuret of Mercury ■{ 116.07 I Sulphur---------------------Iron L 16 28 Iron 28 Sulphuret of Iron 44 and this is not only true with regard to the compounds of these two metals with sulphur, for it has been fully proved that the* 24 THE THEORY OF EQUIVALENT PROPORTIONS. same quantity of any substance whatever, which combines with 100.07 of mercury, will also combine with exactly 28 of iron, provided this latter metal be capable of entering into chemical combination with that substance. To give another example. If a rod of zinc be suspended in a clear solution of acetate of lead, the latter metal will be deposited on the zinc in a beautiful arborescent form. Now if this lead deposit be collected and weighed, and if, also, the loss sustained by the rod of zinc be carefully determined, it will be found that, for every 103.56 grains of metallic lead precipitated, there are 32.52 grains of zinc dissolved; these 32.52 grains of zinc may be obtained from the solution in the state of oxide, combined with 8 grains of oxygen; but it is known, also, that 103.56 grains of lead combine with 8 of oxygen to form litharge: hence it is clear, that as 32.52 grains of zinc and 103.56 grains of lead each combine with 8 grains of oxygen to form their respective oxides, these numbers must represent the equivalents of these metals, and the experiment itself proves that these are actually the proportions in which they replace each other in their union with acetic acid. But some substances enter into combination with each other in more than one proportion, forming several distinct com- pounds—how are these proportions regulated? It is an im- portant and well-established law, and one which of all others gives the most beautiful harmony to the science, "that when one body, A, unites with another body, B, in two or more proportions, the quantities of the latter united with the same quantity of the former bear to each other a very simple ratio." For example, there are five compounds of nitrogen and oxygen known ; the equivalent number of nitrogen, as lately deduced from the analyses of sal-ammoniac, nitrate of silver, and ni- trate of lead, is 14. The simplest compound of nitrogen and oxygen known is nitrous oxide, or "laughing gas;" it is, there- fore, considered as a protoxide, and to be composed of nitro- gen 14, oxygen 8. The next compound, nitric oxide, is the gas obtained by the action of nitric acid on metallic copper, or mercury; and analysis shows that it contains just twice as much oxygen as nitrous oxide: it is, therefore, composed of nitrogen 14, oxygen 16 (8 x 2). The third compound, viz: nitrous acid, is formed by adding 50 measures of oxygen gas to 200 measures of nitric oxide; its composition is, nitrogen 14, oxygen 24 (8 x 3). The fourth compound, viz: hyponi- THE THEORY OF EQUIVALENT PROPORTIONS. 25 trie acid, is formed by mixing together 4 volumes of nitric oxide and 2 volumes of oxygen, both perfectly dry; its com- position is, nitrogen 14, oxygen 32 (8 X 4); and the fifth compound, viz: nitric acid, is composed of nitrogen 14, oxygen 40 (8 x 5). Here the most simple relation is observed be- tween the quantities of oxygen in the different compounds; they are all simple multiples of the smallest quantity, while the proportion of nitrogen remains unchanged throughout. Occasionally, however, the proportions vary; for example, there are two compounds of iron and oxygen known—the first is composed of iron 28, oxygen 8; but the second is not iron 28, oxygen 16—but iron 28, oxygen 12 (8 + 4). Here, though the relation of the two oxides is not so simple as* in the former case, there is, nevertheless, no infraction of the great general law, " that bodies unite with each other in their com- bining proportions only, or in multiples of them, but in no intermediate proportion." We have not 30 or 40, &c., of iron uniting with 15 or 20, &c, of oxygen, but a simple multiple of the equivalent of iron, 28, combines with once and a half of the equivalent number representing oxygen, viz: 12. Compound bodies have likewise their""equivalent numbers," and combine with each other according to the same laws with those which regulate the union of simple substances. The equivalent number of a compound body is always the sum of the equivalent numbers of its constituents; thus the combining equivalent of nitric acid is 54, being composed of nitrogen 14 and oxygen 40 (8 X 5); that of baryta is 76.64, being com- posed of barium 68.64, and oxygen 8; but nitric acid and ba- ryta combine together, forming a neutral salt called nitrate of baryta, the equivalent of which is 130.64 (nitric acid 54 -f baryta, 76.64). Again, the equivalent number of sulphuric acid is 40 (sulphur 16 4- oxygen 24 (8 X 3)), and that of soda is 30.97 (sodium, 22.97 + oxygen, 8); but sulphuric acid and soda combine together, forming likewise a neutral salt, sulphate of soda, the equivalent of which is 70.97, the sum of the combining numbers of its constituents. Now, on bringing a solution of nitrate of baryta into contact with a solution of sulphate of soda, mutual decomposition of the two salts takes place; the solution, however, remains neutral, there is no re- dundancy either of acid or of base. This fact, which appears to have been first noticed by the Saxon Chemist, Wenzel, as far back as 1777, is easily explained. The salts resulting 26 CHEMICAL NOTATION : SYMBOLS AND FORMULAE. from the decomposition are each composed of a single equiva- lent of acid and of base, like the salts from which they are formed. Thus Nitrate of Soda 84.97 ___________A___________ f Nitric acid-----------------Soda 54 30.97 Nitrate of Sulphate of Baryta -^ )■ Sod? 130.64 Baryta---------------Sulphuric acid 7C.64 40 70.77 Sulphate of Baryta 116.64. Here it will be seen that the change which takes place is the substitution of equivalent quantities of the different bodies for each other; the two bases exchange acids, and the neu- trality of the liquid is preserved, because each base meets with its precise equivalent of the new acid, with which it enters into combination. It also follows, as a consequence of the same law, that the neutrality of the liquid will still be preserved, whatever may be the proportions in which the salts may be mixed; the decomposition will go on to the extent of the equivalents present and no further, the excess of either salt remaining unaffected. SYMBOLS AND FORMULAE. Having thus briefly explained the meaning and use of the figures in the third and fourth columns of the table, we may return to the consideration of the use of the letters in the second column, which constitute the symbols of the elements. These symbols afford a means of exhibiting, in a concise and comprehensible form, the composition of a compound; the mode in which its elements may be supposed to be arranged; and the changes which occur in its constitution by the substi- tution of one element for another. We will take the reaction between nitrate of baryta and sulphate of soda, which we have just been considering, by way of illustrating the appli- cation of these symbols, and the great advantages attending their use. This reaction would be written thus, in the form of an equation: BaO,N054-NaO,S03=BaO,S03-f-NaO,NOs. CHEMICAL NOTATION. 27 Here we have a most comprehensive view, not onlyof the whole reaction, but likewise of the composition of the different compounds therein concerned. The collocation of letters, BaO,N05 shows at once that nitrate of baryta is composed of nitric acid and baryta; it shows, further, that baryta is a compound of barium and oxygen, and nitric acid a compound of nitrogen and oxygen; that in baryta one equivalent of barium is combined with one equivalent of oxygen, and that in nitric acid one equivalent of nitrogen is combined with five equivalents of oxygen. But the formula has a still more significant meaning. BaO,N05 expresses, not an indefinite quantity of nitrate of baryta, but 130.64 parts by weight of that salt. The equivalent number of a compound is, as we have stated above, the sum of the equivalent numbers of its constituents. On referring to the table, the equivalent num- ber of barium will be found to be 68.64; that of oxygen, 8; and that of nitrogen, 14. BaO stands, then, for 76.64 parts by weight of baryta (68.64 + 8), and NOa. stands for 54 parts by weight of nitric acid (14 + (8 x 5); BaO,NOs consequently represents 130.64 parts by weight of nitrate of baryta. The same observations apply to the collocation of letters NaO, S03; they express not only the construction of the salt sul- phate of soda, and the composition of its constituents, but they signify 70.97 parts by weight of sulphate of soda. These are the salts which react on each other, and they are therefore placed on one side of the equation, with the sign + between them; on the other side of the equation we have the results of the decomposition, viz. (BaO,S03) (116.64 parts by weight of sulphate of baryta) and NaO,N05 (84.97 parts by weight of nitrate of soda); but 130.64 + 70.97 = 201.61; and H6°64 + 84.97 = 201.61; both sides of the equation agree, and the decomposition is therefore complete. In writing the formula for nitric acid, it will be observed that, in order to express the fact that it contains five equiva- lents of oxygen, a small 5 is placed underneath the O; now, whenever a figure is seen in this situation, it is always to be understood as affecting that element only at the foot of which it is placed. For example, Fe203 means a compound of two equivalents of iron and three equivalents of oxygen; S202 a compound of two equivalents of sulphur and two equivalents of oxygen. When, however, a large figure is placed before a collocation of letters, it affects the whole compound ex- 28 CONSTRUCTION AND USE OF FORMULA. pressed by those letters; thus 3N05 means three equivalents of nitric acid; 3Fe203 represents three equivalents of sesqui- oxide of iron; and 3S202 three equivalents of hyposulphurous acid. When formulae representing a reaction are thrown into the form of an equation, certain other signs are sometimes necessary. For example, when terchloride of gold and pro- tosulphate of iron, both in solution, are brought into contact in certain proportions, the whole of the gold is precipitated in the metallic form. The reaction is concisely expressed thus: AuCl3+6(FeO,S03)=2(Fe203,3S03) + Fe2Cl3 + Au one equivalent of terchloride of gold and six equivalents of protosulphate of iron, give rise to two equivalents of persul- phate of iron, one of sesquichloride of iron, and one of me- tallic gold. Now, here, as six equivalents of protosulphate of iron are required, the entire formula of that salt is placed within brackets, the figure 6 being prefixed; had the brackets been omitted, the formula would only have been affected by the 6 as far as the comma, and it would have read six equiva- lents of protoxide of iron, and one equivalent of sulphuric acid. Again, one of the products of this reaction is two equivalents of persulphate of iron ; the whole formula of per- sulphate of iron is therefore placed within brackets, the figure 2 being prefixed: had this been omitted, it would have been interpreted two equivalents of sesquioxide of iron, and three of sulphuric acid, and thus the equation would no longer be intelligible. Some chemists employ certain other abbreviations. Thus, in writing down the composition of certain minerals, instead of using the symbol for oxygen they express the number of equivalents of that element by dots or points placed over the symbol of the element with which it is associated; thus Fe signifies protoxide of iron, and 2 Fe or Fe signifies two equivalents of the same oxide; S expresses sulphuric acid, and S3 or 3S, three equivalents of that acid. When there are two equivalents of the electro-positive element, they are sometimes written by simply placing a dash underneath the sym- bol, thus Fe signifies sesquioxide of iron; Al means alumina; sometimes, however, the symbol itself is repeated instead thus, CONSTRUCTION AND USE OF FORMULAE. 29 AlAl,FeFe. Compounds of sulphur are, in like manner oc- casionally expressed by placing commas over the element with which the sulphur is associated; thus As, As, As are some- times written for the three sulphurets of arsenic, and Sn, Sn, and Sn, for the three sulphurets of tin. The formulae of certain organic acids are, likewise, often abbreviated; thus A, T, C, are written for acetic, tartaric, and citric acids, in- stead of the formulae representing their composition as C4H3 03; C3H4O10; C12H5On; which is sometimes annexed in pa- renthesis with the prefix of the equal sign, thus A= (C4H303). The great advantages of this system of notation are particu- larly appreciated in the organic department of Chemistry; besides the immense assistance it offers to the memory, it ena- bles Chemists to represent their theoretical views respecting the arrangement of the elements of certain compounds which would be wholly impossible from a mere statement of their per-centage composition as determined by analysis. We not unfrequently meet with two or more compounds which, though wholly unlike in their physical and chemical properties, yield nevertheless upon analysis the same elements in the same pro- portion; without the use of formulae it would be quite impossi- ble to give an intelligible representation of the constitution of such compounds, but with the aid of the symbolic language we can do so with the utmost perspicuity. The following may serve as an illustration. By distilling benzoic acid with sulphuric acid and pyroxylic spirit, an oily, fragrant liquid is obtained, which yields on analysis a per-centage composition answering to the formula C it 04. An oil of the same composition, but possessing to- tally different properties, is obtained by acting on oil of anise with dilute nitric acid. Lastly, by the action of dilute nitric acid on cymol (a hydrocarbon obtained from oil of cummin) a crystalline substance having acid properties is obtained, the composition of which is likewise Cl6H804. In the language of chemistry these bodies are said to be isomeric; but it is evident that even the empirical formula, C16H804, does not point out the true constitution of each substance. The symbolic lan- guage, nevertheless, enables the chemist to exhibit, at a glance, his theoretical ideas respecting them. Thus the first of these 30 GENERAL PRINCIPLES OF CHEMICAL NOMENCLATURE. oily compounds is considered to be a salt of the oxide of the hypothetical radical methyle (C4II3) viz: the benzoate, and its composition is written thus:— (C4H3)0 + C14H503=C16H804. The second is regarded as the hydruret of another hypo- thetical radical anisyle (Clfill704), and is thus expressed:— (CMH7O4)H=C10H,O4. m The third, from the circumstances of its derivation, and from its great analogy to benzoic acid, may be considered as the hydrated oxide of another hypothetical radical (C16H702), cor- responding to benzoyl, and be written thus:— (C16H702)0 + HO=C16H804. NOMENCLATURE. We have already mentioned that the 63 elementary sub- stances may be very conveniently arranged into two grand classes, viz: the metalloids and the metals. It has also been stated that, in giving names to these different bodies, no rule has, generally speaking, been observed, each particular dis- coverer following his own fancy in his selection. The names of compound bodies, however, are constructed in accordance with certain rules, and the system of nomenclature still fol- lowed is that of Lavoisier, which was constructed as far back as the year 1787, and which, though in some of its details it does not exactly accord with the views of the chemists of our day, is retained from the confusion and inconvenience which it has been felt would be introduced into the science, by mak- ing any alterations which might not meet the absolute approval of the chemical philosophers of all countries. Of all the simple substances, the one which is the most plen- tifully diffused is oxygen; it is, moreover, the element, the combinations of which are, on the whole, the most important. The founders of the chemical nomenclature naturally, there- fore, directed their especial attention to the compounds of oxygen, and made them the basis of their system. Oxygen forms, with other simple bodies, three classes of compounds. I. Acids. II. Bases. III. Neutral or indif- ferent substances. The members of the two latter classes have received the name of oxides; oxide of potassium, oxide of iron, and oxide of lead furnish examples of basic oxides, and oxide of carbon may be quoted as an instance of an indifferent oxide. At the time the nomenclature was constructed, it was GENERAL PRINCIPLES OF CHEMICAL NOMENCLATURE. 31 supposed that there could not exist more than two compounds of oxygen and the same body possessing acid characters; hence names were only provided for two acids with the same radical. To express the acid containing the smallest proportion of oxygen, the termination ous was given to the element forming the radical of the acid, and the termination ic was appended to signify the acid containing the largest proportion of oxygen. Thus two compounds of sulphur and oxygen were known, the first was called sulphurous and the latter sulphur^ acid. But the progress of science has pointed out the existence of other acid compounds of sulphur and oxygen. One of these acids contains less oxygen than sulphurous acid; another contains more than sulphurous, but less than sulphuric acid. To give names to these new substances, without disturbing the general principles of the nomenclature, the term hypo (from the Greek i>*6, under) was introduced. Thus hyposvl^hwcoiis acid ex- presses very conveniently the acid containing less oxygen than sulphurous acid, and Tw/posulphune acid, that containing less oxygen than sulphuric, but more than sulphurous acid. In other cases acids were discovered containing more oxygen than the ic compound, and to meet such cases the term hyper (from the Greek vnie, over) was introduced; thus an acid compound of chlorine and oxygen is known which contains more oxygen than chloric acid, the name /perchloric acid was given to this substance; it is now, however, more generally called per- chloric acid. It frequently happens that the same body forms several compounds with oxygen which are either basic or indifferent. The Greek language is again resorted to for furnishing a means of distinguishing these different oxides. Thus there are three oxides of manganese and oxygen known; the first, written symbolically, is MnO, and is called the protoxide; the second is written Mn203,* and, as it contains once and a half as much oxygen as the protoxide, it is called the sesquioxide; these two oxides are bases, that is, they combine with oxygen acids forming definite salts; the formula of the third is Mn02, and, as it contains twice as much oxygen as the protoxide, it * It is written Mn203 instead of MnOl£, in order to avoid the inconvenience of introducing fractions, and to obviate the necessity of dividing the atom of oxygen, on the supposition that the equivalent numbers are actually expressive of the absolute weights of the individual atoms. 32 GENERAL PRINCIPLES OF CHEMICAL NOMENCLATURE. is called the deutoxide: this oxide is indifferent, that is, it does not form salts with oxygen acids; it is generally called peroxide of manganese, because it contains the largest propor- tion of oxygen with which the metal can combine to constitute an oxide: there are other compounds of manganese and oxy- gen, but these are distinct acids. Salts are named according to a very simple rule, the names of acid and base being so combined that the name of the acid shall determine the genus, that of the base the species. When the name of the acid terminates in ic, the generic name of the salt terminates in ate, thus salts of sulphuric? acid are sulphates. When the name of the acid terminates in ous, the generic name of the salt terminates in ite: thus salts of sul- phurous acids are called sulphiYes. In the same manner we have hyposulphates and hyposulphites. The same acid some- times combines with the same base in more than one propor- tion; thus we have" two compounds of chromic acid and po- tassa, the symbols for which are KO,Cr03 and KO,2Cr03, and they are called respectively the chromate and the bi- chromate of potassa. Salts also exist, in which the quantity of acid is less than that which exists in the neutral salt; these compounds are designated s?io-salts. And, lastly, we are furnished in common alum with an instance of what is called a double salt, where a new and characteristic compound is formed by the union of two distinct salts. The formula for dry alum is KO,S03 + AL203,3S03, which shows it to be com- posed of sulphate of potash and sulphate of alumina. The names given to the compounds formed by chlorine, iodine, and the other metalloids, either with the metals or with each other, are in strict accordance with the rule adopted for the oxygen compounds: thus we have chloride*, oichlor- ides, sesquichlorides, and perchlorides; iodides, hromidcs. fluorides, sulphides (sometimes called sulphurets), carbides(or carburets), phosphides (or phosphurets), hydrides (hydrurets), &c. Water is remarkable as acting sometimes the part of an acid and sometimes that of a base; when in the former ca- pacity the compound is called a hydrate, as the hydrate of potassa; when in the latter, the compound ought, in strictness to be named by adding the word ivater to that of the acid' though this rule is often infringed. Thus the strongest sul- phuric acid of commerce is known to have the composition SO3+HO, it ought therefore to be called sulphate of water, GENERAL PRINCIPLES OF CHEMICAL NOMENCLATURE. 33 though it is generally termed hydrated sulphuric acid, or hy- drate of sulphuric acid. Certain of the metalloids form, amongst each other, ener- getic acids, as chlorine and hydrogen, iodine and hydrogen, fluorine and hydrogen, &c; these are called hydrogen acids, and are named respectively hydrochloric, hydriodic, and hydro- fluoric acids. It is here that the present nomenclature seems most defective, though it has not yet been thought advisable to make any important change, for the reasons already al- luded to. We have, lastly, to remark that, from the great analogy subsisting between certain compounds of sulphur with the metalloids and metals, and the corresponding compounds with oxygen, the terms sulphur acids and sulphur bases have been introduced to designate two classes of compounds, which act towards each other precisely as oxygen acids and oxygen bases, giving rise to a series of true salts called sulphur salts. Sulphur and carbon, for example, combine together and form a compound which corresponds in its properties so completely with carbonic acid, that it is called sulphocarbonic acid; it enters into combination with monosulphuret of potassium, forming a compound analogous to carbonate of potassa, and which has received the name of sulphocarbonate of monosul- phuret of potassium. 3 PAET I. QUALITATIVE ANALYSIS. CHAPTER I. GENERAL REMARKS ON CHEMICAL ANALYSIS. Chemistry is distinguished from most other sciences by being essentially experimental. Its object is the investiga- tion of the material constituents of the globe, and the study of their different properties and relations; the student is, therefore, constantly engaged in observing the phenomena presented on submitting the different substances that come under his notice to the action of various agents, and in the accumulation of facts derived from experimental inquiry. It is, indeed, this circumstance which gives to Chemistry its principal charm. The tyro no sooner begins to read than he begins to experimentalize: and being thus enabled, to a cer- tain extent, to verify for himself the facts brought before him, he acquires an interest in his pursuit which attaches him daily more and more to it. In order to pursue analytical chemistry with any chance of success, the student must possess certain qualifications. These may be stated to be—habits of strict order and scrupulous neatness; a dexterity of manipulation which practice alone can give; a firm conviction that the laws of nature are un- changeable, and that variations in experimental results must consequently imply either a non-fulfillment of certain neces- sary conditions, or some error in manipulation; and a rigorous honesty, not only in recording results, but in experimenting, and in interpreting the phenomena which present themselves in the course of an investigation. 36 QUALITATIVE ANALYSIS. The determination of the constituent parts of a compound body is termed its analysis; and this may be either of two kinds, according to the object which the operator has in view. If he merely seek a knowledge of the general nature of the substance, he is satisfied when, by the application of certain tests, and by the performance of certain operations, he has obtained evidence of the presence of those elements of which the compound is made up, and the analysis he performs is called qualitative. But, if he desire to appeal to the balance, and to ascertain not only the nature, but the actual amount of the elements present, he must shape his analysis in such a manner as to separate the constituents of the compound com- pletely from each other, and obtain them either pure or in some other well-known form of combination; he then performs a quantitative analysis. For example, if, on the addition of a few drops of solution of ferrocyanide of potassium to a neutral and clear liquid, a beautiful blue precipitate be ob- tained, the operator is at once satisfied of the presence of iron; and if he is working qualitatively only, this experiment is, with regard to that particular element, conclusive, it re- quires no additional confirmation; but if he desire to estimate the exact amount of iron present, he must conduct his ana- lysis in such a manner as to separate every particle of the metal in the state of sesquioxide, in which state it is weighed, and the amount of metal deduced by calculation. Now, be- fore the chemist can proceed to estimate the proportions of the constituents of a compound body, he must know exactly how many elements are present, and what those elements are. The qualitative analysis always, therefore, precedes the quan- titative ; and it will be necessary to separate the two courses of study, and to treat each individually. In either case, a cer- tain amount of skill and manipulation is required; but, as this subject is one of sufficient extent for a separate treatise, we refer the reader to '■'■Morfit's Chemical,and Pharmaceutic Manipulations" which furnishes all the necessary instruction in detail. QUALITATIVE ANALYSIS. 37 CHAPTER II. ON REAGENTS. Those substances which are employed by the chemist to give him information as to the nature of the subject of his examination have received the general name of Reagents; though the manner in which they act, and the phenomena to which they give rise, are exceedingly varied. These bodies are of the highest importance to the analyst; indeed the ju- dicious use of them, and the correct interpretation of the ap- pearances presented by their action, constitute the skill of the analytical chemist. We shall here describe the preparation and uses of the most important of these substances, with- out, however, making any attempt to classify them. The reagents to which we shall direct attention, are as follows:— 1. Litmus Paper. This is an exceedingly delicate test of the presence of an acid; it is most conveniently prepared by dipping thin un- sized paper into an infusion of the coloring principle in hot water until it acquires a full blue color. The paper is dried by exposure to the air, and kept carefully protected from the light, which injures and finally destroys the color. The blue color of this paper is instantly changed red by contact with a fluid having an acid reaction. 2. Red Litmus Paper. This is a valuable test of the presence of an alkali. To pre- pare it, a few drops of hydrochloric acid are mixed with a large quantity of water, and the blue paper immersed in it until it becomes slightly reddened: it is then removed and dried for use. The blue color is restored by contact with an alkali. 3. Turmeric Paper. This is prepared with an infusion of turmeric in the same 38 QUALITATIVE ANALYSIS. manner as litmus paper; it should have a fine yellow color; it indicates the presence of an alkali by changing to a red brown. 4. Cfeorgina Paper. This, when properly prepared, is an excellent test of both acids and alkalies; by the former it is colored red, and by the latter green. It is prepared by dipping paper into the colored infusion of the petals of the Georgina purpurea, and should have a fine violet color. 5. Solution of Lndigo. One part commercial indigo is digested in ten parts of con- centrated sulphuric acid, and the solution diluted with water till it is just distinctly blue. It is an excellent test for free chlorine, and nitric acid, both of which, aided by heat, dis- charge the color. 6. Starch Paste. Common arrowroot starch is rubbed with cold water, and boiling water then added until a thin paste is formed. It is an invaluable test for free iodine; when brought into contact with which, an intense blue compound is formed. With free bromine it forms a yellow compound. 7. Lead Paper. Paper is saturated with a strong solution of basic acetate of lead, cut into strips and dried. It forms an extremely de- licate test of the presence of sulphuretted hydrogen, which instantly communicates to it a deep brown black color. 8. Sulphuric Acid. (S03.) * The commercial oil of vitriol always contains sulphate of lead, sometimes also nitric acid, arsenic, and tin. The first of these impurities is removed by diluting the acid with water; a turbidity indicates sulphate of lead, which is inso- luble in the diluted acid. Nitric acid is indicated by the blue color of solution of indigo being discharged when boiled with the acid. Arsenic is indicated by passing a stream of sulphuretted hydrogen through the clear diluted acid; a yel- * A. A. Hayes (Sillimaris Journal, July, 1848) gives an economical process for manufacturing pure acid. QUALITATIVE ANALYSIS. 39 low precipitate is formed: if the precipitate be brown, it in- dicates tin. From all these impurities it may be freed by distillation; the first portions being rejected, and not more than three-fourths of the acid in the retort drawn over; for almost every qualitative operation the commercial acid may be employed. Sulphuric acid is of the most extensive use to the chemist, from its strong affinity for bases.* It liberates most other acids from their combinations, thus enabling their detection; and, from its powerful affinity for water, it effects remarkable changes in many substances in which the elements of that fluid exist. It is a powerful oxidizing agent, and in a diluted state it serves as a test for baryta, strontia, and lead, which it precipitates from their solutions. 9. Nitric Acid. (NOs.) This acid, the aquafortis of commerce, is prepared by dis- tilling equal weights of oil of vitriol and nitre. It almost al- ways contains sulphuric and hydrochloric acids, from which it may be freed, by adding nitrate of silver as long as a pre- cipitation takes place, and then re-distilling. This operation may, however, be avoided, if in the original preparation of the acid the first portions, about one-tenth or one-eighth of the whole, be collected in a separate receiver; these portions will contain all the impurities, and the remainder will be quite pure. Nitric acid is used as a solvent for metals, sulphurets, &c, and as a powerful oxidizing agent. 10. Hydrochloric Acid. (HC1.) The muriatic acid of commerce is not sufficiently pure for analytical purposes. It contains sulphuric acid and iron, sometimes also sulphurous acid, chlorine, and arsenic. Pure muriatic acid is conveniently obtained from the common mu- riatic acid of commerce; a quantity of the latter is introduced into a retort, to about one-third its capacity. Oil of vitriol is then poured into it gradually by a funnel tube which dips under the acid. The heat generated by the mixture drives over muriatic acid gas, which is sufficiently purified by passing through a good quality of the liquid acid contained in the re- ceiver, the beak of the retort dipping under the surface. Two or more Woolfe's bottles half filled with water, being con- * Krameric acid, it is said, separates sulphuric acid from the sulphate of baryta. 40 QUALITATIVE ANALYSIS. nected with the receiver, the acid in the first will be found nearly or quite pure, that in the second perfectly pure. A gentle heat may be applied to the retort to extract nearly all the muriatic acid, and the sulphuric acid may be subsequently heated in a capsule to strengthen and partially purify it. Hydrochloric acid is very extensively used as a solvent, and for the detection of silver, mercury, lead, and ammonia. 11. Kitromuriatic Acid, or aqua regia. (N04+ CI) HO. This acid is prepared by adding nitric acid to twice or thrice its volume of strong hydrochloric acid; both acids un- dergo decomposition, hyponitric acid, chlorine, and water be- ing formed. When the liquid is saturated with chlorine, this mutual decomposition ceases; but it recommences on the re- moval of the chlorine either by heat or by its combination with some other substance. Aqua regia is consequently the most powerful of solvents: its principal use in analytical che- mistry is for dissolving gold and platinum, and for decomposing certain metallic sulphurets. 12. Acetic Acid. (C4H303, or A.) The acetic acid of commerce frequently contains traces of sulphuric acid, but it may be obtained sufficiently pure for most analytical operations. If required quite free from all impurities, it is most conveniently prepared by distilling a mixture of ten parts of neutral acetate of lead with three of sulphate of soda, in a retort, with a cooled mixture of two and a half parts of sulphuric acid, and an equal weight of water : the distillation is continued to dryness. The acid thus ob- tained leaves no residue on evaporation. Acetic acid is em- ployed as a solvent, and for acidifying liquids in the place of the mineral acids. 13. Oxalic Acid. (C203, or 0.) HO. The commercial acid is purified by two or three recrystalli- zations. It should leave no residue on ignition. It is em- ployed as a precipitant of certain substances, particularly lime, for the detection of which it is a very valuable reagent All the oxalates are soluble in the stronger acids. & QUALITATIVE ANALYSIS. 41 14. Tartaric Acid. (C8H4O10=T.) The commercial acid is sufficiently pure; well-defined crys- tals should be selected. It should be kept in powder, as its solution decomposes by keeping. It is employed to prevent the precipitation of certain metallic oxides by alkalies, and as a test for potassa. 15. Potassa. (KO.) The best method of preparing this valuable reagent is to dissolve two parts of pure carbonate of potassa in twenty parts of boiling water in an iron pot, and to add in small por- tions at a time, to the boiling liquid, cream of lime, made by slaking one part of quicklime with boiling water; after boiling a few minutes the vessel is covered and allowed to stand for twenty-four hours; the clear liquid is then decanted. To ob- tain the potassa in the solid state, the liquid is evaporated to an oily consistence in a silver basin, poured out on a silver dish, and allowed to cool; it is then broken into fragments and preserved in well-stoppered bottles. Solutions of potassa, after being neutralized by nitric acid, should give no precipi- tate with chloride of barium, or nitrate of silver, nor should it effervesce on the addition of an acid. Silicic acid is a fre- quent impurity of potassa. It is detected by evaporating the alkali to perfect dryness, and adding water. Silicic acid, if present, remains undissolved. The uses of potassa in analytical chemistry are very nume- rous; as a precipitant; as a solvent; as a means of separating certain oxides from others; and as a test for ammonia, which, aided by heat, it expels from all its salts. Of the bases which it precipitates, some are soluble in an excess—hence a means for their separation from those which are insoluble. 16. Carbonate of Potassa. (K0,C02.) This salt is best prepared by calcining pure cream of tar- tar: the incinerated mass is boiled in distilled water, filtered, and the clear liquid evaporated to dryness in a clean iron ves- sel with constant stirring towards the end of the process; the dried mass must be kept in a well-stoppered bottle, and one part dissolved in five or six of distilled water for use. The carbonate of potassa of commerce usually contains alkaline sulphates and chlorides, alumina and silica. Carbonate of 42 QUALITATIVE ANALYSIS. potassa is extensively employed as a precipitant, and for the decomposition of many insoluble salts, particularly organic, with metallic bases. 17. Carbonate of Soda. (NaO,C02.) This salt is obtained pure by heating the best bicarbonate of soda of commerce for some time to low redness: its uses are the same as those of carbonate of potassa. It is an in- dispensable reagent in blowpipe operations; as a flux; as a solvent; and as a decomposing agent. 18. Ammonia. (NH3.) HO. Sal ammoniac is mixed with an equal weight of slaked lime, a little water added, and the mixture heated in a stoppered retort. The disengaged gas is first allowed to pass through a small quantity of water in a wash bottle, and from thence into another bottle nearly filled with distilled water immersed in a vessel containing ice-cold water; this bottle, for better security against sudden absorption, may be furnished with a safety tube. The water will absorb the gas, and become possessed of all its chemical properties in a very high degree. It should be kept in small well-stoppered bottles, and not in one large one, as every time it is exposed to the air it absorbs a certain quantity of carbonic acid, its freedom from which is proved by its not rendering lime-water turbid. Ammonia is in constant use for neutralizing acids, its peculiar fitness for which consists in its not introducing any fixed matter; for precipitating insoluble bases; and for separating them from each other. Some of the bases which it precipitates are redissolved by an excess. 19. Carbonate of Ammonia. (NH40,C02.) The sesqui-carbonate of ammonia of commerce is dissolved in four parts of distilled water, and one of liquor of ammonia added. The solution when evaporated should leave no re- sidue. This reagent is employed as a precipitant, and is very useful as a substitute for carbonate of potassa in cases where the introduction of a fixed base would be inconvenient. It is of special use in the separation of baryta, strontia, and lime, from magnesia, the latter of which earths is not precipitated in the presence of ammoniacal salts. QUALITATIVE ANALYSIS. 43 20. Chloride of Ammonium. (NH4C1.) Sal-ammoniac of commerce is purified by two or three re- crystalizations. Its solution in water should be neutral, and hydrosulphuret of ammonia should not discolor it: it should volatilize entirely when heated on platinum foil. The salt should be dissolved for use in eight parts of distilled water. It is of great use in analysis as a precipitant of various sub- stances soluble in potassa, but insoluble in ammonia, and for keeping in solution certain oxides or salts when others are precipitated by ammonia or other reagents. [Its property of decomposing several oxides and sulphurets at a high tem- perature and forming very volatile chlorides with the metals, enabling their separation from the more fixed chlorides, ren- ders it an important reagent in analysis. Rose uses it in his new method for estimating arsenic, antimony and tin.*] 21. Hydrosulphuret of Ammonia. (NH4S,HS.) This reagent is prepared by transmitting sulphuretted hy- drogen gas through solution of ammonia, till the liquid gives no precipitate with sulphate of magnesia. It must be kept in well-stopped bottles free from lead. When first prepared it contains excess of sulphuretted hydrogen, is nearly colorless, and does not give a precipitate of sulphur when mixed with an acid; but by exposure to the air it gradually absorbs oxygen, and assumes a yellow tint from the presence of excess of sul- phur, of which element it now yields a precipitate on the addi- tion of an acid. It is necessary to bear in mind these facts. Hydrosulphuret of ammonia is of great use for subdividing into two groups those metals which are precipitated as sul- phurets by sulphuretted hydrogen, from their acid solutions; some of these sulphurets being soluble, others insoluble in hy- drosulphuret of ammonia. It also subdivides into groups those metals that are not precipitated by sulphuretted hydrogen from their acid solutions; some of these metals being precipi- tated by hydrosulphuret of ammonia, while others remain in solution: it likewise precipitates certain oxides as hydrates by the action of its ammonia alone, and certain salts that are dissolved only in free acids; phosphate of lime, for instance, • Chem. Gaz., vi. 166, 411. 44 QUALITATIVE ANALYSIS. from its solution in hydrochloric acid. Neutral solutions of magnesia-salts, though yielding a precipitate to caustic am- monia, give none with hydrosulphuret. 22. Sulphuret of Potassium. (KOS202+2KS2.) When sulphuret of copper is to be separated from sulphur combinations soluble in alkaline sulphurets, sulphuret of po- tassium prepared by boiling sulphur with solution of caustic potassa, is substituted for hydrosulphuret of ammonia, in which sulphuret of copper is partially soluble. 23. Oxalate of Ammonia. (NH40,0.) This reagent is prepared by slightly supersaturating a solu- tion of pure oxalic acid with carbonate of ammonia, and crys- talizing: one part of the salt is dissolved in twenty or twenty- four parts of water for use; it is employed for the detection and precipitation of lime, and is more convenient than oxalic acid, as its solution does not decompose by keeping, and more- over when mixed with a solution of lime previously neutral, liberates no free acid to retain oxalate in solution. 24. Sulphuretted Hydrogen. (HS.) Fragments of protosulphuret of iron are covered with water in a gas evolution apparatus connected with a wash bottle; sulphuric or hydrochloric acid is poured into the bottle through a tube funnel, and the evolved gas received into a bottle containing cold distilled water as long as it continues to be absorbed. The solution must be preserved in well-stopped bottles. Sulphuretted hydrogen is a valuable reagent for se- parating metals into groups, and also as a means of reduction and of detection of individual metals. 25. Ferrocyanide of Potassium. (K2,Cfy.) The commercial yellow prussiate of potassa is sufficiently pure for analytical purposes; one part is dissolved for use in ten or twelve parts of water. It is of especial use for the de- tection of sesquioxide of iron and oxide of copper. 26. Ferricyanide of Potassium. (K3,Cfy2.) This reagent is prepared by transmitting a stream of chlo- QUALITATIVE ANALYSIS. 45 rine gas through a solution of the above salt until it ceases to produce a blue precipitate, with a solution of sesquichloride of iron. Its crystals have a magnificent red color; to procure them the solution is concentrated by evaporation, and ren- dered feebly alkaline by carbonate of potassa. This reagent serves to detect protoxide of iron by the formation of a cha- racteristic blue precipitate. 27. Chromate of Potassa. (KO,Cr03.) Bichromate of potassa of commerce is dissolved in water, and carbonate of potassa added till the solution reacts slightly alkaline; from the concentrated liquid yellow crystals may be obtained. It is employed principally as a test for lead, with which it forms a pigment known as chrome yellow. 28. Sulphate of Potassa. (KO,S03.) The salt of commerce is purified by two or three crystali- zations, and dissolved for use in ten or twelve parts of water; it is used for the detection and separation of strontia and ba- ryta, and is preferable to sulphuric acid, which disturbs the neutrality of solutions. 29. Bisulphate of Potassa. (KO,2S03.) This is the fusible salt remaining when nitrate of potassa is decomposed by two equivalents of oil of vitriol in the process for making nitric acid; it is extensively employed in blowpipe operations; in solution it indicates lithia, boracic acid, nitric acid, hydrofluoric acid, bromine, and iodine, and separates ba- ryta and strontia from other earths and metallic oxides. Rose recommends it as a flux for highly aluminous minerals, and J. C. Booth, for chromic and other similar ores. 30. Bitartrate of Potassa. (KO,HO,T.) The cream of tartar of commerce is sufficiently pure; it is useful in certain cases for separating metals from each other. 31. Cyanide of Potassium. (KCy.) Eight parts of roasted ferrocyanide of potassium are fused at a bright red heat in a covered crucible with three parts of dry carbonate of potassa; the fused mass is poured carefully into a warm dish, and when cold broken into fragments, and 46 QUALITATIVE ANALYSIS. kept in a well-closed bottle: it must not be kept in solution, but dissolved as required in four or five parts of water. In analysis its most important application is as a means of sepa- rating cobalt from nickel. As a blowpipe reagent mixed with an equal weight of carbonate of soda, it is exceedingly valua- ble from its powerful reducing action; and from its easy fusi- bility it is of special application in the reduction of arsenic. 32. Antimoniate of Potassa. (KO,Sb05.)* A mixture of one part of crude antimony with four parts of powdered nitre is thrown a little at a time into a crucible at a dull red heat; the mass is kept in a pasty state, with occa- sional stirring, for about half an hour, after which it is cooled, well washed, and heated to bright redness for half an hour, with two-thirds of its weight of pure carbonate of potassa. The cooled mass is digested with about fifty parts of warm water, and filtered for use when cold. It should not contain excess of alkali. Its use is as a test for soda, with which it forms a very sparingly soluble crystalline precipitate. As compounds of antimonic acid with the alkaline earths, and most of the metallic oxides are also insoluble, this reagent is inapplicable in their presence. 33. Caustic Baryta. (BaO.) Sulphuret of barium is boiled with excess of oxide of copper or oxide of lead, and filtered when the liquid gives a white precipitate, with acetate of lead: it is then diluted with water, and preserved in well-closed bottles. Its most important use is as a precipitant of magnesia, and for the detection of car- bonic acid. 34. Chloride of Barium. (BaCl.) To prepare this useful reagent, six parts of heavy spar (sul- phate of baryta) are exposed to an intense red heat, with a mixture of one part of powdered charcoal and one and a half of flour or resin; the resulting sulphuret of barium is boiled with slight excess of hydrochloric acid filtered, and crystal- ized two or three times. The solution of these crystals must be neutral to test-papers, not affected by sulphuretted hydro- gen, or hydrosulphuret of ammonia: it must, moreover, leave * Fremy's mode of preparation is given in Chem. Gaz., vi. 396. QUALITATIVE ANALYSIS. 47 no residue when mixed with excess of sulphuric acid, filtered and evaporated. Its most important use is as a means of de- tecting and estimating sulphuric acid. From the property which baryta possesses of forming soluble salts with some acids, and insoluble salts with others, it is likewise a valuable re- agent for distinguishing one group of acids from another. 35. Nitrate of Baryta. (BaO,NOs.) Native carbonate of baryta is digested with dilute nitric acid, the solution filtered and crystallized two or three times. Its uses and applications are the same as those of chloride of barium, and in cases where a chloride would be inadmissible. 36. Phosphate of Soda. (HO,2NaO,POs.) The commercial salt is crystallized and dissolved for use in ten or twelve parts of water. It serves as a test for alkaline earths in general, but especially for the detection and estima- tion of magnesia, which it precipitates with the addition of ammonia as the basic phosphate of ammonia and magnesia. 37. Phosphate of Soda and Ammonia. (NaO,NH40,P05.) HO. This salt (microcosmic salt) is prepared by boiling one hun- dred parts of crystallized phosphate of soda with sixteen of sal-ammoniac. Chloride of sodium separates, and the liquid, when filtered and evaporated, yields the double salt in fine crystals. When this salt is heated on charcoal or platinum wire, it loses water and ammonia, meta-phosphate of soda is formed, which, in consequence of its excess of acid, has the power of fusing almost every chemical compound. Hence its great use as a blowpipe reagent, in preference to borax, the beads or buttons formed by the fusion of which are less dis- tinctly colored. 38. Nitrate of Potassa. (KO,N05.) The nitre of commerce is purified by repeated crystaliza- tions: its solution should give no precipitate with nitrate of silver, or chloride of barium: it is extensively employed as an oxidizing agent. 48 QUALITATIVE ANALYSIS. 39. Biborate of Soda. (NaO,2B03.) The borax of commerce is purified by recrystalization. It should be exposed to a gentle heat in a platinum crucible till it no longer swells up; it is then powdered and kept for use. When heated on the ring of platinum wire, it should give a clear transparent glass. This glass possesses the property of dissolving most metallic oxides, the smallest portions of which communicate to it a color; hence its important use as a blow- pipe reagent. 40. Nitrate of Silver. (AgO,N05.) Standard silver is dissolved in nitric acid, evaporated to dryness, and heated till all the copper present is converted into black oxide, which may be known by dissolving a portion of the fused salt in water and adding ammonia, which should not make the solution blue. The fused mass is dissolved in water, filtered and crystalized; the crystals are dissolved for use in fifteen or twenty parts of distilled water. It may be known to be pure by the filtrate from the precipitate, which it forms with excess of hydrochloric acid, leaving no residue when evaporated on a watch-glass. It is employed for arranging acids into groups, and is of special application in testing for, and estimating hydrochloric acid. 41. Ammonia Nitrate of Silver. (AgON05, + 2NH3.) Ammonia is dropped into solution of nitrate of silver till the precipitate which first forms is nearly redissolved. It is employed for the detection of arsenic. 42. Sulphate of Copper. (CuO,S03.) Blue vitriol is purified by two or three crystalizations. A solution of one part of this salt mixed with two and one quarter parts of protosulphate of iron is employed for the precipita- tion of hydriodic acid, as protiodide of copper. Ammonia- sulphate of copper prepared in the same manner as the cor- responding silver salt is also employed as a test for arsenic. 43. Iodide of Potassium. (KI.) The commercial salt is tested for carbonate of potassa by treating it with hot alcohol, in which the latter salt is insolu- QUALITATIVE ANALYSIS. 49 ble. It is a reagent for certain metals, particularly for lead and mercury, with which it forms characteristic precipitates. 44. Neutral Acetate of Lead. (PbO, A.) The best sugar of lead of commerce is dissolved in ten or twelve parts of distilled water: it is useful for arranging acids into groups, and for the special detection of chromic acid. 45. Basic Acetate of Lead. (3 PbO, A.) Seven parts of well-washed litharge and six of the best neu- tral acetate of lead are gently heated and agitated with thirty parts of water till the sediment has become perfectly white; the liquid is then decanted and preserved for use in a well- closed bottle. It has the same applications as the last de- scribed salt, but its chief use is as a test for sulphuretted hydrogen. 46. Protosulphate of Iron. (FeO,S03.) Clean iron nails are digested with dilute sulphuric acid till hydrogen ceases to be evolved. The solution is filtered, and the crystals obtained washed with water slightly acidified with sulphuric acid and dried. This salt is a powerful deox- idizing agent, and is of especial application as a test for nitric acid. It also precipitates gold in the metallic state, and forms a blue compound with ferricyanide of potassium. 47. Lime Water. (CaO.) HO. Fresh slaked lime is agitated with cold water, allowed to set- tle, and the clear fluid preserved in well-stopped bottles. It serves to detect carbonic acid, and as a means of distinguish- ing certain organic acids,—citric, tartaric, paratartaric; and also to liberate ammonia from its combinations. 48. Sulphate of Lime. (CaO,S03.) The precipitate formed on adding chloride of calcium to dilute sulphuric acid is well washed, digested, and agitated with water, and the fluid filtered for use. It is employed to distinguish between lime, strontia, and barytes. 49. Chloride of Calcium. (CaCl.) Pure carbonate of lime is dissolved in dilute hydrochloric 4 50 QUALITATIVE ANALYSIS. acid. The solution must be perfectly neutral. It is of great use for the classification of organic acids, as it precipitates some and forms soluble compounds with others. 50. Protochloride of Tin. (SnCl.) Granulated tin is boiled with concentrated hydrochloric acid, the metal being in excess; it is then diluted with four or five times its quantity of water, slightly acidulated with hydro- chloric acid and filtered. It must be kept in well-closed bottles containing fragments of metallic tin to prevent the protochloride from passing into the state of perchloride. It is a powerful reducing agent. It also serves to detect mercury, and, when mixed with nitric acid, it indicates the presence of gold. 51. Bicldoride of Platinum. (PtCl2.) The solution of the metal in aqua regia is evaporated to dryness in the water bath, and redissolved in eight or ten parts of water. It is of great use in analytical chemistry for the detection and estimation of potassa and ammonia. 52. Sesquichloride of Iron. (Fe2Cl3.) Clean iron nails are digested with diluted hydrochloric acid ; the decanted acid liquid is then boiled with successive addi- tions of nitric acid, in a capacious vessel, till all effervescence ceases, and till it no longer tinges solution of red prussiate of potassa blue; it is then precipitated with excess of ammonia, and the well-washed hydrated peroxide of iron is heated with hydrochloric acid, care being taken that it is not all dissolved, it being necessary that the test should not contain excess of acid; it is then filtered for use. It is employed as a means of classifying organic acids which are not precipitated by chloride of calcium, and is also of great use in the analysis of the phosphates of the alkaline earths. 53. Sulphurous Acid. (S02.) This is prepared by transmitting the gases produced by the action of six parts of oil of vitriol on one part of charcoal (carbonic and sulphurous acid gases) through ice-cold water till no more is absorbed. It must be kept in well-closed bot- tles, and should always smell strongly of the acid. It is a QUALITATIVE ANALYSIS. 51 powerful means of reduction ; it precipitates mercury from its solution, converts chromic acid into oxide of chromium, arse- nic acid into arsenious acid, &c. 54. Hydrofluosilicic Acid. (3 HF, + 2 SiF3.) Equal weights of powdered fluor spar and quartz are gently heated, together, in a retort, with six parts of oil of vitriol, and the gas evolved passed into water, the extremity of the delivering tube dipping into mercury placed at the bottom of the jar in order to prevent the tube from becoming choked up with the silicic acid which is precipitated the instant the gas comes into contact with water. The gelatinous mass is filtered through linen, and the filtrate preserved for use. Hy- drofluosilicic acid forms an insoluble compound with potassa, which base it is sometimes employed to separate from chloric acid. It is also used to discriminate between baryta and strontia, with the former of which it forms a crystalline deposit. 55. Chlorine Water. (CI.) HO. The gas evolved by heating finely powdered peroxide of manganese with five or six times its Aveight of hydrochloric acid is conducted into ice-cold water, until the fluid is satu- rated. It must be kept in a well-closed bottle and preserved from the light. It is employed to expel iodine and bromine from their combinations. 56. Chloride of Mercury. (HgCl.) The corrosive sublimate of commerce is purified by crys- tallization, and dissolved for use in 12 or 14 parts of water. It forms characteristic colored precipitates with certain acids. 57. Protonitrate of Mercury. (Hg20,N05.) Mercury is gently heated with an equal weight of nitric acid of 1.23, till the formation of red fumes ceases; it is then boiled with the undissolved metal till a few drops of the solu- tion are so completely precipitated by common salt, that no precipitate occurs in the filtered liquid on the addition of pro- tochloride of zinc. The solution is then agitated till it is cold, and the crystals formed, shaken with 20 parts of cold water, to which a small quantity of nitric acid has been added. The bottle in which this reagent is kept should contain a small 52 QUALITATIVE ANALYSIS. quantity of mercury. Its applications are the same as those of nitrate of silver. It is likewise employed to detect several substances of easy oxidation, formic acid, for instance, which it resolves into carbonic acid and water, a reduction of the metal at the same time taking place. 58. Protonitrate of Cobalt. (CoO,N05.) It is not easy to obtain this reagent quite pure, though for blowpipe experiments it is a matter of great consequence that it should be so. Fresenius gives the following directions for preparing it:—an intimate mixture of two parts of very finely powdered cobalt, four parts of saltpetre, one part of effloresced carbonate of soda, and one part of dry carbonate of potassa, is projected in small portions into a red-hot crucible, Avhich is then exposed to the strongest possible heat till the mass is fusing; when cold, it is reduced to powder, boiled with water, and the well-washed mass dissolved in hydrochloric acid; the gelatinous mass is carefully evaporated to dryness; the residue boiled with water, filtered, and carbonate of ammonia (car- bonate of potassa is better) added to the filtrate while kept at the boiling heat till all acid reaction ceases; the filtered solu- tion is precipitated by carbonate of potassa, and the precipi- tate obtained washed and dissolved in nitric acid. The solu- tion is evaporated to dryness at a gentle heat, and one part of the residue dissolved in ten parts of water for use. Solu- tion of nitrate of cobalt is employed to distinguish certain metals in the oxidating flame of the blowpipe. Thus alumina acquires a beautiful pale blue color, magnesia a rose-red tint, and zinc a bright green. A few drops of the solution are placed on the substance to be operated upon by means of a platinum wire or dropping tube. 59. Distilled Water. (HO.) No other water should be employed in analysis. It should give no precipitate or even turbidity with chloride of barium, nitrate of silver, oxalate of ammonia or lime water, and should leave no residue on evaporation. 60. Alcohol. (C4H602.) Rectified spirits of wine, sp. gr. about .840, are sufficiently strong for most purposes. What is termed absolute alcohol, QUALITATIVE ANALYSIS. 53 and which is sometimes required, is prepared by adding car- bonate of potassa, that has recently been exposed to a red heat, to ordinary alcohol until it ceases to dissolve any more; the whole is allowed to digest for 24 hours; the liquid is then poured off, mixed with a sufficient quantity of quicklime to absorb the whole, and slowly distilled from a retort on a water bath at the temperature of about 180°; it is then obtained of a sp. gr. of .7947. It must not redden litmus paper, and must volatilize without leaving any residue. Alcohol is used as a solvent, and hence for the precipitation from solution, of substances insoluble in it. The characteristic tint imparted by certain substances to its flame serves for their detection. 61. Ether. (C4H50.) Sulphuric ether of commerce when free from acid, is suffi- ciently strong and pure for all purposes. In inorganic ana- lysis it is employed to detect and isolate bromine. 62. Acetate of Potassa. (KO, A.) Prepared by dissolving pure carbonate of potassa in water and adding acetic acid until the solution is perfectly neutral. Is particularly useful for the detection of tartaric acid as the precipitated bi-salt is insoluble in the liberated acetic acid. It is also employed in analyses of the alkaline earthy phos- phates. 63. Basic Silicate of Potassa. (3KO,Si03.) Employed in solution to detect phosphoric acid in phosphate of alumina. It is obtained by digesting gelatinous hydrate of silica in potassa water. 64. Succinate of Ammonia (Neutral). (NH40,S = (C4H203).) Employed to distinguish baryta from strontia; and from lime, when hydrofluosilicic acid is not at hand. It is also used to separate protoxide of manganese from peroxide of iron. 65. Bicarb. Potassa. (KO,2C02.) Is used in solution to distinguish magnesia from alumina and also baryta, strontia and lime from protoxide of manga- nese. 54 QUALITATIVE ANALYSIS. 66. Carbazotic Acid. (C12H2N3013 + Aq.) A very sensitive test for potassa, and may be prepared by adding cautiously and portionwise one part of finely powdered indigo to eleven parts of nitric acid (sp. gr. 1.43), and after the liquid is quiet, adding during boiling more acid until nitric oxide ceases to be given off. The solution on cooling drops the acid in crystals, which must be purified by solution in potash, precipitation by nitric acid and recrystallization from water. 67. Nitrate of Nickel. (NiO,N05.) Used in solution to distinguish soda from potassa. 68. Chloride of Gold. (AuCl3.) Prepared by dissolving pure gold leaf with aid of heat in aqua regia, evaporating to dryness and redissolving in water. It is used for detecting protoxide of tin and also for convert- ing protochlorides and protoxides into perchlorides and per- oxides and chlorides. 69. Sulphate of Alumina. (A1203,3S03.) Prepared by dissolving pure alumina in sulphuric acid and crystallizing. Is employed to detect potassa and ammonia. 70. Cyanide of Mercury. (Hg,Cy.) This reagent serves to detect palladium, and in some cases platinum. 71. Chloride of Lead. (Pb,Cl.) Used in solution as a precipitate for silver when lead is present in large proportion. The ordinary precipitants of silver, hydrochloric acid and chloride of sodium, have no effect in dilute solutions, but solution of chloride of lead being very weak even when concentrated, throws down only the silver. 72. Infusion of Galls. The aqueous infusion or tincture is used as a delicate test for peroxide of iron, in neutral solutions, with which it forms a black precipitate. It is also employed as a test for titanic QUALITATIVE ANALYSIS. 55 and tantalic acids, and in organic analysis for gelatin, which it precipitates from solutions in dirty white curdy flocculae. 73. Zinc. (Zn.) Zinc is employed for the reduction and precipitation of many metallic salts and oxides. Its principal use is for the precipitation of antimony and of tin and for separating silver from chloride of silver. The zinc must be previously purified by digestion in nitric acid which leaves the tin and antimony undissolved, converts the arsenic into arsenic acid, and dis- solves the iron and cadmium. These latter two are precipi- tated by an excess of carbonate of ammonia; the filtered liquid is then evaporated to dryness, the residue ignited, dissolved in nitric acid and the solution precipitated with carbonate of potassa, which leaves the arsenic in the liquid. The precipi- tate is well washed, ignited and then reduced at a red heat with hydrogen. (Smedt.) 74. Iron. (Fe.) Used in wire with polished surface for the detection of copper, which it precipitates in a metallic state. 75. Copper. (Cu.) Employed in bright strips for the reduction and precipitation of mercury and in Reinsch's process for the detection of arsenic. The student is recommended to prepare, as far as possible, his own reagents. He should at any rate assure himself by careful testing of their purity; by so doing he will not only save himself from much subsequent embarrassment, but he will be gaining much valuable experience in qualitative ex- aminations. . 56 QUALITATIVE ANALYSIS. CHAPTER III. ON THE COMPORTMENT OF SUBSTANCES WITH REAGENTS. 1. METALLIC OXIDES. By means of certain reagents this extensive class of com- pounds may be arranged into a series of groups ; some of which, again, by other reagents may be subdivided into sec- tions, the whole forming a very convenient classification. First Group.—Metallic oxides not precipitated from their solutions by sulphuretted hydrogen, hydrosulphuret of am- monia, or alkaline carbonates. The alkalies proper: potassa, soda, lithia, ammonia. Second Group.—Metallic oxides not precipitated from their solutions by sulphuretted hydrogen, precipitated by hydrosul- phuret of ammonia only under certain circumstances, as salts, and precipitated by alkaline carbonates. The alkaline earths: baryta, strontia, lime, magnesia. Third Group.—Metallic oxides not precipitated by sul- phuretted hydrogen, but precipitated as oxides by hydrosul- phuret of ammonia. Alumina, glucina, oxid^of chromium, thorina, yttria, oxides of cerium, zirconia, titanic acid, tantalic acid. Fourth Group.—Metallic oxides not precipitated from their acid solutions by sulphuretted hydrogen, but completely pre- cipitated by hydrosulphuret of ammonia as sulphurets. Oxide of zinc, oxide of nickel, oxide of cobalt, protoxide of manganese, protoxide and sesquioxide of iron, and sesquioxide of uranium. Fifth Group.—Metallic oxides completely precipitated from their solutions, whether acid, alkaline, or neutral, by sulphu- retted hydrogen, their sulphurets being insoluble in alkaline hydrosulphurets. Oxide of lead, oxide of silver, oxides of mercury, oxide of bismuth, oxide of cadmium, oxide of copper, oxide of palladium, sesquioxide of rhodium, oxide of osmium. Sixth Group.—Metallic oxides completely precipitated from their acid solutions by sulphuretted hydrogen, but not from QUALITATIVE ANALYSIS. 57 their alkaline solutions, their sulphurets being soluble in alka- line sulphurets. Oxide of antimony, oxide of arsenic, oxide of tin, oxide of platinum, oxide of iridium, oxide of gold, oxides of selenium, tellurium, tungsten, vanadium, and molybdenum. GROUP 1. The Alkalies Proper, Potassa, Soda, Lithia, Ammonia. POTASSA (KO). General Characters: When pure it is quite white, dissolving in water with the disengagement of heat, and attracting both water and carbonic acid from the atmosphere. It is highly caustic, and eminently alkaline; nearly all its salts are soluble in water; it is capable of being precipitated by very few re- agents. Its presence is, however, evinced by the following. Bichloride of platinum produces a bright yellow crystalline precipitate of double chloride of platinum and potassium (KCl, + PtCl2) very sparingly soluble in water, and the forma- tion of which is promoted by the presence of free hydrochloric acid. It is quite insoluble in strong alcohol. Previous to applying this test, the operator must be certain of the absence of ammonia, and the solution should be concentrated. Tartaric acid added in excess produces a granular crystal- line precipitate (KO,HO,T) soluble in strong acids and in carbonated and caustic alkalies, but insoluble m tartaric and acetic acids; the formation of the precipitate is facilitated by agitation and by the addition of alcohol. Carbazotic acid dissolved in alcohol produces even in dilute solutions a bright yellow crystaline precipitate. Perchloric acid produces a sparingly soluble white crystal- ine precipitate. Hydrofluosilicic acid, poured'in excess into concentrated so- lutions of potassa gives a gelatinous translucid precipitate, in- soluble in muriatic acid but losing transparency in its presence. Concentrated sulphate of alumina forms crystals of alum when poured into strong solutions of potassa previously satu- rated with an acid (hydrochloric). Before the blowpipe, potassa salts, if free from soda, heated on a platinum wire in the inner flame, tinge the outer flame 58 QUALITATIVE ANALYSIS. violet; if soda salts be present, potassa may be detected by fusing a clear bead of borax with a small quantity of oxide of nickel, and then adding the mixture, the brown color of the bead is changed to blue.* SODA (NaO). General Characters: They are very similar to those of potassa; its dilute solution or that of any of its salts affords no precipitates with any of the above reagents for potassa; but Antimoniate of potassa, if properly prepared, produces in neutral and even in very diluted solution, if well agitated, and provided no other oxide but potassa be present, a crys- taline precipitate (NaO,Sb05). Hydrofluosilicic acid pro- duces in concentrated soda solutions a gelatinous precipitate of silicofluoride of sodium. Before the blowpipe, soda salts are distinguished by the strong yellow colour which they communicate to the outer flame, which reaction is not prevented by a very considerable excess of potassa. According to Kobell, one part of chloride of sodium may hereby be detected in 25 or 30 parts of chloride of potassium.—See note below. * Potassa as well as soda may be detected in the presence of magnesia by Chapman's method, as follows: " 1st. A small quantity of boracic acid (perfectly pure) is to be fused before the blowpipe in a loop of platinum wire; 2d, a portion of the compound under examination, with a particle of oxide of copper, is then to be added to it; and, 3d, the whole subjected to an oxidating flame. If magnesia alone be present, the greater portion of it will remain undissolved, together with the oxide of copper, in the flux, the bead continuing colorless; if, on the contrary, potash or soda be mixed with the magnesia, these bodies will be immediately dissolved by the boracic acid, forming borate of potash or soda, in which the oxide of copper dissolves, communicating to the compound its peculiar colors, the bead becoming green whilst hot and blue when cold. " If the alkaline salt be in excess, the magnesia will be also dissolved. If the contrary be the case, the coloration from the dissolved oxide of copper will still be effected; but the magnesia will be perceived in the centre of the globule as a white or light-colored insoluble mass. "It must be observed that salts of baryta or strontia fuse likewise with boracic acid, giving rise to borate of baryta or strontia, in which, as in the alkaline borates, oxide of copper dissolves, producing a green or blue coloration. If pre- sent, therefore, in the magnesia compound, these bodies must be removed by sulphuric acid before attempting to ascertain the presence of the alkalies by the above method. We can finally examine a fresh portion of the assay matter for potash by chloride of platinum, and for soda by the production of its well-known yellow flame." QUALITATIVE ANALYSIS. 59 LITHIA (LiO). General Characters: When pure, this oxide is white; it is not so soluble in water as potassa or soda; its solution rapidly absorbs carbonic acid, when exposed to the air. Carbonate of lithia is very sparingly soluble in water. When a solution of a lithia salt is boiled with phosphate of soda no precipitate occurs, but if ammonia be added, a very sparingly soluble double phosphate of soda and lithia is deposited. Tartaric and oxalic acids give no precipitate in salts of lithia. Before the blowpipe, salts of lithia are detected by the fine crimson tinge which they communicate to the outer flame, when heated in the inner flame on platina wire. Potassa salts do not interfere with this reaction; but soda salts de- stroy it, substituting for the crimson their own peculiar yellow color. Lithia may be distinguished from strontia by fusing the suspected substance with chloride of barium, the presence of which, according to Plattner and Chapman, prevents chlo- ride of strontium from imparting a crimson flame, whilst it does not impair the fine red color characteristic of lithia. AMMONIA (NH40). General Characters: The solution of pure ammonia in water is when concentrated highly caustic and alkaline; it has a powerful and penetrating smell, by which its presence can generally be detected. It attracts carbonic acid from the atmosphere. Most of its salts are soluble in water; and nearly all of them are totally volatilizable by heat. When present in an uncombined state in a quantity too small to be detected by the smell, its presence may be evinced by the production of white clouds, when a feather dipped in strong hydrochloric, or acetic acid (the former is preferable), is held over the liquid. Behavior of Ammonia and Ammoniacal Salts with Reagents. Bichloride of platinum produces a yellow crystaline preci- pitate (NH4Cl + PtCl2) having a great resemblance to the cor- responding double salt of potassium. Tartaric acid produces, in concentrated solutions, only a crystaline bitartrate of ammonia much more soluble than the corresponding potassa salt. 60 QUALITATIVE ANALYSIS. Carbazotic acid produces no precipitate except in very con- centrated solutions. When mixed and triturated with hydrate of lime, or caustic potassa, ammoniacal salts part with their ammonia, which may then be detected either by its smell or by strong acetic acid, or by reddened litmus paper. This reaction is facilitated by the application of slight warmth. GROUP 2. The Alkaline Earths, Baryta, Strontia, Lime, Magnesia. BARYTA (BaO). General Characters: When pure it is of a grayish white color; it combines with water with the evolution of great heat, and is completely dissolved. Its concentrated aqueous solu- tion deposits crystals of hydrate. It is powerfully caustic and alkaline; it combines greedily with carbonic acid, forming a white insoluble compound, which is poisonous. Behavior of Soluble Barytic Salts with Reagents. Alkaline carbonates produce a white precipitate (BaO,C02) soluble with effervescence in free acids. Ammonia and caustic alkalies do not produce any perma- nent precipitate, provided atmospheric air be excluded. Sulphuric acid, or solution of any soluble sulphate, (sulphate of lime preferable,) produces, even in the most dilute solutions, a white precipitate (BaO,S03) wholly insoluble in all acids and alkalies. Hydrofluosilicic acid produces after awhile a colorless crystaline precipitate (3BaFl, + 2SiFl3) silico fluoride of ba- rium, almost completely insoluble in free nitric or muriatic acids. Neutral phosphate of soda produces a white precipitate (2 BaO,HO,P05) soluble in free acids. Oxalic acid, or binoxalate of potassa, produces in concentra- ted solutions only, a white precipitate (BaO,0 + aq.) soluble in free acids; the formation of this precipitate is favored by ammonia. The absence of strontia and lime must be ascer- tained previous to the use of this test. QUALITATIVE ANALYSIS. 61 Chromate of potassa produces a yellow precipitate (BaO, Cr03) soluble in nitric acid and in caustic alkalies. Hydrosulphuret of ammonia gives no precipitate in barytic solutions. Ferrocyanuret of potassium produces in strong solutions, after some time, a yellowish white precipitate of ferrocyanuret of potassium and barium. Before the blowpipe, baryta cannot positively be detected; most of its salts impart a yellow color to the flame of alcohol, but it is not characteristic. STRONTIA (StrO). General Characters: It greatly resembles baryta, but it is not so heavy, neither is its hydrate so soluble in water; its aqueous solution is consequently less caustic. Behavior of Soluble Strontia Salts with Reagents. Alkaline carbonates, the caustic alkalies and phosphate of soda, behave towards solutions of strontia salts precisely as towards solutions of baryta salts. Sulphuric acid produces a white precipitate (StrO,S03) in- soluble in free acids, but not altogether insoluble in water: in very dilute solutions, therefore, sulphate of lime and other soluble sulphates do not occasion an immediate precipitate. Hydrofluosilicic acid occasions no precipitate even in concen- trated solutions, and this acid affords a means of separating strontia from baryta, for the latter is precipitated by it, while the former unites with it, forming a salt readily soluble in a slight excess of acid. Chromate of potassa in cold and dilute solutions produces no precipitate; but, by boiling, a copious yellow precipitate (StrO,Cr03) is determined. _ Oxalic acid produces a white precipitate (StrO,0 + aq.) even in dilute neutral solutions: in very dilute solutions the precipitate is immediately determined by the addition of am- monia. t # # Ferrocyanuret of potassium gives no precipitate. Hydrosulphuret of ammonia does not produce any precipi- tate. Before the blowpipe sulphate of strontia fuses to an opales- cent mass, and colors the outer flame carmine red. Chloride 62 QUALITATIVE ANALYSIS. of strontium, heated on the ring of platinum wire at the apex of the blue flame, tinges the whole flame immediately deep crimson; but as the assay fuses the color disappears, by which it is distinguished from chloride of lithium. The presence of chloride of barium prevents the production of the colored flame. Soluble salts of strontia, digested with alcohol, and inflamed, give rise to an intense and characteristic carmine red color. LIME (CaO). General Characters: When pure, it is white and infusible. It has an acrid, caustic, alkaline taste. It has a powerful affinity for water, in combining with which it emits great heat, and falls into a bulky powder. The hydrate of lime is far less soluble in water than the hydrates of the two pre- ceding oxides, one part requiring for a perfect solution from 450 to 500 parts of water. The solution is slightly caustic, and gradually absorbs carbonic acid from the atmosphere, until the whole of the lime is converted into carbonate. Behavior of Solutions of Salts of Lime with Reagents. The caustic and carbonated alkalies, and phosphate of soda, behave with calcareous solutions precisely as with solutions of baryta and strontia. Sulphuric acid and the soluble sulphates occasion no pre- cipitate in very dilute solutions; but, on the addition of alco- hol, a precipitate (CaO,S03) immediately takes place: in concentrated solutions a bulky precipitate is produced, solu- ble, though not remarkably so, in nitric and hydrochloric acids. Hydrofluosilicic and perchloric acids do not produce any precipitate in solutions of calcareous salts. Oxalic acid and the soluble oxalates occasion an immediate precipitate (CaO, 0+2aq.) in neutral solutions, soluble in the mineral acids, but nearly insoluble in acetic acid. The formation of this precipitate is increased and quickened by the addition of ammonia. Hydrosulphuret of ammonia does not produce any precipi- tate. Ferrocyanuret of potassium gives a white precipitate onlv QUALITATIVE ANALYSIS. 63 in very strong solutions. The precipitate is soluble in hy- drochloric acid. Before the blowpipe, chloride of calcium, unless it has been fused, heated on the ring of the platinum wire tinges the outer flame red, but the color is more feeble than with chloride of strontium. Pure lime and the carbonate emit a very strong light. Soluble lime salts impart a yellowish red tinge to the flame of alcohol. Plattner detects lime in barytic and strontia salts by fus- ing them with salt of soda upon a platinum foil:—if the salts are pure the flux remains clear,—if they contain lime it remains undissolved. MAGNESIA (MgO). General Characters: It is a white infusible powder, possessed of a feeble but distinct alkaline reaction. Like lime, it is more soluble in cold than in hot water: 36,000 parts of boiling water, and 5,142 parts at 32°, being required to dissolve one part of the earth. Caustic magnesia does not emit any heat on being moistened with water. Behavior of Magnesian Salts with Reagents. Ammonia, in neutral solutions, occasions a white bulky pre- cipitate (MgO,HO). If the solution be acid, or if ammoniacal salts be present, no precipitate takes place, in consequence of the property possessed by magnesia of forming double salts with ammonia. Caustic potassa produces a voluminous flocculent precipi- tate, which disappears on the addition of muriate of ammonia; but, on boiling with excess of potassa, the precipitate reap- pears, in consequence of the decomposition of the ammoniacal salt. Carbonate of potassa produces in neutral solutions, and in the absence of ammoniacal salts, a white voluminous precipi- tate 2 (HO,MgO,) + 3 (MgOjCOJ^ which is increased by boiling, in consequence of the expulsion of the carbonic acid which in the cold keeps a portion of magnesia in solution in the form of bicarbonate. Carbonate of ammonia, by boiling, and in the absence of ammoniacal salts, occasions a slight precipitate of subcarbon- ate. 64 QUALITATIVE ANALYSIS. Sulphuric acid produces no precipitate (MgO,S03), being very soluble in water. Phosphate of soda alone does not produce any precipitate in very dilute cold solutions; but, if ammonia be added, a crystalline precipitate of basic phosphate of magnesia and ammonia (2MgO,NH4O,PO5+2HO + 10HO) is formed in highly diluted solutions. This precipitate is insoluble in am- moniacal salts, but soluble in free acids. Oxalate of ammonia, in the absence of ammoniacal salts, forms a white precipitate (MgO,0 + 2 aq), but oxalic acid gives none in neutral solutions. Hydrosulphuret of ammonia gives no precipitate in neutral solutions, unless they are very concentrated, or contain free ammonia. Before the blowpipe, in the absence of other metallic oxides, salts of magnesia, when ignited on charcoal, then moistened with solution of protonitrate of cobalt, and again strongly ignited, acquire a feeble red tint, visible only on cooling of the button. General Remarks on the Oxides of the Second Group. From the property of magnesia to form soluble double salts with ammonia, this earth may be kept in solution by the addi- tion of sal-ammoniac and ammonia, while baryta, strontia, and lime are precipitated by carbonate of ammonia. The magnesia is detected in the filtered liquid by phosphate of soda. The immediate formation of a precipitate, on the addition of hy- drofluosilicic acid, is characteristic of baryta. Strontia, in combination with baryta, is detected by converting both earths into chlorides, and digesting with absolute alcohol, in which chloride of barium is almost insoluble. Chloride of strontium is detected in the alcoholic solution by the carmine red flame it communicates to the alcohol when ignited; and lime is de- tected by oxalate of ammonia. To discover the alkalies in the presence of the oxides of the second group, the baryta, strontia, and lime are first removed by boiling with carbonate of ammonia and caustic ammonia, and from the filtered liquid the magnesia is precipitated by water of baryta; the excess of baryta is removed by adding sulphuric acid in slio-ht ex- cess, and boiling; the whole is then filtered, and the clear fil- trate evaporated to dryness in a platinum dish, and ignited; QUALITATIVE ANALYSIS. 65 the residue is redissolved in water, and the solution tested for potassa, soda, and lithia, by dividing it into three portions, and proceeding with each in the manner above directed for the discovery of the alkalies. A portion of the original so- lution is tested for ammonia by heating with caustic potassa, and applying a feather moistened with strong acetic acid to the mouth of the tube. GROUP 3. Metallic Oxides not precipitated by sulphuretted hydrogen, but precipitated as oxides by hydrosulphuret of ammonia, Alumina, Yttria, Glucina, Thorina, Zirconia, Oxide of Chromium, Oxides of Cerium, Titanic Acid, Tantalic Acid. ALUMINA (Ala03). General Characters: When pure it is white, and in the state of powder it is light, and not at all compact. It has neither taste nor smell, but it adheres to the tongue, thereby occasioning a slight sense of astringency. By the heat pro- duced by a stream of oxygen gas directed against the flame of a spirit-lamp, it slowly melts, and gives a limpid and color- less globule, which, on cooling, becomes crystaline. It is quite insoluble in water, although it possesses a powerful affi- nity for that fluid, from which it can only be deprived by heat- ing to redness. It condenses moisture from the atmosphere in a remarkable manner. The hydrate of alumina has a strong affinity for vegetable coloring principles. Behavior of Aluminous Solutions with Reagents. Potassa produces in neutral solutions a bulky precipitate (Al203,HO), entirely soluble in excess of the precipitant, but reprecipitated by solution of salammoniac, which destroys the solvent, NH4Cl + KO becoming KC1 + NH40. Ammonia occasions a bulky precipitate, not soluble in ex- cess of the precipitant, and insoluble also in solution of sal- ammoniac. . The alkaline carbonates precipitate Al203,110, with tne evolution of carbonic acid. 5 66 QUALITATIVE ANALYSIS. Phosphate of soda produces, in neutral solutions, a precipi- tate soluble in free acids, and in potassa. Silicate of potassa (soluble glass) produces a precipitate of silicate of alumina in solutions of alumina in potassa. Before the bloivpipe, alumina, and many of its compounds, may be detected by heating the assay on charcoal, then moist- ening it with solution of protonitrate of cobalt; and again heating it strongly in the oxidating flame, a fine blue color is produced. GLUCINA (GIO). Oxide of Beryllium. — General Characters: This earth, when pure, has neither smell nor taste. It is insoluble in water, and infusible; but it does not harden in the fire like alumina, neither is the paste which it forms with water plas- tic. After ignition it is less soluble in acids. Behavior of Solutions of Glucina with Reagents. Potassa precipitates and redissolves it; but, by continuous boiling in a dilute alkaline liquor, the earth is again com- pletely precipitated. Solution of sal-ammoniac likewise pre- cipitates it from its solution in potassa. Ammonia produces a voluminous precipitate, insoluble in excess of precipitant; the presence of chloride of ammonium does not prevent the formation of this precipitate. The carbonated alkalies occasion a bulky precipitate, which is soluble in great excess of the precipitants, but more easily in carbonate of ammonia than in carbonate of potassa. Phosphate of soda produces a voluminous precipitate. Free acids produce no precipitate in glucina solutions. Before the Blowpipe, glucina and its salts cannot well be detected; they do not become blue when strongly heated with protonitrate of cobalt, like alumina, but take a gray or black shade. YTTRIA (YO). General Characters: This earth is of a pale yellow color. Its specific gravity is 4.842; hence it is heavier than baryta, the specific gravity of which is 4.00. It is soluble in acids after ignition. It gradually absorbs carbonic acid from the QUALITATIVE ANALYSIS. 67 atmosphere. Many of its salts have a faint amethyst red color and a sweet taste. Behavior of Salts of Yttria with Reagents. Potassa produces a white voluminous precipitate, insoluble in excess of the precipitant even by heat. Ammonia behaves in the same manner. The carbonated alkalies produce precipitates soluble in ex- cess of the precipitants, particularly in carbonate of am- monia. From the latter solution, crystals of double carbonate of ammonia and yttria may be obtained. When yttria con- tains peroxide of iron, or of cerium, it is very sparingly soluble in a solution of carbonate of ammonia. Sulphate of potassa produces, after a time, a precipitate which is completely redissolved by the addition of water, even if the water contain sulphate of potassa in solution. Phosphate of soda produces a precipitate soluble in hydro- chloric acid, from which it is again thrown down by boiling. Ferrocyanide of potassium occasions a white precipitate. Oxalic acid gives, in faintly acid solutions, a white precipi- tate, soluble in hydrochloric acid. Before the bloivpipe, yttria cannot with certainty be de- tected. According to Plattner, phosphate of yttria may be recognized by its giving a regulus of phosphuret of iron with boracic acid and iron, and from the difficulty with which it is dissolved by microcosmic salt. THORINA (TbO). General Characters: This rare earth is, when quite free from manganese, white. It is the heaviest of all the earths, its sp. gr. being 9.402. Its solutions have an astringent taste; it absorbs carbonic acid from the air. When moist, the hydrate dissolves readily in acids; but after having been dried'it is acted on with difficulty. The calcined earth is only attacked by hot sulphuric acid. Sulphate of thorina is, ac- cording to Berzelius, distinguished from all other oxidized bodies known, by its property of being precipitated by boil- ino-, and slowly redissolving on cooling. Behavior of Solutions of Thorina with Reagents. Potassa and ammonia produce a quickly subsiding precipi- tate insoluble in an excess of the precipitants. 68 QUALITATIVE ANALYSIS. The carbonated alkalies produce a precipitate dissolving readily in an excess of the precipitants. Sulphate of potassa produces a double salt, insoluble in water containing sulphate of potassa. Ferrocyanide of potassium occasions a heavy white precipi- tate soluble in acids. Before the blowpipe, the reactions of thorina have not been studied. ZIRCONIA (Zr„03). General Characters: When pure and calcined, zirconia is a white infusible powder; when ignited, it becomes brilliantly incandescent; it is sufficiently hard to scratch glass. Its sp. gr. is 4.3. After having been ignited, it is soluble only in concentrated sulphuric acid. Its soluble salts have a purely astringent taste without any sweetness. Behavior of Solutions of Zirconia with Reagents. Potassa and ammonia produce precipitates insoluble in an excess of the precipitants. The carbonated alkalies produce precipitates slightly soluble in an excess of the precipitants; the hydrate of zirconia is soluble in carbonate of ammonia, but very sparingly so in the carbonates of the fixed alkalies. Ferrocyanide of potassium occasions a white precipitate. Sulphate of potash produces, after a time, in hot solutions, a white double salt almost insoluble in pure water. Before the bloivpipe, zirconia cannot be recognized except by the brilliant light it affords when ignited. OXIDE OF CHROMIUM (Cr203.) General Characters: After ignition it is of a fine green co- lor, and is only soluble in hot sulphuric acid: the hydrate is of a grayish green color, and is readily soluble in acids, form- ing green solutions under reflected, and red by transmitted light; but if the hydrate has been strongly dried, but not ig- nited, it dissolves in acids with difficulty. Behavior of Solutions of Oxide of Chromium with Reagents. Potassa produces a bluish green precipitate (Cr203,HO), QUALITATIVE ANALYSIS. 69 readily soluble in an excess of the precipitant forming a green solution, from which the green anhydrous oxide is reprecipi- tated by boiling- either alone or with chloride of ammonium. ill'! Ammonia and carbonate oj ammonia produce a bluish green precipitate, partially soluble in the precipitant, to which it imparts a red color; but the precipitation is complete hj boiling the ammoniacal solution. Carbonate of potassa produces a bluish green precipitate, soluble completely in considerable excess of the precipitant, and not reprecipitated by boiling. Phosphate of soda produces a light green precipitate. Any compound of oxide of chromium when fused with nitre gives rise to the formation of chromate of potassa (KO, Cr03), which is soluble in water, and to which it communicates a yellow color. Before the blowpipe, the presence of oxide of chromium is easily detected by the beautiful green bead obtained when it is heated Avith borax or microcosmic salt, both in the inner and outer flame: oxide of copper gives also a green bead, but only in the outer flame. OXIDES OF CERIUM (CeO.Ce203). General Characters: The hydrated protoxide of cerium, when first precipitated, is white, but it gets rapidly yellow by exposure to the air by absorbing oxygen; it has never been obtained in a pure anhydrous state. Peroxide of cerium is a powder of a brick red color; it is easily dissolved by acids; when heated with hydrochloric acid, chlorine is evolved. Behavior of Solutions of Oxide of Cerium with Reagents. Potassa and Ammonia produce bulky precipitates, insoluble in excess of the precipitants; the precipitate is first yellowish white, but by exposure to the air it becomes deep yellow. ^ The alkaline carbonates produce a precipitate soluble in a slight degree in an excess of the precipitants, which thereby acquire a yellow color. Ferrocyanide of potassium occasions a white precipitate in neutral solutions. Sulphate of potassa forms after a time, a crystalline double salt very sparingly soluble in water, and not at all soluble in solution of sulphate of potassa. 70 QUALITATIVE ANALYSIS. Before the blowpipe, pure salts of cerium may be detected by fluxes. Red or dark yellow beads are obtained Avith borax or microcosmic salt in the oxidating flame, according to the quantity dissolved; these beads on cooling, or when subjected to the reducing flame, become quite colorless. TITANIC ACID (TiO). General Characters: It is a white, insipid, infusible powder: when heated, it assumes a fine yellow color, but again becomes colorless on cooling. It reddens infusion of turnsole even after having been exposed to a red heat, though the calcination ren- ders it insoluble in acids, except boiling sulphuric. Behavior of Solutions of Titanic Acid with Reagents. Ammonia precipitates a white gelatinous hydrate (TiO,HO), soluble with great readiness in acids, and soluble also in small quantities in the carbonated alkalies: it is precipitated from its solution in carbonate of ammonia by long boiling: its so- lution in carbonate of potassa or soda is precipitated by boil- ing with sal-ammoniac. Titanic acid is precipitated as a heavy white powder from its acid solutions by continued boiling: this precipitate can- not, however, be washed on a filter with pure Avater (Rose): according to Berzelius it can be completely precipitated from its solution in sulphuric acid by long-continued boiling. The caustic alkalies and hydrosulphuret of ammonia do not precipitate titanic acid in the presence of a sufficient quantity of tartaric acid. Ferocyanide of potassium produces a red brown precipitate. A bar of metallic zinc or iron placed in a solution of an alka- line titanate in hydrochloric acid, effects a reduction of the acid by the nascent hydrogen: and a blue or violet colored oxide of titanium gradually subsides slowly, becoming white. Titanic acid precipitated by boiling is likewise reduced by zinc or iron in an acid liquid. Sulphite of ammonia (NH40,S02), aided by a gentle heat completely precipitates titanic acid. Before the blowpipe, pure titanic gives with microcosmic salt a violet bead; the reaction is observed better on addino- metallic tin; in the presence of peroxide of iron the glass ap* pears, when strongly heated in the reducing flame, yellow and QUALITATIVE ANALYSIS. 71 on cooling, red; with borax no alteration is produced by the presence of iron, the bead being colorless in the outer flame, but turning milky when heated again. In the inner flame it is slightly yellow. TANTALIC ACID (Ta03). General Characters: The hydrated acid is a powder of a milky white color, insipid and inodorous. It reddens moist- ened turnsole paper. It dissolves Avholly in hydrofluosilicic and partially in sulphuric acid, but is precipitated from the latter by water, a circumstance Avhich may be regarded as character- istic of tantalic acid. The solution of tantalic acid dissolved in binoxalate of potassa, is precipitated of an orange yellow color, by infusion of galls. It is not precipitated by sulphu- retted hydrogen; but alkaline hydrosulphurets throw it clown unaltered, with the disengagement of sulphuretted hydrogen. Behavior of Solution of Tantalic Acid with Reagents. Ferrocyanide of potassium occasions a yellow precipitate. The hydrate of tantalic acid is easily soluble in caustic al- kalies, and at a boiling temperature, it is soluble also in alka- line carbonates with the evolution of carbonic acid; it is soluble also in hydrofluoric acid, and in binoxalate of potassa. At a certain temperature hydrated tantalic acid loses water and becomes anhydrous. When hot it is yelloAV, but in cool- ing it regains its Avhite appearance; in this state it is soluble only Avith great difficulty in acids and alkalies. When a so- lution of tantalic acid is precipitated by sulphuric acid, and brought into contact Avith zinc and hydrochloric acid, it dis- solves, forming a fine blue liquid, which subsequently turns brown. Before the blowpipe it gives a limpid bead, with microcosmic salt. The borax bead is clear when hot, but becomes milky on cooling. General Remarks on the Oxides of the Third Group. Alumina and glucina are both dissolved readily by caustic potassa; but the tAVO earths are distinguished from each other by the latter being precipitated from its alkaline solution by boiling, and by its hydrate being soluble in carbonate of am- monia. Yttria, thorina, and zirconia are not soluble in caus- 72 QUALITATIVE ANALYSIS. tic potassa: yttria is distinguished from the other two earths by the double salt Avhich it forms Avith sulphate of potassa being soluble in solution of sulphate of potassa; whereas the double salts formed by thorina and zirconia are not soluble in sulphate of potassa. These two latter earths are not very easily distinguished from each other; but the precipitate pro- duced by carbonated alkalies in solutions of thorina is much more soluble in carbonate of potassa than the corresponding precipitate in solution of zirconia. Thorina is, moreover, more than double the density of zirconia, Avhich is distin- guished again by the glaring Avhite light Avhich it produces when strongly ignited. The color of the salts of oxide of chromium, and their behavior before the bloAvpipe, is quite sufficient to distinguish this oxide from all the other members of the group. Oxide of cerium is characterized by the deep yelloAV color which it acquires by exposure to the air. Ti- tanic and tantalic acids are distinguished by the blue color produced on bringing a rod of zinc or iron into contact with their acid solutions; and tantalic acid is distinguished from titanic acid by the ready solubility of its hydrate in caustic potassa, and by its precipitation from its hydrochloric solution by sulphuric acid. This group may be conveniently subdivided into two sec- tions by the comportment of its members with caustic potassa: thus alumina, glucina, oxide of chromium, and hydrated tan- talic acid are soluble in caustic potassa: the other members are insoluble. GROUP 4. Metallic Oxides not precipitated from their acid solutions by sulphuretted hydrogen, but completely precipitated by hy- drosulphuret of ammonia as sulphurets—Oxides of Zinc, Nickel, Cobalt, Protoxide of Manganese, Protoxide and Ses- quioxide of Iron, Sesquioxide of Uranium. OXIDE OF ZINC (ZnO). General Characters:—When pure it is white; it becomes yellow when heated, but on cooling its Avhiteness usually re- turns, though sometimes it retains its yellow tinge. It is QUALITATIVE ANALYSIS. 73 sometimes obtained crystaline, and is then always yellow. When the metal is burned in the air, the oxide is obtained of snoAvy Avhiteness, and in light flocks. In this state it is known as "philosophical wool." It has a remarkable affinity for alumina; a combination of the two oxides in atomic propor- tions is met with in the mineral kingdom crystalized in regular octohedrons, and is knoAvn under the name of Gahnite. Behavior of Solutions of Oxide of Zinc with Reagents. Potassa and ammonia produce in neutral solutions a white gelatinous precipitate (ZnO, HO), readily soluble in an ex- cess of the precipitants. Sulphuretted hydrogen produces in neutral solutions a Avhite precipitate (ZnS): in acid Solutions no precipitate is formed. Hydrosulphuret* of ammonia completely precipitates salts of oxide of zinc, as (ZnS,) insoluble in an excess of the pre- cipitant, as Avell as in potassa and ammonia, but soluble in IICI and dilute S03 acids. The carbonates of the fixed alkalies precipitate basic car- bonate of zinc (3 HO, ZnO + 2 ZnO, C02), quite insoluble in an excess of the precipitants, but soluble in potassa and in ammonia. The presence of any salt of the latter prevents the formation of this basic salt, a soluble double salt of zinc and ammonia being formed. Carbonate of ammonia produces a white precipitate, soluble in an excess of the precipitant. Phosphate of soda produces a precipitate soluble in acids, and in potassa and in ammonia. Oxalic acid and binoxalate of potassa occasion precipitates which are soluble in acids and in fixed alkalies, but the forma- tion of which is not prevented by sal-ammoniac. Ferrocyanide of potassium produces a Avhite gelatinous pre- cipitate, insoluble in free hydrochloric acid. Ferricyanide of potassium produces a yellowish red precipi- tate, soluble in hydrochloric acid. Before the blowpipe, zinc salts are easily detected. Heated with carbonate of soda on charcoal in the reducing flame me- * Otto proposes to separate zinc from manganese when they exist in solutions containing a large proportion of muriate of ammonia, by adding ammonia which produces no precipitate, and then passing a stream of sulphuretted hy- drogen. If any manganese is present in the precipitate it may be dissolved out by acetic acid in which sulphuret of zinc-is insoluble. 74 QUALITATIVE ANALYSIS. tallic zinc is produced, which volatilizes, and on coming into contact with the air is again oxidized, and the charcoal be- comes covered with a sublimate, which Avhen hot is yellow, and on cooling white, and gives Avhen heated in the oxidating flame, with a few drops of protonitrate of cobalt, a beautiful and characteristic green color. OXIDE OF NICKEL (NiO). General Characters:—The pure oxide is of a deep ash gray color; it is not magnetic; it dissolves readily in acids; its hydrate is of an apple-green color. Behavior of Solutions of Oxide of Nickel with Reagents. Potassa produces a bright green precipitate, insoluble in an excess of the precipitant, but soluble in carbonate of am- monia. Ammonia precipitates the same green hydrate, but an ex- cess redissolves it, forming a clear blue solution, from which potassa again precipitates the hydrate. If free acid or am- moniacal salt is present no precipitate is produced. • Sulphuretted hydrogen does not precipitate acid solutions of nickel. In neutral solutions, after a time, an inconsiderable black precipitate is formed; but in the presence of an alkaline acetate, aided by a gentle heat, sulphuretted hydrogen effects a complete precipitation. Hydrosulphuret of ammonia produces a black precipitate, partially soluble in an excess of the precipitant and Avholly soluble in nitro-muriatic acid; hence after the subsidence of the precipitate the fluid remains black. Alkaline carbonates produce a pale green precipitate, so- luble in carbonate of ammonia. Phosphate of soda occasions a very pale yellow precipitate. Ferrocyanide of potassium produces a pale yelloAvish green precipitate, insoluble in HC1 acid. Cyanide of potassium throws down a greenish Avhite pre- cipitate (NiCy), Avhich an excess redissolves into a brownish yelloAV liquid (NiCy,KCy); on the addition of a mineral acid, cyanide of nickel is again precipitated, and hydrocyanic acid set free. Before the blowpipe, salts of nickel, heated in the outer flame Avith borax or microcosmic salt, give a reddish colored QUALITATIVE ANALYSIS. 75 bead. The addition of nitre changes the color to dark purple or blue: heated in the inner flame on charcoal Avith carbonate of soda, reduction takes place, and renders the bead gray. OXIDE OF COBALT (CoO). General Characters:—As obtained by the calcination of the carbonate, it is of an ash gray color; as obtained by the combustion of the metal, it is blue or grayish blue; as pre- cipitated from its solutions by caustic potassa, it has a fine blue color. When this precipitate is boiled for some time, it assumes by degrees a violet, and finally a dirty red tinge, which according to Proust, is the hydrate: the blue precipi- tate is considered by some chemists to be a basic salt. It dissoWes by fusion Avith vitreous fluxes, communicating to them a magnificent blue color, or, if in excess, black. Behavior of Solutions of Oxide of Cobalt with Reagents. Potassa produces a blue precipitate, insoluble in an excess of the precipitant, but soluble in carbonate of ammonia; the precipitate becomes green by exposure to the air, and dingy red when boiled. Ammonia* produces a blue precipitate, which an excess redissolves, forming a solution which is at first green, but Avhich by exposure to the air becomes broAvn; if sal-ammoniac be present in sufficient quantity, neither potassa nor ammonia produce any precipitate, though, if air have access, the solu- tion gradually becomes brown. The alkaline carbonates produce a red precipitate, which upon being boiled becomes blue. Phosphate of soda occasions a blue precipitate in neutral solutions. Ferrocyanide of potassium gives a green precipitate, which gradually turns gray. Ferricyanide of potassium gives a dark reddish brown pre- cipitate. Sulphuretted hydrogen in acid solutions occasions no pre- cipitate : in neutral solutions, after a time, a slight black pre- cipitate, the solution acquiring a dark color. * If the cobalt is pure the solution of its protoxide in carbonate and caustic ammonia has a fine red color, but if nickel is present, the shade is dirty purple or even brownish black. Caustic potassa does not precipitate from such a solu- tion. 76 QUALITATIVE ANALYSIS. Cyanide of potassium precipitates cyanide of cobalt as a broAvnish -white precipitate from acid solutions, soluble in ex- cess of the precipitant, and not again precipitated by acids. Hydrosulphuret of ammonia produces a black precipitate, quite insoluble in excess. Before the blowpipe, salts of cobalt are distinguished by the beautiful blue color they communicate to borax and microcos- mic salt, in both oxidating and reducing flames. Heated Avith carbonate of soda in the reducing flame, a gray powder, me- tallic cobalt, is produced. OXIDE OF MANGANESE (MnOA.* General Characters:—It is of a grayish green color. When prepared by igniting the carbonate or oxalate in an atmo- sphere of hydrogen, it absorbs oxygen from the air, gradually becoming broAvn. The oxide, prepared by fusing the chloride with anhydrous carbonate of soda, undergoes no alteration by exposure to the air. The hydrate Avhen first precipitated is white, but on exposure to the air it gradually becomes brown. This oxide possesses, in common with magnesia and oxide of iron, the property of only being partially precipitated by am- monia, and of carrying Avith it a portion of silicic acid when precipitated from a liquid holding this acid in solution. The salts of oxide of manganese are sometimes colorless, and some- times of a pale rose color. Behavior of Solutions of Oxide of Maganese with Reagents. Potassa and ammonia produce precipitates which at first are white, but soon become colored; first yellow, then broAvn, and finally nearly black: if ammoniacal salts be present, am- monia occasions no precipitate, and potassa only a partial one, which slowly becomes brown by exposure to the air. A clear ammoniacal solution containing oxide of manganese gradually gets turbid by exposure to the air, brown hydrated sesquiox- ide of manganese being deposited. The carbonated alkalies produce a Avhite precipitate of car- bonate of manganese, which assumes an amethyst shade after long exposure, and is sparingly soluble in sal-ammoniac. * The protoxide forms the base of nearly all the salts of manganese, for the salts of the peroxide easdy resolve themselves into salts of protoxide with disen- gagement of oxygen. QUALITATIVE ANALYSIS. 77 Phosphate of soda produces a white precipitate persistent in the air. Ferrocyanide of potassium produces a pale red precipitate, soluble in free acids. Ferricyanide of potassium ghres a brown precipitate, inso- luble in free acids. Sulphuretted hydrogen does not precipitate either acid or neutral solutions. Hydrosulphuret of ammonia produces a flesh-red precipitate insoluble in excess, but soluble in mineral acids and even in strong acetic acid ; by exposure to the air it becomes oxidized, finally assuming a brownish black color. By fusing any salt of manganese on platinum foil with a mixture of nitre and carbonate of soda, manganate of soda of a fine green color is produced ; the smallest portion of manganese may in this manner be detected. Before the blowpipe, fused in the oxidating flame with borax or microcosmic salt, salts of manganese give an amethyst co- lored bead, the color of Avhich disappears in the reducing flame, but may again be produced in the oxidating flame. PROTOXIDE OF IRON (FeO). General Characters: This oxide, AAdiich is only obtained pure with extreme difficulty, is black, and has frequently a metallic lustre: it is brittle, fuses at a high temperature, and on cool- ing is converted into a brittle, brilliant, but not vitreous mass. It is dissolved in acids Avith great difficulty, after having been exposed to a red heat; but the salts formed are identical Avith those obtained by dissohing the metal itself in the respective acids. It is very feebly magnetic, by Avhich it is distinguished from the ferrosoferric oxide, Avhich is strongly magnetic. It combines Avith water, forming a hydrate Avhich, Avhen pure, is Avhite; but by contact Avith the atmosphere it speedily becomes colored; first gray, then green, then bluish-black, and finally yellow. When boiled in an hermetically closed vessel, it parts with its Avater, and becomes black. It is the basis of all the protosalts of iron. Behavior of Solutions of Protoxide of Iron with Reagents. Potassa and ammonia produce a flocculent precipitate of 78 QUALITATIVE ANALYSIS. hydrated protoxide of iron, which at first is nearly white, but Avhich readily becomes colored by exposure to the air. The presence of ammoniacal salts prevents the precipitation of ox- ide of iron by ammonia, and in some degree by potassa. Alkaline carbonates produce a white carbonate, gradually becoming colored, though not so readily as the oxide. It is soluble in sal-ammoniac, but a colored precipitate makes its appearance by exposure to the air. Phosphate of soda produces a white precipitate, which after a time becomes green. Ferrocyanide of potassium produces a precipitate, which, if air be entirely excluded, is Avhite (K,Fe3Cfy2); but, if air or a small quantity of sesquioxide of iron be present, it has a blue tinge; by exposure to the air, or by contact Avith nitric acid or chlorine, it absorbs oxygen, and gbTes rise to the formation of Prussian blue. The transformation will be understood from the following equations : (a.) 3 FeCl + 2 K2,Cfy=3 KCl + KFe3Cfy2. (6.) 3 (K,Fe3Cfy2) + 40=2 (Fe4Cfy3) + 3 KO + FeO. (a.) Three equivalents of protochloride of iron and two equivalents of ferrocyanide of potassium react in such a man- ner as to form three equh'alents of chloride of potassium and one of the Avhite compound. (b.) Three equivalents of the white compound combine Avith four equivalents of oxygen to form tAvo equivalents of Prus- sian blue, three equivalents of potassa, and one of oxide of iron. Prussian blue is insoluble in hydrochloric acid; its color is discharged by the fixed caustic alkalies. Ferricyanide of p>otassium produces a beautiful blue preci- pitate, insoluble in acids, but easily decomposable by alkalies. The composition of this substance is Cfy2F3, and it is thus formed:— 3 FeCl + K3Cfy2=3 KCl+Cfy2Fe3. Three equivalents of protochloride of iron, and one equiva- lent of ferricyanide of potassium, produce three equivalents of chloride of potassium, and one of Turnbull's blue. Sulphuretted hydrogen does not precipitate acid solutions of oxide of iron; and neutral compounds very incompletely. Hydrosulphuret of ammonia produces a black precipitate, speedily becoming brown by exposure to the air. It is insoluble QUALITATIVE ANALYSIS. 79 in alkalies and alkaline sulphurets, but easily soluble in mine- ral acids. Before the blowpipe,* protosalts of iron heated on charcoal with borax or microcosmic salt in the oxidating flame give dark red beads, becoming lighter on cooling; in the inner flame the color produced is green, Avhich disappears on cooling, if the metal be not present in too large quantity. When fused with soda on charcoal in the reducing flame, a metallic magnetic poAvder is obtained. SESQUIOXIDE OF IRON (Fe203). General Characters: Its color and physical appearance dif- fer according to its mode of preparation. It is met with in nature of a gray color, and crystaline; as prepared by the calcination of the subsulphate of the sesquioxide, it has a fine red color; from the sulphate its color is deeper, and when made from the nitrate it is brownish black; and it is some- times met with quite black. By the action of a high heat it is converted into ferroso-ferric oxide (FeO,Fe2o3) with the disengagement of oxygen gas. It does not dissolve very readily save in concentrated acids, after having been strongly heated, though much more easily than the protoxide. It is not easily precipitated from its solutions by means of an alkali or an earth. If too little alkali be added, a subsalt is thrown doAvn; if too much, a portion is precipitated with the oxide. When iron is oxidized by degrees in contact with a large quantity of water, a hydrate of the sesquioxide of a clear orange color is formed. Behavior of Solutions of Sesquioxide of Iron with Reagents. Potassa and ammonia produce a voluminous reddish brown hydrate, insoluble in excess. The precipitation is prevented by the presence of organic acids, sugar, &c. The carbonated alkalies^ throvf doAvn precipitates of rather a lighter color, carbonic acid being at the same time disen- gaged. * Chapman gives the details of his mode of separating the protoxide from the peroxide of iron in Chem. Gaz., 6, 107. f Recently precipitated hydrated peroxide of iron is entirely soluble in an ex- cess of carbonate of ammonia, but the peroxide may again be thrown down entirely by diluting the liquid largely with water. 80 QUALITATIVE ANALYSIS. Phosphate of soda produces a AAdiite precipitate (2 Fe203, 3P05+13aq.) A\hich becomes brown, and finally dissolves on the addition of ammonia. Ferrocyanide of potassium produces a beautiful precipitate (Fe4Cfv3) by the folloAving reaction:— 2 Fe2Cl3+3 K2Cfy=Fe4Cfy3+6 KC1. Tavo equivalents of sesquichloride of iron and three of fer- rocyanide of potassium give rise to one equivalent of Prussian blue, and six equivalents of chloride of potassium. Sulpho-cyanide of potassium changes the color of neutral or acid solutions to a deep blood red color, owing to the form- ation of a soluble sulphocyanide of iron. This is the most un- erring test, as it will detect the slightest trace of iron even in the most dilute solution. Sulplturetted hydrogen produces in neutral and acid solu- tions a Avhite deposit of sulphur, the sesquioxide being reduced to protoxide thus :— Fe203+HS=2 FeO + HO + S. Hydrosulphuret of ammonia produces in neutral solutions a black precipitate, insoluble in excess, and becoming brown by exposure to the air. This precipitation is preceded by the reduction of the sesquioxide into protoxide. Before the blowpipe, salts of sesquioxide of iron behave in the same manner as those of the protoxide. SESQUIOXIDE OF URANIUM (Ur203).* General Characters: The hydrate is a beautiful yellow poAvder, soluble in acids, forming fine yellow solutions ; heated to about 300°, it loses its Avater and becomes anhydrous; it then has a dark green color. Heated above that tempera- ture, it loses oxygen and becomes converted into uranoso-ura- nic oxide (UrO,Ur203) of a deep gray color. Sesquioxide of uranium reddens moistened turnsole paper, though it blues paper stained red Avith infusion of logAvood. It produces, therefore, the reaction of acid and base. According to Berze- lius, this substance should more properly be called uranic acid ; its properties being rather those of an electro-negative than of an electro-positive oxide. It forms definite compounds * As the indications of peroxide are more characteristic than those of the pro- toxide, the latter should be converted into the former by heating with nitric acid. QUALITATIVE ANALYSIS. 81 with bases, all of which are insoluble in water; and, when precipitated from its solution in an acid by means of an alkali, the latter is divided into two portions, and the precipitate ob- tained is a uranate. Behavior of Solutions of Sesquioxide of Uranium with Reagents. Caustic alkalies precipitate uranates of the bases of a pale yellow color. Alkaline carbonates produce pale yellow precipitates, solu- ble in an excess, but again precipitated by boiling. Sulphite of ammonia produces at a boiling temperature a yelloAV precipitate. Ferrocyanide of potassium gives a red brown precipitate. Sulphuretted hydrogen reduces salts of sesquioxide with the deposition of sulphur; but sesquioxide is again produced by exposure to the atmosphere, or by the action of oxidizing agents. Hydrosulphuret of ammonia produces a black precipitate. Before the bloivpipe, heated alone on charcoal, sesquioxide of uranium is com-erted into protoxide; heated with micro- cosmic salt on platinum Avire in the oxidating flame, it dis- solves, producing a clear yellow glass, which on cooling becomes green. General Remarks on the Oxides of the Fourth Group. Of the seven oxides constituting this group,, oxide of zinc alone is soluble in caustic potassa. It is thus readily separated from the other six, and it is distinguished from alumina, oxide of chromium, &c, members of the third group, by its being again precipitated from its alkaline solution by sulphuretted hydro- gen. Oxides of zinc, cobcdt, iron, and manganese, form Avith ammonia soluble double salts not precipitable by alkalies. Oxide of iron is easily eliminated from the other three oxides by converting it into sesquioxide, by boiling with nitric acid. It is then completely precipitated by ammonia, provided no non-volatile organic matter be present. The same is the case Avith sesquioxide of uranium. Hydrate of oxide of nickel is dissolved by ammonia, but again precipitated by potassa. Hydrated oxide of nickel, and hydrated oxide of cobalt are both soluble in carbonate of ammonia, which is not the case with hydrated protoxide of manganese, Avhich may thus, therefore, be 6 82 QUALITATIVE ANALYSIS. separated from them. The perfect separation of oxide of nickel from oxide of cobalt, is attended with great difficulties. The presence of nickel may be recognized by the behavior of the solu- tion of its cyanide in cyanide of potassium Avith hydrochloric acid, Avhich precipitates it, the same not being the case with cyanide of cobalt. In the former case a double cyanide of nickel and potassium (NiCy,KCy) is formed ; but in the latter, with the presence of free hydrocyanic acid, a cobaltocyanide of potassium is formed. Thus:— 2CoCy + 3KCy+HCy=K3C02Cy6+H. Two equivalents of cyanide of cobalt, three equivalents of cyanide of potassium, and one equivalent of hydrocyanic acid, give rise to one equivalent of cobaltocyanide of potassium, and one of hydrogen. Noav, though the solution of cyanide of cobalt in cyanide of potassium is not precipitated by an acid, it may be so in the presence of nickel, and if that metal be present in the proportion of three equivalents to two equiva- lents of cobalt, the Avhole of the latter will be precipitated— the three equivalents of nickel replacing the three equivalents of potassium in the cobaltocyanide of potassium, and giving rise to cobaltocyanide of nickel (N3Co2Cy6). Thus : 3(NiCy+KCy)+Co2K3Cy6=6KCy+Co2Ni3Cy6. Three equivalents of the double cyanide of nickel and potas- sium, and one equivalent of the cobaltocyanide of potassium, giving rise to one equivalent of cobaltocyanide of nickel, and six equivalents of cyanide of potassium. The bloAvpipe is, moreover, an infallible test of the presence of oxide of cobalt. GROUP 5. Metallic Oxides completely precipitated from their solutions, Avhether acid or alkaline, or neutral, by sulphuretted hydrogen, their sulphurets being insoluble in alkaline sulphurets—Oxides of Lead, Silver, Mercury, Bismuth, Cadmium, Copper, Palladium, Rhodium, and Osmium. OXIDE OF LEAD (PbO). General Characters: When pure, this oxide is yellow, but its powder has a reddish tint. When certain lead salts, as the subnitrate and oxalate, are decomposed by heat without QUALITATIVE ANALYSIS. 83 fusion, they furnish an oxide of a pure sulphur yellow color, which by trituration becomes red: in this state it is sometimes called massicot. By allowing a solution of oxide of lead, in caustic soda, to remain for some months exposed to the air, white, semi-transparent, dodecahedron crystals of anhydrous oxide may be obtained. The same crystals, according to Payen, are formed on mixing a dilute solution of acetate of lead, with great excess of caustic ammonia, and exposing to the rays of the sun. Oxide of lead becomes of a deep red color Avhen heated, regaining its primitive color on cooling : at a red heat it fuses and cools in semi-transparent, deep brick-red, crystalline scales; at a still higher temperature it undergoes partial decomposition, the metal being reduced. It absorbs carbonic acid slowly from the air; hence an effer- vescence generally attends its solution in an acid. Pure water is capable of retaining in solution from 7^^ to T3-Jp of oxide of lead; but water containing the smallest traces of saline matter does not dissolve it. The hydrate is white, and ab- sorbs carbonic acid rapidly from the air. It loses its Avater at about 300°. Oxide of lead combines with alkalies and earths; its combinations with potassa and soda are crystal- izable. It enters into fusion Avith, and dissolves, the earths with great facility. Its best solvent is nitric or acetic acids. Behavior of Solution of Oxide of Lead with Reagents. Potassa and ammonia produce white precipitates, which are basic salts, soluble in a great excess of potassa* but inso- luble in ammonia. The carbonated alkalies produce white precipitates, soluble in potassa. Phosphate of soda occasions a white precipitate, soluble in potassa. Oxalic acid produces, in neutral solutions, a white preci- pitate. . . . Ferrocyanide of potassium produces a white precipitate, soluble in potassa. Iodide of potassium produces a yellow precipitate, soluble in great excess by heat, and separating on cooling, in magni- ficent yellow spangles. * One part of protoxide of lead requires eleven parts of potassa or 13 of soda for its solution. 84 QUALITATIVE ANALYSIS. Chromate of potassa produces a fine yellow precipitate solu- ble in potassa, but insoluble in dilute nitric acid. Hydrochloric acid and soluble chlorides produce a heavy white precipitate, soluble in boiling water, out of Avhich it separates on cooling, in brilliant crystals. This precipitate is soluble in qiotassa. Sulphuretted hydrogen produces a black precipitate, both in acid and neutral solutions. Hydrosulphuret of ammonia produces a black precipitate, insoluble in excess. Sulphuric acid and soluble sulphates produce a white pre- cipitate (PbO,S03)* sparingly soluble in dilute acids, but so- luble in solution of potassa, and assuming a black color Avhen moistened with hydrosulphuret of ammonia. Before the blowpipe, on charcoal, mixed with carbonate of soda, salts of lead are immediately reduced, furnishing a metallic globule, which gradually sublimes, leaving a yellow residue. The metallic globule can easily be flattened under the hammer. OXIDE OF SILVER (AgO). General Characters: As obtained by dropping solution of nitrate of silver into caustic potassa, it is a grayish brown powder ; but, if the solutions are concentrated and boiling, the oxide precipitates as a heavy black poAvder. Exposed to the rays of the sun, it disengages a certain quantity of oxygen, and turns black. It is entirely reduced by ignition. It is slightly soluble in pure water, and in water of barytes. It reacts alkaline to test paper, and displaces from their combi- nations with the alkalies a portion of the acids, Avith which it forms insoluble compounds. It combines Avith caustic am- monia, giving rise to a dangerous substance (fulminating silver). It readily dissolves in nitric and other acids. Behavior of Solutions of Oxide of Silver with Reagents. Potassa and ammonia produce a light brown precipitate, readily soluble in ammonia. The presence of ammoniacal salts wholly or in part prevents precipitation by potassa. The carbonated alkalies produce a white precipitate, soluble in carbonate of ammonia. * Sulphate of lead is soluble in 47 parts of acetate of ammonia of sp. gr. 1.036. (JBischof.) QUALITATIVE ANALYSIS. 85 Phosphate of soda produces, in neutral solutions, a yellow precipitate, soluble in ammonia. Solution of ignited phos- phate of soda (2NaO,PO5+10HO) gives a white precipitate. Ferrocyanide of potassium gives a white precipitate. Ferricyanide of potassium produces a reddish broAvn preci- pitate. Chromate of potassa produces a rich broAArn precipitate. Protosulphate of iron produces a white precipitate, consist- ing of metallic silver. Hydrochloric acid and the soluble chlorides produce a Avhite curdy precipitate even in exceedingly dilute solutions. This precipitate becomes A-iolet, and finally black, Avithout, how- ever, suffering decomposition by exposure to light. It is inso- luble in diluted acids, but readily soluble in ammonia. When heated it fuses, without decomposition, into a horny mass. If the solution of silver be exceedingly dilute, hydrochloric acid produces an opalescent appearance. A bar of metallic zinc precipitates silver from its solution in the metallic state. Sulphuretted hydrogen produces a black precipitate, both in acid and in neutral solutions. Hydrosulphuret of ammonia gives a black precipitate, inso- luble in excess. Before the blowpipe, mixed with carbonate of soda, and heated on charcoal, salts of silver are readily reduced Avhile no incrustation takes place. SUBOXIDE OF MERCURY (Hg20). General Characters: It is a black poAvder, Avhich a very gentle heat converts into metallic mercury and oxide of mer- cury, and a stronger heat into mercury and oxygen gas. The black poAvder obtained by the long-continued agitation of the metal, and Avhich Avas supposed to consist of this oxide, is pro- bably only the metal in a state of very fine division. The soluble salts of this oxide redden litmus paper, and are de- composed, Avhen mixed Avith much water, into soluble acid and insoluble basic salts. Behavior of Salts of Suboxide of Mercury with Reagents. Potassa and ammonia produce a black precipitate insoluble in excess. 86 QUALITATIVE ANALYSIS. Alkaline carbonates produce a dirty yellow precipitate which turns black by boiling. Phosphate of soda produces a white precipitate. Ferrocyanide of potassium produces a white gelatinous precipitate. Ferricyanide of potassium giAres a reddish brown precipi- tate, Avhich gradually becomes Avhite. Iodide of potassium produces a greenish yelloAV precipitate, rendered black by a larger quantity, and soluble in an excess. Chromate of potassa produces a red precipitate. Sulphuretted hydrogen produces a black precipitate, both in acid and neutral solutions. Hydrosulphuret of ammonia produces a black precipitate, insoluble in excess, but decomposed by potassa into sidphuret of mercury and metallic mercury. It is not decomposed or dissolved by boiling nitric acid, but easily by aqua regia. A bar of metallic zinc throws down an amalgam of zinc and mercury. Hydrochloric acid and soluble chlorides produce a white precipitate, nearly insoluble in acids, but rendered black by potassa and ammonia, the suboxide being formed. Protochloride of tin produces a gray precipitate, which, boiling, resolves into globules of metallic mercury. A drop of solution of a salt of suboxide of mercury, rubbed with a rag on a piece of bright copper, leaves a silvery stain, Avhich disappears Avhen it is heated to redness. Before the blowpipe, mixed -with carbonate of soda, and heated in a glass tube, metallic mercury sublimes in the form of a gray poAvder, Avhich, on being rubbed with a glass rod, is resolved into globules. OXIDE OF MERCURY (HgO). General Characters: It is a brick-red crystalline powder; but when finely pulverized has a yelloAV tinge. At a slightly elevated temperature it turns black, but it regains its red color on cooling. At a red heat it is resolved into oxygen gas and metallic mercury, and is entirely volatilized. In this manner the presence of impurities, red lead, or brick-dust, may be detected. It dissolves readily in acids, but is not acted on by ammonia, and is not entirely insoluble in Avater. QUALITATIVE ANALYSIS. 87 Behavior of Solutions of Oxide of Mercury with Reagents. Potassa produces a yellow precipitate (HgO,HO) insolu- ble in excess. If an insufficient quantity of the alkali be added, the precipitate is reddish brown. The presence of ammoniacal salts causes the formation of a white precipitate, which is a compound of amidide of mercury with undecom- posed mercury salts. Thus, 2HgCl + NH3=(HgNH2HgCl) + HCl. Fixed carbonated alkalies produce a reddish brown pre- cipitate, insoluble in excess, but converted, in the presence of ammoniacal salts, into white (HgCl2N2H3Cl2) + (Hg2Cl2+ HgO.) (Buflos.) Carbonate of ammonia produces a white precipitate. Phosphate of soda produces a Avhite precipitate. Ferrocyanide of potassium produces a Avhite precipitate, which eventually becomes blue, OAving to the formation of Prussian blue. Ferricyanide of potassium produces, in solutions of the nitrate and sulphate, a yelloAV precipitate; in solutions of the chloride, none. Sulphuretted hydrogen and hydrosulphuret of ammonia give rise to different colored precipitates according to the quantity of the reagent added. If it be added in small quan- tity, and the solution agitated, the precipitate is white, being a compound of sulphuret of mercury and undecomposed salt; the addition of larger quantities causes the precipitate to assume, successively, a yellow, orange, broAvn, red, and black color. The sulphuret of mercury is soluble in solution of potassa, but not in boiling nitric acid, though it dissolves readily in aqua regia. Iodide of potassium produces a cinnabar red precipitate, soluble in excess. It crystalizes out of a hot solution in mag- nificent crimson spangles. Protochloride of tin, Avhen added in excess, separates the metal in the form of a gray powder, Avhich may be united into globules by boiling with hydrochloric acid. All the salts of mercury are decomposed Avhen heated in a glass tube with a slightly moistened alkaline carbonate, the metal subliming in small globules: the metal is likewise reduced Avhen the solu- tion is brought into contact Avith clean metallic copper, and rubbed. 88 QUALITATIVE ANALYSIS. OXIDE OF BISMUTH (BiO). When pure it is of a straAV yelloAV color, and melts at a strong red heat to an opaque glass, Avhich, Avhile hot, is dark broAvn or black, but on cooling becomes yellow; when melted Avith silica, alumina, or metallic oxides, it dissolves them readily. The oxide precipitated by water retains nitric acid, from Avhich it may be freed by caustic potassa or soda, which convert it into a hydrate. It is easily reduced by ignition with organic substances or charcoal poAvder. It dissolves readily in Avater, forming colorless salts. Behavior of Solutions of Oxide of Bismuth with Reagents. Potassa and ammonia produce a Avhite precipitate, insolu- ble in excess. Alkaline carbonates and phosphate of soda produce white precipitates. Ferrocyanide of potassium occasions a white precipitate, insoluble in hydrochloric acid. Ferricyanide of potassium produces a light yellow precipi- tate soluble in hydrochloric acid. Iodide of potassium produces a brown precipitate, readily soluble in excess. Chromate of potassa produces a yellow precipitate, soluble in dilute nitric acid, and insoluble in potassa. Sulphuretted hydrogen and hydrosulphuret of ammonia produce a black precipitate, both in acid and neutral solutions, insoluble in excess, and in dilute nitric acid, but soluble in boiling nitric acid. The neutral salts of bismuth are distinguished by their property of being decomposed by Avater into a soluble acid, and an insoluble basic salt. The chloride* of bismuth exhibits this property in the most marked manner. The insoluble basic bismuth salt is distinguished from the basic salt of an- timony, formed under similar circumstances, by its being in- soluble in tartaric acid. Before the blowpipe, heated on charcoal in the reducing flame, salts of bismuth are easily reduced to brittle globules, which spring to pieces under the hammer; the charcoal, at the same time, becomes covered with a yelloAV incrustation. * Alcohol dissolves chloride of bismuth without decomposing it. QUALITATIVE ANALYSIS. 89 OXIDE OF CADMIUM (CdO). General Characters: The color of this oxide varies accord- ing to its state of aggregation. It is sometimes of a deep red broAvn, sometimes clear broAvn, and occasionally black. It is infusible, and does not volatilize at exceedingly high temperatures; but, when mixed with powdered charcoal, it is reduced by heat, and the metal burns and volatilizes. By long-continued gentle ebullition of the metal, the oxide may be obtained, according to Herapath, in long purple needles, opaque, and grouped in rays. Its hydrate is Avhite; it loses its water by heat, and absorbs carbonic acid from the air. It is not soluble in the fixed alkalies, but it dissolves in caustic ammonia. It dissolves easily in acids, forming colorless so- lutions. Behavior of Solutions of Oxide of Cadmium with Reagents. Potassa and ammonia produce a Avhite precipitate (HO, CdO), insoluble in potassa, but easily soluble in ammonia. The carbonated alkalies produce a Avhite precipitate (CdO, C02), insoluble in excess. Ammoniacal salts do not prevent the formation of this precipitate. Phosphate of soda produces a white precipitate in neutral solutions. Oxalic acid produces a precipitate soluble in ammonia. Ferrocyanide of potassium produces a slightly yelloAV pre- cipitate, soluble in hydrochloric acid. Ferricyanide of potassium produces a yellow precipitate, also soluble in hydrochloric acid. Sulphuretted hydrogen and hydrosulphuret of ammonia produce a rich yelloAV precipitate, insoluble in excess, and in dilute acids and alkalies, unalterable in the air, but decom- posed by boiling with concentrated nitric acid. A bar of metallic zinc precipitates the metal from its solu- tions in the form of small glancing, gray-colored spangles. Before the blowpipe, heated with carbonate of soda on char- coal, the metal is reduced and volatilizes, leaving a dark yel- Ioav red incrustation. OXIDE OF COPPER (CuO). General Characters: It is pulverulent, and of a black 90 QUALITATIVE ANALYSIS. color; at a high temperature it fuses, and on cooling ex- hibits a crystaline fracture. By particular management, Becquerel obtained it in the form of fine tetrahedral crystals, having a high metallic lustre. Heated Avith charcoal, or in contact with organic matter, it is reduced either to metallic copper or to the suboxide. It dissolves easily in acids with the disengagement of heat, and its solutions have mostly a blue or a green color. Its hydrate is blue; but at the temperature of boiling Avater it becomes black, a property Avhich interferes with its employment as a pigment. It does not unite in the humid Avay Avith the caustic alkalies; but at a red heat it com- bines Avith both alkalies and earths, forming blue or green compounds. Caustic alkalies containing organic matters dis- solve it, forming blue or purple compounds. Behavior of Solutions of Oxide of Copper with Reagents. Potassa produces a voluminous blue precipitate (HO,CuO), which by boiling loses water and becomes black. Ammonia added in small quantities produces a green basic salt, which dissolves in excess, forming a fine blue solution. In this solution potassa produces in the cold, after a time, a blue precipitate, Avhich by boiling becomes black. Carbonate of potassa produces a greenish blue precipitate of basic carbonate of copper, Avhich by boiling is converted into black oxide. Carbonate of ammonia behaves precisely as ammonia. Phosphate of soda produces a greenish white precipitate, soluble in ammonia, forming a blue solution. Ferrocyanide of potassium produces, even in very dilute solutions, a chocolate brown precipitate, insoluble in dilute acids, but decomposed by potassa. This is a very delicate test. Ferricyanide of potassium produces a yellowish green pre- cipitate, insoluble in dilute acids. Cyanide of potassium produces a yellowish green cyanide, soluble in excess of cyanide of potassium. Chromate of potassa produces a reddish brown precipitate, soluble in ammonia, forming an emerald green solution, solu- ble also in dilute nitric acid. Sulphuretted hydrogen and hydrosulphuret of ammonia produce a black precipitate, slightly soluble in excess of hy- drosulphuret of ammonia, but insoluble in caustic alkalies, and QUALITATIVE ANALYSIS. 91 in sulphuret of potassium, and in dilute acids. It is readily decomposed by boiling nitric acid, and is completely soluble in cyanide of potassium. Metallic iron, when introduced into solutions of oxide of copper, becomes covered Avith a deposit of reduced copper. Before the blowpipe, salts of copper heated Avith borax or microcosmic salt in the oxidating flame, give a grass green bead, becoming blue on cooling; in the reducing flame the glass is red and opaque, mixed with carbonate of soda; and heated on charcoal in the inner flame the metal is reduced, and gives a bead of metallic copper. OXIDE OF PALLADIUM (PdO). General Characters: It is a black powder, acted on Avith great difficulty by acids. The hydrate is of a deep brown color, and parts Avith its water only at a high temperature. Its solution in nitric and nitro-hydrochloric acid has a red broAvn color. Behavior of Solutions of Oxide of Palladium with Reagents. Potassa precipitates a yelloAvish brown basic salt, soluble in excess. Ammonia precipitates from solution of chloride of palladium a pink compound of chloride of palladium and ammonia (Pd C1,NH3), soluble in excess of ammonia. In the nitrate of palladium, ammonia gives no precipitate.* Carbonated alkalies precipitate a yelloAvish broAvn basic salt, soluble in excess of the precipitants. Cyanide of potassium and cyanide of mercury producer yelloAvish Avhite precipitate of cyanide of palladium, soluble in great excess of hydrochloric acid. Sulphuretted hydrogen and hydrosulphuret of ammonia produce a black precipitate, insoluble in hydrosulphuret of ammonia. Palladium salts are reduced by sulphurous acid, and^ by being heated with a salt of oxide of iron, or with a formiate. * The neutral solutions of -protonitrate of palladium give yellow precipitates with the neutral phosphates, arscuiates, oxalates, tartrates and citrates. 92 QUALITATIVE ANALYSIS. SESQUIOXIDE OF RHODIUM (R,03). General Characters: The metal, as Avell as the anhydrous sesquioxide, is insoluble even in boiling aqua regia. Both, hoAvever, are dissolved on fusion with bisulphate of potassa, or on heating a mixture of both Avith chloride of sodium to red- ness, and passing over it a stream of chlorine. The color of the hydrated oxide is greenish gray. The haloid salts of this metal are red: the oxysalts yelloAV, red, or broAvn. Behavior of Salts of Sesquioxide of Rhodium with Reagents. Potassa does not occasion any immediate precipitate; but after protracted digestion a precipitate of a brownish yellow color makes its appearance. Ammonia and carbonate of ammonia produce, after a time, a yelloAV precipitate, composed of sesquioxide of rhodium and ammonia, which is soluble in hydrochloric acid. Hydrosulphuret of ammonia and sulphuretted hydrogen produce, after a time, a dark broAYn precipitate, insoluble in an excess of the former. All the salts of rhodium are decomposed, and the metal is reduced by exposure to a gentle heat, in contact with dry hy- drogen gas. OXIDES OF OSMIUM (OsO; 0<203; 0s02; Os04). The presence of osmium is discovered in the salts by mixing them Avith a little carbonate of soda, and heating on platina foil, the metal is converted into osmic acid, which possesses an extremely acrid and penetrating odor like chloride of sul- phur, attacking powerfully the olfactory and respiratory or- gans, and producing, even in minute quantities, a burning sensation in the eyes. It communicates also a considerable brilliancy to flame. The metal itself is -whitish, like platinum, but less brilliant. It is easily pulverized. It dissolves in ni- tric acid and in aqua regia, osmic acid, passing over Avith the water of the acid. Osmic acid is easily reduced by many metals and organic compounds. Solutions of salts of oxide of osmium are precipitated by hydrosulphuret of ammonia and sulphuretted hydrogen, as a brownish black sulphuret insolu- ble in hydrosulphuret of ammonia. QUALITATIVE ANALYSIS. 93 General Remarks on the Oxides of the Fifth Group. The metallic oxides constituting this group admit of a divi- sion into two sections by their comportment with hydrochloric acid. Three of them, viz: oxide of lead, oxide of silver, and oxide of mercury are precipitated by that reagent; the others are not. Of the chlorides thus formed, chloride of silver is easily separated from the other two by ammonia, in which it is perfectly soluble, and from Avhich it is again precipitated by nitric acid. The same alkali decomposes subchloride of mer- cury, converting the metal into black protoxide, from which chloride of lead may be removed by boiling water, and the metal tested for in the clear solution by any of the reagents mentioned under its head. The insolubility of sulphuret of mercury in nitric acid serves to separate this metal from all the others in the group. The precipitates caused by potassa and ammonia in solutions of oxide of cadmium and oxide of copper, are soluble in ammonia; those of the others are not; but the hydrated oxide of copper is soluble also in carbonate of ammonia. Hydrated oxide of cadmium has no such pro- perty ; moreover, the blue color of the ammoniacal solution of oxide of copper is perfectly characteristic of that metal. Cad- mium, again, is distinguished by the color of its sulphuret, which, being insoluble in hydrosulphuret of ammonia, distin- guishes it from the yellow sulphurets of some of the metals in the next group, all of Avhich are soluble in hydrosulphuret of ammonia. Oxide of bismuth is readily detected by the de- composition of its salt by water. Salts of palladium are re- cognized by their behavior Avith cyanide of mercury and cya- nide of potassium. The insolubility of oxide of rhodium in acids, and the color of its salts, serve to distinguish this metal; and the presence of osmium compounds is recognized by the penetrating odor of osmic acid. GROUP 6. Metallic Oxides completely precipitated from their acid solu- tions by sulphuretted hydrogen; but not from their alkaline solutions, their sulphurets being soluble in alkaline sul- phurets—Oxides of Antimony, Arsenic, Tin, Platinum, 94 QUALITATIVE ANALYSIS. Iridium, Gold, Selenium, Tellurium, Tungsten, Vana- dium, and Molybdenum. ANTIMONiC ACID (SbO). General Characters: It is a Avhite poAvder, soluble in small quantities in boiling Avater. This oxide is insoluble in nitric acid; but it dissolves in hydrochloric acid, and the solution is decomposed by water, a basic salt being separated. Behavior of Solutions of Antimonic Acid with Reagents. Potassa and ammonia produce a white precipitate partially soluble in excess of the reagent. Alkaline carbonates and j'hosphate of soda behave in a simi- lar manner. Metallic zinc throws down metallic antimony as a black powder; if nitric acid be present, the sesquioxide is precipi- tated at the same time. Sulphuretted hydrogen throws down from acid solutions an orange yellow precipitate, readily soluble in excess and in po- tassa; but very sparingly soluble in ammonia, and entirely insoluble in carbonate of ammonia. It is insoluble in dilute acids, but is decomposed by concentrated and boiling hydro- chloric acid; the precipitate is very incompletely formed in neutral solutions. Hydrosulphuret of ammonia produces an orange yellow precipitate, completely soluble in excess. The solution of double tartrate of antimony and potassa (tartar emetic) is only precipitated after a time by alkalies and their carbonates. Antimony possesses the property of forming a gaseous combination Avith hydrogen; the union of these tAvo bodies may be brought about by adding zinc and sulphuric acid to a solution containing the oxide, Avhich becomes deoxidized by the zinc; a portion of the metal unites Avith the hydrogen of the water, which is at the same time decomposed. Antimoni- uretted hydrogen is inflammable, burning Avith a bluish green flame, and emitting copious fumes of sesquioxide; if the flame be alloAved to impinge on a cold surface, such as a porcelain plate, a dark spot of reduced antimony will be produced. If the gas, as it proceeds from an evolution flask, be allowed to pass along a horizontal tube of hard German glass, and the QUALITATIVE ANALYSIS. 95 tube be heated to redness at a certain point, decomposition of the gas will take place at that spot; on both sides of which a brilliant mirror of metallic antimony will be deposited: if now a stream of dry sulphuretted hydrogen be allowed to pass through the tube, the bright mirror will vanish, and a deposit of a more or less intense yelloAV color will take its place, the antimony being converted into sulphuret. If now the flask in Avhich sulphuretted hydrogen is generating be re- moved, and its place supplied by one containing the materials for generating hydrochloric acid gas, and if a gentle stream of this gas be sent through the tube, the yelloAV deposit will vanish, the sulphuret being converted into chloride, which being volatile may be conveyed with the gas into a vessel of water, in which the presence of antimony may then be proved by acidulating it with hydrochloric acid, and transmitting through it a stream of sulphuretted hydrogen gas. Before the blowpipe, mixed with carbonate of soda on char- coal, oxide of antimony is easily reduced, and brilliant metal- lic globules obtained: the metal fumes and volatilizes, covering the charcoal with a Avhite incrustation, amongst Avhich needle- shaped crystals frequently appear. ARSENIOUS ACID (As03). General Characters: As met with in commerce, this acid is almost completely pure; it is Avithout smell and almost Avith- out taste ; if kept for some time in contact with the tongue, it induces a slightly bitter taste, which, hoAvever, leaves one of sweetness. It sublimes before entering into fusion; but with certain precautions it may be fused in close vessels, and obtained on cooling in the form of a colorless transparent glass. When sublimed in a current of air, it forms fine octahedral crystals. Its vapor is without color or taste; the odor which accompa- nies it is due either to the reduction of the metal or to the formation of a lower oxide. This acid has tAvo isomeric modi- fications, one of which is represented by the vitreous and the other by the milky variety. The latter was supposed to be merely the result of an admixture of Avater; but ithas been ascertained that the two varieties differ both in their specific gravity and in their chemical properties. The milky variety is much more soluble in Avater than the other, 100 parts of Avater at the ordinary temperature dissolving 1.25 of the for- 96 QUALITATIVE ANALYSIS. mer and 0.96 of the latter, and at the boiling temperature 11.47 of the former and 9.63 of the latter; while at 32° water retains in solution 2.9 parts of the milky and 1.78 of the vitreous acid. The aqueous solution of the vitreous variety reddens paper tinged with infusion of turnsole; that of the milky appears, on the other hand, to have rather an alkaline reaction. Rose has observed that a saturated solution of the vitreous acid in hydrochloric acid deposits on cooling octahedral crystals, during the formation of which flashes of light may be observed in the dark: neither of these phenomena occur Avith the milky variety. The great diversity of statements made with regard to the solubility of arsenious acid in Avater, have arisen not only from the difference of the tAvo varieties in this respect, but also probably from the different manner in Avhich the experiments have been made. Arsenious acid dissolves much more readily in acids than in Avater, and is deposited unaltered on cooling from hot solutions. It forms a class of salts called arsenites, all of which are poisonous, though not so eminently so as the acid itself. The best antidote to this poison is hydrated sesquioxide of iron, perfectly free from alkali, and Avhich has not been dried, but preserved in a gela- tinous state saturated Avith Avater: arsenious acid forms with this oxide a basic insoluble salt. Perhaps the best method of administering this antidote is in the form of a completely satu- rated solution of the hydrated sesquioxide in acetic acid. Behavior of Solutions of Arsenious Acid with Reagents. Sulphuretted hydrogen produces in aqueous solutions of arsenious acid a very slow and incomplete precipitation; but in the presence of free hydrochloric acid an immediate preci- pitate of sulpharsenious acid (AsS3) of a bright yelloAV color is produced. This precipitate is easily soluble in alkalies, alkaline carbonates, and alkaline sulphurets; it is also decom- posed by boiling nitric acid, though it is nearly insoluble in hydrochloric acid. When fused Avith a carbonated alkali and nitre, it is decomposed, the products being arseniated and sul- phated alkali. When an alkaline solution of sulpharsenious acid is boiled Avith oxide of copper, sulphuret of copper and arseniated alkali are formed. When a mixture of sulpharse- nious acid and carbonate of soda is heated in a current of dry hydrogen gas, as shoAvn in Fig. 1, a reduction of a portion of QUALITATIVE ANALYSIS. 97 the arsenic compound takes place, and a metallic mirror is forme'd within the tube, thus:— 2AsS3+4NaO,C02=NaO,As03+3NaS,AsS3+4C02. Two equivalents of sulpharsenious acid, and four equivalents of carbonate of soda, producing one equivalent of arsenite of soda, and three equivalents of sulpharsenico-sulphuret of sodium + four of carbonic acid. When the vapors of sulpharsenious acid are passed over ignited lime, sulphuret of arsenic and calcium and arseniate of lime are formed, with the separation of arsenic. When sulpharsenious acid is fused with cyanide of potas- sium, sulphocyanide of potassium is formed, and arsenic set I1*GG tllllS * 2AsS3+3KCy = 3KCyS2+2 As. This experiment is best made by introducing a mixture of one part of sulpharsenious acid with ten or tAvelve parts of a mix- ture of two parts of dry carbonate of soda and one part of cyanide of potassium, into a glass tube draAvn out as shown in Fig. 1, and heated to redness; while a current of dry car- bonic acid gas is passed over it, the arsenic is deposited on Fig. 1. d M'/,.„i,:H : ■Jllll the cold surface of the narrow part of the tube in the form of a black mirror. A is the flask containing lumps of solid marble, provided with a funnel tube, through Avhich hydrochloric acid is poured for the generation of carbonic acid. B is a smaller flask con- taining oil of vitriol, in passing through Avhich the carbonic acid becomes dried. C, the mixture of sulpharsenious acid with carbonate of soda and cyanide of potassium heated by a spirit lamp; d, the metallic mirror. Sulpharsenious acid is also reduced by heating it with a mixture of equal parts of carbonate of soda and cyanide of 7 98 QUALITATIVE ANALYSIS. potassium in a small tube of hard German glass closed at one end, and drawn out into a long and open point at the other. Hydrosulphuret of ammonia produces in acid solutions of arsenious acid a yellow precipitate of sulpharsenious acid; in neutral or alkaline solutions no precipitate occurs. Nitrate of silver produces in neutral solutions a yellow pre- cipitate of arsenite of silver (2AgO,As03), soluble in dilute nitric acid and ammonia. Ammonio-nitrate of silver produces the same precipitate in acid solutions. Sulphate of copper (neutral) produces a yellowish green precipitate of arsenite of copper in neutral solutions, but none in the free acid. Ammonio-sulphate of copper produces the same precipitate in acid solutions. Neutral chromate of potassa produces a green color, but no precipitate in a solution of arsenious acid. If the liquids are added in reversed order, the green colored solution congeals in a few moments to a jelly.— (Schiveitzer.) Arsenic, like antimony, forms a gaseous compound with hy- drogen ; the combination of the two elements may be effected by bringing together arsenious acid or an arsenite with zinc,* water, and sulphuric or hydrochloric acid (chemically pure); this property is taken advantage of as a test for the metal, and forms a valuable means of isolating it. The materials for ge- nerating the hydrogen are Fis- 2- introduced into the evolu- fj A tion flask, A, Fig. 2, and the gas being filtered by passing through a tube filled with dry cottonwool, B, is inflamed at the point of the bent tube, C, (suf- ficient time being allowed to expel the atmospheric air from the apparatus,) and a porcelain plate de- pressed on the flame. If, af- ter burning for some time, no incrustation or blacken- * It is indispensable that the zinc be previously purified, and freed of arsenic and antimony. QUALITATIVE ANALYSIS. 99 ing appears on the plate, it is a sign that the materials in the evo- lution flask are free from arsenic; additional assurance is, how- ever, obtained by heating a portion of the horizontal tube to redness at b, by means of a spirit lamp; no incrustation must be observed in the tubes. The liquid to be tested for arsenic is now introduced into the evolution flask through the funnel tube; and if it contains any traces of the poison, the flame of the hydrogen will acquire a bluish white color, owing to the reduction and separation of the arsenic, and fumes of arsenious acid will make their appearance. On now depress- ing the porcelain plate upon the flame, brown arsenic spots will be obtained: these incrustations have a shining metallic appearance, those of antimony being black and possessing scarcely any metallic lustre. On applying the flame of the spirit lamp to the horizontal part of the tube, a beautiful in- crustation of metallic arsenic will be formed on the cold part of the tube, which is darker and less silvery than that formed by antimony under similar circumstances; and on cutting off the tube near the deposit, and applying heat, the arsenic is con- verted into arsenious acid, which is recognized by its garlic odour, and which may be dissolved in hot water, and tested by nitrate of silver and sulphate of copper. The following modification of Marsh's apparatus by the Acade- my of Sciences of Berlin, is de- scribed by Dr. Ure in his Supple- ment to his Dictionary of Arts, Manufactures and Mines:— A is a narrow glass cylinder open at top, about ten inches high, and one and a quarter, or one and a half inch in diameter inside. B is a glass tube about one inch in diameter outside, drawn to a point at bottom, and shut with a cork at top. Through the cen- tre of this cork a small tube C passes down air-tight, and is fur- nished at top with a stop-cock, into which the small bent glass tube (without lead) E is cemented. The bent tube E is joined to the end of F by a perforated cork. Fig. 3. kh 100 QUALITATIVE ANALYSIS. This apparatus is used as follows:—Introduce a few oblong slips of zinc free from arsenic into B, and then insert its air-tight cork with the attached tubes. Having opened the stop-cock, pour into the tube A as much of the suspected liquid, acidulated with dilute pure sulphuric acid, as will rise to the top of the cork after B is full, and immediately shut the stop-cock. The generated hydrogen will force down the liquid out of the lower orifice of B into A, and raise the level of it above the cork. The extremity of the tube F being dipped beneath the surface of a weak solution of nitrate of silver, and a spirit flame being placed a little to the left of the letter E, the stop-cock is then to be slightly opened, so that the gas which now fills the tube B may escape so slowly as to pass off in separate small bub- bles through the silver solution. By this means the Avhole of the arsenic contained in the arseniuretted hydrogen will be de- posited either in the metallic state upon the inside of the tube E, or with the silver into the characteristic black powder. The first charge of gas in B being expended, the stop-cock is to be shut, till the liquid be again expelled from it by a fresh disengagement of hydrogen. The ring of metallic arsenic de- posited beyond E may be chased onwards by placing a second flame under it, and thereby formed into an oblong, brilliant, steel-like mirror. It is evident that, by the patient use of this apparatus, the whole arsenic in any poisonous liquid may be collected, weighed, and subjected to every kind of chemical verification. By means of the perforated cork, the tube F may readily be turned about, and its taper point raised into such a position as, when the hydrogen issuing from it is kin- dled, the flame may be made to play upon a surface of glass or porcelain, in order to form the arsenical mirror. The most satisfactory method, howeArer, of distinguishing between the metallic mirrors* formed by antimony and arsenic * Maclagan proposes to discriminate between an arsenical and antimonial stain by the difference of temperature at which they undergo sublimation. The results of a series of experiments give confidence in this mode as the readiest and mo^ satisfactory. The degree of heat employed ranges from 335° to 565°, at which temperature arsenic is volatilized whilst antimony remains permanent. The heat is applied by means of a "bath of olive oil, which may be urged even to its boiling-point without at all affecting an antimonial stain, whilst the heat so employed will entirely sublime an arsenical crust into a crystaline sublimate of arsenious acid. It will always be best, if it is possible, to have a thermometer in the oil bath, that the extreme temperature employed may be stated in evidence if asked for. But this is not indispensable; olive oil does not begin to boil till the heat rises above 600°; and this heat, however long applied, does not cause QUALITATIVE ANALYSIS. 101 under similar circumstances, is founded on the decomposition of sulphuret of antimony by hydrochloric acid gas, and the volatility of the chloride of antimony thus formed. We can thus not only distinguish an arsenical from an antimoniacal deposit, but Avhen both metals are present we can separate them perfectly. We proceed thus-:—The mirror having been obtained, a feeble stream of dry sulphuretted hydrogen is sent through the tube, a gentle heat being at the same time ap- plied : if the metal be arsenic alone, sulphuret of that metal of a light yellow color will be formed; if it be antimony alone, the sulphuret is either orange red or nearly black; if both antimony to volatilize. Stains which are so faint as not to appear distinctly me- tallic till the tube is held over a sheet of white paper, maybe distinguished in this way. The pure arsenical metallic stain entirely disappears from the spot where it was deposited, the pure antimonial remains unchanged ; whilst the mixed arsenical and antimonial becomes visibly less, a portion has undergone sublimation, whilst the residue, however long the heat may be prolonged, re- mains fixed. If, in addition to the disappearance of the stain from the portion of the tube immersed in the oil, we can observe the formation of a crystaline sublimate in the upper portion of the tube, the proof may be said to be absolute. Very small quantities of arsenic may be rendered distinctly visible in this form. I have operated upon stains produced from a Marsh's apparatus, which con- tained less than a thousandth of a grain of arsenic, and have yet been able to see distinctly the crystaline character of the sublimate. The gentle and gradual way in which the heat is applied in the oil bath causes the sublimate to deposit itself in fewer but much larger crystals, and thus makes it much more appre- ciable by the eye or lens than could be supposed by those who have been in the habit of subliming small stains of arsenic by a spirit-lamp flame. In the case of some poisoned swine which I examined, and where, from one of the articles, I could obtain in the tube a mere shade of brown, and when, by the spirit- lamp, this was sublimed into a mere white cloud, I was able, by again heating in the oil-bath, to obtain a sublimate distinctly of crystaline appearance to the naked eye. In order, therefore, to determine whether a stain be arsenical or antimonial, all that is required is to operate with Marsh's apparatus and the narrow glass tube; if a stain is procured, to seal up the point, immerse it in the oil-bath, and heat this steadily. The heating does not require to be prolonged. Ten minutes after the temperature has risen to about 500°, will have affected the stain if it is arsenical. It is well remarked by Taylor, that, in such investiga- tions, we have to determine the presence of arsenic in antimony, not of antimony in arsenic- and therefore, if any sublimation in the oil-bath can be observed at all, the question as to the presence of arsenic is settled. To enable us to ob- serve this more readily, it is a good plan to make a small scratch on the tube at each limit of the stained portion before heating it; and thus, by its diminution, we may pronounce upon its nature, although no sublimate should be distinctly visi- ble. Should any peculiar case occur, in which it might be of importance to de- termine that antimony was present,as wellas arsenic, the heat must be continued for a longer period. I have found that a large pure arsenical stain, weighing on a delicate balance 0.036 gr., required an hour and a half of heating at 500° in a narrow tube to sublime it entirely. But long before one-third had been sublimed, the tube was lined with splendid crystals of arsenious acid. The heat, to sub- lime the whole arsenic, need never be raised beyond 520°; but, even if the oil boils, it does not affect the correctness of the experiment." 102 QUALITATIVE ANALYSIS. Fig. 4. metals be together, then both are converted into sulphurets; but the sulphuret of arsenic being more volatile than the sul- phuret of antimony, it will be deposited in a more advanced part of the tube. A current of dry hydrochloric acid gas is now passed through the tube ; chloride of antimony is formed with- out the application of heat, and is entirely removed in the cur- rent of gas. The sulphuret of arsenic remains unaltered, and may be distinguished from sulphur by its solubility in ammonia. It Avas the late Mr. Marsh, of Woolwich, who first took ad- vantage of the property of arsenic to form a gaseous compound Avith hydrogen, and employed it as a test for the metal. The apparatus he employed is shown in an improved form in Fig. 4. The stop-cock being re- moved from the tube, a few fragments of pure zinc are introduced into the bend of the tube, and pure dilute sulphuric acid poured upon them; the gas evolved having been proved to be free from arse- nic, the suspected liquid is introduced, and the gas burned against a porcelain plate as above described. Oxygen compounds of arsenious acid may be re- duced by heating them in one of the small tubes figured above, over a spirit lamp, Avith a mixture of carbonate of soda and charcoal; the metal volatilizes and condenses in the cool part of the tube, forming a mirror of great lustre. Arsenious acid is reduced by merely heating it to redness in contact with a splinter of charcoal. Metallic copper, Avhen boiled with an acidified mixture con- taining arsenious acid, becomes covered with a steel-gray crust of metallic arsenic. This is an exceedingly delicate test, and -will, according to its discoverer, Reinsch,* detect arsenic Avhen present in no more than a millionth part of the liquid; but as various other metals, silver, gold, platinum, bismuth, and antimony, are likewise precipitated under similar circum- stances, it is necessary to submit the crust to a careful exa- mination, f When arsenious acid is heated with a dry acetate * Maclagan has shown fChem. Gaz., vi. 450,) that Reinsch's test is less deli- cate than that of Marsh. f Abreu has recently announced the following method of " determining the na- ture of one or several metals mixed up with organic matter." It will comprise the compounds of the following metals:— Arsenic. Antimony. Mercury. Tin. Copper. Zinc. Lead. Silver. QUALITATIVE ANALYSIS. 103 and hydrate of potassa, oxide of kakodyl is produced, the insup- portable odor of which serves to detect very minute traces of _ The following is the plan of operation:—The experimenter should begin by examining attentively with a lens the substances vomited and evacuated, those found in the digestive canal, and the mucous surface of this canal. This will frequently furnish valuable indications; and in some cases it is possible to find in the digestive canal, especially in its mucous folds, solid particles of the poi- sonous substance. In this latter case the particles of poison should be carefully removed with a small forceps,and their nature ascertained if possible by the or- dinary methods; but supposing no definite result to follow from this physical examination, we proceed as follows:—The suspected matter to be examined is cut into small pieces with a pair of very small scissors; and a known weight of it, which should never exceed 200 grms., conveyed into a flask capable of holding two quarts, with half its weight of pure fuming muriatic acid. A cork with two perforations is adapted to the neck of this flask, into one of which is fitted a tube from 55 to 60 centimetres in length, and one centimetre internal diameter. It dips a few millimetres into the muriatic acid. The second perforation is destined for a tube curved at right angles, the second vertical branch of which passes through a cork into some distilled water contained in a test-tube; this cork has also a second perforation, into which is fitted a straight tube not dipping into the water. When this arrangement is made, the flask is placed on a sand bath, and the test-tube immersed in cold water, which is changed from time to time. The sand is kept at a temperature near the boiling-point of the liquid, and the flask is agitated from time to time for at least four hours. The organic matter is gradu- ally disintegrated, and finally forms a dense homogeneous liquid of a more or less dark color. The flask is then removed from the sand-bath, and boiled over an Argand lamp for two or three minutes, upon which some crystals of chlorate of potash are gradually introduced through the large tube, taking care to agitate the flask constantly until from sixteen to eighteen grms. have been used for every 100 grms. of suspected substance employed. A violent reaction takes place, with an abundant disengagement of chlorinated gases; the liquid gradually clears, and at last becomes perfectly transparent and of a yellow color, the intensity of which appears to depend especially on the large excess of chlorine remaining in solu- tion. Both the liquid in the flask and the water in the test-tube present the pe- culiar odor of chlorine in the highest degree. Some small fragments of charcoal and of a resinous substance float upon the liquid in the flask ; their quantity is very small in investigations of blood, but very considerable in examinations of the tissues of the liver and other parenchymatous organs. The apparatus is allowed to cool, the liquid in the flask filtered through Swedish paper, and mixed with the water in the test-tube and with the wash- waters. A current of well-washed sulphuretted hydrogen is passed through the united liquids for a considerable time,and the whole is then left till the morning in a corked flask. In all cases there will be a more or less abundant precipitate, which should be examined for all the metals comprised in our table except silver and zinc. This precipitate may nevertheless contain only sulphur and a little organic substance, which should be got rid of by the following plan :— The precipitate is thrown upon a filter without folds, washed with distilled water, and boiled in a small flask with its weight of pure and fuming muriatic acid, to which a few fragments of chlorate of potash are added. When the re- action is complete, a little distilled water is added, and the whole heated witJi great care, in order to expel the whole of the free chlorine. It is again filtered through Swedish paper, and a very transparent liquid is thus obtained with but a faint tint of yellow. The arsenic, antimony, mercury, copper, lead and 104 QUALITATIVE ANALYSIS. arsenic. The following is the reaction which gives rise to the formation of this poisonous compound : 2(KO,C4H303) + 2KO + As03=C4H6AsO + 4(KO,C02). Two equivalents of acetate of potassa, two of potassa, and one of arsenious acid, producing one equivalent of oxide of ka- kodyl, and four of carbonate of potassa. To prepare an organic mixture suspected to contain arsenic for the reception of sulphuretted hydrogen, Fresenius digests it in a Avater-bath, with an equal av eight of concentrated pure hydrochloric acid, and as much water as will give the whole a thin consistence. Chlorate of potassa is then added, in por- tions of about half a drachm, at intervals of about five minutes, and until the contents of the basin have assumed a bright yellow, perfectly homogeneous, and a thin liquid appearance. When this point is attained, about tAvo drachms more of chlo- rate of potassa are added to the mixture, and the basin is re- moved from the Avater-bath. When cool, it is filtered, and the residue Avashed, until all acid reaction ceases. The filtrate is concentrated to about a pint, and excess of sulphurous acid added, to reduce the arsenic acid to arsenious acid, the former being far less readily precipitated by sulphuretted hydrogen than the latter. The excess of sulphurous acid is then ex- pelled by heat, and the fluid exposed to a sIoav stream of sul- phuretted hydrogen gas for about twelve hours. The sul- phuret of arsenic thus obtained is washed and dried over a water-bath, and treated Avith fuming nitric acid, evaporated to dryness, moistened with pure sulphuric acid, and gently heated, first on the Avater-bath, and aftenvards at a higher temperature (not, however, above 300°), until the mass begins to crumble. The residue is treated with boiling-Avater, filter- ed; and the limpid fluid, after being acidified with hydrochloric acid,*is again precipitated by sulphuretted hydrogen. The pure sulphuret of arsenic thus obtained is mixed with carbon- ate of soda and cyanide of potassium, and reduced in an atmosphere of carbonic acid, as above described. MM. Duflos and Hirsh proceed as folloAvs.—The suspected mass (the stomach, for instance, Avith its contents) is digested in a tubulated retort, with an equal weight of pure hydro- tin, if the suspected matter contained any, will have to be sought for in this liquid. As zinc is not precipitated by sulphuretted hydrogen from an acid solution, it must be sought for in the liquid obtained by filtration after the action of the sulphu- retted hydrogen. The silver will be found in the residue from the first filtration. QUALITATIVE ANALYSIS. 105 chloric acid; the retort is connected with a receiver in which a little Avater is placed, the object of which is to collect any chloride of arsenic, that might volatilize during the process. The retort is heated by a bath of chloride of calcium until the mass acquires the consistence of paste, when it is allowed to cool. It is then mixed with twice its Aveight of strong alcohol, and after some time the undissolved portion is collected on a filter, and washed with alcohol. The alcoholic liquid and the washings are lastly introduced into a retort, and the alcohol distilled off. The residue in the retort is mixed Avith the acid liquor which passed into the receiver during the first distilla- tion, and the mixture is exposed to sulphuretted hydrogen. Danger and Flandin heat the organic substance with one- sixth of its weight of concentrated sulphuric acid; the sub- stance is carbonized without foaming; it is continually stirred till the charcoal is dry; a small quantity of nitric acid, or aqua regia, is then added, and the whole extracted with water. They observe, however, that the carbonizing process must only be had recourse to, when all attempts to obtain evidence of the poison Avithout it have failed. Dr. Letheby proposes the following method of treating or- ganic substances, by Avhich he states that it is not difficult to discover 3iotassa'and sul- phuric acid, a broAvnish red gas is produced, as in the case of a chloride: this gas, hoAvever, is bromine, and the color va- nishes on the addition of ammonia ; this reaction serves, there- v QUALITATIVE ANALYSIS. 137 fore, to distinguish between bromides and ehlorides, and for detecting the presence of the latter in the former. HYDRIODIC ACID (IH). This acid gas, likewise, resembles in its properties hydro- chloric acid: it is absorbed rapidly, and in large quantities, by Avater, the solution being colorless and fuming: there is also a strong analogy betAveen the compounds of iodine and those of bromine and chlorine. Behavior of Solution of Iodides* with Reagents. Nitrate of Silver produces a yellowish white precipitate, which blackens by exposure to the light, is insoluble in dilute nitric acid, and very sparingly soluble in ammonia. * Dr. Cantu detects the presence of iodine and bromine in mineral waters by the following method: "The water under examination is evaporated in a porcelain capsule to about half its bulk; carbonate of potash, of absolute purity, is then added (I say absolute purity, as the ordinary carbonate of potash contains sensible traces of iodine and bromine*) in slight excess, and boiled for some time in order to decompose the earthy salts contained in it; the liquid is allowed to become cool, and is then filtered: it is'now evaporated to dryness, taking care, however, not to heat the saline matter too highly in the desiccation ; the residue, if in smalt quantity, is powdered in the same capsule, and is treated with alcohol of 40°, in order to separate the salts soluble in this menstruum, among which will be found the bromides and iodides if they existed in the water. The liquid is evaporated to dryness at a gentle heat; and if it contain organic matter, as is generally the case, this is destroyed by ignition at a low red heat; a few drops of dilute acetic acid are next added in such proportion as to be in slight excess, taking care that the small quantity of carbonate of potash taken up by the alcohol is dissolved and neutralized. It is now again evaporated to dryness, to expel the excess of carbonic acid, avoiding a degree of heat that would decompose the acetate of potash, as this would communicate a brown tinge to the liquid and obscure the action of the test. At this point the residuary matter is dissolved in the smallest possible quantity of pure water, with two or three drops of a weak solution of starch recently prepared. This being done, a small quantity of the test liquor (consisting of a mixture of 10 parts of sulphuric acid of 66° with 1 part of nitric acid of 25°) is placed in a glass with a narrow base; then the solution of the saline residue is poured very gently down the side of the glass * To obtain carbonate of potash free from chlorides, bromides and iodides, it is necessary to proceed in the following manner:—Bitartrate of potash, colorless and crystalized, is calcined to whiteness, the residue treated with distilled water, and the solufbn evaporated to the consistence of syrup; alcohol of 40° (Beaume?) is then added, agitating thoroughly the mixture, and allowing it to react for some time the alcoholic liquor being afterwards decanted; the saline residue is brought on a filter, and washed with alcohol until a portion of the latter, being evaporated to dryness and examined with the proper tests, no longer gives any indication of the presence of iodides, bromides or chlorides. 138 QUALITATIVE ANALYSIS. Nitrate of suboxide of mercury produces a yellowish green precipitate. Chloride of mercury produces a beautiful scarlet precipitate. Acetate of lead produces an orange yellow precipitate, solu- ble in hot water, and in nitric acid, and crystalizing out of its solution in brilliant golden-colored scales. Protochloride of palladium produces a black precipitate in solutions of alkaline iodides: no precipitate is afforded by this reagent in solutions of bromides. An aqueous solution of one part of crystalized sulphate of copper, and tAVO and a half of protosulphate of iron, produces a dingy white precipitate (Cu2I): this mixture has no effect in solutions of chlorides and bromides. Chlorine, nitric acid, concentrated sulphuric acid and per- oxide of manganese eliminate iodine from solutions of iodides, the solutions becoming colored; and, if the solution is con- centrated, iodine separates as a black precipitate: on ap- plying heat, the characteristic violet vapors of iodine make their appearance : with excess of chlorine, a colorless chloride of iodine is formed. With starch paste free iodine forms a blue compound, and this reagent serves to detect minute traces of iodine in insolu- ble as well as in soluble compounds of that element. The sub- stance under examination is mixed in a retort with concen- trated nitric acid, and a strip of widte cotton cloth, moistened with solution of starch, suspended from the stopper; in a few hours the cloth will become colored blue if the most minute trace of iodine be present: nitric acid is better as an oxidiz- ing agent than chlorine, because of the formation of the co- lorless chloride of iodine, above referred to. The blue color of the iodide of starch disappears by heat, and by the action of certain deoxidizing agents. If a solid iodide be heated with concentrated sulphuric acid and peroxide of manganese, violet vapors of iodine will make their appearance. Before the blowpipe, metallic iodides, when treated with so as to rest on the test-liquor without mixing with it. By operating in this maimer, if iodides or bromides existed in the water, and the coexistence of these substances is almost constant, there will quickly appear two zones in the saline solution, one of a clear topaz-yellow, sometimes inclining to green, and the other of a blue color, floating on it." QUALITATIVE ANALYSIS. 139 cupriferous microcosmic salt, impart a beautiful and deep green color to the flame. BROMIC ACID (HO,Br05). When concentrated, it is very sour but not caustic: it has very little odor: it first reddens, and then discolors blue litmus paper; sidphurous phosphorous acids, and all the hydracids decompose it, liberating bromine: most of the bromates are soluble in water, and are converted by ignition into bromides, Avith evolution of oxygen: they are decomposed with violent deflagration AAThen heated Avith combustible substances, such as carbon, sulphur, and phosphorus. These mixtures likewise detonate violently when moistened with a drop of concentrated sulphuric acid. Bromates, Avhen treated Avith concentrated sulphuric and other oxygen acids in the cold, evolve oxygen and red vapors of bromine; they are likewise reduced by sul- phuretted hydrogen with separation of sulphur. Behavior of Solutions of Bromates with Reagents. Nitrate of suboxide of mercury produces a light yelloAV pre- cipitate, soluble in nitric acid. Acetate of lead produces a white precipitate, soluble in much water. Nitrate of silver produces a white precipitate, soluble in ammonia, but soluble with difficulty in dilute nitric acid. Sulphuretted hydrogen reduces bromates to bromides; sul- phuric acid being formed and sulphur separated. Sulphurous acid reduces bromates to bromides, sulphuric acid being formed. IODIC ACID (HO,I05). The aqueous solution of this acid is, when concentrated, very sour: it first reddens, and then destroys the color of litmus paper: it oxidizes all metals but gold and platina, and detonates violently when heated with combustible substances: with sulphuric, nitric, and phosphoric acid, it forms crystaline compounds, and Avhen mixed with vegetable acids a decompo- sition of both takes place; carbonic acid being liberated, and iodine precipitated. The iodates are mostly insoluble in water; the neutral alkaline iodates are soluble. 140 QUALITATIVE ANALYSIS. Behavior of Solutions of Iodates with Reagents. Nitrate of silver produces a white precipitate, soluble in ammonia and difficultly in nitric acid. Chloride of barium, chloride of calcium, and acetate of lead, give white precipitates, soluble in nitric acid. Iodates, when heated alone, are decomposed into iodides and oxygen; they deflagrate Avhen heated Avith combustibles: they are decom- posed by protochloride of tin, sulphurous acid, binoxide of tin, sulphuric acid, and iodine being separated; the latter may be made eAddent by adding starch paste. Sulphuretted hydrogen reduces iodates to iodides, sulphuric acid and water being formed, and iodine separated. HYDROCYANIC ACID (HCy). In its pure, anhydrous state, this acid possesses the follow- ing properties: it is colorless, inflammable, very volatile, and possessing a strong odor analogous to that of bitter almonds: its taste is at first cool, then burning and disagreeable. Its specific gravity is 0.6957 at 66°, it boils at 80°, it volatilizes rapidly in the air, producing a degree of cold sufficient (if it be not perfectly anhydrous) to cause it to assume a solid form: it is feebly acid to test paper: it is the most energetic poison known, one drop being sufficient to destroy an animal of con- siderable size. It is rapidly decomposed, even in close Aressels, becoming darker and darker in color, and eventually quite black: a trace of sulphuric acid prevents this decomposition from taking place; strong acids cause its elements so to ar- range themselves with the elements of Avater as to produce formic acid and ammonia; thus H,C2N + 4HO=NH4,0,C2H03 Hydrocyanic Fonniate of ammonia. aci'l. by distillation the formic acid may be separated, the ammonia remaining in combination with the acid Avhich occasioned the decomposition. The alkalies are reduced by hydrocyanic acid, their metal- lic radicals combining with cyanogen, and Avater being formed, thus:— KO + HCy=KCy+HO. the metallic cyanides thus formed have an alkaline reaction; QUALITATIVE ANALYSIS. 141 they are decomposed gradually when dissolved in water, rapidly when boiled, and instantly in contact Avith an acid, the result of the decomposition being formiate of the oxide of the metallic base and ammonia. Cyanide of potassium and cyanide of sodium may, however, be heated to redness out of contact of air, without suffering decomposition; but in contact with oxides of tin, lead, copper, and many other metals, they are converted into cyanates, the metals being reduced thus:— KCy+2PbO=KO,CyO + 2Pb. The greater number of the metallic cyanides are insoluble in water: they comport themselves differently under the influence of heat, some being resolved into the metal and cyanogen, as is the case with cyanide of mercury, and others into carburets and nitrogen: the compounds of cyanogen with gold, silver, and other heavy metals, are not decomposed by dilute, and with difficulty with concentrated nitric acid; hydrochloric acid and sulphuretted hydrogen, howeA-er, decompose them easily and completely. The cyanides of iron, cobalt, manganese, and chromium, when brought into contact with alkaline cya- nides, unite with their cyanogen, forming peculiar salt radi- cals, in Avhich the presence of the heavy metal cannot be de- tected by the usual tests. Behavior of Solutions of Cyanides with Reagents. Nitrate of silver produces a white curdy precipitate (AgCy) insoluble in dilute nitric acid, and sparingly soluble in ammo- nia, easily soluble in cyanide of potassium, and leaving pure silver when ignited; when moistened Avith hydrochloric acid, hydrocyanic acid is disengaged. Acetate of lead produces a white precipitate (PbCy). Subnitrate of mercury produces, in hydrocyanic acid, a gray precipitate of metallic mercury, cyanide of mercury remaining in solution, thus:— Hg20 + HCy=HgCy + Hg+HO. Oxide of mercury dissolves freely in hydrocyanic acid, and alkalies occasion no precipitate in the solution; in no other alkaline fluid can oxide of mercury be held in solution; this reaction serves therefore as a test of the presence of hydro- cyanic acid. In the presence of hydrochloric acid, ammonia produces a precipitate. A solution of protosulphate of iron, which has been par- tially oxidized by exposure to the air (magnetic oxide of iron), 142 QUALITATIVE ANALYSIS. occasions the formation of Prussian blue in solution of an alkaline hydrocyanate containing free hydrochloric acid; this reaction forms an excellent test for hydrocyanic acid, but it is essential that an alkali should be present, as also hydrochloric acid, to dissolve any oxide and sesquioxide of iron that may have been precipitated by the alkali together with the blue compound. Protosulphate of iron produces, in solutions of alkaline ferrocyanides, a pale blue precipitate. Sulphate of copper produces a chocolate brown precipitate. Sesquichloride of iron produces, in solutions of alkaline ferricyanides, a deep blue precipitate. Insoluble ferro- and ferri-cyanides are decomposed by fu- sion Avith alkaline carbonates, soluble alkaline ferro- and ferri-cyanides being formed. By distilling a ferrocyanide with dilute sulphuric acid, hydrocyanic acid is produced, and by heating it Avith a great excess of concentrated sulphuric acid, carbonic oxide is formed by the following reaction:— K2,FeC6N3, + 9HO=6CO + 2KO + FeO + 3NH3. One equivalent of ferrocyanide of potassium and nine equiva- lents of water from the oil of vitriol and the water of crystal- ization of the ferrocyanide, give rise to six equivalents of carbonic oxide, tAvo equivalents of potassa, one of protoxide of iron, and three of ammonia; the sulphuric acid, iron, potassa, and ammonia arrange-themselves into a crystaline anhydrous iron alum, having the following composition (Fownes):— 2(PeiO,+8SOJ)+NKOj80^ The most delicate and valuable test of the presence of hydro- cyanic acid that has hitherto been proposed, is that of Pro- fessor Liebig, and is dependent on the fact that the higher sulphurets of ammonium are instantly deprived, by cyanide of ammonium, of the excess of sulphur they contain above the monosulphuret sulphocyanide of ammonium (NH4,CyS2) being formed, Avhich produces, Avith persalts of iron, a very deep blood-red color. Mr. Alfred Taylor recommends the fol- lowing method of applying this test:—Place the diluted hydro- cyanic acid in a watch-glass, and invert over it another Avatch- glass, holding m its centre one drop of hydrosulphuret of ammonia containing sulphur in excess; there is no apparent change in the hydrosulphuret, but if the watch-glass be re- moved after the lapse of from half a minute to ten minutes, QUALITATIVE ANALYSIS. 143 according to the quantity of hydrocyanic acid present, sulpho- cyanide of ammonium will be obtained on gently heating the drop of hydrosulphuret and evaporating it to dryness. The addition of a drop of a solution of a persalt of iron to the dried residue brings out the blood-red color instantly, which is in- tense in proportion to the quantity of sulphocyanide present; the Avarmth of the hand may be employed to expedite the evolution of the vapor. This test is even more delicate and expeditious than the nitrate of silver test, in Avhich the vapors are received in a solution of that salt, and will, according to Taylor, detect in five minutes hydrocyanic acid not exceeding T4 3 of a grain in ten drops of a liquid. HYDROSULPHURIC ACID OR SULPHURETTED HYDROGEN (HS). This acid is a colorless gas, which under a strong pressure becomes liquid ; it has a highly offensive odor resembling that of putrid eggs; its taste is acid, astringent, and bitter; it is inflammable, burning with a blue flame, and disengaging sul- phurous acid; it explodes violently when mixed with oxygen or atmospheric air and ignited; when mixed with chlorine, sulphur is deposited and hydrochloric acid formed; it is highly deleterious when inspired, even when mixed with a large quantity of air; it is absorbed by water, which acquires its peculiar smell and a nauseous sweet taste; the solution red- dens litmus paper, and decomposes by exposure to the air, sulphur being deposited; most metallic oxides are decomposed by sulphuretted hydrogen, sulphuret of the metals and water being formed. The alkalies and alkaline earths, and the oxides of chromium, tantalum, and titanium, do not exchange their oxygen for sulphur in the moist way. The sulphurets of the metals of the alkalies, and the alkaline earths, are soluble in water; they are decomposed by dilute mineral acids with the evolution of sulphuretted hydrogen, which is readily recognized by its odor and by its action on paper moistened with solution of lead. The sulphurets of the metals of the fourth group are insoluble in water, but are likewise decom- posed by dilute mineral acids; all the other metallic sulphurets but sulphuret of mercury are decomposed by strong nitric acid, sulphuric acid being formed and sulphur generally sepa- rated ; aqua regia effects their decomposition more easily, it also dissolves sulphuret of mercury. As some metallic oxides, 144 QUALITATIVE ANALYSIS. when dissolved in acids, are precipitated by sulphuretted hy- drogen, while others are not, and as the precipitated sulphurets differ in color and in other properties, sulphuretted hydrogen becomes a valuable reagent for detecting and separating me- tallic compounds. Most metallic sulphurets are decomposed by heat with access of air, evolving sulphurous acid; the alkaline sulphurets thus treated are converted into sulphates. When sulphuretted hydrogen, or a solution of an alkaline or earthy sulphuret, is brought into contact Avith nitrate of silver or acetate of lead, black precipitates are formed ; either of these salts is, therefore, a certain test of the presence of this acid in the gaseous state; a strip of paper moistened Avith solution of subacetate of lead is generally employed. III.—Acids not precipitated by either Chloride of Barium or Nitrate of Silver. NITRIC ACID (N05). General Characters: This acid, which has neA7er been ob- tained in an anhydrous state, forms Avith Avater, Avhen pure, a colorless solution, which when concentrated fumes in the air; it is very easily decomposed, mere exposure to the light of the sun causing it to become yelloAV and disengage oxygen gas ; it is one of the strongest of the acids, and constitutes a reagent of the greatest value, from the facility Avith which it parts with a portion of its oxygen. The yellow fuming acid, con- taining nitrous acid, possesses generally the greatest oxidating power; the most highly concentrated acid is in many cases without action on bodies on which a diluted acid acts with violence; thus the concentrated nitric acid does not attack lead or tin, while the addition of a small quantity of water causes an energetic action to take place. Organic substances are for the most part resolved by the concentrated acid into carbonic acid and water, the action in many cases being suf- ficiently energetic to cause them to take fire; the diluted acid generally converts^ them into oxalic, malic, and carbonic acids. Nearly all metallic oxides are dissolved by nitric acid, the exceptions are oxides of tin and antimony, tellurous and tungstic acids. All the neutral salts of nitric acid are soluble in Avater, and all are decomposed at a strong red heat, the nature of the products depending on the nature of the base; thus the alkaline nitrates yield oxygen and nitrogen, while QUALITATIVE ANALYSIS. 145 other metallic nitrates give oxygen and an inferior oxide of nitrogen. When nitrates are ignited in the presence of other substances susceptible of oxidation, they take the liberated oxygen, and in some cases the combination is attended by deflagration; thus a nitrate thrown on red-hot charcoal causes the latter to throw off brilliant scintillations, a mixture of a nitrate with cyanide of potassium deflagrates vividly Avhen heated on a platinum plate, and phosphorus and sulphur brought into contact Avith a heated nitrate occasion a violent detonation. Methods of Detecting Nitric Acid in Solutions of the Nitrates. Hydrochloric acid, added in excess to solution of a nitrate, gives it the property of dissolving gold leaf, in consequence of the following reaction :— K0,N05+2HC1=N04+KC1+2H0 + C1. One equivalent of nitrate of potassa, and two of hydrochloric acid, give rise to one equivalent of hyponitric acid, one of chloride of potassium, two of water, and free chlorine: the solubility of gold leaf* in a liquid which has been heated with hydrochloric acid, is a certain proof, therefore, of the presence of nitric acid. When a solution containing a nitrate is mixed with half its volume of concentrated sulphuric acid, allowed to cool, and a crystal of protosulphate of iron added, the liquid round the crystal assumes a reddish brown color in consequence of the following reaction:— 10(FeO, SO.) + 4S03+KO,N05= 3(Fe203,3S03) + KO,S03 + 4(FeO,S03)N02. Ten equivalents of protosulphate of iron, four equivalents of sulphuric acid, and one of nitre, give rise to three equiva- lents of persulphate of iron, one of sulphate of potassa, and four of protosulphate of iron in a peculiar state of combination with nitric oxide: as the latter is very unstable, and is decom- posed by heat, nitric oxide being set free, it is necessary that the liquid should be allowed to cool before making the experi- ment. When a nitrate is heated in a test tube, with copper tilings and concentrated sulphuric acid, nitric oxide gas is set free, * Chlorates, perchlorates, chromates, bromates. &c, mixed with HCl acid also dissolve gold leaf. 10 146 QUALITATIVE ANALYSIS. which, combining with the oxygen of the air in the tube, forms ruddy fumes of nitrous acid. When a solution of a nitrate is mixed with sulphuric acid, and a sufficient quantity of a solution of indigo in sulphuric acid added, to give it a blue color, and the mixture heated, the color is either discharged or turned yellow in consequence of the oxidation of the indigo at the expense of the nitric acid set free from the nitrate. This test is not, however, decisive, as other substances, especially free chlorine, cause the same discoloration. The following test Avas proposed by Runge. Metallic zinc is dissolved in mercury in such a proportion that the fluidity of the mercury is only slightly diminished. A portion of this amalgam is placed in a little porcelain capsule, and barely covered with a neutral solution of protochloride of iron: a small piece of the nitrate is then laid upon the mercury in the solution, and after some time a black stain is produced upon the mercury, just at the spot where the nitrate had been placed.* NITROUS ACID (N03). The properties of this acid in a state of purity are not well known. It is a very volatile liquid, which, at a low tem- perature, is colorless, but at ordinary temperatures it is a gas of a dark yellowish red color; when brought into contact with water, it is decomposed, being resolved into nitric acid and nitric oxide, thus:— 3N03=N05+2N02. Almost all its salts are soluble in water: they very much resemble the nitrates in their properties, from which they may thus be distinguished :— When submitted to gentle distillation, nitrites expel nitric oxide gas, (the salt in solution being converted into a nitrate,) and by boiling they are rapidly converted into solutions of nitrates. When heated with concentrated sulphuric acid, they evolve nitric oxide gas, nitric acid remaining in solution; nitrites * Berthemot proposes to detect nitric acid even to the Tff ^ by adding a few drops of the suspected liquor to a drachm or so of pure sulphuric acid and stirring the mixture with a glass rod moistened at the end with a little brucine. If any nitric acid is present the liquid becomes red and afterwards yellow. QUALITATIVE ANALYSIS. 147 reduce chloride of gold and nitrate of mercury to the metallic state. When treated with hydrochloric acid, solutions of nitrites do not acquire the property of dissolving gold leaf. CHLORIC ACID (HO,C105). When concentrated, it is a yellowish oily-looking liquid, very sour, reddening, and finally bleaching, litmus paper; it is very unstable, being resolved by heat into perchloric acid, oxygen, and chlorine: it converts sulphurous into sulphuric acid, and is at the same time itself reduced to chlorine: it also converts sulphuretted hydrogen into sulphuric acid, sul- phur, and water: and all its compounds, with bases, are solu- ble in water: they do not possess bleaching properties, but when mixed Avith sulphuric acid they are decomposed; per- chloric acid, chlorine, hypochloric acid and oxygen being formed, the solution becoming yelloAV, and it then possesses the power of destroying the color of blue vegetable infusions, and by the application of heat decolorizes solution of indigo. The akaline chlorates, when ignited, disengage oxygen, and be- come converted into chlorides: most other chlorates are re- solved by heat into metallic oxides, and a mixture of oxygen and chlorine. AYhen triturated Avith sulphur or phosphorus, chlorates detonate with dangerous violence: a mixture of a chlorate with- sugar bursts into a flame on being touched with a drop of concentrated sulphuric acid. The compounds of perchloric acid (HO,C107), with bases, are distinguished from chlorates .by their greater stability, not being decomposed by acids or reducing agents ; their solutions do not therefore become yellow on being mixed Avith sulphuric acid. The per chlorate of potassa is remarkable for its difficult solubility in Avater. The compounds of hypochloric acid (C104) with bases have bleaching properties, and are decomposed on the addition of an acid with the evolution of chlorine only ; they are powerful oxidizing agents, and are decomposed by heat or even by ex- posure to lio-ht: they decompose manganese and lead salts, precipitating from the former hydrated peroxide of manga- nese, and from the latter, first chloride, and then brown per- oxide of lead. 148 QUALITATIVE ANALYSIS. ORGANIC ACIDS. I.—Acids precipitated by Chloride of Calcium;—Oxalic, Tartaric, Paratartaric, Citric, and Malic Acids. OXALIC ACID (HO,C203, or O). General Characters: It crystalizes in four-sided prisms, which are colorless, very soluble in Avater, very acid, and emi- nently poisonous. These crystals contain three equivalents of water of crystalization, which when sharply heated they lose, the dry acid subliming: at a high temperature oxalic acid is decomposed into water, carbonic, and formic acids, without blackening, by Avhich it is distinguished from most other organic acids. The alkaline oxalates are soluble in water, as are also some other oxalates with a metallic base: they are all decomposed at a red heat; alkaline and earthy oxalates being thereby converted into carbonates. Behavior of Solutions of Oxalic Acid and Oxalates with Re- agents. Chloride of calcium, and all soluble lime salts, produce a white precipitate eA-en in highly dilute solutions (CaO,0 + 2 aq.), insoluble in water as Avell as in oxalic and acetic acids, but readily soluble in hydrochloric and in nitric acids; the pre- sence of ammonia promotes the precipitation of oxalic acid by salts of lime. Chloride of barium produces a white precipitate (BaO,0 + aq.)almost insoluble in Avater, but soluble in nitric and in hy- drochloric acids. Nitrate of silver gives a Avhite precipitate, soluble in nitric acid and in ammonia. Acetate of lead produces a Avhite precipitate. When heated with concentrated sulphuric acid, oxalic acid and dry oxalates are decomposed, and the oxalic acid resohed into carbonic acid and carbonic oxide gases, Avhich escape with efferA-escence. The latter gas may, if present in suffi- cient quantity, be kindled; it burns with a full flame: if the mixture becomes black, it is a proof that it contains some other organic substance. QUALITATIVE ANALYSIS. 149 TARTARIC ACID (C8H4O10+2HO; or T). This acid crystalizes in large rhombic prisms, which are so- luble in Avater and have a pleasant acid taste ; the solution de- composes by keeping, becoming coA'ered with a mouldiness; Avhen heated, the crystalized acid loses water, and gives rise to the formation of a series of new compounds; and Avhen treated at a high temperature with a strong solution of hy- drate of potassa, it is converted into acetate and oxalate of po- tassa, thus:— 2HO,C8H4OirHO,C4H3Q3+2IIO,C203. Crystalized tartaric acid. Acetic acid. Crystalized oxalic acid. The alkaline tartrates are soluble in water; all the salts of tartaric acid that are insoluble in Avater are easily soluble in hydrochloric acid. Behavior of Tartaric Acid and Solutions of Tartrates with Reagents. Chloride of calcium produces a white precipitate almost in- soluble in Avater, but soluble in ammoniacal salts, the presence of Avhich, therefore, prevents its formation ; it is soluble also in cold potassa, but excess must be avoided, or hydrate of lime will be precipitated; if the potassa solution be boiled, tartrate of lime separates as a gelatinous mass, Avhich redis- solves as the solution cools. Lime water produces in solutions of neutral tartrates a white precipitate dissolving in tartaric acid, and also in am- moniacal salts. Chloride of barium produces a white precipitate soluble in dilute acids. Acetate of lead occasions a Avhite precipitate of tartrate of lead, Avhich when ignited out of access of air is decomposed, metallic lead in a fine state of division being formed, Avhich burns Avhen projected into the air. Nitrate of silver produces a white precipitate of tartrate of silver, which by boiling is reduced to a shining mirror, adhering to the glass by agitation; the reduced metal separates in thin laminae. Where a salt of potassa (the acetate answers best) is added to free tartaric acid, and the mixture agitated, a sparingly so- luble crystaline bitartrate of potassa separates; the addition 150 QUALITATIVE ANALYSIS. of alcohol further diminishes the solubility of this salt, which is freely dissolved in alkalies and in mineral acids. Tartaric acid possesses the property of preventing the pre- cipitation of several metallic oxides by alkalies, in conse- quence of the formation of soluble tartrates not decomposed by alkalies; among the metallic oxides which it thus affects are alumina, peroxide of iron, and protoxide of manganese. Tartrates, Avhen heated, carbonize, emitting a peculiar odor; the tartrates of the alkalies and alkaline earths are thus converted into carbonates. PARATARTARIC ACID or RACEMIC ACID (C4H205,HOor R,HO). This acid is isomeric with tartaric acid, from which it is distinguished by the insolubility of its lime salt in excess of acid, in ammoniacal salts, in an excess of racemic and tartaric acids, and by the formation after a time of a precipitate with solution of gypsum. CITRIC ACID (CiaH5On,3HO or Ci,3HO). This acid forms large transparent crystals, very soluble in water, and of a strong but pleasant acid taste; its solution, like that of tartaric acid, decomposes by keeping. The acid itself carbonizes Avhen heated to redness, emitting a pungent acid vapor; when heated with sulphuric acid in excess, it is decomposed into carbonic acid, carbonic oxide, acetic acid, and water, thus:— C„HsO„+3110=2C02, + 2CO, + 2C4H303, + 2HO. The alkaline citrates are soluble in water; the insoluble salts of citric, and in fact of all organic acids are decomposed by boiling with carbonate of soda, soluble alkaline salts being thus obtained. Behavior of Citric Acid and Solutions of Soluble Citrates with Reagents. Chloride of calcium produces in solutions of citrates, but not in citric acid, a white precipitate of neutral citrate of lime, insoluble in potassa, but readily soluble in sal-ammoniac, (and free acids,) from which, however, a basic citrate of lime (Ci,3CaO + CaO + aq.) is precipitated by boiling. Lime water produces no precipitate in the cold; but, by QUALITATIVE ANALYSIS. 151 boiling, basic citrate of lime is deposited, which is redissolved as the solution cools: this reaction serves to distinguish citric acid from most other organic acids. Acetate of lead produces a white precipitate, sparingly soluble in ammoniacal salts and in ammonia, but readily so- luble in citrate of ammonia. Citric acid, like tartaric acid, prevents the precipitation of certain metallic oxides by alkalies. MALIC ACID (C8H408,2HO, or M,2HO). This acid, which occurs in several acid fruits, crystalizes with some difficulty, and deliquesces rapidly when exposed to the air:, at the temperature of 230° it gradually decomposes into fumaric acid, (C4H,03,HO,) crystalizing in micaceous scales; at a higher temperature it is, in a great measure, con- verted into maleic acid (C8H?06,2HO), which rises as a crys- taline sublimate, fumaric acid remaining in the retort. The salts which this acid forms with bases are mostly soluble in water. Behavior of Malic Acid and Solutions of Malates with Reagents. Chloride of calcium does not produce any precipitate till alcohol is added, when Avhite malate of lime is deposited. Lime water produces no precipitate either in hot or cold so- lutions of malates, by which this acid is distinguished from tartaric, racemic, citric, and oxalic acids. Acetate of lead produces a white precipitate, which, by re- pose, crystalizes in needles, and which fuses under the boiling point of water. The best test of malic acid is, probably, its comportment under heat. The precipitate is insoluble in an excess of malic acid. II.—Acids precipitated by Sesquichloride of Iron; Succinic, Benzoic, Tannic, and Gallic Acids. SUCCINIC ACID (C4H203,HO or^HO). This acid is crystaline and volatile; its vapor is exceed- ingly acrid and penetrating; by distillation with sulphuric acid it yields a new acid, the nature of which has not yet 152 QUALITATIVE ANALYSIS. been exactly determined. The salts which it forms with bases are mostly soluble in Avater. Behavior of Succinic Acid and Solutions of Succinates with Reagents. Sesquichloride of iron produces a broAvnish red voluminous precipitate, soluble in acids, and decomposed by ammonia, hydrated sesquioxide of iron being formed. Acetate of lead produces a Avhite precipitate of succinate of lead, soluble in excess, and in tartaric, nitric, and acetic acids. As the alkaline and earthy succinates are insoluble in al- cohol, the acid, after the addition of alcohol and ammonia, is precipitated by chloride of barium. BENZOIC ACID (C14H503HO, or Bz,HO). This acid is obtained by sublimation, in the form of light flexible pearly scales, or by precipitation as a crystaline powder. When pure it has no smell. It is fusible and vola- tile, its vapor being, like that of succinic acid, very irritating. It is not very soluble in cold Avater, more so in hot, and readily soluble in alcohol. Most of its salts are soluble in water. Behavior of Benzoic Acid and Solutions of Benzoates with Reagents. On the addition of hydrochloric acid to the solution of a benzoate in water, benzoic acid separates as a Avhite crystaline poAvder. Sesquichloride of iron produces a pale yelloAV precipitate, decomposed by ammonia, and by strong acids, which combine Avith sesquioxide of iron, benzoic acid being precipitated. Acetate of lead does not immediately precipitate free ben- zoic acid; but it produces a Avhite flaky precipitate in solutions of fixed alkaline benzoates. TANNIC ACID (C18H509,3HO, or Qt,3HO). When pure, this acid is nearly white, but not all crystaline. It is very soluble in Avater; the solution absorbs oxygen from the air, and is converted into gallic and ellagic acids. It has a most astringent but not bitter taste. It is almost insoluble QUALITATIVE ANALYSIS. 153 in ether. On the addition of a mineral acid, a precipitate composed of tannic acid and the acid employed is determined. Solution of gelatine produces an insoluble curdy precipitate. The Avhole of the tannic acid in a solution may be removed by a piece of animal membrane. Solution of starch, and most of the vegetable bases also produce precipitates. Sesequichloride of iron gives a dark blue black precipitate. GALLIC ACID (C7H03,2HO, or G,2HO). This acid forms beautiful prisms of a silky lustre, and a slightly yelloAV color. It is not very soluble in cold, but dis- solves in three parts of boiling Avater. Its alkaline solution, when exposed to the air, becomes first yelloAV, then green, red, brown, and finally nearly black, by the absorption of oxygen. It is not precipitated by gelatine; its solution in hot sulphuric acid is precipitated by Avater as a reddish brown, crystaline powder, possessing coloring properties, and Avhich, Avhen heated, yields fine red prisms. By the action of heat it is converted into pyrogallic and metagallic acids. Solutions of gallic acid give with salts of sesquioxide of iron a dark blue precipitate; Avith salts of oxide of iron the precipitate is black. III.—Acids not precipitated by Chloride of Calcium or by Sesquichloride of Iron: Acetic, Formic, Uric, and Me- conie Acids. ACETIC ACID (C4H303,HO, or Ac03.HO, or A,HO). The hydrated acid at temperatures below 60° is a crystal- ine solid. It melts at 62° or 03°, forming a liquid of a pun- gent, peculiar, and agreeable smell, and a burning acid taste. It has a poAverful action on the skin, on which it raises a blister, producing a painful sore. It boils at 248°, and its vapor is inflammable. It is decomposed by anhydrous sul- phuric acid, and also by chlorine, tAVO neAv acids, sulpliacetic and chloroacetic acids being formed. It is also decomposed Avhen passed in a state of vapor through a red hot tube, the products being carbonic acid and acetone. Thus: C4Ii303=C02+C3H30. Acetone. 154 QUALITATIVE ANALYSIS. Acetates, when heated, are decomposed with the same trans- formation. The greater number of the acetates are soluble in water. Acetate of silver and acetate of protoxide of mer- cury are crystaline, and only sparingly soluble. When heated with dilute sulphuric acid, acetates are decomposed Avith the liberation of acetic acid; Avhen heated Avith concentrated sul- phuric acid and alcohol acetic ether is disengaged, which may be known by its peculiar odor; when an acetate is heated with potassa and arsenious acid, oxide of kakodyl is disen- gaged. With excess of oxide of lead, acetic acid forms a so- lution Avhich has an alkaline reaction. Sesquichloride of iron exhibits no reaction with acetic acid; but in solutions of neu- tral acetates peracetate of iron is formed, which imparts to the solution a blood-red color. FORMIC ACID (C2H03,HO;orFo03,HO). This acid, in its most concentrated state, fumes in the air, and has a very pungent acid smell. At a low temperature it crystalizes in brilliant scales. It is highly corroshre, acting powerfully on the skin, and producing painful sores. It boils at 212°, and its vapor is inflammable; all its salts are soluble in water. They have a general resemblance to the acetates, but are, nevertheless, quite distinct. When heated to redness, they give off carbonic acid and carbonic oxide, leaving the metal reduced, or carbonic oxide, leaving a metallic oxide. By the property which this acid and its salts pos- sess of reducing the oxides of the precious metals, it is distinguished from acetic acid. When nitrate of silver, or protonitrate of mercury, are added to concentrated solutions of alkaline formiates, sparingly soluble precipitates are formed, and on the application of heat a reduction instantly takes place, carbonic acid and water being formed, thus: HO,C2H03+2HgO=2Hg + 2C02+2HO. By gently heating chloride of mercury with an alkaline formiate, it is reduced first to subchloride, and then to me- tallic mercury. When formic acid is heated with concentrated sulphuric acid, it is decomposed into water and carbonic oxide, thus- HO,C2H03 + HO,S03=2CO + HO,S03+2HO. The sulphuric acid withdraAvs from the formic acid the ele- ments of water, and a transposition of its atoms takes place. QUALITATIVE ANALYSIS. 155 The same decomposition occurs on heating a formiate with sulphuric acid. URIC ACID (CI0H4N4O5,HO, or U,HO). This acid is separated from its compounds by mineral acids as a white crystaline poAvder. It is very sparingly soluble in water, the solution reddens litmus; all its salts are likewise very sparingly soluble. When uric acid is dissolved in nitric acid, the solution eAraporated to dryness, and ammonia added, a beautiful purple red color is obtained. By fusion with alkalies, uric acid disengages ammonia. MECONIC ACID (C14H0lt,3HO, or Me,3HO). This acid, which is found only in opium, crystalizes, when pure, in the form of beautiful white silvery scales. It is so- luble in Avater and in alcohol. The solution is decomposed by boiling; it is also decomposed by hydrochloric acid; and en- tirely so when heated with excess of potassa; oxalic acid, car- bonic acid, and a coloring matter being the products. Its dis- tinguishing character is that of causing a deep blood red color in solutions of persalts of iron, without, hoAvever, any preci- pitation taking place. CHAPTER IV. ON SYSTEMATIC QUALITATIVE ANALYSTS. In the last chapter the chemical comportment of a great number of substances Avith reagents has been described. Amongst the bases there haAre been omitted only a feAv metal- lic oxides of very rare occurrence, the history of which, and their relation to different reagents, have not been as yet made out; and amongst the acids, nearly all in the inorganic, and a great number of those in the organic kingdom that are of any thing like frequent occurrence, have been included. Now, when the student has made himself experimentally acquainted 156 QUALITATIVE ANALYSIS. with the relations of these substances to reagents, and when he has become familiar with all the reactions that have been described, he is in a position certainly to pronounce a correct opinion as to the nature of almost any simple compound, by Avhich is meant any arrangement of single base Avith a single acid, that may be presented to his notice; but if he be called upon to decide the nature of a compound, consisting perhaps of a mixture of several substances, it is clear that a mere knoAAdedge of the action of reagents alone will not serve him, but that he must possess the knoAyledge of a method of sepa- rating the various substances from each other, and of deter- mining the absence, as well as the presence, of certain bases and acids: in short, he must know how to proceed on a sys- tematic method of examination, Avithout Avhich chemical ana- lysis Avould be little better than mere guess-work, and its cor- rectness or incorrectness quite a matter of chance. Even in the examination of a compound which is knoAvn to be simple, the greatest advantage is derived from the systematic method, a great saving of time and labor is effected, and the result is arrived at in a far more satisfactory manner than it could be by the indiscriminate application of test after test, following no rule or order, but merely throwing out baits, as it were, with the hope of eventually meeting with appearances, and obserAdng phenomena, that may enable us to recognize the presence of some particular substance. In this chapter our object will be to point out the manner in which this systematic method of qualitative analysis is to be conducted, illustrating the course of proceeding by examples; and our attention will be confined to those substances and combinations only Avhich are of general occurrence. The subject will be thus rendered far more in\dting, and less embarrassing, to the beginner; and, after the student has made himself thoroughly acquainted with the principles on which general examinations are con- ducted, and has acquired a dexterity in conducting the mani- pulatory processes, he will afterwards find no difficulty in encountering the analysis of compounds in which the rarer substances occur, to the existence of which a careful prelimi- nary examination will, generally speaking, arouse his atten- tion. Preliminary examination.—Before submitting a Compound to analysis, there are certain operations to be performed upon it, which should never be neglected, as they frequently fur- QUALITATIVE ANALYSIS. 157 nish valuable hints for the subsequent examination, and always give some insight into the nature of the substance. In the first place, if the body be a solid, its physical characters, such as its form, density, color, hardness, &c. should be noted; it should next be reduced to powder, and subjected to the action of heat, both alone, and also together Avith certain fluxes. The experiments are conducted in the following manner:— 1st. A small quantity of the substance is heated on a strip of platinum foil, and it is observed whether it undergoes any alteration. If it be wholly or partly volatile, its odor will frequently enable us at once to decide on the presence of some particular substances, such as ammonia, sulphur, arsenic, ben- zoic acid, &c. If fumes are evolved, a portion of the sub- stance may be heated in a test tube, and notice taken of the appearance of a sublimate in the cool parts of the tube. It should be examined carefully Avith a pocket lens, and its phy- sical characters minutely ascertained; sulphur, certain sul- phurets, as those of mercury and arsenic, mercury, arsenic, cadmium, tellurium, selenium, and certain metallic seleniurets, oxide of antimony, arsenious acid, ammoniacal salts, and salts of mercury, may thus be detected. Chlorine, nitrous acid, sulphurous acid, hydrocyanic acid, &c, are thus also fre- quently discovered. If the substance under examination con- tains water, it will be condensed in drops on the upper part of the tube. These drops should be examined by test papers, and it should be noted whether they have an acid, alkaline, or neutral, reaction. If the substance changes color Avithout en- tering into fusion, certain metallic oxides, such as those of tin, lead, bismuth, or zinc, may be looked for; and, if it blackens, the presence of organic matter is nearly certain. It is ad- visable also to heat a little of the substance in a tube, with bisulphate of potassa; nitrates are thus decomposed, deep red fumes of nitrous acid being produced. Compounds of iodine, bromine, and fluorine are likeAvise decomposed, the former yielding violet fumes of iodine, the second, bromine in a gase- ous state, and the last hydrofluoric acid, the presence of Avhich is recognized by its action on the glass. The presence of a sulphate is proved by heating a portion of the thoroughly dried substance in a glass tube, with poAvdered charcoal: the sulphuric acid becomes thereby deoxidized, and fumes of sul- phurous acid are evohed. Metallic sulphurets likeAvise disen- gage sulphurous acid when heated in a tube open at both ends, 158 QUALITATIVE ANALYSIS. being thus exposed to a current of air. Under similar treat- ment metallic arseniurets furnish a crystaline sublimate of ar- senious acid, sometimes mixed with the reduced metal; the sulphurets of arsenic yield arsenious acid and realgar; and compounds of antimony give a white sublimate of oxide of antimony, which is recognized by the readiness with AA-hich it is volatilized by a gentle heat. A similar sublimate is formed on heating metallic tellurets in an open glass tube; but it is distinguished from oxide of antimony by fusing into colorless drops when heated, a character Avhich belongs also to vola- tilized chloride of lead. It is not easy, by means of the blow- pipe, to distinguish lead from bismuth, as the oxides of both metals fuse into a dark yellow mass, Avhich becomes lighter on cooling. The color of oxide of lead is certainly lighter than that of oxide of bismuth, but the distinction is by no means definite. 2d. The substance is heated on charcoal alone, before the blowpipe. If it fuses, and is absorbed, Avholly or partly, by the charcoal, alkaline salts are probably present; if it defla- grates, nitrates, chlorates, bromates, and iodates must be par- ticularly looked for. If, Avhen strongly heated, it leaves a white residue, the alkaline earths may be expected to be met with. 3d. The substance is mixed with carbonate of soda, and heated on charcoal in the reducing flame. By this treatment most metallic oxides are reduced, some with the production of metallic beads Avithout any incrustation taking place on the charcoal, as gold, silver, tin and copper; others are reduced with an incrustation, and Avith or without the production of metallic beads, us bismuth, lead cadmium, antimony, and zinc; and others are reduced without giving either beads or incrust- ations, as iron, cobalt platinum, nickel. Manganese, if pre- sent, is converted, in the outer flame, to manganic acid, Avhich forms, with soda, manganate of soda of a green color. Chro- mium, under similar circumstances, gives rise to chromate of soda of a yellow color. When, however, the substances under examination contain several metallic bases, the student must not expect to meet Avith av ell-defined reactions; he will have to draw his conclusions from a comparison of the phenomena he will observe by submitting the subject of experiment to a va- riety of treatments. The formation of a glass is character- istic of the presence of silicic acid; the bead is, however, QUALITATIVE ANALYSIS. 159 transparent only when there is a great excess of silicic acid. Quartz, felspar, with some other minerals and refractory clays, give limpid beads; but the glasses produced by most minerals containing silicic acid are colored by the metallic oxides present. Silicic acid is remarkable as being almost the only substance insoluble by fusion in microcosmic salt. 4th. The substance is heated in a test tube with concen- trated sulphuric acid; if any volatile acid be present, it will almost certainly be detected by this operation; thus, hydro- sulphuric acid gas (sulphuretted hydrogen) is evolved from sulphurets, and is immediately recognized by its odor; sul- phurous acid gas is liberated from the lower oxides of sulphur; a yellow gas (a mixture of chlorine and hydrochloric acid) is set free from chlorates; a mixture of bromine and oxygen from bromates; hydrochloric acid gas from chlorides; hydrofluoric acid gas from fluorides; bromine and iodine from bromides and iodides: by heating with sulphuric acid also, nearly all organic substances are decomposed; sulphurous and carbonic acid gases, and sometimes carbonic oxide, being evolved. If a cyanide be heated Avith dilute sulphuric acid, hydrocyanic acid is set free. If the substance to be analyzed be a liquid, the first step is to evaporate a portion of it to dryness on platinum foil, in order to see whether it really contains anything in solution, and then to ascertain, by means of test papers, whether it has an acid, or alkaline, or neutral reaction; if the first, it does not necessarily folloAV that the solution contains free acid, for it must be borne in mind that saline solutions of most of the heavy metallic oxides redden litmus paper: it is not difficult, however, to decide whether the acid reaction is occasioned by a metallic salt or by a free acid; the addition of a drop ortAvo of solution of carbonate of potassa generally, in the first case, renders the liquid turbid, while, in the latter case, it remains clear. If the solution be alkaline, it can contain no metallic oxides that are soluble in alkaline liquids; and if it be per- fectly neutral it probably consists only of salt of the alkalies, or alkaline earths. These preliminary experiments having been made, and some insight into the general nature of the substance under examin- ation having thereby been obtained, its relation to solvents is next to be examined. It is reduced to a fine state of division by trituration in an agate mortar, and a portion digested for 160 QUALITATIVE ANALYSIS. some time in a test tube with distilled water; if it be entirely dissolved, the quantitative analysis of the aqueous solution may at once be proceeded with, taking about twenty-five or thirty grains of the substance. If a complete solution do not take place, a drop or tAVO of the clear liquid is to be evaporated to dryness on platinum foil, in order to see whether water has dissolved anything. If the eAraporated liquid leave a residue, then the substance must a second and a third time be digested with fresh portions of distilled water, filtered, and the filtrate set aside for subsequent examination. The undissolved residue is next gradually heated to the boiling point, with dilute hydrochloric acid, and if complete solutions be not effected, the fluid is decanted and the residue digested with concentrated hydrochloric acid, particular attention being paid to the nature of the gases evolved. If an effervescence take place, carbonic acid, sulphuretted hydrogen, and hydrogen gases, may be looked for; the first betrays the presence of carbonates, the second that of sulphurets, the third that of certain metals: the evolution of chlorine indicates peroxides or chromates, and hydrocyanic acid points out the existence of certain cyanides. If complete solution of the substance be not effected by concentrated hydrochloric acid, a fresh portion is to be digested with nitric acid; a few of the metals only escape solution by this acid (gold, platinum, palladium, &c), tin and antimony are oxidized by it, but the oxides are not dissolved: it moreover decomposes all sulphurets, with the single exception of sulphuret of mercury, setting free sulphur, which is easily recognized by its color and levity, and its being completely evaporated when heated on a strip of platinum foil: if nitric acid fail to dissolve the substance completely, aqua regia may be tried, and, if this leave a residue, recourse must be had to fusion with an alkali or an alkaline carbonate, the following preliminary experiments being first performed upon it:— 1st. A small portion is heated on a slip of platinum^foil, the odor of sulphurous acid is conclusive as to the presence of sulphur, and, if no other substance be present, the whole will be dissipated by a very moderate heat; in this case, a pro- longed digestion of the residue in aqua regia will, generally speaking, give a clear solution, the whole of the sulphur be- coming oxidized into sulphuric acid. 2d. A small quantity is moistened with hydrosulphuret of QUALITATIVE ANALYSIS. 161 ammonia; if it immediately becomes black, an insoluble silver, mercury, or lead, salt is present. 3d. A small portion is mixed with carbonate of soda, and heated in the inner blowpipe flame; a metallic reduction, ac- companied by a yellow inciustation, indicates lead. 4th. A small quantity is digested with carbonate of potassa; if it become black, protochloride of mercury is present, which is farther confirmed by mixing a portion of the residue Avith slightly moistened carbonate of soda, and heating it in a glass tube, small globules of mercury are easily recognized with the aid of a lens. 5th. Another small quantity may be digested with ammonia, and the clear ammoniacal liquid supersaturated with nitric acid; the formation of a white precipitate, insoluble in the nitric acid, indicates silver. Besides insoluble compounds of silver, lead, and mercury, the residue, insoluble in aqua regia, may contain sulphates of the alkaline earths, silicates, fluorides, certain phosphates and arseniates, and the insoluble modifications of oxides of tin, antimony and chromium. Sesquioxide of iron also is dissolved only with great difficulty, after having been strongly ignited. All these compounds may, hoAvever, be brought into a soluble state by fusion Avith carbonate of soda, or with a mixture of carbonate of soda and cyanide of potassium; or they may have their constituents transposed in such a manner as to admit of their easy detection by a proper subsequent treatment. For example, if the original substance undissolved by nitric acid or by aqua regia contain sulphates of the alkaline earths, the result of a fusion with carbonate of soda is to bring them to the state of carbonates, Avhich, though insoluble in water, are readily dissolved by dilute hydrochloric acid, and the bases are then easily detected in the hydrochloric solution: the sulphuric acid with which these bases Avere previously combined is found in the aqueous solution of the fused mass, in the form of sul- phate of soda. Again, if the insoluble residue contain chloride, iodide, or bromide of silver or lead, the result of the fusion with an alkaline carbonate, which in this case must be per- formed in a porcelain and not in a platinum crucible, is to transfer the chlorine, bromine, or iodine to the metal of the alkaline base, forming compounds easily soluble in Avater, and therefore easy of detection in the aqueous solution of the fused mass; while the metal or metals with Avhich the chlorine, iodine, 11 162 QUALITATIVE ANALYSIS. or bromine was originally combined, being of course, insoluble in water, may be dissolved in nitric acid, and detected by the appropriate tests. If baryta, strontia, and lime be present, besides the oxides of silver and lead, the two latter metals are precipitated from the nitric solution by sulphuretted hydrogen: the liquor filtered from the precipitate is mixed with hydro- fluosilicic acid, by which the baryta, after a time, is precipita- ted. To the liquor filtered from this precipitate, solution of sulphate of potassa is added, which precipitates the strontia, in company, perhaps, with a little of the lime, and on filtering off the precipitated sulphate of strontia, adding to the filtrate ammonia, and then oxalate of ammonia, a white precipitate, in- dicating the presence of lime, is determined. Silicic acid, if present, passes into the state of silicate of soda, and is dis- covered by adding excess of hydrochloric acid to the aqueous solution of the fused mass, evaporating to perfect dryness, and treating the residue with water; by this treatment the silicic acid is brought to its insoluble condition, and remains undissolved. It thus appears that when we have before us a complex substance, which is partly soluble in water, and not wholly dissolved by either hydrochloric acid, nitric acid, or aqua regia, three distinct analytical operations may be performed on it, viz:—1. Examination of the aqueous solution. 2. Ex- amination of the acid solution. 3. Examination of the inso- luble residue. If the operator be desirous of obtaining a pre- cise knowledge of the mode of arrangement of the different acids and bases in such a complex mixture, he must make these three distinct analyses; but, if his object be only to as- certain what acids and bases are present, he may generally omit a distinct analysis of the aqueous solution, and after a careful preliminary examination he may confine his attention to the acid solution (the substance not having been previously exhausted by water), and to the mass obtained by fusion of the residue with an alkali. 1.—Examination for Bases: Principles on which the method Depends. In the last chapter it was shoAvn that by means of certain general reagents metals may be arranged into groups; some of which by other reagents may again be subdivided into minor groups, each of the individuals composing which may be re- cognized by their comportment with certain other reagents QUALITATIVE ANALYSIS. 163 which may be called special. The general reagents are sul- phuretted hydrogen, hydrosulphuret of ammonia, carbonate of ammonia, caustic ammonia, and potassa, and they are of the greatest use and importance to the analytical chemist in con- ducting a systematic qualitative analysis. Thus, if on the addition of sulphuretted hydrogen to an acid liquid, no pre- cipitate should occur, the operator is assured that none of the metals composing the fifth or sixth groups can be present; and if, after having neutralized the liquid Avith ammonia, no precipitate or decided change of color should occur on the ad- dition of hydrosulphuret of ammonia even on the application of heat, a proof is obtained that the solution can contain no bases, but some one or more of those included in the first or second groups; and, lastly, the addition of carbonate of am- monia will show at once Avhether any of the alkaline earths are present. If this reagent should give no precipitate, then the solution in question can contain no metallic oxides but magnesia and those contained in the first group; and if phos- phate of soda and ammonia should occasion no precipitate, it must be a solution of some salt or salts of some one or more of the alkalies proper. Supposing, however, that sulphuretted hydrogen has occasioned a precipitate in the acid liquid, this precipitate must be a sulphuret of some one or more of the metals of the fifth or sixth groups; and it may contain the whole of the metals of both groups. By digesting it with hydrosulphuret of ammonia, Ave easily separate these tAvo groups; the metals of the sixth being soluble in that reagent, while those of the fifth are insoluble. The tAvo groups being thus separated, the individual metals are sought for by the application of special tests. Again suppose that the filtrate from the precipitate occa- sioned by sulphuretted hydrogen should furnish a precipitate with hydrosulphuret of ammonia, this precipitate may contain any or all of the metals of the third and fourth groups, and it may also contain phosphates, oxalates, borates, and hydnfluates of the alkaline earths; but it can contain no metal belonging to the fifth or sixth groups; neither can it contain either of the alkalies proper. The color of this precipitate furnishes some guide to the substances present: if it be Avhite, it can contain neither iron, cobalt, or nickel; it may, hoAvever, con- tain small quantities of manganese and chromium: if it be black, then iron, cobalt, and nickel, either or all must be pre- 164 QUALITATIVE ANALYSIS. sent. Potassa and ammonia are the general reagents employed for the further examination of the precipitate, which is treated in the following manner:—It is washed and digested Avith dilute hydrochloric acid; if complete solution take place, neither cobalt nor nickel is present, as the sulphurets of these metals are decomposed only by a protracted digestion with concen- trated hydrochloric acid; if complete solution do not take place, then regard must be had to these metals in the subse- quent examination by special tests : nitric acid is added to the hydrochloric solution, and the mixture is boiled : complete solution of everything takes place, with the exception, per- haps, of the separated sulphur, which is removed by filtration. To a portion of the clear solution sal ammoniac is added, and then ammonia in excess. If a precipitate be produced, the whole of the solution is treated in the same manner. The precipitate produced by ammonia may contain the oxides of the second group in the form of certain salts (phosphates, ox- alates, borates, hydrofluates); the oxides of the third group, as oxides, and of the metals of the fourth group, iron, in the state of sesquioxide. The filtrate from the precipitate pro- duced by ammonia may contain all the other metals of the fourth group (nickel, cobalt, zinc, and manganese). Potassa now becomes an important reagent in the further analysis both of the precipitate and the filtrate, as will be seen presently, when Ave minutely describe and illustrate the whole analytical process. But, again, suppose after having acidified with hydrochloric acid the filtrate from the precipitate occasioned by hydrosul- phuret of ammonia, and well boiled it till it has lost all odor of sulphuretted hydrogen, it should give a white precipitate when digested with carbonate of ammonia, the presence of some one or more of the members of the second group (the alkaline earths) may with certainty be inferred : as this precipitate can contain no metallic oxide of either of the other groups, special testing is at once had recourse to for the detection of baryta, strontia, and lime. The filtrate from the precipitate occasioned by carbonate of ammonia can contain only magnesia and the alkalies proper. It is first examined as to its perfect freedom from baryta, strontia, and lime, by testing a small portion Avith sulphate of potassa for the two former earths, and a small portion with oxalate of ammonia for the latter. The absence of these earths being proved, another portion is specially tested for QUALITATIVE ANALYSIS. 165 magnesia by phosphate of soda, and, its presence having been proved, the Avhole of the remainder of the filtrate is eAraporated to dryness, and the ammoniacal salts expelled by ignition ; the residue is dissohed in Avater, and baryta water added as long as any precipitate of magnesia is formed; the solution is then boiled and filtered, and dilute sulphuric acid added to the fil- trate till it becomes acid ; the fluid is then filtered off from the precipitated sulphate of baryta, and the filtrate specially test- ed for the alkalies. ♦ By the above course of treatment, no base can escape de- tection but ammonia, which is specially tested for in the origi- nal solution by heating it with an excess of a concentrated solution of potassa; the ammonia if present is thus discharged in its gaseous form, and its presence is indicated by its odor, or by the white fumes produced on bringing near the mouth of the test tube a feather moistened AAdth strong acetic acid. In folloAving out the foregoing operations, there are certain pre- cautions to be observed, in order to ensure accuracy and to lead to just conclusions. In the first place, it must be borne in mind that, if Ave employ hydrochloric acid to acidify our solution previous to subjecting it to sulphuretted hydrogen, certain metals (silver, mercury, lead) are precipitated as chlo- rides. The two former may be completely removed from the solution by adding a sufficient quantity of hydrochloric acid, and of course, therefore, need not be sought for in the subse- quent analysis. Lead, hoAvever, will not be completely sepa- rated in this manner, and must, therefore, be had regard to. The operator must take especial care that the precipitates of the several groups be most completely removed, by washing, from the solution containing the members of the folloAving groups. The greatest confusion and perplexity will arise from neglecting this precaution. He must also be careful that the precipitation by the general reagents be complete, which ob- ject is attained by adding the reagent by degrees as long as any precipitation takes place ; and in the case of the sulphur- etted hydrogen, by continuing to pass the gas through the solution till it smells strongly of it after agitation, and which sometimes requires tAvo or three hours; the deposition of the newly formed sulphuret is much facilitated by gently heating. Should the preliminary examination have indicated arsenic in the form of arsenic acid, the metal must be brought into the state of arsenious acid by boiling the solution with sulphurous 166 QUALITATIVE ANALYSIS. acid, before subjecting it to the action of sulphuretted hy- drogen. Fig. 5 represents the arrangement of the apparatus for passing a current of sulphuretted hydrogen through a solu- tion; A is a wide-mouthed bottle containing water and frag- ments of proto-sulphuret of iron. It is closed Avith a good sound cork, through Avhich are inserted, Fis- 5- perfectly air tight, tAvo tubes, one sur- ion tin spiz, and digest am j, and».' 8 filiation of v contain i .ViO icra'ilryness. FeiiiJw drops of E [poc: a moist mass ,-,. into 2 parts. e--)issolve the < er portion in ^er, and add & KCy ^precipitate is „,. Tied soluble excess of KCy |* again pre- apitated on adding HCl indicating Ni The solution may contain The alkalies and alkaline earths. Evaporate a few drops on platinum foil: a residue remains. Test a small quantity of the solution with 2 NaO, HO, P05, and NHa, a precipitate is formed. Boil the whole solution with HCl till it has lost all odor of HS; filter and boil with excess of NH4 0, CO,, mixed with NH3 The precipitate may contain BaO, SrO, and CaO Dissolve in a small quantity of HCl Filter and divide into three portions 1. Add a concen trated solution of CaO, S03 an immediate precipitate is formed, indi- cating BaO Confirm by hy- drofluosilicic acid. Addhydrofluo silicic acid as long as a pre- cipitate con- tinues to be formed, filter, and add to the filtrate KO, S03 A white pre- cipitate is formed, indi- cating SrO Confirm bythe crimson tinge which another portion of the HCl solution, when evapo- rated to dry- ness, commu- nicates to the flame of alcohol. 3. Add NaO, SO as long as any precipitation takes place: filter; neutral ize with NH3 then add NH40, "O A white pre cipitate is formed, indi- cating CaO The solution may contain MgO, KO, and NaO Add to a portion 2 NaO, HO, PO, The precipi tate is 2MgO,NH4 O, P05 + aq- indicating MgO The solution may contain KO, and NaO Evaporate to dryness, ignite, re- dissolve in water, and add BaO as long as any precipitation takes place. Boil, filter, and add HO, S03 to remove the ex cess of BaO; again filter and evaporate to dryness; redis- solve the residue in water, and divide into two portions. 1. Add PtCl, with a few drops of HCl A yellow crys taline precipi tate is formed indicating KO 2. Add KO Sb05 A granular crystaline pre- cipitate is form ed, indicating NaO NH3 is detected by adding KO in excess to the original solution and boiling. COURSE OF ANALYSIS FOR THE DETECT! To a nevtra Add To the solution filtered from the BaCl BaO, S03, and neutralized The precipitate may be by NH3, add BaO, S03 CaCl BaO, P05 The precipitate may be BaO, B03 CaO, P05 BaO, 07 CaO, B03 BaF CaO.O Digest with HCl CaF A white residue of BaO, S03 Digest urith A 'M remains, indicating so3 The residue may contain The solution may contain The arfw/iw CaO,~0 CaO, P05 may contain CaF CaO, B03 AgO,iP0, Add HCl Add NH. T„ . . . ■* AgO,0 if a precipitate is formed it is a proof of the presence, of AgQlBO, The residue is The solution may CaF contain P05; or of B03; but if no Confirm by CaO,CT Add NH3 precipitate takes place it is heating a portion a proof of the absence of of the original substance in a A white precipi-tate is produced P05, but not of B03; since CaO, BOs would not pre- tube with sand indicating cipitate if a large quantity and HO, S03 of ammoniacal salts were HF 0 Confirm by adding HO, S03 to the original solution and heating; CO present. P05 must be specially tested for in the original solution with NH3, NH4 Cl, and MgO, S03; B03 must be specially tested for in the original so-ution by the green alcohol is evolved, which flame. x burns with a blue flame. « ■ 1 r Detection of Detection of CIO, Detection of CIO Detection of N03 NO, Heat a portion of Treat a portion of Heat a portion of" the original Mix a portion of the original sub- the original sub- solution gently with HO, S03, V, the original so- stance with stance in the solid 0 is evolved and red fumes a lution with HO, dilute HCl form with A in are given off, indicating the a S03, and add a a deep pungent the cold, Cl is probable presence of A crystal of Fe 0, yellow gas is dis- evolved, indicat- N03 ir S03; a brown engaged, which ing Confirm by the reactions halo is produced explodes on the CIO with chloride of gold and ni- indicating contact of flame, trate of mercury. R N0S disengaging Cl, (See p. 147.) gi Confirm by boil- indicating ing with C10s P S03 and Cu Confirm by heat- ar Red fumes are ing a small por- of evolved. tion of the ori-ginal substance with KCy, an ex-plosion ensues.— (This experi-ment requires to be performed with care.) E !lic jte r -I ^TION OF INORGANIC ACIDS.—Table III. '•ral solution. Add NOc Add AgO, NO. The precipitate may be AgO, P06 AgO,B03 AgO, O AgCl AgBr Agl AgCy AgCsy The residue may consist of AgCl AgCy AgCsy Agl AgB Gently heat with excess of NH3 The solution may contain AgCl AgCy AgBr Add NO* Precipitated AsjCl AgCy AaBr A Bromine has been found in the preliminary examination. Test the original solution for HCy with a mixture of aproto-and a persalt of iron, excess of KO and HCl A blue precipitate is formed, indicating HCy Detection of Bromine. Remove the I from the ori- ginal solution by a mixture of FeO, S03 and CuO, S03 Precipitate the excess of FeO and CuO by KO; pass a stream of Cl through the solution, and agitate with ether. Evaporate the ethereal solu tion to dryness and treat the residue with S03 and MnO, Brown vapors are produced indicating ±>r B Bromine has not been found in the preliminary examination. Wash, dry, and ignite the precipitate; boil with NO... The solution may contain AgO. N05, occasioned by the reduction of the AgCy Add HCl A white precipitate is formed, in- dicating HCy Confirm with the original solution by 1st. The Prussian blue test; 2d. Heat a few drops of the ori- ginal solution for some time with NH4 S; a film of S appears on the watch-glass; a drop of Fe, Cl3 added produces a deep red color, owing to the formation of Sulphocyanide of Potassium. The residue is AgCl indicating HCl The residue may be Agl AgCsy Detection of I Test the original solution with HgCl and with starch paste. Detection of Csy Add to the original solution oCFe,Cl3, it is colored blood- red, indicating Csy COURSE OF ANALYSIS FOR THE DETI CI ilia To a ne / Add Ba Cl To the solution filtered from BaO, S03, and The solution The precipitate neutralized by NH3 may contain CaO, Ci may be Add CaCl Boil for some BaO, S03 The precipitate may contain time, a white BaO, P05 precipitate is BaO, B03 CaO, B03 formed, BaO,!J CaO,0" indicating BaO.Y CaO, P05 — CaO, T Ci BaO,cT CaF BaF Add HCl Divide it into two portions. / ■ ' \ r- A white precipitate is formed indicating To one part add To the other part add 1 ~A KO n so3 i r ~^ \ i The residue The solution The residue The solution 1 maybe may be may be may contain CaO.O CaO, B03 CaO, B03 CaO, T" CaF. CaO, P05 CaO, PO. Boil for some y Add HCl Add NH3 CaO,0 CaF" time, a white precipitate is formed, indi- ( \ f "> Special Taj The The solution See last cating Acii residue is may contain Table. __ Heat a portior CaF CaO,~0 T original sulistar indicating Add NH3 A white NO. nearly to and the HF precipitate is formed. indicating 0 add A'fl A purple c is produced, ij I DETECTION OF ORGANIC ACIDS.-Table IV. a neutral solution. Add AgO, NOB The precipitate may be AgO, B03 AgO, P05 AgO, O AgO,T AgO, Ci AgBr Agl AgCy AgCsy Add N05 and digest. The solution may contain AgO, B03 AgO,P05 AgO.jO AgO.T AgO, Ci The residue may be AgCl AgBr Agl AgCy AgCsy See the other Table. yrjst for Uric rid. a:, rtion of the afjstance with .naf to dryness, c then ,NH3 Apple color udssl, indicating Ef ~x Add Fe, CL The precipitate may be Light brow "i Fe, 0-, 3 S Black Fe203 Fe203 AddNH, * Qt G The residue is FeQ0, The solution may contain. If Qt G combined with NH Divide into three parts. To one part add alcohol and Ba Cl A white precipitate is formed, indicating "s To another part evapo- rated to a small bulk add HCl A white crystaline precipitate is formed, indicating Bz The third part exposed to the air changes to red, indicating a Add dilute S03 A thick precipi tate is formed, indicating DJt Confirm by gelatine. The deep red color may be occasioned by HCsy Detection of HCsy Boil the original solution with S03 The liquor becomes of a red brown color, and by continued boiling deposits a yellow powder, indicating HCsy Detection of A Heat the original solution with S03 and alcohol, acetic ether is evolved, indicating A PART II. QUANTITATIVE ANALYSIS. CHAPTER I. ON THE QUANTITATIVE ESTLMATION OF SUBSTANCES, AND THEIR SEPARATION FROM EACH OTHER. The following Table, exhibiting the Names, Symbols,^ and Chemical Equivalents, or combining Proportions, by Weight, of all those Substances at present considered as Elementary, according to the latest Authorities, is taken from the new edition of Graham's " Elements of Chemistry." Equivalents. Oxygen=100. Names of Elements. Symbol. Hydrogen=l. Hydrogen=12.5. Aluminum . Al 13.69 171.17 Antimony . Sb 129.03 1612.90 Arsenic . . As 75. 937.5 Barium . . Ba 68.64 858.01 Bismuth . . Bi 70.95 886.92 Boron . B 10.9 136.2 Bromine. . Br 78.26 978.3 Cadmium . Cd 55.74 696.77 Calcium . . Ca 20. 250. Carbon . . C 6. 75. Cerium . . Ce 46. 575. Chlorine . . Cl 35.5 443.75 Chromium . Cr 28.15 351.82 Cobalt . . Co 29.52 368.99 Copper . . Cu 31.66 395.70 Didymium ■ ... 234 QUANTITATIVE ANALYSIS. Equivalents. Oxygen=100. Names of Elements. Symbol. Hydrogen=l. Hydrogen=12.5. Erbium . , Fluorine . . F 18.70 233.80 Glucinum . Gl 26.6 331.26 Gold . Au 98.33 1229.16 Hydrogen . H 1. 12.5 Ilmenium . Iodine . I 126.36 1579.50 Iridium . . Ir 98.68 1233.5 Iron . Fe 28. 350.0 Lanthanum . Ln 48. 600.0 Lead . Pb 103.56 1294.50 Lithium . . Li 6.43 80.37 Magnesium . Mg 12.67 158.35 Manganese . Mn 27.67 345.9 Mercury. • Hg 100.07 1250.9 Molybdenum . . Mo 47.88 598.52 Nickel . . Ni 29.57 369.68 Niobium . , Nitrogen . N 14. 175.00 Norium . 9 Osmium . . Os 99.56 1244.49 Oxygen . . 0 8. 100.00 Palladium . Pd 53.27 665.9 Pelopium . Phosphorus . P 32.02 400.30 Platinum . Pt 98.68 1233.50 Potassium . K 39.00 487.5 Rhodium . R 52.11 651.39 Ruthenium . Ru 52.11 651.39 Selenium . Se 39.57 494.58 Silicium . . Si 21.35 266.82 Silver . . Ag 108.00 1350.00 Sodium . . Na 22.97 287.17 Strontium . Sr 43.84 548.02 Sulphur . . S 16.0 200.00 Tantalum . Ta 92.30 1153.72 Tellurium . Te 66.14 801.76 Terbium . . . Thorium. . Th 59.59 744.90 QUANTITATIVE ANALYSIS. 235 Equivalents. Oxygen=100. Names of Elements. Symbol. Hydrogen=l. Hydrogen=12.5. Tin . Sn 58.82 735.29 Titanium . Ti 24.29 303.66 Tungsten . W 94.64 1183.00 Uranium . U 60.00 750. Vanadium . V 68.55 856.89 Yttrium . . Y 32.2 402.51 Zinc . Zn 32.52 406.59 Zirconium . Zr 33.62 420.20 In describing the methods to be pursued for bringing the several substances mentioned in the above table into a state fit for estimation, and separating them quantitatively from other substances, we shall follow, as nearly as possible, the same arrangements which we adopted in treating of the com- portment of substances with reagents, viz., by arranging them into a series of Groups. "With respect to the Bases there will be no difficulty in following out this method; in treating of the Acids, a variation may probably appear desirable. I. BASES. GROUP 1. The Metals of the Alkalies proper, Potassium, Sodium, Ammonium, Lithium. Potassium. This metal is quantitatively determined as sulphate, chlo- ride, nitrate, and as double chloride of platinum and potas- sium. Quantitative determination as Sulphate.—Potassium is in general estimated in the form of this salt when no other bases are present; the solution containing it must be carefully eva- porated to dryness, and the residue dried for some time before it is transferred to a platinum crucible to be ignited; this precaution is necessary to guard against a loss from decrepi- tation. It fuses at a strong red heat without volatilization, or decomposition. Its composition is 236 QUANTITATIVE ANALYSIS. One equivalent of KO ... 47 ... 54.02 One do. of S03 ... 40 ... 45.98 One do. of KO,S03 87 100 If the solution contain excess of sulphuric acid, the hy- drated bisulphate is obtained by evaporation: this salt must be reduced to the neutral sulphate, which is done by igniting it in a platinum crucible containing a fragment of carbonate of ammonia, and loosely shut with its cover; the excess of sulphuric acid flies off in an atmosphere of carbonate of am- monia; a gentle ignition must be continued till the salt assumes the solid state, the neutral sulphate being far less fusible than the acid sulphate. Quantitative estimation as Nitrate.-—When the alkali exists in a solution in the form of nitrate it may be weighed as such; it should not be fused, as it is thereby capable of being par- tially decomposed. It is anhydrous. Its* composition is One equivalent of KO ... 47 ... 46.54 One do. of N05 ... 54 ... 53.46 One do. of KO,NOs 101 100 Quantitative estimation as Chloride.—Potassium may like- wise be weighed in the form of this salt, when it exists as such in a solution, it should not be heated above feeble red- ness, and the crucible should be loosely covered, or a loss may be sustained. Its composition is One equivalent of K ... 39 ... 52.34 One do. of Cl ... 35.5 ... 47.66 One do. of KC1 74.5 100 Quantitative estimation as double Chloride of Platinum and Potassium.—For this purpose the alkali must be in the state of chloride; the solution is evaporated to a small bulk, and excess of bichloride of platinum and free hydrochloric acid added; the mixture is then evaporated to dryness on the water bath, and the crystaline residue digested with spirits of wine, which removes the excess of bichloride ; it is then trans- ferred to a weighed filter, washed with spirits of wine and dried at 212°. Its composition is QUANTITATIVE ANALYSIS. 237 One equivalent of K ... 39 ... 15.97 One do. of Pt ... 98.68 ... 40.41 Three do. of Cl ... 106.5 ... 43.62 One do. ofKCl+PtCl2 244.18 100 If the operator be certain that no other base but potassa is present, and that it exists in the solution in the state of neutral sulphate or as chloride, it may then be determined in an indirect manner, by estimating the sulphuric acid as sulphate of baryta, or the chlorine as chloride of silver, and calculating the amount of alkali present from the quantity of sulphuric acid or of chlorine thus obtained. Sodium. This metal is quantitatively determined as sulphate, carbon- ate and chloride. Quantitative estimation as Sulphate.—The same method is followed as with sulphate of potassa. It does not decrepitate. Its composition is One equivalent of NaO ... 30.97 ... 43.63 One do. of S03 ... 40.00 ... 56.37 One do. of NaO,S03 ... 70.97 ... 100 Quantitative estimation as Chloride.—The salt must be well dried before it is ignited, to prevent decrepitation; the crucible should be loosely covered. Its composition is One equivalent of Na ... 22.97 ... 39.28 One do. of Cl ... 35.50 ... 60.72 One do. of NaCl ... 58.47 ... 100. Quantitative estimation as Carbonate.—As carbonate of soda does not attract moisture from the air so rapidly as the corresponding potassa salt, sodium may be weighed as such. It may be fused without volatilization or decomposition. Its composition is One equivalent of NaO . . . 30.97 .. . 58.46 One do. of C02 ... 22.00 .. . 41.54 One do. of NaO,C02 ... 52.97 ... 100 238 QUANTITATIVE ANALYSIS. Separation of Soda from Potassa.—The only method that yields accurate results is to determine the potassa in the form of double chloride of platinum and potassium, and to estimate the soda either directly or indirectly. The following is the method of proceeding:—The mixed alkalies are converted into chlorides; in most cases this maybe done by simply digesting and evaporating with hydrochloric acid; if, however, the alkalies are combined with sulphuric acid, that acid must first be precipitated by chloride of barium, and the excess of baryta removed by carbonate of ammonia mixed with a little caustic ammonia; the solution is filtered, and the filtrate is evapo- rated to dryness, and ignited: the residue is redissolved in hydrochloric acid, and the alkalies are thus brought to the state of chlorides. If the alkalies are combined with phosphoric acid, the solu- tion is evaporated to dryness, ignited, redissolved in water, and precipitated by neutral nitrate of silver, the fluid is fil- tered from the precipitated phosphate of silver, and the excess of nitrate of silver is removed by hydrochloric acid. If the alkalies are in combination with boracic acid, the best method of separating them is by decomposing the boracic acid into gaseous fluoride of boron: for this purpose the dry com- pound is digested in a platinum crucible with three or four parts of pure powdered fluor spar and concentrated sulphuric acid, and the heat is continued as long as fumes continue to be evolved; the alkalies are thus converted into sulphates, which are changed into chlorides as above directed. The mixed alkaline chlorides, being carefully weighed, are dissolved in a small quantity of water and mixed Avith excess of an aqueous solution of bichloride of platinum; the solution is evaporated to dryness on the water bath, and the dry mass is treated with a mixture of sulphuric ether and spirits of wine; the potassium is estimated as above described; the spirits of wine poured on the evaporated residue must acquire a yellow color; if it does not, it is a proof that sufficient bi- chloride of platinum has not been added, and the experiment must be repeated with a fresh portion. Berzelius recommends to mix the dry chlorides with 3f times their weight of the crystalized double chloride of platinum and sodium, a quantity just sufficient to convert the whole mass into double chloride of platinum and potassium, supposing it to consist entirely of chloride of potassium; the process is conducted precisely as QUANTITATIVE ANALYSIS. 239 before. The soda is either calculated from the difference be- tween the quantity of chloride of potassium found and the original weight of the mixture analyzed, or in a direct man- ner as follows:—The filtrate from the double potassium salt is mixed with solution of sal ammoniac in excess, and strong alcohol added; all the platinum salt is thus removed, and the colorless filtrate being evaporated to dryness, the residue is gently ignited and weighed as chloride of sodium. Pagenstechers method of estimating the amount of Soda in crude Potash.—This is founded on the property possessed by a saturated solution of sulphate of potassa of still dissolving a large amount of sulphate of soda. A certain weight of the sample to be examined is mixed with water, and sulphuric acid added to it until the liquid has an acid reaction; it is then evaporated to dryness, and the residue ignited and weighed. The powdered saline mass is well agitated in a graduated cylinder with six times its weight of a concentrated solution of sulphate of potassa, the liquid drawn off the sedi- ment with a syphon, and the same quantity of the solution of the sulphate of potassa again poured over the residue. After some time the residue is brought upon a weighed filter, the funnel covered during filtration, the filter, when the liquid has drained off, weighed moist, and then, after being dried at 212°, the difference is the evaporated water of the solution of sulphate of potassa, the degree of concentration of which is known. It is known, therefore, how much of the salt was dissolved in the evaporated water; this quantity is subtracted from the weight of the saline residue. If the potassa was free from soda, the weight of the sulphate of potassa now remaining must be the same as that first obtained; but if it contained soda, this has been removed as sulphate of soda, and the weight of the first saline residue has been reduced. From the loss the amount of the soda present can be calcu- lated ; if the loss = V, the amount of the soda is calculated thus:— As 70.97(NaO,SO3): 52.97(NaO,C02):: V: X X=the amount of carbonate of soda present in the specimen. It should, however, be observed that when soda is used to adulterate potassa, a kind is employed that contains about 20 per cent, of sulphate of soda. Before making the weighings, it is well to take the specific gravity of the filtered solution of the sulphate of potassa; if it is the same as before it can have 240 QUANTITATIVE ANALYSIS. removed nothing, and if it has taken up sulphate of soda its density has naturally been raised.—Chem. Gfaz., Jan. 1848. Indirect separation of Potassa from Soda.—This method is founded on the difference which exists between the combining numbers of potassium and sodium, and is applicable to both sulphates and chlorides. It is deduced from the following considerations:—Suppose the alkalies to be in the state of sulphates, and 100 grains of the mixture to have yielded 152.8 grains of sulphate of barytes =52.6 grains of sulphuric acid. Let the quantity of sulphate of potassa present be called A, and that of sulphate of soda B : then A+B=100, or 100—B=A. That is the proportion of sulphate of potassa in the mixture is the weight of the mixture analyzed minus the proportion of sulphate of soda :— Now one part of sulphate of potassa contains ..... .4598 sulphuric acid. And one part of sulphate of soda contains ..... .5637 do. The 52.6 grains of sulphuric acid found in the mixture must, therefore, be (A x .4598)+ B X .5637: that is, the number of units present of sulphate of potassa multiplied by the quan- tity of sulphuric acid in one unit, added to the number of units present of sulphate of soda multiplied by the quantity of sulphuric acid in one unit:— (A x .4598) + (B x .5637)= 52.6 consequently _ 52.6—(Bx.5637). .4598 but A has been shown above to be = 100—B; substituting this value, therefore, for A, we have 100—B = 52-6~B x -563T .4598 or, 100 x .4598—(B x .4598)= 52.6—(B x .5637) or, 45.98—(B x .4598) = 52.6—(B x .5637) and, putting the two B's on the same side of the equation, we have (B x .5637) —(B X .4598)= 52.6—45.98 52.6—45.98 6.62 ao ^ or, JL> =---------------=------= bo. i. .5637 — .4598 .1039 The mixture contains, therefore, 63.7 per cent, of sulphate of soda, and 36.3 per cent, of sulphate of potassa. Suppose the alkalies to be in the state of chlorides, and 133 QUANTITATIVE ANALYSIS. 241 grains of the mixture to have given 287 grains of chloride of silver = 71 grains of chlorine : Then let the quantity of chloride of potassium be A And that of chloride of sodium B then A + B = 133 ; and A = 133 —B. Now one part of chloride of potassium contains ..... .4766 chlorine. And one part of chloride of sodium contains ..... .6072 do. Therefore, as before, 71 = (A x .4766) + (B x .6072,) ., A 71 — (Bx. 6072) consequently A =----^—---->; or,133-B = H-(Bx-6072); .4766 or, 133 x .4766—(B x .4766) = 71—(B x .6072); or, 63.38—(B x .4766)= 71—(B X .6072); and (B x .6072)—(B x .4766)= 71—63.38; therefore B = 71-63.38 _1M_ = ^ .6072—.4766 .1306 The mixture is, therefore, composed of 58.34 grains of chloride of sodium, and 74.66 grains of chloride of potassium. From the above calculations the following rule for the indi- rect determination of soda and potassa, when together pre- sent in a mixture, in the state of sulphates, is derived:— From the quantity of sulphuric acid subtract the product obtained, by multiplying the weight of the mixture into the quantity of sulphuric acid in a unit of sulphate of potassa, and divide the remainder by the difference between the quan- tity of sulphuric acid in a unit of sulphate of soda, and the quantity in a unit of sulphate of potassa; the quotient is the quantity of sulphate of soda in the mixture. Example.—In 100 grains of a mixture of the two sul- phates, 50 grains of sulphuric acid are found. 5Q-(100 x .4598) 50-45^98 = 4^ 3g<69 = ^ .5637 —.4598 .1039 .1039 phate of soda; consequently, 100 — 38.99 = 61.31 = the sul- phate of potassa. The same rule applies to the determination of the alkaline chlorides, substituting chlorine for sulphuric acid; the results 16 242 QUANTITATIVE ANALYSIS. are tolerably accurate, but the determinations of sulphuric acid and chlorine require to be made with the greatest care. Alkalimetry.—The commercial value of the several varieties of potash and soda depends entirely on the amount of car- bonated or caustic alkali which they contain ; it is important, therefore, to the purchaser of these articles to be in possession of a simple and expeditious method of determining, with tole- rable accuracy, the amount of available alkali in the crude salt—a complete chemical analysis of such a heterogeneous mixture requiring great skill and time. Two methods are adopted for this purpose:—The first, that of day Lussac, depends on the constant saturating power of sulphuric acid of a certain determinate strength, being founded in common with every other process involving chemical combination or decom- position on the law of definite proportions: the second, that of Fresenius and Will, depends on the determination of the amount of carbonic acid evolved from a given weight of the salt, during its decomposition by sulphuric acid. 1. Modification of the method of Gay Lussac.—Prepara- tion of the standard acid: 170.1 grains of pure carbonate of soda, obtained by igniting the best bicarbonate in a platinum crucible, are dissolved in four or five ounces of hot distilled water: common oil of vitriol is diluted with ten or twelve parts of water, and when cold, the burette, Fig. 6, which is accurately divided into 100 equal parts, each division corresponding to 10 grain measures of water, is Fis- 6- filled to 0 with the diluted acid; the solution of car- bonate of soda is transferred into a small beaker, and a sufficient quantity of infusion of litmus added, to communicate to it a distinct blue color; the acid is then poured gradually from the burette into the alkaline liquor, until the blue color changes to dis- tinct red, which it does by a very slight excess of sulphuric acid; the addition of the acid, when the point of saturation is nearly attained, must be made with great care, and the operator must be careful not to mistake the wine red color, which the liquor assumes from the evolution of carbonic acid, for the distinct red produced by a slight excess of the sul- phuric acid. As this mistake may, however, be made, it is better towards the close of the operation, after the addition of every drop of acid, to moisten QUANTITATIVE ANALYSIS. 243 a glass rod with the test liquid, and make a streak with it on blue litmus paper. As soon as an excess of sulphuric acid has been employed, the paper remains red after being dried, which is not the case if the reddening has been occasioned by carbonic acid; the test liquor being saturated, the quantity of acid which has been required to produce the effect is accurately observed: suppose it to be 90 measures, this, then, is the quantity equivalent to 170.1 grains of car- bonate of soda, or 100 grains of soda. A standard acid is thus prepared, the precise strength of which is known, but as it is more convenient to have an acid 100 measures of which shall be equal to 100 grains of soda, every division of which on the burette represents, therefore, a grain of soda, the 90 measures are made up to 100 by the addition of 10 measures of water, and a stock of acid is then prepared, any vessel accurately divided into 100 equal parts serving for the pur- pose. When a sample of commercial soda has to be tested, 100 grains taken from different parts of the mass are care- fully weighed out, dissolved in water, and filtered, if necessary, from any insoluble residue; the solution is then neutralized with the standard acid in the manner and with the precautions above described, and of course the number of measures re- quired represents in grains the quantity of carbonate of soda in the specimen: thus, suppose 47 measures of acid are required, the sample is at once seen to contain 47 per cent. of soda= 80.38 per cent, of carbonate; the same method may be employed in analyzing carbonate of potassa, and the dif- ferent variety of pearl-ashes, but as the equivalent number of potassium is higher than that of sodium, a different calculation becomes necessary, though the same test acid may be used: thus, the equivalent number of sodium is 22.97, that of soda being 30.97, and that of carbonate of soda 52.97; the equiva- lent number of potassium is 39, that of potassa 47, and that of carbonate of potassa 69. The same quantity, therefore, of acid that is required to neutralize 30.97 grains of soda, would neutralize 47 grains of potassa; but as these numbers bear very nearly the ratio of two to three, the calculation becomes very simple: we have only to multiply the number of divisions of the burette required to saturate 100 grains of the potash specimen by three, and divide by two, to get the per centage amount of potassa with sufficient accuracy for most practical purposes: thus, suppose 30 measures of acid are required, the 244 QUANTITATIVE ANALYSIS. sample contains—-—=45 per cent, of potassa =66 per A cent, of carbonate. There are, however, one or two circumstances, besides the unavoidable errors of manipulation, which prevent this method from attaining a high degree of accuracy. Both the soda and pearl-ash of commerce contain a variety of impurities; soda contains sulphate of soda, chloride of sodium, sulphuret of sodium, basic silicate of soda, hydrate of soda, hyposulphite, and sometimes sulphite of soda: of these sulphuret of sodium, which may be detected by the odor of sulphuretted hydrogen evolved on moistening the specimen with sulphuric acid, sili- cate of soda, hyposulphite and sulphite of soda, (which may be detected by dissolving a portion of the specimen in sulphuric acid, colored with a few drops of chromate of potassa, the solution becomes green if either of the two latter salts is present,) all these salts interfere with the accuracy of the results. It is true that by heating the specimen with chlorate of potassa, the sulphuret of sodium, as well as the sulphite and hyposulphite of soda, becomes converted into sulphate, which is without any influence in the operation; but another source of inaccuracy is at the same time introduced, inasmuch as the hyposulphite of soda, if present, upon its conversion into sulphate, decomposes one equivalent of carbonate of soda, thus:— NaO,S202+40+NaO,CO=2(NaO,S03) + C02. The carbonate under examination becomes then under- estimated, while the error arising from the presence of basic silicate of soda is without remedy. The method next to be described overcomes these difficulties, and is, moreover, after a little practice, more easy of execution. 2. Method of Fresenius and Will. — The alkalimetrical process above described seeks its object by determining the amount of alkali, calculating it from the measure of acid which it requires for its neutralization. In the method now to be^ described the result is obtained by determining the quantity of carbonic acid with which the alkali was combined. The process is conducted as follows:* a and b are two flasks. Wide-mouth medicine bottles even may be employed. * A New Method of Alkalimetry, &c, by Drs. C. R. Fresenius and H. Will. Edited by J. Lloyd Bullock. 1844. Taylor and Walton. QUANTITATIVE ANALYSIS. 245 b must have a capacity of from 2J to 3 ounces of water: it is advisable that a should be somewhat smaller, say of a capacity of about 1J to 2 ounces. Both flasks are closed by means of doubly per- Fis- 7- forated corks: these perforations serve for the reception of the tubes, c, d, and e. All these tubes are open at both ends; when operating, the end of the tube d is closed by means of a small piece of wax. The sub- stance to be examined is weighed and projected into the flask b, into which water is then poured to the extent of one-third of its capacity, a is filled with common English sulphuric acid to about half its capacity. Both flasks are then corked, and the ap- paratus is weighed. The air in the whole apparatus is then rarefied by applying suction to the tube e; the consequence is, that the sulphuric acid contained in a ascends into the tube c, and thus a portion of it flows over into b; immediately upon its coming into contact with the carbonate contained in this flask the evolution of carbonic acid begins briskly. The peculiar con- struction of the apparatus compels the carbonic acid evolved to pass through the sulphuric acid contained in a, before it is permitted to escape through the tube e, this being the only aperture of the apparatus. It is obvious that this transmis- sion through sulphuric acid will retain all the moisture with which the carbonic acid may be charged more completely than could be done in any other manner. Upon the influx of the sulphuric acid the fluid in b becomes heated, and expands together with the air contained in the flask: upon cooling, both acquire their original volume again, owing to which a new portion of sulphuric acid flows over into b as soon as the evo- lution of gas has ceased: the process is, however, expedited by applying suction to the tube e every time the evolution of gas ceases, and in this way the operation may be accomplished in a few minutes. When the carbonate is completely decom- posed (which is immediately ascertained by no further evolu- tion of gas taking place upon the influx of fresh portions of sulphuric acid into b), a somewhat larger quantity of the sul- 246 QUANTITATIVE ANALYSIS. phuric acid contained in a is, by means of renewed suction, made to pass over into b: the fluid in this flask becomes here- upon heated to such an extent as to expel all the carbonic acid which it had absorbed in the course of the operation. As soon as the evolution of gas has completely ceased, the aperture of the tube d is opened by taking off the piece of wax and suction applied to the tube e, until all the carbonic acid still contained within the apparatus is replaced by air. The apparatus is then allowed to cool, wiped dry, and weighed. The loss of weight indicates, with the greatest possible exact- ness, the amount of carbonic acid which was contained in the test specimen. A common apothecary's balance, that will turn with one-sixth of a grain, is sufficiently delicate for weighing not only the whole apparatus, but the test specimen also; and it is not one of the least of the advantages of this method, that it enables the operator to experiment on a much larger scale than is possible in an ordinary analysis. The quantity of the sample employed is recommended by the author to be 6.29 grammes (=97 grains) of potash, and 4.84 grammes ( = 74.7 grains) of soda, these quantities containing in their state of purity exactly 2 grammes (=30.88 grains) of carbonic acid; consequently, every 2 centigrammes (=.3088 grains) of carbonic acid that are given off, indicate one per cent, of carbonate; all trouble of calculation is thus avoided. Previous to submitting the sample to analysis, it must be thoroughly dried by exposure to heat over a lamp for about five minutes in a Berlin crucible, and allowed to cool with the cover on: it must also be ascertained whether any insoluble earthy carbonates are present, which is done by dissolving the specimen in water, filtering and well washing the residue: if the sample contain sulphuret, sulphite, or hyposulphite of the alkali, a teaspoonful of yellow chromate of potassa is added to the solution in the flask, which decomposes both the sul- phurous acid and the sulphuretted hydrogen at the moment of their liberation, all the products of the decomposition, viz: sulphate of chromium, water, and sulphur, remaining in the apparatus. The amount of caustic soda, and potassa, present in the specimen, the determination of which is of great im- portance, is found by comparing the quantity of carbonic acid evolved from a given weight of the alkali in its ordinary state with that evolved from a similar quantity after it has been mixed in a moist state with carbonate of ammonia, and dried QUANTITATIVE ANALYSIS. 247 at a high temperature, by which means all the caustic alkali becomes carbonated. Should any bicarbonates be present, they are converted into neutral carbonates, by the application of a gentle red heat: in order to ascertain their presence the solution to be examined is mixed with solution of chloride of calcium in excess, filtered, and ammonia added to the filtrate, a turbidity indicates the presence of bicarbonate. The presence of free soda in the commercial article is de- tected by the alkaline reaction which the solution of the sam- ple exhibits after the addition of chloride of barium in excess. Drs. Fresenius and Will apply the same method to the analysis of carbonates, the bases of which form insoluble compounds with sulphuric acid. The apparatus is, however, somewhat modified, in order to allow of the introduction of nitric acid in the place of sulphuric acid into the bottle b. For this pur- pose the tube d is expanded to a bulb in its upper part, and drawn out to a fine point at its lower end; it must be adjusted into the cork of b in such a manner as to allow of its being raised or depressed, still, however, preserving the bottle air- tight. It is filled with dilute nitric acid, and a wax stopper having been inserted into its upper aperture it is introduced into the cork, so that its point just reaches the surface of the water in b, through which the carbonate to be analyzed is diffused. The nitric acid is prevented from escaping from the tube by the wax stopper. The whole apparatus is weighed, the tube d is then cautiously depressed, so that its point nearly reaches the bottom of the flask, and by removing the wax stopper the nitric acid gradually escapes into b, occasioning the decomposition of the carbonate, the liberated carbonic acid escaping through the tube c, and becoming deprived of moisture by the sulphuric acid in a, previous to escaping through e. When the decomposition is complete, the car- bonic acid which has been absorbed by the water in b is ex- pelled by plunging the apparatus into hot water, air having been previously drawn through the flasks by suction at the tube e. As soon as the whole is cool the flasks are wiped dry and weighed. The loss indicates the amount of carbonic acid. It is scarcely necessary to say that nitric acid is here em- ployed, in consequence of its forming soluble compounds with the bases of such carbonates as may require to be analyzed in this apparatus, viz: those of lime, strontia, and baryta. It having been stated on the authority of the American 248 QUANTITATIVE ANALYSIS. chemists, 3fessrs. Rogers,* that sulphuric acid is capable of absorbing a large amount of carbonic acid, and that the ele- gant alkalimetrical method of Drs. Fresenius and Will must in consequence be involved in serious errors, the author of this Treatise made and published! some experiments on the sub- ject; the results being of a perfectly satisfactory character, he has thought it worth while to reproduce them here. Carbonate of soda, prepared by igniting the pure bicar- bonate, was first analyzed. Ex. 1.—70 grains lost 28.99 grains of carbonic acid=41.41 per cent. Ex. 2.—64.6 grains lost 26.8 grains = 41.48 per cent. Theory requires 41.54 per-cent. Carbonate of potassa, prepared by igniting the pure bicar- bonate. Ex. 1.—79.24 grains lost 25.2 grains of carbonic acid = 31.81 per cent. Ex. 2.—90.55 grains lost 28.84 grains = 31.84 per cent. Theory requires 31.88 per cent. Carbonate of strontia, analyzed by the method, with nitric acid, above described. 78.84 grains lost 22.75 grains of carbonic acid = 29.75 per cent. Theory requires 29.8 per cent. Some experiments were afterwards instituted, with the view of ascertaining whether there was, in fact, any absorption of carbonic acid by the sulphuric acid, and the result showed that if such were the case the quantity absorbed must be very trifling, and incapable of interfering in any way with the suc- cess of any experiment in which sulphuric acid is employed as a desiccating agent for carbonic acid. Ammonium. Ammonia is estimated as chloride of ammonium, and as double chloride of platinum and ammonium ; in the analysis of organic substances it is sometimes determined from the volume of nitrogen gas which is produced by its decompo- sition. Quantitative estimation as Chloride. — When the alkali exists in a solution, either in an uncombined state, or as car- * Chemical Gazette, March 15th, 1848. | Ibid., May 1st, 1848. QUANTITATIVE ANALYSIS. 249 bonate, or combined with a weak volatile acid, or as chloride, it may be weighed in the form of the latter salt, for which purpose slight excess of hydrochloric acid is added to the solu- tion, which is evaporated to dryness on the water bath, the residue being heated thereon till it ceases to lose weight; at this temperature the loss from volatilization is almost inap- preciable. Its composition is One equivalent of NH4 ... 18.0 ... 33.65 One do. of Cl ... 35.5 . .. 66.35 One do. of NH4C1 ... 53.5 ... 100 Quantitative estimation as double Chloride of Platinum and Ammonium.—Ammoniacal salts, soluble in alcohol, may he analyzed by converting the ammonium into a double salt, with bichloride of platinum ; for this purpose the solution is super- saturated with hydrochloric acid, and an aqueous solution of bichloride of platinum added, the mixture is evaporated^ to dryness, and the residue treated precisely as the corresponding potassium salt; it is washed on a weighed filter, with alcohol, and dried at 212°, and its composition is One equivalent of NH4 . . . 18.00 . . . 8.06 One do. of Pt ... 98.68 . .. 47.72 Three do. of Cl ... 106.50 . . . 44.22 One do. NH4Cl+PtCl2 223.18 100 When this double salt is heated to redness it is entirely decomposed, metallic platinum in a fine spongy form alone remaining; this operation may, therefore, be performed on it in order to control the previous determination; the ignition must be carefully effected in a thin Berlin crucible ; a gentle heat being first applied, and gradually increased until the organic matter of the filter is entirely destroyed. The cruci- ble should be covered at first, but the cover must be removed towards the close of the operation, the crucible being then placed obliquely, in order to favor the access of air; every 100 parts of platinum correspond to 8.06 of ammonium, or 7.61 of ammonia. Ammoniacal salts, insoluble in alcohol, are analyzed by igniting them with a mixture of caustic soda and hydrate of 250 QUANTITATIVE ANALYSIS. lime;* the ammonia is liberated from its previous combination, and is received into and condensed in hydrochloric acid; it is subsequently estimated as double chloride of platinum and ammonium, in the manner already described. The process is conducted as follows:—The salt to be analyzed having been thoroughly dried in the water bath, is weighed, and intimately mixed with a sufficient quantity of soda-lime to fill one-half a combustion tube of hard German glass, about 14 or 16 inches long, and half an inch internal diameter; in the operation of mixing, forcible pressure must be carefully avoided, or the ammoniacal salt will undergo partial decomposition, even in the cold; the combustion tube is drawn out to a point, and bent obliquely upward at its closed end, soda lime is first introduced so as to occupy about an inch of the end of the tube; this is followed by the mixture, the remainder of the tube is filled to within an inch of the top with soda lime that has served to rinse out the mortar, and, finally, a stopper of recently ignited asbestos is inserted ; the tube is now laid in a horizontal position on the table, and a few smart taps given to it, in order to open a channel above the mixture for the passage of the ammoniacal gas. The condensing apparatus, containing a small quantity of hydrochloric acid, is now at- tached to the tube by means of a perforated cork, the com- bustion tube is placed in the furnace, and the whole apparatus having been proved to be air-tight, the tube is gradually heated with red-hot charcoal, commencing at the interior por- tion, and proceeding gradually towards the closed end, until the tube is red-hot throughout its whole length; when the evolution of ammonia has ceased, the point of the combustion tube is quickly broken off, and air drawn through the appa- ratus, so as to bring the whole of the ammonia into the hy- drochloric acid. The only source of error to be apprehended in conducting this operation arises from the powerful affinity subsisting between hydrochloric acid and ammonia, in conse- quence of which the acid is apt to rush back with violence, and enter the combustion tube, thus spoiling the whole ana- lysis. The inventors of the method, Drs. Will and Varren- trapp, recommend mixing the substance analyzed with an * Prepared by slaking a weighed amount of the best caustic lime with solu- tion of soda of such a strength that there shall be about one part of hydrated soda to two of anhydrous caustic lime; the mixture is heated to feeble redness in a Hessian crucible, pulverized, and kept in a well-closed phial. QUANTITATIVE ANALYSIS. 251 equal amount of sugar, which gives rise to the evolution of other and more permanent gases serving to dilute the am- monia. The accident may, however, be better prevented by employing a capacious condensing apparatus, provided with an extra bulb, as seen in Fig. 8, which shows the disposition Fig. 8. of the whole apparatus, and using a moderate quantity of hydrochloric acid; or even better, by employing a condensing apparatus recommended by Mr. Warren de la Rue, and de- scribed in the Memoirs of the Chemical Society, with which the recession of the acid into the combustion tube is rendered almost impossible. The operation being over, the contents of the condensing apparatus are transferred to an evaporating basin, and the apparatus repeatedly rinsed out with water; bichloride of platinum in excess is then added, and the re- mainder of the process conducted as has been already directed. Separation of Ammonia from Potassa and Soda.—When all three alkalies are present in combination with the same volatile acid, the ammoniacal salt may be expelled from a weighed portion of the mixture by careful ignition, and the amount of ammonia calculated from the loss of weight. If the mixture contain ammonia in the form of chloride or car- bonate, it may likewise be expelled by heat from the salts of the other alkalies, but if the ammonia be present in combina- tion with a non-volatile acid, or if the mixture cannot be dried at a temperature insufficient to expel ammonia, it must be determined by combustion with soda-lime, and the other alka- lies must be estimated from a separate portion, having pre- 252 QUANTITATIVE ANALYSIS. viously gently ignited it to expel all the ammonia. If no potassa be present, ammonia may be separated from soda by bichloride of platinum. Lithium. This metal is generally estimated in the form of phosphate of soda and lithia, the composition of which is Two equivalents of NaO . .. 61.94 . . . 16.34 Two do. of LiO ... 28.86 .. . 7.61 Four do. of P05 ... 288.08 ... 76.05 378.88 100 According to Rammelsberg, however, the double phosphate of soda and lithia is a salt of very variable composition, and perfectly useless for quantitative purposes. If there be no other base present, lithia may be estimated as sulphate, the composition of which is One equivalent of LiO . . . 14.43 . . . 26.5 One ' do. of S03 ... 40.00 . . . 73.5 54.43 100 Separation of Lithia from Potassa and Soda.—From an accurately weighed quantity of the mixture, the potassa is precipitated as chloride of platinum and potassium ; the excess of platinum is removed from the filtered solution by sulphu- retted hydrogen, or by evaporating to dryness and igniting the residue. According to Rose, the lithia is then precipitated as phosphate of soda and lithia, and the amount of soda is calculated from the loss sustained by the whole. Rammels- berg, however, considering the double phosphate of soda and lithia as unworthy of confidence in a quantitative determina- tion, recommends to convert the soda and lithia into chlorides, and to digest them with a mixture of anhydrous alcohol and ether, equal parts of each, in which chloride of lithium is easily soluble, while a mere trace only of chloride of sodium is dissolved. _ An accurate method of quantitatively deter- mining lithia in the presence of the other alkalies is, however, yet a desideratum. QUANTITATIVE ANALYSIS. 253 GROUP 2. The Metals of the Alkaline Earths:—Barium, Strontium, Calcium, and Magnesium. Barium. Oxide of barium or baryta is weighed as carbonate and sulphate, most frequently as the latter, which is completely insoluble in water, and in all diluted acids. Quantitative estimation as Sulphate.—To the solution con- taining the earth, heated to 212°, dilute sulphuric acid is added as long as precipitation is occasioned; the fluid is well agitated, poured into a beaker or a Phillips' precipitating jar, and allowed to stand till it is settled, and the supernatant fluid become quite clear: it is then transferred to a filter, the amount of ash yielded by which is known, and washed with hot distilled water until the wash water* no longer pro- duces any precipitate with chloride of barium; it is then dried and ignited, the heat being continued until the organic matter of the filter is completely destroyed, and the contents of the crucible perfectly white; when quite cold, it is weighed. Its composition is One equivalent of BaO ... 76.64 .. . 65.7 One do. of S03 ... 40.00 ... 34.3 One do. of BaO,S03 .. . 116.64 100 Quantitative determination as Carbonate.—In certain cases the precipitation of baryta by sulphuric acid is inadmissible; it is then thrown down in the form of carbonate by carbonate of ammonia, mixed with a little caustic ammonia; the preci- pitate is allowed to settle in a warm place, and it is washed on the filter with water, rendered slightly alkaline by am- monia. It may be heated to redness, without losing carbonic acid. * The addition of strong alcohol to the washed precipitate prevents a passage of any particles through the filter. The after use of water for washing does not then give a turbid filtrate. 254 QUANTITATIVE ANALYSIS. Its composition is One equivalent of BaO . . . 76.64 . . . 77.69 One do. of CO, ... 22.00 . . . 22.31 98.64 100 Baryta is estimated as carbonate when it exists in com- bination with an organic acid: the salt is carefully ignited in a platinum crucible, first covered, and afterwards, with free access of air, the heat is continued till the residue is perfectly white; it is then allowed to cool, moistened with carbonate of ammonia, and again gently ignited. Separation of Baryta from the Alkalies.—The compound is dissolved in water or in hydrochloric acid, if necessary; and the baryta precipitated as sulphate, the alkalies being in this case obtained also in the state of sulphates by evaporating the filtered solution; or as carbonate, in which case the alka- lies may be obtained as chlorides, which is the most con- venient form if they have subsequently to be separated from each other. Strontium. Oxide of Strontium.—Strontia is also weighed as sulphate and as carbonate; it is precipitated in the form of both salts precisely as baryta; but, as sulphate of strontia is not alto- gether insoluble in water, spirits of wine are added to the fluid, to diminish its solubility: when this is inadmissible, it is better to precipitate the earth as carbonate, washing the salt on the filter with water containing ammonia and car- bonate of ammonia. The composition of sulphate of strontia is One equivalent of SrO . . . 51.84 . . . 56.44 One do. of SO, ... 40.00 . .. 43.56 One do. of SrO,S03 ... 91.84 100 The composition of carbonate of strontia is One equivalent of SrO . .. 51.84 . .. 70.20 One do. of CO, ... 22.00 ... 29.80 73.84 100 QUANTITATIVE ANALYSIS. 255 Separation of Strontia from Baryta—The hydrochloric solution of the earths is mixed with excess of hydrofluosihcic acid, and allowed to remain at rest for some hours: the crys- taline precipitate of silico-fluoride of barium is collected on a weighed filter, washed and dried at 212°: the strontia in the filtrate is estimated either as sulphate or as carbonate. The composition of silico-fluoride of barium is One equivalent of Ba ... 68.64 46.98 = 52.45 BaO; One do. of Si ... 21.35 14.60 Three do. of Fl ... 56.10 38.42 One do. of (BaFl,SiFl2)* 146.09 100 Separation of Strontia from the Alkalies.—This is effected in the same manner as the separation of baryta. Calcium. Oxide of Calcium, or Lime, is estimated as sulphate and as carbonate. As sulphate of lime is soluble to a-considerable extent in water, it is necessary to add to the solution about to be precipitated by sulphuric acid twice its volume of alcohol, and to wash the sulphate of lime on the filter with spirits of wine: it is ignited previous to weighing. The composition of sulphate of lime is One equivalent of CaO ... 28 ... 41.17 One do. of S03 ... 40 ... 58.83 One do. of CaO,S03 ... 68 ... 100 Quantitative determination as Carbonate.—If the lime salt be soluble in water, and if the solution be perfectly neutral, oxalate of ammonia is added as long as a precipitate is pro- duced ; the oxalate of lime is allowed to settle completely, which usually requires some hours; the vessel (a beaker, or a Phillips' precipitating jar) being covered, and placed in a warm situation, it is then filtered, and the salt, having been thoroughly washed with hot water, is dried and exposed to a, dull red heat for about twenty minutes ; the oxalateof lime is by this means converted into carbonate; but, as it is possible that it may have lost carbonic acid during ignition, it is safer, * According to Berzelius the formula of silico-fluoride of barium is (3BaFl, 2SiFI3). 256 QUANTITATIVE ANALYSIS. before weighing, to moisten it with a few drops of solution of carbonate of ammonia, to evaporate to dryness on the water bath, and again expose it to a very gentle ignition. The composition of carbonate of lime is One equivalent of CaO ... 28 ... 56 One do. of C02 ... 22 ... 44 One do. of CaO,C02 50 100 If, however, the lime salt can only be held in solution by a free mineral acid, or if it will not bear the addition of ex- cess of ammonia without a precipitation taking place, as is the case with phosphate of lime for example, the Jime is best estimated as sulphate, because, oxalate of lime being soluble in mineral acids, it would be impossible to precipitate it from a solution containing free nitric or hydrochloric acid ; oxalate of lime is, however, insoluble, or nearly so in acetic acid, and likewise in oxalic acid. According to Fresenius, very accu- rate results may, therefore, be obtained by adding to the hy- drochloric solution of the lime salt sufficient ammonia to occasion a slight precipitate, then a drop or two of hydro- chloric acid to redissolve this precipitate, then oxalate of ammonia in excess, and finally, acetate of potassa, a portion of which becomes decomposed by the free hydrochloric acid, liberating a corresponding quantity of acetic or oxalic acid, in which, as before observed, oxalate of lime is almost entirely insoluble. Separation of Lime from Baryta.—This is best effected by adding to the acid solution of the two earths very diluted sulphuric acid, as long as precipitation occurs; if the sul- phuric acid be sufficiently diluted, no lime will be precipitated. Separation of Lime from Strontia.—This is effected with some difficulty; the only good method is that recommended by Stromeyer, which is based on the complete solubility of nitrate of lime in absolute alcohol, and the insolubility of nitrate of strontia in the same menstruum. The two earths are converted into nitrates, excess of nitric acid being care- fully avoided, the solution is evaporated to dryness in a flask that can be closed, and the residue digested for several hours with absolute alcohol: being frequently shaken, the mixture is then filtered, and the undissolved residue washed with alcohol; both earths are then estimated as sulphate. QUANTITATIVE ANALYSIS. 257 Separation of Lime from Baryta and Strontia.—When all three earths are together in a solution, the baryta is first pre- cipitated by hydrofluosilicic acid, the lime and the strontia are obtained from the solution filtered from the silico-fluoride of barium in the form of sulphates, by the addition of sul- phuric acid and evaporation to dryness—the mixed sulphates are fused in a platinum crucible with three times their weight of mixed carbonates of potassa and soda: the fused mass is extracted with water, and the earths are thus obtained in the state of carbonates. They are next converted into nitrates, and separated by alcohol, as above directed. Separation of Lime from the Alkalies.—The process for effecting this is very simple: the lime is separated by oxalate of ammonia with the usual precautions; the filtered solution is evaporated to dryness, and ignited to expel the ammoniacal salts; the residue is dissolved in water, and the alkalies de- termined according to the method already described. Magnesium. Oxide of magnesium or magnesia is weighed as sulphate, or pyrophosphate, and sometimes as pure magnesia. Quantitative estimation as Sulphate. — The earth is de- termined in the form of this salt when no other fixed consti- tuent is present; the solution containing it is mixed with excess of sulphuric acid, evaporated to dryness, and ignited in a platinum crucible ; the residue is again treated with dilute sulphuric acid, evaporated to dryness, and again gently ignited; the residue is pure anhydrous sulphate of magnesia, the composition of which is One equivalent of MgO ... 20.67 ... 34.07 One do. of S03 ... 40.00 ... 65.93 One do. of MgOSo3 ... 60.67 ... 100 Quantitative estimation as Pyrophosphate. — Muriate of ammonia is added to the solution, then ammonia in excess; should a precipitate hereupon occur, a fresh quantity of mu- riate of ammonia is added, by which the precipitate is redis- solved ; solution of phosphate of soda is then dropped into the mixture as long as precipitation takes place. The whole is well agitated, and allowed to repose for several hours; the precipitate is collected on a filter, the amount of ash furnished 17 258 QUANTITATIVE ANALYSIS. by which is known, and washed with water containing about one-eighth of ammonia, in which the basic phosphate of mag- nesia and ammonia (P052MgO,NH4,0-f24 aq.) is scarcely sensibly soluble ; the washed salt is dried and carefully ignited, together with the filter; the latter requires considerable time for incineration, which is best effected by cutting in strips and burning it on the lid of the crucible. The composition of the ignited salt is Two equivalents of MgO . . . 41.34 ... 36.46 One do. of P05 ... 72.02 ... 63.54 One do. of 2MgO,P05 113.36 100 Separation of Magnesia from Baryta and Strontia.—The two latter earths are precipitated by carbonate of ammonia, a sufficient quantity of sal ammoniac having previously been added to the solution to prevent the precipitation of the mag- nesia : the precipitated carbonates of baryta and strontia are dissolved in hydrochloric acid, and the baryta separated from the strontia by hydrofluosilicic acid, the magnesia is deter- mined in the filtrate as pyrophosphate ; if no strontia be pre- sent, the baryta may be precipitated as sulphate. Separation of Magnesia from Lime.—There are several methods of effecting this. 1st. By oxalate of ammonia. Sal ammoniac is added to the solution of the two earths, then slight excess of ammonia; the lime is then precipitated by oxalate of ammonia, with the proper precautions, and the magnesia in the filtrate determined as pyrophosphate. 2d. By sulphate of lime. For this purpose the two earths must be in the state of sulphates; the mixture, having been ignited, is digested with a saturated solution of sulphate of lime, and the insoluble residue washed on a filter with the same salt; the whole of the sulphate of magnesia is thus removed, the sulphate of lime being quite insoluble in a saturated solution of sulphate of lime remaining on the filter: it is heated to redness and weighed; and from the difference in weight, be- fore and after the operation, the amount of sulphate of mag- nesia is calculated. 3d. By chlorate of potassa. The hydro- chloric solution of the two earths is evaporated to dryness, and ignited in a platinum crucible : chlorate of potassa is then added in small quantities at a time, until the evolution of chlorine ceases. The mass on cooling is extracted with water, QUANTITATIVE ANALYSIS. 259 which dissolves the chloride of calcium, and leaves a residuum of pure magnesia, the chloride of magnesium having, under the influence of heat, aided by the chlorate of potassa, been completely decomposed : the lime is determined in the aqueous solution by oxalate of ammonia. Separation of Magnesia from the Alkalies.—The best me- thod is the following, recommended by Berzelius:—The bases are brought to the state of chlorides, to a concentrated solu- tion of which finely powdered and perfectly pure red oxide of mercury is added in excess, mutual decomposition of the chloride of magnesium and of the oxide of mercury takes place, chloride of mercury being formed, which combines with the alkaline chlorides, forming a soluble double salt; and magnesia, which remains undissolved, on extracting the eva- porated and ignited mass with water. The solution, filtered from the magnesia, is evaporated to dryness, and heated, to expel the chloride of mercury: the alkaline chlorides alone remain, which are separated from each other as directed (page 238); the magnesia may be contaminated with unde- composed oxide of mercury, from which, however, it is readily freed by heat. This method is well adapted for the analysis of mineral waters, soils, &c. The following method, proposed by Liebig, also gives accurate results; baryta water is added to the hydrochloric solution to alkaline reaction, magnesia is thereby precipitated, baryta being a stronger base than mag- nesia, in consequence of which, it deprives it of its electro- negative element; to the solution, filtered from the precipitated magnesia, carbonate of ammonia, mixed with caustic ammonia, is added, the excess of baryta is thereby removed, and is fil- tered off; the alkalies are contained in the filtrate in the form of chlorides, and are separated from each other in the usual manner. GROUP 3. Aluminum, Clucinum, Yttrium, Thorium, Zirconium. Chromium. Aluminum. Alumina is precipitated from its solutions by ammonia, or carbonate of ammonia, sal ammoniac having been previously 260 QUANTITATIVE ANALYSIS. added and heat applied. The precipitate, which is very bulky, requires long-continued washing with hot water, its ignition must be carefully performed in order to avoid loss by spirting. It shrinks very much in drying. Its composition is Two equivalents of Al ... 27.38 ... 53.29 Three do. of 0 ... 24.00 ... 46.71 One do. of A1203 ... 51.38 100 It is never weighed in any other form than as pure alumina. Separation of Alumina from the Alkaline Earths and Alkalies.—To the hydrochloric solution of the mixture mu- riate of ammonia is added, then ammmonia quite free from carbonic acid; the alumina is precipitated, carrying with it a little magnesia; it must be separated by filtration as rapidly as possible, the funnel being covered with a glass plate to prevent the access of carbonic acid, which would determine the precipitation of the earthy carbonates: the precipitate on the filter is well washed with hot water, it is then, while still moist, dissolved in hydrochloric acid, and boiled with exces3 of pure potassa; the small quantity of magnesia remains un- dissolved, and, having been separated from the alkaline ley by filtration, it is well washed, dissolved in a small quantity of hydrochloric acid, and added to the solution containing the alkaline earths and the rest of the magnesia. The potassa ley contains the whole of the alumina, which is precipitated by adding excess of hydrochloric acid, and, finally, super- saturating with ammonia: the alkaline earths and alkalies are separated from each other in the manner directed in the last section. The success of this process depends on the freedom of the ammonia from carbonic acid, and on the rapid filtering and careful washing of the precipitated alumina. If alumina has to be separated from baryta only, the latter earth may effectually be removed by sulphuric acid. Separation of Alumina from Lime only.—The alumina is precipitated by ammonia free from carbonic acid, with the precautions just prescribed; and the lime in the filtrate is precipitated by oxalate of ammonia. Separation of Alumina from Magnesia alone.—This may be effected by either of the following methods :—If the quan- tity of magnesia be small, the mixture of the two earths may be dissolved in hydrochloric acid, excess being avoided, and QUANTITATIVE ANALYSIS, 261 the solution boiled with excess of caustic potassa, by which the alumina is dissolved, magnesia remaining behind. If the quantity of magnesia be considerable, sal ammoniac is added to the hydrochloric solution of the two earths, and the alumina is precipitated by ammonia; but, as it carries with it a small quantity of magnesia, it must be redissolved in hydrochloric acid and treated with caustic potassa as above; it is not safe to treat at once the hydrochloric solutions of the earths with excess of caustic potassa when the quantity of magnesia is considerable, it being in this case very difficult to separate them by an alkaline ley. The best method of separating alumina from magnesia is probably to precipitate the former by bicarbonate of potassa, and to estimate the magnesia in the filtrate as pyrophosphate of magnesia: the alumina pre- cipitated in this manner carries with it a portion of potassa, which it is almost impossible to remove by washing; it must, therefore, be redissolved in hydrochloric acid and reprecipi- tated by carbonate of ammonia. Gclucinum. Oxide of Cflucinum.—Grlucina, like alumina, is only weigh- ed in its pure form as precipitated from its solution by caustic ammonia. Its composition is Two equivalents of Gl ... 53.0 . . . 68.83 Three ditto of 0 ... 24.0 . . . 31.17 One ditto of G1208 . . 77 100 Separation of Grlucina from Alumina.—Two methods have been proposed. The first depends on the solubility of glucina in carbonate of ammonia, and the insolubility of alumina in that reagent. The solution containing the two earths is mixed in a flask with a very considerable excess of a concen- trated solution of carbonate of ammonia, the flask is closed, and occasionally shaken; when it is observed that the preci- pitate ceases to diminish in bulk, the alumina is separated by filtration, and the filtrate evaporated to dryness, and ignited to expel the ammoniacal salts; the residue, provided no other base or fixed acid be present, is pure glucina: or both the earths may be together precipitated by ammonia, and the pre- cipitate digested with carbonate of ammonia till the glucina is entirely dissolved. 262 QUANTITATIVE ANALYSIS. The second method is to dissolve both earths in a hot and concentrated solution of caustic potassa, to allow the ley to cool, and then to dilute it considerably with water, and again boil; the glucina is in this manner precipitated, while the alumina remains in solution. The third method is that proposed by Berthier. The earths are dissolved in sulphuric acid, the solution concen- trated, and sulphate of ammonia added, which causes the separation of the greater portion of the alumina in the form of an alum: to the decanted and diluted liquid sulphate of ammonia is added, and it is boiled until sulphurous acid ceases to be liberated; the alumina is entirely precipitated, and the glucina remains in solution, and may afterwards be precipi- tated by ammonia: or both earths may be together precipi- tated by ammonia, and, while moist, treated with sulphurous acid, which redissolves both, but on boiling the solution the alumina is completely precipitated. The separation of glucina from lime, magnesia, and the alkalies, is effected in the same manner as the separation of alumina. Yttrium. Oxide of Yttrium, or Yttria, is weighed as the pure earth, in which state it is precipitated by caustic alkalies; it must, however, be observed, that when it is dissolved in nitric or in sulphuric acid, potassa must be the precipitant employed; in the latter case it is, according to Wohler, almost impossible to procure it free from sulphate of potassa. Its composi- tion is One equivalent of Y ... 32.2 . . . 80.09 One do. of 0 . . . 8.0 .. . 19.91 One do. of YO . . . 40.2 100 Separation of Yttria from Alumina and Grlucina*—This is easily accomplished by digesting the mixture of the three earths in caustic potassa in which yttria is insoluble. Separation of Yttria from Magnesia and the Alkalies.— * Berthier's mode of separating Glucina from Yttria is to add sulphite of ammonia to their solution, and boil the mixture. The basic sulphite of Yttria which, falls is insoluble in water, and the glucina may be precipitated from the residual solution by ammonia. QUANTITATIVE ANALYSIS. 263 From magnesia yttria is separated by caustic ammonia, sal- ammoniac having been previously added to the solution; from the alkalies it is separated precisely in the same manner as alumina. Thorium. Of Oxide of Thorium or Thorina, little is known: from alumina it is distinguished by its insolubility in caustic po- tassa, and as it is completely precipitated from its solutions by ammonia, even in the presence of sal-ammoniac, it may thus be separated from magnesia and lime. Thorina forms, with sulphate of potassa, a double salt, quite insoluble in sulphate of potassa; this salt may, therefore, be employed to separate it from most other substances, but it must be concen- trated, hot, and in excess; the double salt, after being washed with a cold and saturated solution of sulphate of potassa, is dissolved in boiling water, and the thorina precipitated by caustic potassa. Its composition is One equivalent of Th ... 59.59 . . . 88.16 One do. of 0 ... 8.00 . . . 11.84 One do. of ThO . . . 67.59 100 Zirconium. Oxide of Zirconium, or Zirconia, is precipitated from its solutions by ammonia and by caustic potassa; the latter is the best precipitant, the former often throwing down subsalts instead of the pure earth. Sulphate of potassa added in crystals and in sufficient quantity to saturate the liquid, which must be first completely neutralized by potassa, throws down the whole of the earth in the form of a double salt; it must be washed with water containing ammonia, and then boiled with caustic potassa, which leaves hydrate of zirconia in a pure state. Its composition is Two equivalents of Zr ... 67.24 . . . 89.37 Three do. of 0 ... 8.00 . . . 10.63 One do. of Zr203 . . 75.24 100 The solubility of zirconia in bicarbonate of potassa affords a means of separating it from alumina, lime, magnesia, stron- tia, baryta and the fixed alkalies; but an accurate method of 264 QUANTITATIVE ANALYSIS. separating it from yttria and glucina remains to be disco- vered. Chromium. Oxide of Chromium is usually estimated quantitatively in its pure state; the solution containing it is heated to the boil- ing temperature, and, ammonia being added in slight excess, it is boiled for about half an hour, or until the solution is perfectly colorless; the precipitate is collected on a filter, washed with boiling water, dried, and ignited. Its composi- tion is Two equivalents of Cr ... 56.30 . . . 70.11 Three do. of 0 ... 24.00 . . . 29.89 One do. of Cr203 . . 80.30 100 The ignition of this oxide must be performed with care, as at a particular temperature it suddenly -becomes incandescent with a sort of explosion, whereby a portion may be projected from the crucible. The crucible should be closed with its cover. When chromium exists in a solution in the form of chromic acid, it may be estimated as chromate of baryta, or chromate of lead, by adding respectively nitrate of baryta or nitrate of lead to the solution; it may also be precipitated by proto- nitrate of mercury, the resulting chromate being decomposed by ignition into mercury, oxygen, and oxide of chromium; from the weight of the latter the quantity of chromic acid maybe calculated; it is better, however, to reduce the chromic acid to oxide of chromium in the solution previous to precipi- tating it, which is done by concentrating the solution and boiling it with excess of hydrochloric acid, mixed with alco- hol, till the liquid assumes a pure green color. The reduced oxide of chromium is precipitated by ammonia, after the alco- hol has been expelled by a gentle heat. Estimation of Chromium in its compounds by Carbonic Acid.—This method has lately been proposed by H. Vohl* and is applicable to the determination of the metal whether occurring in the form of oxide or as chromic acid, but when the metal exists as oxide of chromium, it must in the first * Liebig's Annalen, September 1847, and Chem. Gaz., January 1st, 1848. QUANTITATIVE ANALYSIS. 265 place be converted into chromic acid, the process depending on the conversion of oxalic into carbonic acid by the oxygen furnished by the reduction of chromic acid into oxide of chro- mium; thus m 2(Cr03) + 3(C203)=Cr203+6C02 for each equivalent of chromic acid, three equivalents of car- bonic acid are formed, or QQ parts by weight for 50.31 parts of chromic acid. To determine the amount of carbonic acid, the author employs the alkalimetrical apparatus of Fresenius and Will (page 244.) If merely the chromium has to be de- termined, any oxalate may be taken, but, if the alkalies are to be determined in the residuary liquid, oxalate of ammonia or baryta is employed. The analysis is very simple: when the chromium exists in the (?ompound in the form of acid, the salt is taken then just as it is, and the process is precisely the same as in the analysis of manganese (to be described further on). If the salt is a chloro-chromate, before allowing the sulphuric acid to pass over, oxide of mercury must be mixed with the salt, to prevent the elimination of chlorine or muri- atic acid: after the operation the amount of chlorine can be determined from the perchloride of mercury by nitrate of sil- ver, and the quantity of chlorochromic acid contained in the salt calculated from it. The determination is less simple when the salt contains oxide of chromium. In the first place, the oxide must be converted into chromic acid, and this is best effected in the following manner:—The salt to be examined is dissolved in water, and caustic potassa added to it until the whole of the hydrated oxide of chromium has redissolved; upon which, keeping the solution cold, chlorine is passed into it until the green color is changed into a yellowish red one; an excess of potassa is now added to this liquid, which is evaporated in the water-bath, and heated to faint redness in a platina cruci- ble,. The whole of the chlorate of potassa is decomposed, chromate of potassa and chloride of potassium remaining; these are dissolved, transferred with oxide of mercury into the apparatus, and the operation conducted as with chromates. The amount of oxide of chromium can be easily calculated from the quantity of carbonic acid which has escaped; 6 equivalents of carbonic acid are set free for each equivalent of oxide of chromium:— Cr203+03= 2Cr032(Cr03) + 3(C203)=Cr203+6C03 266 QUANTITATIVE ANALYSIS. In analyzing a salt in which both chromic acid and oxide of chromium occur, two determinations must be made. In the first place, the carbonic acid is determined, which the salt yields as it is, and the chromic acid calculated from the amount; upon which the liquid is treated as a salt of the oxide, the quantity of carbonic acid first obtained subtracted from that last obtained, and the amount of oxide of chromium calculated from the difference. This method will, according to M. Vohl, render it possible for every one to submit to analysis those compounds of chro- mium which occur so frequently adulterated in commerce. Separation of Oxide of Chromium from Alumina.—The usual method is to fuse the mixture of the two oxides with twice its weight of carbonate of sbda, and twice and a half of its weight of nitre ;* the oxide of chromium becomes converted into alkaline chromate, which is extracted with water, and the alumina which remains undissolved is freed from alkali by dis- solving in hydrochloric acid, and precipitating by ammonia. According to Dr. Schaffhaeutl, however, a portion of alumina in this process always dissolves along with the alkaline chro- mate; he therefore recommends to convey the precipitate ob- tained by adding ammonia to the solution containing the two oxides into a hot concentrated solution of caustic potassa, and to boil the whole down till near solidification; when quite cold, water is added, and the whole of the alumina dissolves with- out carrying with it a trace of oxide of chromium. Separation of Oxide of Chromium from the rest of the Al- kaline Earths.—This is also effected by fusing the mixture with carbonate of soda and nitre, the earths are thus obtained in the form of carbonates, and are to be separated from each other. Separation of Oxide of Chromium from the Alkalies.—The oxide of chromium is precipitated by ammonia, sal-ammoniac having previously been added to the solution. The alkalies are determined in the filtrate according to the directions pre- viously given. * Prof. J. C. Booth recommends bisulphate of potassa as the best flux for Chromic ores. QUANTITATIVE ANALYSIS. 267 GROUP 4. Zinc, Nickel, Cobalt, Manganese, Iron. Zinc. Oxide of Zinc is precipitated from its solutions, for the pur- pose of quantitative estimation, by carbonate of soda, or by hydrosulphuret of ammonia; in either case it is subsequently brought to the state of oxide, in order to be weighed. Precipitation as Basic Carbonate.—Carbonate of soda is added in excess to the solution, which is then boiled for some time ; if, however, ammoniacal salts be present, a considerable excess of carbonate of potassa must be added, and the solution must be evaporated to dryness at the boiling temperature; in order to decompose the ammoniacal salts, the dry mass is well washed with hot water, and the residue, which is basic carbon- ate of zinc (3HO,ZnO + 2ZnO,C02), is strongly ignited, by which it becomes converted into oxide. Precipitation as Sulphuret.—The solution, if it be acid, is first supersaturated with ammonia, the alkali being added in sufficient quantity to redissolve the oxide of zinc, which first precipitates; hydrosulphuret of ammonia is then added till it no longer occasions a precipitate, and the sulphuret of zinc, which is white, and very voluminous, is allowed completely to subside before filtration; the sulphuret is washed with water containing hydrosulphuret of ammonia, and then digested with concentrated hydrochloric acid until the solution ceases to smell of sulphuretted hydrogen; the resulting chloride of zinc is then precipitated as basic carbonate, and subsequently con- verted into oxide in the manner and with the precautions just described: it is to be observed, that it must not be neglected to examine whether the filtrate from the carbonate of zinc is free from oxide of zinc, which is done by adding to it a few drops of hydrosulphuret of ammonia; the formation of a white bulky precipitate indicates the presence of dissolved oxide of zinc, which must be collected and treated as above. The com- position of oxide of zinc is One equivalent of Zn ... 32.52 ... 80.25 One do of 0 ... 8.00 . .. 19.75 One do of ZnO ... 40.52 ... 100 268 QUANTITATIVE ANALYSIS. Separation of Oxide of Zinc from Oxide of Chromium.— The solution is mixed with tartaric acid, excess of potassa is then added, and the clear solution is precipitated with color- less sulphuret of potassium; the sulphuret of zinc is treated as above, the oxide of chromium is contained in the filtrate, and is obtained by evaporating it to dryness and fusing the ignited residue with nitre and carbonate of soda; the alkaline chromate thus obtained is treated as directed (p. 264); then both the oxides are combined with acids that form soluble salts with baryta; their separation can, according to Fresenius, be accomplished by digesting the acid solution for several hours with excess of artificially produced carbonate of baryta: the whole of the oxide of chromium is removed, and is mixed with the excess of carbonate of baryta, from which it is separated by dissolving in hydrochloric acid, and adding excess of sul- phuric acid; the oxide of zinc remains in solution, and is pre- cipitated by carbonate of potassa. Separation of Oxide of Zinc from Alumina.—The solution containing the two oxides is supersaturated with ammonia, alumina is precipitated, and oxide of zinc remains in solution. If, to a solution of the mixed oxides, excess of cyanide of po- tassium be added, heat being avoided, alumina is precipitated, and oxide of zinc retained in solution. If to a solution of the two oxides in sulphuric acid, excess of acetate of baryta be added, and then sulphuretted hydrogen passed into the solu- tion, sulphuret of zinc is precipitated, while alumina remains dissolved; the sulphuret of zinc is separated from the sulphate of baryta by digesting the mixture in hydrochloric acid, the oxide of zinc is then precipitated from the solution as basic carbonate, and the alumina is precipitated by ammonia. Separation of oxide of Zinc from Magnesia.—Sal-ammo- niac is added to the solution, and then sufficient ammonia to retain both oxides in solution: the zinc is precipitated from the ammoniacal solution by hydrosulphuret of ammonia, and the magnesia in the filtrate determined in the usual manner. Another plan which has been proposed is to precipitate both oxides by carbonate of potassa; and then, having added a sufficient quantity of cyanide of potassium to dissolve the zinc, the whole is evaporated to dryness at a boiling tempera- ture, a little more carbonate of potassa having first been added: on treating the dry mass with water, the magnesia re- mains undissolved, and the zinco-cyanide of potassium is held in solution. QUANTITATIVE ANALYSIS. 269 Separation of Oxide of Zinc from the Alkalies and Alka- line Earths.—The bases are all brought into the state of acetates by adding acetate of baryta to the sulphuric acid solution as above described: the zinc is precipitated by hy- drosulphuret of ammonia. To separate oxide of zinc from lime, baryta, and strontia, it has been recommended to treat the mixed solution with carbonate of potassa, until it acquires an alkaline reaction, then to add excess of cyanide of potas- sium, and apply heat: the earthy carbonates remain undissol- ved, while that of zinc is taken up. The solution is boiled with hydrochloric and nitric acids, until all hydrocyanic acid is expelled, and the oxide of zinc is then precipitated with car- bonate of soda, those precautions being taken which are ne- cessary when a salt of ammonia is present. Nickel. Oxide of Nickel is precipitated from its solutions either as hydrated oxide by caustic potassa, or as sulphuret by hydro- sulphuret of ammonia: in either case it is converted into an- hydrous protoxide to be weighed. Precipitation as Hydrated Protoxide.—Pure solution of caustic potassa is added, and the solution heated to boiling; the voluminous apple-green precipitate, which is formed, re- quires protracted washing with hot water; after which it is dried and ignited: ammoniacal salts do not interfere with the precipitation of oxide of nickel by caustic potassa, but with carbonate of potassa it is not so complete. Precipitation by Hydrosulphuret of Ammonia.—The com- plete precipitation of nickel in the state of sulphuret by hydrosulphuret of ammonia is not easy, in consequence of the partial solubility of sulphuret of nickel in that reagent. To insure success the hydrosulphuret of ammonia must be per- fectly saturated and colorless, and not added in great excess; the vessel must be covered, and placed in a warm situation; the fluid above the precipitate should be free from color; the sulphuret of nickel is washed on the filter with water, to which a few drops of hydrosulphuret of ammonia have been added; it is then dried, transferred to a beaker, and digested at a gentle heat (until completely dissolved) with concentrated aqua regia; the filter is burnt, and its ashes added to the solution: this is better than digesting the filter and precipi- tate together in aqua regia; since, as Fresenius observes, the 270 QUANTITATIVE ANALYSIS. presence of organic matter prevents the complete precipita- tion of oxide of nickel by caustic alkali: the solution filtered from the separated sulphur is precipitated by potassa, washed, dried, and ignited. The composition of anhydrous protoxide of nickel is One equivalent of Ni ... 29.57 . . . 78.76 One do. of 0 ... 8.00 . . . 21.24 One do. of NiO ... 37.57 100 Separation of Oxide of Nickel from Oxide of Zinc.—. Several methods have been proposed:—1st. Berzelius's Method. The greater part of the oxide of zinc is first ex- tracted by caustic potassa; the residue, after being well washed and heated, is mixed with pure pulverized sugar, and carefully carbonized in a porcelain crucible. The crucible is then surrounded with magnesia in a larger Hessian crucible, and heated for an hour in a blast furnace as strongly as pos- sible. The oxides are reduced, and the zinc is driven off in vapor; the nickel is dissolved in nitric acid, evaporated to dryness in a platinum crucible, and ignited. The loss of weight gives the quantity of oxide of zinc. The principal point to be attended to is to extract all the potassa from the mixed oxides: the sugar must be perfectly pure, with which view it should be crystalized from an alcoholic solution. 2d. Ullgrens Method.—The oxides are precipitated by carbonate of soda, the whole evaporated, and the residue gently heated, so that they remain perfectly insoluble when the mass is treated with water. The oxides are washed and dried, and then being placed in a tube, with a bulb, are reduced by hydrogen at a low red heat; the tube is allowed to cool, while a continuous current of hydrogen is passed through it; it is then closed at one end by fusion, filled with a concentrated solution of carbonate of ammonia, corked up, and placed in a warm situation for twenty-four hours; the oxide of zinc, which is not reduced, is dissolved in the carbonate of ammo- nia; the oxide of nickel is reduced, and the metal, after being well washed with carbonate of ammonia, is dried and weighed; the oxide of zinc is obtained from the ammoniacal solution by evaporation. The oxides must be finely pulverized before they are exposed to the action of hydrogen gas. 3d. Rose's Method.—The mixed oxides, after having been QUANTITATIVE ANALYSIS. 271 ignited, are placed in the bulb of a reduction tube, which communicates on the one side with an apparatus, from which dry hydrochloric acid gas is liberated, and, on the other, with a flask containing a very dilute solution of ammonia. As soon as the air is expelled the bulb is gradually heated to redness, the oxides are converted into chlorides, the chloride of nickel remains in the bulb, and the volatile chloride of zinc passes into the solution of ammonia, in which it dissolves. The oxides are then determined in the usual manner. This method, though tedious and somewhat complicated, yields very accurate results. 4th. Smith's 3Iethod.—The oxides are converted into ace- tates; and, excess of acetic acid being added, sulphuretted hydrogen is passed through the solution, by which the whole of the zinc is precipitated as sulphuret, while the oxide of nickel remains in solution: this method, which is well adapted for the analysis of German silver, the constituents of which are copper, zinc, and nickel, has been found by 31. Louyet to yield very accurate results. Separation of Oxide of Nickel from Oxide of Chromium. —The mixed oxides are fused with nitre and carbonate of soda; the oxide of chromium is thus converted into chromic acid, and is dissolved on boiling with water as alkaline chro- mate. Separation of Oxide of Nickel from Alumina.—Excess of cyanide of potassium is added, heat being avoided; alumina is precipitated, and oxide of nickel retained in solution; ac- cording to Berthier, on adding sulphite of ammonia to a solu- tion of the two oxides, the alumina only is precipitated. Separation of Oxide of Nickel from 3Iagnesia.—This is effected in the same manner as the separation of oxide of zinc from the same earth. Separation of Oxide of Nickel from Baryta, Strontia, and Lime. Cyanide of potassium is added in excess, and then carbonate of potassa, the whole is boiled, and the insoluble carbonates separated by filtration from the nickel cyanide. The solution is boiled with hydrochloric acid until all the hydrocyanic acid is expelled; potassa in excess is then added, and the solution boiled till all the ammonia is liberated, the oxide of nickel is then precipitated by potassa. 272 QUANTITATIVE ANALYSIS. Cobalt. This metal is precipitated from its solutions either by caustic potassa, or by hydrosulphuret of ammonia ; it is weighed either as oxide or in the metallic state; when great or even moderate accuracy is required, it must be estimated in the latter form, as the ignited hydrated protoxide is of indefinite composition, varying according to the degree of heat employed. Precipitation as Hydrated Protoxide.—The solution is boiled with excess of caustic potassa; the precipitate, which at first is bluish, becomes, after long boiling, of a dirty rose red color; if ammoniacal salts are present, they must be de- composed, and the ammonia discharged by long-continued boiling, with great excess of caustic alkali; the precipitated hydrate requires long-continued washing with hot water, on being dried and ignited it turns black: in this state it is weighed; if the operator has determined on reducing it to reguline cobalt, he proceeds in the following manner. Reduction of Oxide of Cobalt to Reguline Cobalt.—The small Berlin crucible d, Fig. 9, having been carefully weighed, a certain known quantity of the previously weighed oxide is introduced, and the weight of the crucible again accurately noted; a stream of hydrogen gas, dried by passing through the U-shaped chloride of calcium, tube b, is then caused to flow through the apparatus, from the flask a, and a flame applied to the crucible containing the oxide; the heat must at first be gentle,' but it must gradually be raised to full redness, this high temperature being necessary to prevent the reduced QUANTITATIVE ANALYSIS. 273 metal from acquiring a pyrophoric property, which would cause it to inflame on coming in contact with atmospheric air; the hydrogen reduces the metallic oxide, giving rise to a proportional amount of water, which escapes in the form of steam between the top of the crucible and its cover, and at the aperture through which the tobacco-pipe, c, enters. When it is seen that water no longer continues to form, the flame is removed from the crucible, and it is allowed to cool, while a stream of hydrogen still continues to pass over it; the cru- cible is then again weighed, and from the amount of reduced metal obtained the quantity contained in the whole of the protoxide precipitated is calculated. If a sufficiently high temperature has not been employed, the reduced cobalt oxid- izes at common temperatures, but if a full red heat has been employed, it absorbs oxygen very slowly. Precipitation as Sulphuret.—Sal ammoniac is added to the solution, then slight excess of ammonia, and finally hydro- sulphuret of ammonia as long as precipitation takes place; the resulting sulphuret of cobalt is washed with water, contain- ing a little sulphuret of ammonium, then digested with aqua regia, and precipitated by potassa, precisely as sulphuret of nickel. The hydrated oxide, after being washed, dried, and ignited, is reduced by hydrogen in the manner just described. Rose recommends that, in the presence of ammoniacal salts, cobalt should always be precipitated by hydrosulphuret of ammonia. Separation of Cobalt from Nickel.—Several methods have been proposed by different chemists, but until recently Phil- lips' process was the one generally preferred, and is as fol- lows :— 1. Method of Phillips.—Both oxides are dissolved in an acid, and the solution supersaturated with ammonia, having previously added a sufficient quantity of sal ammoniac, to pre- vent any precipitation from taking place; the solution, which has a sky-blue color, is largely diluted with water, which should have been previously well boiled, to free it from atmo- spheric air: caustic potassa is added to the hot solution, and the vessel is closed with a cork; oxide of nickel is precipitated, and oxide of cobalt remains in solution; when the former has completely settled, the supernatant liquid, which should have a rose-red color, is poured through a filter, and the oxide of nickel washed with hot water, ignited, and weighed; the oxide 18 274 QUANTITATIVE ANALYSIS. of cobalt in the filtrate is precipitated by hydrosulphuret of ammonia: the reason why it is necessary to dilute the solution of the two oxides with water, free from atmospheric air, is, that oxide of cobalt in an ammoniacal solution is converted into peroxide of cobalt, which, precipitating as a black pow- der," would contaminate the oxide of nickel. The more dilute the solution is, the less easily does the oxide of cobalt become oxidized. When a large quantity of ammoniacal salt is pre- sent, the quantity of caustic potassa required to precipitate the oxide of nickel is very considerable. According to Fre- senius, the separation by this method is not complete, the cobalt invariably containing traces of nickel, and the preci- pitated nickel often traces of cobalt. 2. Liebigs 3Iethod.—This is founded on the following con- siderations :—When any salt of cobalt is warmed with cyanide of potassium, and an excess of hydrocyanic acid, it is con- verted into the percyanide of cobalt and potassium, or cobalti- cyanide of potassium, (Co2Cy6,K3,) the aqueous solution of which does not undergo any decomposition by boiling with either of the mineral acids. On the other hand, the precipi- tate produced by cyanide of potassium in solutions of salts of nickel is redissolved by cyanide of potassium, but the solution is decomposed by dilute sulphuric acid, cyanide of nickel being precipitated. When, therefore, a mixture of a cobalt and a nickel salt containing free acid is treated with excess of cya- nide of potassium, and slightly warmed, we obtain in solution the double cyanide of nickel and potassium, and cobalti- cyanide of potassium, (NiCy + KCy) + (C02Cy6K3,) and on adding dilute sulphuric acid in the cold, three cases present themselves. 1st. If the cobalt and nickel exist in the solution in the proportion, by weight, of two cobalt to three nickel, wTe have in the solution, 3(NiCy,KCy)4-(Co2Cy6K3,) and the three equivalents of nickel replacing the three equivalents of potas- sium, in the cobalticyanide of potassium, produce cobalti- cyanide of nickel, (Co2Cy6Ni3,) which is precipitated of a bluish white color, leaving in the solution no trace of either cobalt or nickel. 2d. If the solution contain less nickel than corresponds to the above proportions, a certain quantity of cobalticyanide of potassium remains in solution, while cobalticyanide of nickel is still precipitated. QUANTITATIVE ANALYSIS. 275 3d. If the solution contain more nickel than corresponds to the above proportions, cobalticyanide of nickel is still pre- cipitated, together with the excess of cyanide of nickel, which, by long boiling with hydrochloric acid, is completely converted into chloride of nickel, which remains in solution. Now cobalticyanide of nickel, though insoluble in hydro- chloric acid, is decomposed by boiling with caustic potassa into protoxide of nickel, and cobalticyanide of potassium, thus, Co2Cy6Ni3 + 3KO=Co2Cy6K3+3NiO,and chloride of nickel is also decomposed by caustic potassa into protoxide of nickel and chloride of potassium. Hence, the following method of analyzing mixtures of cobalt and nickel, which is applicable to all proportions. Hydrochloric acid is added to the solution of the metals, and then cyanide of potassium in such excess that the pre- cipitate at first formed is redissolved, the whole is boiled, adding from time to time hydrochloric acid, until hydrocyanic acid ceases to be evolved. Caustic potassa is then added in considerable excess, and the boiling continued until the hy- drated protoxide of nickel is completely precipitated; it is then filtered, the filtrate contains the whole of the cobalt in the form of cobalticyanide of potassium ; it is evaporated to dryness with excess of nitric acid, the residue fused, and treated with hot water: peroxide of cobalt remains, which is dissolved in hydrochloric acid, and the solution treated as al- ready directed. In analyzing ores of nickel, which contain small quantities only of cobalt, considerable excess of hydrochloric acid must be taken to precipitate the cyanides dissolved in cyanide of potassium, and the mixture must be continued in ebullition for a full hour. Rose's Method.—This is founded on the greater tendency in the protoxide of cobalt than in the protoxide of nickel to pass to a higher degree of oxidation. Both metals are dis- solved in hydrochloric acid; the solution must contain a sufficient excess of free acid: it is then diluted with much water; if 20 or 30 grains of the oxide are operated on, about 2 lbs. of water are added to the solution. As cobalt possesses a much higher coloring power than nickel, not only in fluxes, but also in solutions, the diluted solution is of a rose color, even when the quantity of nickel present greatly exceeds that of the cobalt. A current of chlorine is then passed through 276 QUANTITATIVE ANALYSIS. the solution for several hours ;* the fluid must be thoroughly saturated with it, and the upper part of the flask above the liquid must remain filled with the gas after the current has ceased. Carbonate of baryta in excess is then added, and the whole allowed to stand for 12 or 18 hours, and frequently agitated; the precipitated peroxide of cobalt and the excess of carbonate of baryta are well washed with cold water, and dissolved in hot hydrochloric acid ; after the separation of the baryta by sulphuric acid, the cobalt is precipitated by hydrate of potassa, and, after being washed and dried, is reduced in a platinum or porcelain crucible by hydrogen gas, in the man- ner shown in Fig. 9. The fluid filtered from the superoxide of cobalt is of a pure green color; it is free from any trace of cobalt. After the removal of the baryta by means of sul- phuric acid, the oxide of nickel is precipitated by caustic potassa. To insure accurate results, it is indispensably ne- cessary to wait a considerable time, at least 12, or even better, 18 hours after the addition of the carbonate of baryta, as the superoxide of cobalt is precipitated very slowly. Another 3Iethod.—The two oxides are covered with prussic acid, and then potassa added till a portion remains undis- solved. The solution is kept boiling for a quarter of an hour, moist hydrated oxide of mercury is then added till a portion remains undissolved; a green precipitate occurs containing all the nickel, with the excess of oxide of mercury. By igni- tion, pure oxide of nickel remains. Acetic acid is added to the filtrate to acid reaction; it is then precipitated with blue vitriol. The blue precipitate contains all the cobalt; this is dried, ignited, redissolved in hydrochloric acid; the copper, precipitated by sulphuretted hydrogen, and then from the filtrate the cobalt by potassa. The method depends upon the fact, that nickelo-cyanide of potassium is decomposed by oxide of mercury, while cobalto-cjanide of potassium experiences no change. Separation of Oxide of Cobalt from Oxide of Zinc.—The above method may, according to Rose, be employed for the separation of these two oxides; and also for that of other oxides from oxide of cobalt, which are strongly basic, and which are not converted into superoxides: oxide of zinc may, * Mr. Henry employs a solution of bromine till the solution smells strongly of it; he finds this to answer equally well with the chlorine, and the process is rendered less tedious and unpleasant. QUANTITATIVE ANALYSIS. 277 likewise, be separated from oxide of cobalt by Liebig's process with cyanide of potassium, cobalticyanide of zinc is gradually dissolved in boiling hydrochloric acid, and a clear solution is obtained: on the addition of caustic potassa and boiling, both the cobalt and the zinc are retained in solution, the former as cobalticyanide of potassium, and the latter as oxide; and, from the solution, zinc is precipitated by sulphuretted hydrogen; the methods of Berzelius* and Ullgren,^ for the separation of oxide of nickel from oxide of zinc, may likewise be em- ployed for the separation of oxide of cobalt. * This method is employed by Berzelius for separating completely oxide of zinc from oxide of cobalt, and oxide of nickel. It can, of course, be resorted to for separating oxide of zinc, when mixed with only one of these oxides :— After having separated the greatest portion of the oxide of zinc by boiling the mixture with a solution of caustic potash, the residuum is washed with cold water, and then with boiling water, until all the potash is removed. The oxide is heated to redness, and weighed. It is then intimately mixed in a platinum crucible, with pulverized sugar. [Such as will leave no ashes after ignition.] (Berzelius advises the operator to take the crystals of sugar deposited from an alcoholic solution; but the sugar candy of commerce, when chosen in perfectly defined and colorless crystals, leaves no appreciable trace of ashes.) The sugar is carefully carbonized ; the porcelain crucible with the cover on, is put in a Hessian crucible, and the space between the two crucibles is filled up with caustic magnesia, the latter crucible, also covered over, is exposed for one hour in a wind furnace to the strongest heat possible. The oxides are reduced by this treatment; the cobalt and the nickel remain in the state of carburets, and the zinc volatilizes completely. The two metals left behind are dissolved in nitric acid, and the solution is evaporated to dryness in the water bath in a counterpoised platinum crucible, the residuum is ignited to bright redness, and the oxide is weighed. The loss of weight indicates the quantity of oxide of zinc expelled. One of the principal conditions of success in this experiment is, that the mix- ture of the oxides be perfectly washed before being ignited, for,if it still contains potash, the latter acts upon the porcelain crucible; it is advisable to test by boiling water, whether the oxides, after having been ignited, and before being mixed with sugar, contain potash, because, should any be left, it might, as yet, be elimi- nated by a renewed washing. •J- M. Ullgren's method is as follows:—The solution of the oxides of zinc, of cobalt, and of nickel, is precipitated by carbonate of soda, having previously sepa- rated the earthy and other metallic oxides which might be present. The whole is then evaporated to dryness at a gentle heat, so that by adding water, the car- bonate of soda alone dissolves. The oxides are then collected on a filter, washed, weighed, and reduced in a glass tube at a dark red heat, by means of hydrogen gas. When water ceases to be produced, the tube is allowed to cool, the cur- rent of hydrogen gas being continued all the time. One of the extremities is then closed by means of the blow-pipe, and it is filled with solution of carbonate of ammonia; it is corked up and maintained for two days at a temperature of about 40° Cent. (104° Fahr.) The carbonate of ammonia dissolves the oxide of zinc completely, which has not been reduced by the hydrogen gas at the low temperature which was sufficient for the red notion of the two other oxides, and the cobalt and nickel, free from zinc, are washed with carbonate of ammonia. The 278 QUANTITATIVE ANALYSIS. Separation of Oxide of Cobalt from Oxide of Chromium.^— This is effected in the same manner as the separation of oxide of nickel from oxide of chromium. Separation of Oxide of Cobalt from Alumina.—Cyanide of potassium is added, heat being avoided; the cobalt^ is dis- solved as cobalticyanide of potassium, and the alumina pre- cipitated; according to Berthier, the separation may likewise be effected by sulphite of ammonia. Separation of Oxide of Cobalt from the Alkaline Earths.— This is effected in the same manner as the separation of the oxide of nickel. Manganese. This metal is quantitatively estimated as protoxide, as red oxide, or as protosulphate. Quantitative estimation as Protoxide.—Ebelman prefers reducing the higher oxides of manganese to the state of prot- oxide for the purpose of weighing. To perform the experi- ment, he introduces the oxide into a small platinum crucible, the lid of which has a small platinum tube in the centre, through which a current of dry hydrogen gas is conveyed by means of a green glass tube, of a diameter nearly equal to that in the crucible cover (see Fig. 9), heat is applied by means of a spirit-lamp; the reduction is complete after a few minutes, and a rapid current of gas is passed into the crucible while cooling; the oxide obtained is quite pure; it dissolves in hydrochloric acid without rendering it black, and without disengaging chlorine. Its composition is One equivalent of Mn. . . . 27.67 . . . 77.57 One do. of 0 ... 8.00 . . . 22.43 One do. of MnO . . . 35.67 100 Quantitative estimation as Red Oxide.—The solution is heated to boiling with excess of carbonate of soda. Should ammoniacal salts be present, the solution must be treated in the same manner as in the precipitation of carbonate of zinc, ammoniacal liquor is carefully evaporated; the oxide of zinc is left behind, and it is then ignited and weighed. It is essential to the success of this operation, that the oxides submitted to this reductive process, be in a very fine state of division, in order that all the oxide of zinc may be in contact with the carbonate of ammonia. QUANTITATIVE ANALYSIS. 279 under similar circumstances; the precipitate is thoroughly washed, dried, and ignited, by which it is decomposed into the red oxide (manganoso—manganic oxide); sometimes the solution is precipitated with caustic potassa, and the hydrated protoxide thus formed is converted into red oxide by strong ignition; it must be remembered, however, that hydrated protoxide of manganese is soluble in sal-ammoniac. It is sometimes convenient also to precipitate manganese as sul- phuret, by adding colored hydrosulphuret of ammonia to the solution to which sal-ammoniac and ammonia have been add- ed, the precipitate, having been washed with water contain- ing hydrosulphuret of ammonia, is digested with hydrochloric acid, and the solution precipitated by carbonate of ammonia. The composition of red oxide of. manganese is Three equivalents of Mn ... 83.01 . . . 72.17 Four do. of 0 ... 32.00 . . . 27.83 One do. of MnO + Mn203 . . 115.01 100 Quantitative estimation as Sulphate.—Oxide of manganese is converted into protosulphate in the same manner and Avith the same precautions as magnesia: the salt must be ignited very feebly, or it will lose sulphuric acid. Its composition is One equivalent of MnO ... 35.67 ... 47.13 One do. of S03 ... 40.00 . . . 52.87 One do. ofMnO,S03 . 75.67 100 Separation of Oxide of 3Ianganese from Oxides of Cobalt and Nickel.—Rose's original method, which, though compli- cated, gives very accurate results, is the following:—The metals are first precipitated together as oxides by caustic potassa, they are then ignited, weighed, and converted into chlorides by introducing them into a bulbed tube, and trans- mitting over them a current of dry hydrochloric acid gas, a moderate heat being at the same time applied: it requires a lone time thus to convert the oxides completely into chlo- rides ; when the conversion is complete, dry hydrogen gas is passed through the apparatus, the bulb containing the chlo- rides being strongly heated, the hydrogen displaces the chlo- rine from the chlorides of cobalt and nickel, forming with it hydrochloric acid gas; and the operation must be continued 280 QUANTITATIVE ANALYSIS. as long as white clouds are formed, on holding a glass rod that has been dipped in ammonia at the end of the apparatus where the excess of gas escapes: the hydrogen is allowed to pass through the tube till it is quite cold, the chloride of man- ganese, which has not been decomposed by the process, is dissolved out by water; the reduced cobalt and nickel are washed with very dilute hydrochloric acid, and, finally, with water ; the two metals are then separated from each other by one of the methods above given, and the manganese is pre- cipitated from the solution of the chloride, to which has been added the washings from the cobalt and nickel by carbonate of soda. Rose states that nickel may be conveniently separated from manganese in the same manner .as cobalt, namely, by chlorine and carbonate of baryta. A method of separating oxide of cobalt from oxide of manganese was proposed by Barreswil: it consists in adding carbonate of baryta to the solution, and then passing a current of sulphuretted hydro- gen through it, by which, according to Barreswil, cobalt only is precipitated; this method has not, however, been found successful by other chemists. A plan for the separation of oxides of cobalt and nickel from oxide of manganese was pro- posed by Wakenroder, and has obtained the approval of Rose: it is based on the fact that, although nickel and cobalt are not precipitated from their acid solutions by sulphuretted hy- drogen, their sulphurets precipitated by hydrosulphuret of ammonia are not dissolved by very dilute hydrochloric acid. The acid solution of the three oxides is made ammoniacal, and the metals are precipitated by hydrosulphuret of ammonia: the solution is then rendered slightly acid by dilute hydro- chloric acid; the sulphuret of manganese is dissolved with facility, small portions also of the sulphuret of cobalt and nickel may also be dissolved, but they may be removed by reprecipitatmg the solution with ammonia and hydrosulphuret of ammonia, and treating it anew with dilute hydrochloric acid. Blanganese from Cobalt {Liebig's 3Iethod).—The metals are precipitated by cyanide of potassium, an excess of which redissolves the cyanide of cobalt, and a part also of the pro- tocyanide of manganese, while another portion remains un- dissolved, this is filtered off and washed: the filtrate is heated to ebullition, a few drops of hydrochloric acid, insufficient, QUANTITATIVE ANALYSIS. 281 however, to acidify the solution, are added from time to time, and the manganese and cobalt are separated from one another in the same manner as nickel is separated from cobalt. Ebelman has recently proposed to separate manganese from cobalt or nickel, by exposing the mixture of the oxides to a current of dry sulphuretted hydrogen, at a temperature a little below redness. The oxides are converted into sul- phurets, the sulphuret of manganese is dissolved by very weak hydrochloric acid, in the cold. The smallest quantity of cobalt may, he says, be detected in this manner. He ap- plies the same process to the separation of arsenic from tin. Separation of Oxide of 3Ianganese from Oxide of Zinc.— The oxides are dissolved in excess of acetic acid, and the zinc is precipitated by sulphuretted hydrogen; the solution must be acid, and contain no other acid but acetic. Separation of Oxide of 3Ianganese from Oxide of Chro- mium.—This is effected in the same manner as the separation of oxide of zinc from oxide of chromium. Separation of Oxide of 3Ianganese from Alumina.—Caus- tic potassa is added in excess to the solution, which is then boiled; the alumina, which is at first precipitated with the oxide of manganese, is redissolved, and is determined in the filtrate in the usual manner; the oxide of manganese is dis- solved in hydrochloric acid, and precipitated as carbonate. According to Berthier, alumina may be separated from oxide of manganese by boiling with sulphite of ammonia. Separation of Oxide of 3Ianganese from 3Iagnesia.—Mu- riate of ammonia is added in sufficient quantity to the solu- tion, and the manganese is precipitated as sulphuret by hy- drosulphuret of ammonia; the filtrate contains the whole of the magnesia; it is acidulated with hydrochloric acid, and boiled, to decompose the excess of hydrosulphuret of ammonia, filtered to separate the sulphur, and the magnesia determined in the filtrate as sulphate (provided no other base be present), or as double phosphate of ammonia and magnesia. Separation of Oxide of Manganese from Lime.-—When the quantity of oxide of manganese present is small, the solution is mixed with muriate of ammonia, and, oxalate of ammonia having been added, the solution is quickly filtered; the lime is thus separated as oxalate, and is determined in the usual manner: the oxide of manganese in the filtrate is precipitated by hydrosulphuret of ammonia, but, if the quan- 282 QUANTITATIVE ANALYSIS. tity of oxide of manganese be considerable, this method will not be successful, as a portion of that metal would be pre- cipitated both as oxide and as oxalate, together with the lime; in this case, the solution having been mixed with muriate of ammonia and caustic ammonia, the manganese is precipitated by hydrosulphuret of ammonia, and filtered quickly, both funnel and receiving vessel.being covered, to prevent the formation of carbonate of lime; the filtrate is digested with hydrochloric acid, to destroy the excess of hydrosulphuret of ammonia, then supersaturated with ammonia, and the lime precipitated as oxalate. Separation of Oxide of 3Ianganese from Alumina, Mag- nesia, and Lime.—When all three earths are contained in a solution, together with oxide of manganese, the method of separation depends on the quantity of the latter present; if it be small, the alumina is first precipitated by caustic am- monia, sal ammoniac in sufficient quantity having been pre- viously added to the solution; the alumina carries with it small quantities both of magnesia and of lime, from which it is separated by digestion with caustic potassa; in filtering the alumina, care must be taken to guard both funnel and receiving vessel as much as possible from the air, to prevent the precipitation of carbonate of lime; the filtrate from the alumina is mixed with oxalate of ammonia, by which the lime is separated. The oxide of manganese and the magnesia are contained in the filtrate from the oxalate of lime, and are separated from each other as above directed; the small quan- tities of magnesia and oxide of manganese which had been precipitated with the alumina, and which remain undissolved in the alkaline ley, are dissolved in hydrochloric acid, and added to the filtrate from the oxalate of lime. When the quantity of oxide of manganese is considerable, it is sepa- rated from the filtrate from the alumina, by hydrosulphuret of ammonia, the solution filtered from the sulphuret of man- ganese is boiled with hydrochloric acid, to decompose the excess of hydrosulphuret of ammonia; ammonia added, and the lime precipitated as oxalate. The solution filtered from the oxalate of lime contains the magnesia which is precipi- tated, and estimated in the usual manner. The small quan- tities of magnesia and oxide of manganese which have been precipitated, together with the alumina, having been removed QUANTITATIVE ANALYSIS. 283 by caustic potassa, are dissolved in hydrochloric acid, and estimated separately. Examination of Commercial Oxide of 3Ianganese, to ascer- tain its practical value.—Several methods have been proposed. First Method.—By estimating the amount of chlorine evolved during the solution of the ore in hydrochloric acid, the value of the oxide being in exact proportion to the quan- tity of chlorine produced. Three methods of estimating the chlorine have been employed. 1 (a). By noting the quantity of protosulphate of iron which it peroxidizes. If the oxide of manganese be per- fectly pure, 43.67 parts (one equivalent) will produce 35.5 parts (one equivalent) of chlorine, which will peroxidize 278 parts (two equivalents) of crystalized protosulphate of iron, thus:— Mn02+2HCl=MnCl4-2HO + Cl, and 2(FeO,S03) + HO + Cl=Fe203,2S03+HCl. Hence 25 grains of pure oxide of manganese yield chlorine sufficient to peroxidize 159 grains of protosulphate of iron; 25 grains of the powdered specimen are weighed out, and a quantity not less than 359 grains of crystalized protosul- phate of iron. The oxide of manganese is thrown into a flask containing about one ounce of strong hydrochloric acid slightly diluted, and a gentle heat applied. The protosul- phate of iron is gradually added in small quantities to the acid, so as to absorb the chlorine as it is evolved, and the addition of that salt continued till the liquor, after being heated, gives a blue precipitate with red prussiate of potassa, and has no smell of chlorine, which are indications that the protosulphate of iron is present in excess; by weighing what remains of this salt, the quantity that has been added is ascertained, say m grains. If the whole of the specimen consisted of peroxide, it would require 159 grains of proto- sulphate of iron, and that quantity would therefore indicate 100 per cent, of peroxide; but, if a portion of the manga- nese only is peroxide, a proportionally smaller quantity of the protosulphates will be consumed, and that quantity will give the real proportion of peroxide, by the proportion, as 159 : 25 : : m to the quantity required. 1 (b). The chlorine evolved is passed through water in which lime is diffused; chloride of lime is formed; a certain quantity of protosulphate of iron is dissolved in water, and 284 QUANTITATIVE ANALYSIS. the solution of chloride of lime is added thereto, until the iron liquor ceases to strike a blue color with a drop of solu- tion of red prussiate of potash: then, comparing the quantity of the solution of chloride of lime required with the quantity that was produced, the quantity of chlorine generated, and hence the total quantity of available oxygen, is known. The theory of the process may be expressed as follows:— Mn02+2HCl=MnCl + 2HO + Cl the liberated chlorine combines with the lime, forming CaO, Cl, and CaO,Cl+2(FeO,S03)=CaCl+Fe203,2S03 1 (c). Baumann conveys the chlorine into a solution of nitrate of silver, and calculates the amount of real peroxide of manganese in the specimen from the quantity of chloride of silver formed. Second Method.—By converting oxalic acid into carbonic acid by means of the second atom of oxygen which the per- oxide of manganese contains. Mn02-4-C203, producing MnO, and 2C02, 100 grains of the specimen are introduced into a weighed flask, and 150 grains of oxalic acid dissolved in 500 grains of water are poured upon it; to this 350 grains of oil of vitriol are to be added, and the orifice of the flask closed by a cork, through which passes a tube containing -fragments of recently fused chloride of calcium; the Aveight of this cork and tube are to be included in the tare of the flask. On the addition of the oil of vitriol, a brisk effervescence takes place, OAving to the escape of carbonic acid, which, passing over the fragments of chloride of calcium in the tube, is dried, so that the gas alone passes off. When the action slackens, a gentle heat may be applied, until all the oxide of manganese has dissolved; the small quantity of a light brownish sediment, which generally falls, is easily distinguished from the par- ticles of black oxide. As soon as the action is quite over, the flask is allowed to cool, and as it still contains a quantity of carbonic acid gas, this is removed by taking out the cork, and bloAving air gently into the flask by a glass tube; the cork is then to be replaced, and the flask with its contents weighed; the difference of weight represents the amount of carbonic acid evolved; one-fourth of the oxygen of Avhich had been derived from the peroxide of manganese by its conversion into protoxide, which remains combined with sul- phuric acid in the liquor, and the quantity of peroxide in the QUANTITATIVE ANALYSIS. 285 100 grains of the one are thus directly found. Example.— Suppose the flask and the materials together to weigh 1876 grains, and after the action has terminated 1816.5 grains: the loss, 59.5 grains, is carbonic aoid, consisting of 16.3 grains of carbon, and 43.2 grains of oxygen; the oxygen derived from the mineral is, therefore, = 10.8, which -4 represents 59 grains of pure peroxide of manganese in 100 grains of the substance experimented upon. 3d. Method of Fresenius and Will*—This is founded on the same principle. A certain weighed quantity of finely powdered manganese is projected into B, (see fig. 7,) and about 2J parts of neutral oxalate of potash, prepared by saturating the common binoxalate with carbonate of potash, and crystalizing, or two parts of neutral oxalate of soda, and as much water added as will fill about one-third of the flask; the apparatus is then prepared as directed in p. 245, B is then closed, the apparatus Aveighed, and, by sucking the tube e, some sulphuric acid is made to pass from a into b. The evolution of carbonic acid commences immediately, and in a very uniform manner: as soon as it stops, some more sulphuric acid is sucked over from a into b, and the operation thus continued till all the manganese is completely decom- posed: this operation will require from six to ten minutes: its completion is ascertained not only by no further evolution of carbonic acid taking place upon a further influx of sul- phuric acid into b, but also by no black powder remaining at the bottom of the flask: some more sulphuric acid is then sucked over into b, in order to heat the fluid contained therein, so as completely to expel all the carbonic acid evolved during the course of the operation; the wax stopper is then removed from a, and the tube d sucked until the air no longer tastes of carbonic acid; the apparatus is then al- lowed to cool and Aveighed. The entire examination may thus, according to the authors, be performed in a quarter of an hour; from the loss of weight of the apparatus, (the amount of carbonic acid expelled,) the amount of available oxygen is found, or what, in fact, is the same, the amount of peroxide contained in the manganese under examination, ac- * New Method of Alkalimetry, by Drs. Fresenius and Will, edited by J. Lloyd Bullock, page 116, et seq. 286 QUANTITATIVE ANALYSIS. cording to the following arrangement. Two equivalents of carbonic acid stand to one equivalent of peroxide of manga- nese in the same proportion as the amount of carbonic acid found stands to x, x being the quantity of real peroxide con- tained in the specimen. Let us suppose that our experiment had been made with four grammes (61.76 grs.) of manganese, and that Ave had obtained 3.5 grammes (54.03 grs.) of car- bonic acid. The arrangement Avould be 4 : 43.67 : : 3.5 : x x=3.47. Thus, four grammes of the manganese containing 3.47 grammes of peroxide, 100 parts of the same substance must contain 86.7 parts. To render, however, this calculation un- necessary, Ave need only ascertain Avhat amount of manganese must be taken to make the number of centigrammes of car- bonic acid obtained immediately indicate the per centage amount of peroxide. The calculation must, therefore, be 4 : 43.67 : : 100 : x x = 0.993. Thus, if we take 0.993 grammes (15.33 grains) of the spe- cimen, the number of centigrammes of carbonic acid expelled will indicate the per centage amount of peroxide. But as the quantity of carbonic acid obtained would be too minute to admit of a direct determination of its weight, it is advi- sable to take a multiple of 0.993 grammes, and to divide the number of centigrammes of carbonic acid obtained by the same number, which has served as a multiplier. The multi- ple by 3, i. e. 2.98 grammes, is deemed by the authors the quantity best adapted for the examination. Should the man- ganese contain carbonated alkaline earths, which is sometimes the case, it must undergo a preliminary process previous to the examination. To ascertain the presence or absence of carbonate of lime or baryta in the manganese under examin- ation, it is sufficient to moisten a sample powder with dilute nitric acid; their presence is certain if any effervescence take place. The specimen, in that case, is treated as follows: —2.98 grammes of the specimen is projected into b, covered Avith very dilute nitric acid, one part acid to twenty parts of Avater, and alloAved to stand at rest for a feAV minutes; the supernatant fluid is then poured upon a small paper filter, the manganese remaining in the flask is repeatedly Avashed with water, as well as the solid particles on the filter, (the super- QUANTITATIVE ANALYSIS. 287 natant water being ahvays poured on the filter,) and the latter then thrown into b, taking care not to lose a particle of man- ganese; the further operation is conducted as usual. The neutral oxalate of potash is preferable to free oxalic acid, or to binoxalate of potash, since, when employing the former substance, the evolution of carbonic acid commences only upon the influx of sulphuric acid into b, whilst free oxalic acid or binoxalate of potash, begin to evolve carbonic acid immediately upon coming into contact with manganese and water; and this would, of course, interfere Avith the cor- rectness of the results, rendering it almost impossible to determine the exact weight of the apparatus before, the commencement of the operation. Such is the method of examining ores of manganese proposed by the German che- mists: the results are most accurate, and the manipulation is so simple, that it will no doubt entirely supersede all the other methods that have been described. It will be observed that, from the almost absolute identity of the equivalent number of carbonic acid multiplied by 2, 22 x 2 = 44, with that of peroxide of manganese, 43.67, the calculation of the quantity of real peroxide in a specimen of manganese becomes, a problem of the utmost simplicity; and that, if we take 100 grains of the specimen, the loss of weight in grains will de- note the per centage proportion of pure peroxide. One atom of peroxide of manganese, Mn02= 43.67 contains one atom of oxygen, separable by sulphuric acid, and capable of con- verting one atom of oxalic acid into tAvo atoms of carbonic acid. Thus:— Oxalic acid C203+0 = 2(C02) « " 36 +8 = 44 Dr. Ure recommends 250 grains of oxalate of potash to 100 grains of the sample. Ebelmen's method is to treat the oxide of manganese with muriatic acid; the chlorine disengaged is received in a solu- tion of pure sulphurous acid, part of which acid is converted into sulphuric acid. When the reaction is completed, solution of chloride of barium, and a little muriatic acid, are poured in the liquor; the muriatic acid being employed for dissolving the sulphite of baryta, Avhich is produced simultaneously with the sulphate, and which, being but sparingly soluble, would remain mixed with it; the liquor is then boiled, for the pur- pose of expelling the excess of sulphurous acid, filtered, and 288 QUANTITATIVE ANALYSIS. the precipitate of sulphate of baryta is dried, from the weight of which the quantity of the peroxide of manganese contained in the sample is calculated: 100 of sulphate of baryta cor- responds to 37.5 of peroxide of manganese. A simple manner of analyzing manganese is the follow- ing. A certain quantity of the purified and well-dried manganese is introduced into a small counterpoised retort, to which a counterpoised tube, containing chloride of calcium, is adapted. After calcining it, the augmentation of the weight of the chloride of calcium indicates the quantity of water Avhich has volatilized, and which proceeds from the hydrated sesquioxide, a portion of which is ahvays contained in the peroxide: the diminution of the weight of the retort indicates how much Avater and oxygen have escaped. Yet it is not possible, by merely calcining in the retort, to convert the peroxide of manganese completely into manganoso-man- ganic oxide; Avherefore the contents of the retort must be emptied in a small platinum crucible and therein ignited, until, after repeatedly Aveighing it, the Aveight remains con- stant. The mass becomes thus completely converted into manganoso-manganic oxide. If the ignition is carried on Avith a spirit-lamp with circular wick, small quantities only must be operated upon, and the mass must be kept red hot for a long time, in order to obtain a complete conversion. When the quantity of the mass is considerable, an ordinary fire is used. 100 of oxygen disengaged, represent 818.85 of pure peroxide. Whence it may be seen that great precision is re- quired in this experiment, since a small quantity of oxygen corresponds to a great quantity of peroxide. 100 parts of water eA'aporated, correspond to 981*76 of hydrate of sesqui- oxide. Iron. This metal is, under all circumstances, Aveighed as sesqui- oxide,* if it exist in the solution in the form of a protosalt, it must be peroxidized by heating with nitric acid as long as fumes of nitrous vapor are discharged: ammonia is the pre- * Liebig proposes a direct means of estimating iron in the dry way as fol- lows:—The finely powdered ore is mixed with cyanide of potassium and car- bonate of potassa, and then heated in a porcelain crucible to high redness. The alumina and silica remain with the scories, and the reduced metal maybe sepa- rated by washing with cold water and then weighed. QUANTITATIVE ANALYSIS. 289 cipitant employed, as the oxide precipitated by potassa or soda is ahvays contaminated by a certain quantity of the al- kali, from Avhich it is almost impossible to free it by washing: the hydrated sesquioxide shrinks greatly on drying, and, by ignition, loses all its water. Iron is sometimes precipitated as sulphuret by hydrosulphuret of ammonia: the solution must not contain free acid: it must be Avell Avashed on the filter with water, to which a few drops of hydrosulphuret of / ammonia have been added, the funnel being protected from the air with a glass plate to prevent a portion of the sulphuret from becoming oxidized into sulphate, which Avould dissolve and be carried through the filter: the washed sulphuret is, together with the filter, digested Avith dilute hydrochloric acid, filtered, and the filtrate peroxidized by nitric acid and pre- cipitated by ammonia. When iron has to be separated from other bases, it is sometimes precipitated by succinate of am- monia : the solution must be very exactly neutralized by am- monia, the alkali being added in drops in a Arery diluted state until the small quantity of sesquioxide of iron which it pre- cipitates is not redissolved by applying a gentle heat, the supernatant liquid possessing a red color; the neutral succi- nate of ammonia is then added, upon which succinate of per- oxide of iron of a broAvn color is precipitated; it is filtered when quite cold, and washed first with cold water, and, finally, with a warm solution of ammonia, in order to remove a por- tion of the succinic acid: it is then dried and ignited in a current of air, in order thoroughly to peroxidize the iron. The sesquioxide of iron is— Two equivalents of Fe ... 56 ... 70 Three do. of 0 ... 24 ... 30 One do. of Fe203 ... 80 ... 100 Separation of Peroxide of Iron from Protoxide of Iron.— This is attended with very great difficulties, and can only be accomplished Avhen the compound is soluble in acids. When no other base but iron is present, as, for example, in native magnetic iron ore, Rose directs that a Aveighed quantity of the substance should be dissohred in hydrochloric acid, and, having boiled Avith nitric acid to peroxidize the whole of the iron, it is to be precipitated by ammonia ; the increase of weight is owing to the acquisition of oxygen, which has com- 19 290 QUANTITATIVE ANALYSIS. bined with the protoxide of the compound, and is half as much in quantity as the oxygen previously existing in the protoxide, for the protoxide of iron, on being fully converted into peroxide, acquires one-half more oxygen than it already possessed. 2 (FeO) + 0 = Fe203. Thus, then, finding first the quantity of oxygen gained by the substance operated on, we find next the quantity of oxygen belonging to the protoxide existing in the compound, and from this it is easy to calculate the quantity of the protoxide. When this is found, the quantity of peroxide contained in the substance is learned from the difference in weight between the quantity of the compound submitted to analysis and the quantity of protoxide made out by calculation. It is easy, howeArer, to see that, as the proportion of protoxide of iron is generally very small in comparison with that of peroxide, the greatest accuracy in experimenting is necessary, in order to arrive at correct results, a very trifling error becoming a very considerable one in the subsequent calculation of the quantity of protoxide. Another method, given by Rose, for determining the quan- tity of oxygen in a compound consisting merely of protoxide and peroxide of iron, is by converting the oxides into metallic iron by igniting them in a current of dry hydrogen gas, and determining not only the quantity of iron revived, but also the weight of the Avater formed. To determine experimentally the quantity of peroxide of iron in a soluble compound of peroxide and protoxide, a weighed quantity of the pulverized mixture is introduced into a flask, the whole of the atmospheric air from which is then expelled by a current of carbonic acid gas; hydrochloric acid sufficient to dissolve the compound is then added, and the flask quickly and securely closed. Solution being effected, recently prepared perfectly clear sulphuretted hydrogen water is added in excess, and the flask again closed, and allowed to remain at rest for some days; the peroxide of iron is reduced to pro- toxide by the sulphuretted hydrogen, and a proportional quantity of sulphur is deposited; this is carefully collected on a small weighed filter, Avashed and dried at a gentle heat; the filter must be protected from the atmosphere during the process of filtration; from the weight of the sulphur the quantity of oxygen that has entered into combination with QUANTITATIVE ANALYSIS. 291 Fig. 10. the hydrogen of the decomposed sulphuretted hydrogen is found, this oxygen Avas derived from the peroxide of iron; and, by multiplying it by three, the Avhole quantity of oxygen that was present in the substance in the form of sesquioxide of iron is found. Every sixteen grains of sulphur that are deposited indicate the abstraction of three grains of oxygen, and the presence of seventy grains of sesquioxide in the spe- cimen. Another method of analyzing a mixture of the two oxides is the following, given by Fresenius:—A knoAvn quantity of the finely divided substance is introduced into the flask A (Fig. 10), which is then filled with carbonic acid through the tube d; hydrochloric acid, not in great excess, is then added through the funnel c, and the solution of the com- pound assisted by heat; a stream of carbonic acid passing all the time through the apparatus, hot water is next added, and the solu- tion boiled and allowed to cool; pure recently preci- pitated carbonate of baryta is now mixed into a milky fluid, and poured into the flask through the funnel till it predominates; the whole mixture is then di- gested at a very gentle heat. The flask is filled with boiling Avater nearly up to the end of the tube b, Avhich, being depressed as far as necessary into the liquid, the clear fluid is draAvn off; the tube is then raised, and the flask again filled with boiling water; Avhen the precipitate has settled, the clear fluid is again drawn off by the syphon b; the flask is then rinsed out Avith boiling water, and the precipitate thrown on a filter, and Avell washed Avith boiled water, as much as possible out of access of air: the amount of peroxide of iron in the Avashed precipitate is then determined. The liquid is drawn off by the syphon, and the filtrate from the precipitate contains the whole of the dissolved protoxide of iron; the so- 292 QUANTITATIVE ANALYSIS. lution is concentrated, the iron peroxidized, and, finally, pre- cipitated after the removal of the baryta. Indirect 3Iethod of determining the quantity of Protoxide of Iron in a mixture of Protoxide and Peroxide.— Rose's Method.—A weighed portion of the substance is dissolved in hydrochloric acid in a flask, which has previously been filled Avith carbonic acid gas; the solution being effected, solution of chloride of gold and sodium is added in excess, and the flask closed; reduction takes place, and metallic gold is pre- cipitated, Avhich is collected, washed, ignited, and Aveighed; from the quantity obtained, the quantity of oxygen, Avhich was necessary to convert the protoxide of iron into peroxide, is ascertained by calculation, thus:— 6FeCl + AuCl3= 3Fe2Cl3+Au one equivalent of precipitated gold corresponds to six equiva- lents of protochloride or protoxide of iron. Fuch's Method.—A Aveighed portion of the substance is dissolAred, as in Rose's method, in hydrochloric acid, in a flask Avhich has previously been filled Avith carbonic acid gas; a Aveighed slip of clean copper is introduced, and the flask, having been filled nearly to the brim Avith boiled Avater, accu- rately closed; the mixture is digested until the fluid becomes colorless, or nearly so; the slip of copper is then removed from the flask, dried, and Aveighed; the diminution in Aveight indicates the amount of chlorine consumed to convert the original protochloride of iron into perchloride, every equiva- lent of copper corresponding to an equivalent of chlorine, and every one equivalent of chlorine converting two equivalents of protochloride of iron into perchloride 2FeCl+Cl=Fe2Cl3; it follows that every equivalent of dissolved copper corres- ponds to tAvo equivalents of perchloride of iron in the solution, or, Avhat amounts to the same, to tAvo equivalents of peroxide of iron present in the analyzed substance. The quantity of iron actually present in the specimen must be determined by peroxidizing a solution of a Aveighed quantity, and precipitat- ing by ammonia. The method is founded on the fact that, Avhen air is excluded, hydrochloric acid is incapable of dis- solving copper; but that on the addition of peroxide of iron, or Avhen that substance is already present in the mixture, the acid dissolves a quantity of copper corresponding thereto. Separation of Iron from 31anganese.—The iron in the so- lution is first brought to the state of sesquioxide, and is then QUANTITATIVE ANALYSIS. 293 precipitated by succinate or benzoate of ammonia, a sufficient quantity of sal-ammoniac having previously been added; the precipitated succinate is treated in the manner already de- scribed, and the manganese in the filtrate is precipitated by carbonate of soda. Another method of separation is by di- gesting the solution of the tAvo metals with excess of recently precipitated carbonate of baryta, Avhich throAvs down the iron as basic carbonate of peroxide; the Avashed precipitate is dis- solved in hydrochloric acid, the baryta separated by sulphuric acid, and the iron precipitated by ammonia; the filtrate from the basic carbonate of peroxide of iron contains the mangan- ese, together Avith a soluble baryta salt; the latter is removed by sulphuric acid, and the manganese precipitated by carbon- ate of soda. Separation of Iron from Cobalt and Nickel.—The iron is peroxidized, and precipitated by succinate or benzoate of am- monia, and the cobalt and nickel in the filtrate separated and estimated by one of the methods described (page 279). Separation of Iron from Zinc.—The iron in the solution is peroxidized by nitric acid, the solution is evaporated to dryness, and all excess of acid removed; the residue is dis- solved in acetic acid; free acetic acid is added, and the zinc precipitated by sulphuretted hydrogen ; the precipitated sul- phuret of zinc should have a pure Avhite color. Separation of Iron fron Chromium.—Rose's Method.—To the solution of the two metals a sufficient quantity of tartaric acid is added, to prevent the precipitation of either of the metals by potassa;* that alkali is then added, and the iron precipitated by sulphuret of potassium; the solution filtered from the sulphuret of iron contains the oxide of chromium: it is evaporated to dryness, ignited, fused with carbonate of soda and nitre, and the chromium in the alkaline chromate thus formed determined as directed (page 264). Berliner's Method.—The oxides are precipitated by ammo- nia or carbonate of ammonia; and, Avhile still moist, digested Avith slight excess of sulphurous acid; the Avhole of the iron dissolves, and also a certain quantity of the oxide of chro- mium, while the remainder of this latter metal is converted into pure subsulphite. The solution is boiled until it is de- * Rose directs ammonia to be added, and the iron to be precipitated by hy- drosulphuret of ammonia; but, according to Fresenius, tartaric acid does not prevent the precipitation of oxide of chromium by ammonia. 294 QUANTITATIVE ANALYSIS. colorized, when it only contains iron. To precipitate this metal, the sulphurous acid is expelled, either by sulphuric acid or by aqua regia; an alkali or an alkaline carbonate is then added, or the iron is precipitated by an alkaline hydro- sulphuret Avithout expelling the sulphurous acid. Liebig's Method.—A mixture of the tAvo metals in solution is first saturated Avith sulphuretted hydrogen, to be certain that the iron is contained in the liquid as protoxide, (an addi- tion of a feAv drops of hydrosulphuret of ammonia ansAvers the purpose,) and then throAvn doAvn by cyanide of potassium, and an excess of the latter added; the iron then dissolves im- mediately as ferrocyanide of potassium, Avhile the oxide of chromium remains behind. Analysis of Chromic Iron Ore.—The finely levigated mi- neral is fused Avith caustic, or preferably bisulphated potassa (Booth), (alkaline carbonate Avill not do). The fused mass is extracted Avith Avater, Athich dissolves the chromate of potassa, together with the excess of potassa; the oxide of iron remains behind, together, perhaps, Ayith a small quantity of the unde- composed ore, which is separated from the sesquioxide of iron by hydrochloric acid: from the hydrochloric solution the iron is precipitated by ammonia, and the chromic acid in the aqueous solution is reduced to sesquioxide of chromium by hydrochloric acid and alcohol: if the mineral contained alu- mina, it AATill be found in the aqueous solution with the alka- line chromate, and will be precipitated together with the oxide of chromium, from which it is separated in the manner described (at page 266.) Separation of Iron from Yttria.—Schcrer's 3Iethod.—To a neutral solution, oxalate of potassa is added: a Avhite crys- taline precipitate, consisting of the double oxalate of yttria and potassa, is gradually formed, which, by ignition, is con- verted into yttria and carbonate of potassa ; the mixture is dissolved in hydrochloric acid, diluted Avith much water, and the yttria precipitated by caustic ammonia: it must be Avell washed Avith boiling Avater, after Avhich it may be ignited and weighed. Berthier's 3Iethod.—The moist hydrates are boiled with sulphurous acid, the yttria is deposited, and the iron remains in solution; to prevent the formation of an ochreous deposit from the action of the air, the solution should be boiled in a flask AATith a long neck, and when no more sulphurous acid is QUANTITATIVE ANALYSIS. 295 disengaged, it should be filled with boiling water and corked: when it has become cold the liquid is decanted on to a filter replaced by boiling water, and finally filtered and edulcorated. Separation of Iron from Alumina.*—The solution con- taining the tAvo oxides (the iron being in the state of sesqui- oxide) is concentrated by evaporation, and digested with excess of caustic potassa, in which the alumina alone dissolves. Br. Knop recommends the addition of a suitable quantity of hydrosulphuret of ammonia to the alkaline ley, or when prac- ticable, the direct precipitation of the tAvo oxides with hydro- sulphuret of ammonia, the precipitate being washed with water containing hydrosulphuret of ammonia, and the alumina sub- sequently extracted with potassa, to Avhich a few drops of hydrosulphuret of ammonia have been added, in order to obtain at once a perfect precipitation and separation of these two bodies. According to Bert liter, the method above described for separating iron from yttria may also be applied for sepa- rating the same metal from alumina. Separation of Sesquioxide of Iron from Magnesia.—Mu- riate of ammonia is added to the solution, then caustic am- monia ; the iron is precipitated, carrying with it a small portion of the magnesia, from which it is freed by again dis- solving in hydrochloric acid; and, after exactly neutralizing Avith ammonia, precipitating by succinate or benzoate of am- monia, the magnesia in the filtrate from the first and second operations is determined as pyrophosphate. Separation of Sesquioxide of Iron from Protoxide of Man- ganese, Magnesia, Alumina, Lime, and Fixed Alkali.— Muriate of ammonia is first added to the solution, the sesqui- oxide of iron and alumina, together with small portions of protoxide of manganese and magnesia, are precipitated by ammonia; it is filtered as quickly and with as little exposure to the air as possible. The precipitate, after being Avell washed, is dissolved in hydrochloric acid, excess being avoided. The solution is supersaturated Avith caustic potassa and digest- ed. Alumina dissolves, and is precipitated from the alkaline ley in the manner directed (at page 260). To the filtrate from the first precipitate by ammonia oxalate of ammonia is added, by Avhich the lime is separated. The filtrate from the oxalate of lime contains the greater part of the magnesia, and * See Chapter VI. 296 QUANTITATIVE ANALYSIS. protoxide of manganese, and the alkali; the residue, insoluble in caustic potassa, consists of sesquioxide of iron, together Avith small quantities of protoxide of manganese and magnesia. After being Avell washed it is dissolved in hydrochloric acid, diluted with water, neutralized Avith ammonia, and the sesqui- oxide of iron precipitated by succinate of ammonia. The filtrate is added to the filtrate from the oxalate of lime, con- centrated by evaporation, and the protoxide of manganese precipitated by hydrosulphuret of ammonia ; the filtrate from the sulphuret of manganese containing the magnesia and the alkali is warmed to decompose the excess of hydrosulphuret of ammonia. It is filtered from the sulphur, and evaporated to dryness Avith sulphuric acid; the magnesia and alkali are hereby comrerted into sulphates. The mixture is ignited in a platinum crucible with a fragment of carbonate of ammonia, in order to convert the bisulphates into neutral sulphates ; the mixture is Aveighed, dissolved in water, and acetate of baryta added in sufficient quantity to remove all the sulphuric acid in the form of sulphate of baryta. The mixture is warmed, and the sulphate of baryta filtered off. The filtrate contains acetates of magnesia and alkali, together with the excess of acetate of baryta: it is evaporated to dryness and ignited in a platinum capsule; by this treatment the acetates are con- verted into carbonates; the carbonate of the alkali present being soluble is easily removed by hot water, the solution may be evaporated to dryness, and the alkali converted into and Aveighed as sulphate. The carbonates of baryta and magnesia remain undissolved; they are dissolved in hydrochloric acid, the baryta separated by sulphuric acid, the filtrate eA^aporated to dryness, and the magnesia estimated as sulphate. This method of separating magnesia from alkalies, giAren by Rose, is very tedious, and requires considerable dexterity in mani- pulation in order to yield accurate results; it is, therefore, far preferable, instead of converting the magnesia and alkali into sulphates, to convert them into chlorides, and to treat the solution with red oxide of mercury, as directed (p. 259). Quantitative determination of Iron in Iron Ores.—The method proposed by Fuch has already been alluded to, (p. 292.) The specimen is dissolved in strong and pure hydro- chloric acid and peroxidized, either by cautiously adding crys- tals of chlorate of potassa, or by passing a current of chlorine through the liquor, till a drop of it let fall into a solution of QUANTITATIVE ANALYSIS. 297 red prussiate of potash gives no tinge of blue. It is then to be boiled for a feAv minutes, to expel the excess of chlorine, and a Aveighed quantity of pure copper introduced ; the boiling is to be continued Avithout intermission till the liquor passes off to a pale yellow green. When no further change of color is observed to take place, the flask must be filled up Avith hot water, and the copper removed, washed in cold Avater, dried and Aveighed. This method requires great care to give results at all approaching to accuracy, and is altogether inapplicable in the presence of arsenic acid. The method which has generally been resorted to, consists in performing, On a small scale, the operations carried on in the blast furnace for the production of the metal, namely, by mixing the ore Avith fluxes varying with the nature of the ore, and exposing it in a cru- cible lined Avith charcoal to an intense long-continued 'heat. The button of cast iron thus obtained indicates the richness of the ore : but as the flux may occasionally retain appreciable quantities of iron, A\diich may also be disseminated throughout the ores, and, moreover, as the metallic button obtained may be contaminated by carbon, silicium, phosphorus, arsenic and manganese, it is evident that no great dependence can be placed on the result of this process. Method of JIarguerite.—This is based on the employment of a normal test solution, and on the reciprocal action of the salts of protoxide of iron and permanganate of potassa (cha- meleon mineral), whereby a quantity of the latter is decom- posed exactly proportionate to the quantity of iron. The ore is dissolved in hydrochloric acid, and the metal brought to the minimum of oxidation, which is done by treating the solution with sulphite of soda, and boiling to expel the excess of sul- phurous acid; the solution of permanganate of potassa is then added cautiously until the pink color appears, and the number of divisions of the burette required for the purposes accurately noted. The theory of the process is as folloAvs:— Mn207,KO=2MnO + 05 + KO 2MnO + O5-f-KO + 10FeO = 2MnO + KO + 5Fe2O3 one equivalent of permanganate of potash is equal to two equivalents of protoxide of manganese, one of potassa, and five of oxygen, and these five equivalents of oxygen suffice to peroxidize ten equivalents of protoxide of iron. There must be a sufficient quantity of free acid present, to keep in solu- tion the peroxide of iron formed, as also the potassa and prot- 298 QUANTITATIVE ANALYSIS. oxide of manganese. The whole of the iron must be at the minimum of oxidation, and the excess of sulphurous acid must be expelled; if the latter precaution be neglected, an erroneous result Avill be obtained, as the sulphurous acid will itself take oxygen from the permanganic acid, and thus react in the same manner as iron. The author found that the only two metals that interfered with the process are copper and arsenic, which, if present as arsenic acid and peroxide of copper, might, by the action of the sulphurous acid, become reduced to arsenious acid and protoxide of copper, Avhich Avould after- wards withdraw oxygen from the permanganic acid; but, by a slight modification of the general process, both of these sources of error may be obviated. The operation is carried on as usual, except that, after having boiled the solution to ex- pel the excess of sulphurous acid, a piece of pure laminated zinc is added, Avhich, acting upon the hydrochloric acid, dis- engages hydrogen; arsenic and copper are hereby reduced to the metallic state. When the solution of the zinc is complete, the precipitated particles of arsenic and copper are removed by filtration, and the clear liquor proceeded with as before. To prepare the permanganate of potassa, 7 parts of chlorate of potassa, 10 parts of hydrate of potassa, and 8 parts of per- oxide of manganese, are intimately mixed; the manganese must be in the finest possible powder, and the potash, having been dissolved in Avater, is mixed Avith the other substances, dried, and the whole heated to very dull redness for an hour. The fused mass is digested in water, so as to obtain as con- centrated a solution as possible, and dilute nitric acid added, till the color becomes of a beautiful A'iolet; it is aftenvards filtered through asbestos, in order to separate the oxide of manganese Avhich it holds in suspension. The solution must be defended from the contact of organic matter, and kept in a glass-stoppered bottle. To convert the solution into a test liquor of known value, a certain quantity, say 10 grains, of pure iron, such as harpsichord Avire, is dissolved in pure hy- drochloric acid; after the disengagement of hydrogen has ceased, and the solution is complete, the liquor is diluted Avith about half a pint of cold Avater, and the solution of the per- manganate of potassa added, until a slight pink color becomes manifest, and the number of divisions of the burette necessary to produce this effect carefully noted; this number is then QUANTITATIVE ANALYSIS. 299 employed to reduce into weight the result of an analysis of ore. Separation of Phosphoric Acid from Iron*—Berthiers 3Iethod.—The compound is dissolved in hydrochloric acid, and sulphurous acid, sulphite of ammonia, and alum in sufficient quantity added; the solution is then boiled, the alumina of the alum is precipitated, carrying Avith it the phosphoric acid. If arsenic be present, it remains Avholly in solution, in the state of arsenious acid. Betermination of the amount of Carbon in Cast Iron.— The specimen is pulverized in a steel mortar, mixed with a sufficient quantity of oxide of copper, and burned, as in the method for determining the carbon in organic substances; the combustion is perfect, and the results are accurate.f Betermination of Sulphur in Iron.—Br. Bromies employs an apparatus similar to that of Will and Varrentrap for nitrogen analyses. Instead, however, of two bulbs there are four, in order that the sulphuretted hydrogen evolved during the solution of the iron in dilute sulphuric, may be completely absorbed by the ammoniacal solution of silver Avith which the bulbs are filled. The silver is estimated in the form of sulphuret of silver. Uranium. This metal is generally precipitated from its solutions by caustic ammonia. The precipitate, which is yellow, is Avashed on the filter with a dilute solution of muriate of ammonia; it is then dried and heated, by which it is converted into the green oxide, the composition of which is One equivalent of Ur ... 60 ... 88.23 One do. of 0 ... 8 . . . 11.77 One do. of UrO 68 100 31. Ebelmen has published the following remarks on the de- termination of this metal.| The tendency of the oxide of uranium to combine Avith bases, gives rise to its frequently * See Chap. VI. ■J" Prof. R. E. and W. B. Rodgers use a mixture of bi-chromate of potassa and sulphuric acid, which, when applied in large excess to finely powdered gra- phite, rapidly converts it into carbonic acid—CA. Gaz., vi. 350. J Ann. de Chim. et de Phys., Juin, 1842 ; and Chem. Gaz., vol. i. p. 207. 300 QUANTITATIVE ANALYSIS. carrying down along with it, in its precipitation by ammonia, bases Avhich are not precipitated when alone by that reagent, such as barytes and lime. If the liquid contains much potash, a considerable quantity is often found in the precipitate, which is easily recognized by the orange yelloAV colour perceptible at various parts of the heated precipitate. Sulphuretted hydro- gen separates uranium from a great number of metals. The oxide may be separated very easily from the peroxide of iron by means of carbonate of ammonia; but those metals whose oxides dissolve in part or wholly in carbonate of ammonia, such as manganese, zinc, cobalt, and nickel, have been regarded difficult of separation from uranium. The use of the carbon- ates of soda and of potash affords a very exact and simple means of effecting their removal; for urinate of potash is not soluble in the subcarbonate of potash, but it dissolves com- pletely, and in very little time, in a liquid saturated with a bicarbonated alkali. When a solution of a salt of uranium is precipitated with a slight excess of carbonate of potash, and the liquid diluted Avith water, the whole of the uranium is dis- solved, and imparts to it a yelloAV color. In both cases the double salt of potash is formed. The carbonate of zinc, co- balt, and manganese are, on the contrary, insoluble in carbon- ate of potash. To effect their separation the solution may be thrown doAvn, either by potash, the precipitate edulcorated and digested with bicarbonate of potash, which will only dis- solve the oxide of uranium, or by slight excess of carbonate of potash, the precipitate being collected on a filter, and washed as long as the liquor Avhich passes through is colored. On adding to a solution of the phosphate or arseniate of ura- nium, in an excess of carbonate of potash, a known quantity of sesquioxide of iron dissolved in nitric acid, those two acids may be completely separated from the uranium, and their pro- portion determined by the increase in weight of the peroxide of iron. The oxide of uranium may also be separated by potash, and the phosphoric and arsenic acids left in solution. To separate the oxide of uranium in solution, it may be saturated with hydrochloric acid, boiled to expel the carbonic acid, and the uranium precipitated by ammonia; but as the liquor contains much potash the precipitate retains a certain quantity, and is not entirely converted into the state of green oxide, which makes it necessary to redissolve it, and precipi- tate again with ammonia. QUANTITATIVE ANALYSIS. 301 To extract uranium with great precision from the urinate of potash dissolved in hydrochloric acid, the Avhole is evaporated to dryness in a platinum crucible gradually heated, and a cur- rent of dry hydrogen conveyed into it as long as the gas Avhich is giAren off possesses an acid reaction. The double chloride of potassium and uranium is converted into uranium (so called) in the form of a black poAvder, which is separated by Avashing from the chloride of potassium. Separation of Uranium from Nickel, Cobalt, and Zinc.— When the oxide of uranium in its preparation from pitchblende is so far purified as to be dissolved in carbonate of ammonia, Wohler directs to mix hydrosulphuret of ammonia with the solution as long as a black precipitate falls; in this Avay the nickel, cobalt, and zinc are entirely separated, no uranium being precipitated. According to Berthier, uranium is com- pletely separated from iron, manganese, cobalt, nickel, and zinc, by boiling the solution after the addition of sulphate of ammonia. The whole of the uranium precipitates in yellow grains as basic sulphite. Analysis of Pitchblende.—Of the various methods which have been employed by different chemists, the following, adopted by Arfwedson, seems on the whole the best. The mineral is reduced to fine poAvder, and digested Avith boiling aqua regia; the solution is evaporated on a Avater bath, to ex- pel the excess of acid, then diluted Avith water, and precipitated by sulphuretted hydrogen, sulphurous acid being previously added to reduce the arsenic acid to arsenious acid: arsenic, copper, lead, and bismuth are in this manner precipitated. The solution is filtered, the excess of sulphuretted hydrogen expelled by boiling, and ammonia added; the precipitate thereby formed is Avashed and dissolved, while yet moist, in carbonate of ammonia, peroxide of iron remains undissolved, and is separated by filtration. The solution is evaporated till the ammonia is volatilized, Avhereupon the peroxide of uranium is rendered insoluble; it is Avashed, dried, and calcined in a platinum crucible, by which it becomes converted into urano- uranic oxide of a green color. The urinates of lime, zinc, cobalt or nickel, Avhich may have been present in the solution, are not decomposed by the calcination; they are readily dis- solved, however, by dilute hydrochloric acid, Avhich acid serves, therefore, to separate them from the urano-uranic oxide, Avhich is thus obtained pure. It is washed first with dilute acid, and then with distilled water. 302 QUANTITATIVE ANALYSIS. From the metallic urinates in solution in hydrochloric acid oxide of uranium may be obtained. For this purpose the solu- tion is precipitated by ammonia, the dried precipitate is re- duced by hydrogen gas, and treated immediately Avith hydro- chloric acid, AA'hich dissolves all the foreign metals, leaving protoxide of uranium insoluble. GROUP 5. Lead, Silver, Jlercury, Bismuth, Cadmium, Copper, Pal- ladium. Lead. This metal is completely precipitated from its acid solutions by sulphuretted hydrogen; it is also precipitated by sulphuric acid, by carbonate of ammonia, by oxalate of ammonia, and by hydrochloric acid, and it may, therefore, be weighed as sulphuret, sulphate, chloride, and as oxide, the latter being produced by igniting with free access of air the carbonate and oxalate. Precipitation as Sulphuret.—A stream of washed sulphur- etted hydrogen gas is transmitted through the solution, ren- dered slightly acid with nitric acid until it is completely satu- rated, a gentle heat is then applied, and the precipitated sulphuret is filtered as quickly and Avith as little access of air as possible, in order to avoid the decomposition of a portion of the sulphuretted hydrogen, which Avould occasion a preci- pitation of sulphur; as it is difficult, even with great care, to prevent this, it is better to convert the washed sulphuret of lead into sulphate, which is done by transferring it, filter and all, into a beaker, and pouring on it concentrated and fuming nitric acid, the sulphur becomes hereby oxidized into sulphuric acid; a gentle heat is applied to assist the action, the mixture is carefully transferred into a small Berlin crucible, and a few drops of sulphuric acid being added, it is evaporated to dryness and ignited. The composition of sulphate of lead is One equivalent of PbO . . . 111.56 . . . 73.61 One do. of S03 ... 40.00 . . . 26.39 One do. of PbO,S03 . 151.56 100 QUANTITATIVE ANALYSIS. 303 With respect to the precipitation of lead by sulphuretted hydrogen, the following observations have been made by Br. Vogel. In precipitating lead with sulphuretted hydrogen it is usual to warm the liquid, to prevent any of the precipitate from passing through the filter, but this may give rise to con- siderable loss. If sulphuretted hydrogen be passed through a moderately strong solution of acetate of lead, until the fil- tered liquor contains no more metal, and is consequently not rendered turbid either by sulphuretted hydrogen or by sul- phuric acid, and if the liquor be now warmed, a further pre- cipitate is produced by sulphuretted hydrogen after filtration; the liberated acetic acid evidently decomposes the sulphuret of lead. The same is the case with nitrate of lead, and re- markably so with the chloride. This is of considerable im- portance Avhere lead has to be separated from chlorides, and where it cannot be precipitated by sulphuric acid. With mercury and bismuth no such decomposition of the sulphuret occurs, and only in a slight degree with antimony. The above behavior may even be employed for the separation of some metals. If, for example, sulphuretted hydrogen be passed into a liquid containing nitrate of bismuth and nitrate of lead, until no further precipitate occurs, and the whole be then heated to boiling, the sulphuret of lead is entirely redis- solved, while the sulphuret of bismuth is not attacked. The lead may then be precipitated from the solution by sulphuric acid. Precipitation of Lead by Sulphuret of Sodium.—A method of estimating lead by means of a normal solution of sulphuret of sodium has been proposed by Bomonte, and is described by him as simple, quick, and accurate, and well adapted for the examination of white lead and acetate of lead, substances which, as met with in commerce, are often greatly adulterated. To prepare the normal solution of sulphuret of sodium, about 300 grains are dissolved in a pound of water, a certain known quantity of lead is dissolved in nitric acid, precipitated, and redissolved by caustic potassa; the solution of sulphuret of sodium placed in a graduated burette is added carefully to the alkaline solution, which is maintained at a temperature near to ebullition. Each addition of the sulphuret produces a black precipitate of sulphuret of lead; from time to time the liquid is boiled, and the precise point at which a drop of the reagent produces no further precipitate is carefully ob- 304 QUANTITATIVE ANALYSIS. served. The number of divisions of the burette which have been required represents the value of the lead employed in the experiment: thus, suppose 10 grains of lead to have been used, and 30 burette divisions of the alkaline sulphuret have been consumed, then, in all analyses of commercial products, for every 30 divisions of the burette that are required the operator may infer that 10 grains of lead are present. The author does not find the success of the experiment to be interfered with by the presence of tin, antimony, arsenic, iron, cobalt, nickel, or zinc. The first three metals are not precipitated by an alkaline sulphuret; in the presence of ex- cess of free alkali, zinc is precipitated after the lead, but the color of the sulphuret being Avhite, renders its presence rather an advantage than otherwise; copper complicates the process. It is necessary in the first place to determine this metal by the method of Pelouze (to be described hereafter). Bomonte then makes a synthetic assay on a mixture formed of a Aveight of copper equal to that found by experiment, and of lead equal in weight to that employed in preparing the standard solution. This assay sIioavs by how many diAdsions the plumbimetric liquor ought to be diminished on examining the alloy. The number is, in fact, the difference between the results of the assay of pure lead, and those of the assay of the mixture of lead and copper. This being done, he examines the alloy in the ordi- nary way. Bismuth cannot be separated from lead in this way, but, commercially speaking, it is not likely that this metal will be found to occur as a contamination, its higher price being a guarantee. Quantitative estimation as Sulphate.—When lead is to be weighed in the form of this salt, the solution is precipitated by dilute sulphuric acid, and then mixed with twice its volume of alcohol, sulphate of lead not being altogether insoluble in water; it is collected on a filter, on which it is washed with spirits of wine. Its composition has been given above. Quantitative estimation as Oxide.—(a.) Precipitation as Carbonate.—Carbonate of ammonia, mixed with a little caustic ammonia, is the precipitant employed, and the solution is heated; it is washed on the filter with pure Avater, and after- wards ignited in a porcelain crucible, by which it is converted into protoxide of lead. The precipitate is removed as com- pletely as possible from the filter, and the latter is ignited QUANTITATIVE ANALYSIS. 305 alone, the residue being afterwards mixed with the ignited precipitate; the object of this is to prevent the reduction of a portion of the protoxide of lead by the organic matter of the filter. The same observation applies to the sulphate. (b.) Precipitation as Oxalate.—Rose prefers oxalate of am- monia as the precipitant of oxide of lead from its solutions, which must be either neutral or weakly ammoniacal. The precipitated oxalate of lead is converted into protoxide by ignition in an open porcelain crucible, having, as in the two former cases, been removed as much as possible from the filter, the latter being ignited alone. The composition of protoxide of lead is One equivalent of Pb ... 103.56 . . . 92.82 One do. of 0 ... 8.00 . . . 7.18 One do. of PbO . . . 111.56 100 Quantitative estimation as Chloride.—The solution is pre- cipitated by excess of hydrochloric acid, concentrated by eva- poration in the water bath, and the residue washed with absolute alcohol, mixed with ether. As chloride of lead is volatilizable, it must not be ignited, but dried at a high tem- perature, at a gentle heat. Its composition is One equivalent of Pb ... 103.56 . . . 74.47 One do. of Cl ... 35.50 . . . 25.53 One do. of PbCl . . 139.06 100 Lead is completely separated from the metals that have hitherto been treated of by means of sulphuretted hydrogen; the solution must be acidified with nitric acid, and considera- bly diluted. Silver. This metal is weighed as chloride, as sulphuret, as cyanide, or in its pure metallic state. Quantitative estimation as Chloride.—To the solution con- tained in a long-necketP flask, and acidified with nitric acid, hydrochloric acid is added in excess; the whole is then well agitated, and allowed to remain for several hours in a warm place: the clear fluid is carefully separated by decantation from the precipitated chloride, Avhich is then Avashed with 20 306 QUANTITATIVE ANALYSIS. water acidulated wTith hydrochloric acid. It is then trans- ferred to a Aveighed porcelain crucible, in which the washing is continued with distilled water till all traces of acid are re- moved, the various washings are collected in a beaker, and, if the whole be not perfectly clear, it must be allowed to stand in a warm place for several hours, and the precipitate, if any should form, must be added to the contents of the porcelain crucible. The chloride of silver, having been perfectly Avash- ed, is heated to incipient fusion, and Aveighed; it may after- wards be completely removed from the crucible by reducing it by means of dilute sulphuric acid and zinc. Should the quantity of chloride obtained in the experiment be small, it may be advisable to collect it on a filter, from Avhich it should, after washing, be removed as completely as possible, and the filter, with the residue remaining on it, burnt, on the cover of the crucible, the ashes mixed with the bulk of the chloride, which is then heated to incipient fusion in a counterpoised porcelain crucible as before. According to Rose, it is not admissible to precipitate silver by the chlorides of potassium, sodium, or ammonium, as these salts, particularly the latter, are capable of retaining traces of silver in solution. In cases where the presence of much chloride of ammonium is unavoid- able, Gay Lussac and Liebig recommend to evaporate the solution filtered from the chloride of silver nearly to dryness, and to treat the residue Avith nitric acid; on exposing the whole to heat, the alkaline chlorides are converted into ni- trates, while the small quantity of chloride of silver remains unaltered, and does not dissolve when the mixture is diluted. The composition of chloride of silver is— One equivalent of Ag ... 108.0 . . . 76.26 One do. of Cl ... 35.5 . . . 24.74 . One do. of AgCl 143.5 100 Quantitative estimation as Sulphuret.—Washed sulphu- retted hydrogen gas is transmitted through the solution as long as a precipitate continues to form; the whole is then warmed, and allowed to settle; it is finally collected on a weighed filter, washed as rapidly as possible out of contact of air, and dried at 212°. Silver may likewise be precipi- tated as sulphuret from neutral and alkaline solutions by hydrosulphuret of ammonia; but, as in this case the precipi- QUANTITATIVE ANALYSIS. 307 tated sulphuret is invariably accompanied by sulphur, it is necessary to convert it for weighing into chloride, by digest- ing it with nitric acid, and then precipitating it with hydro- chloric acid. The composition of sulphuret of silver is One equivalent of Ag . . . 108 . . . 87.09 One do. of S ... 16 . .. 12.91 One do. of AgS 124 100 Quantitative estimation as Cyanide.—Cyanide of potas- sium is added in sufficient quantity to redissolve the precipi- tate which is at first formed, dilute nitric acid is then added, and a gentle heat applied, by which the whole of the cyanide of sihrer is re-precipitated. It is Avashed and dried at 212°. The composition of cyanide of silver is One equivalent of Cy . . . 26 . . . 19.4 One do. of Ag ... 108 ... 80.6 One do. of AgCy 134 100 Silver, Avhen combined with organic acids, is estimated in the metallic state, to which it is reduced by igniting the salt in a porcelain crucible. The heat should be gentle at first, and the coA-er on, to prevent loss during the ignition. The lid is afterwards removed, and a strong heat applied for a considerable time, in order to effect complete combustion of the carbon of the organic acid. Silver is completely sepa- rated from all the metals of the first four groups by sulphu- retted hydrogen. The solutions must, in all cases, be acid. From lead it may be separated by hydrochloric acid, the solution having previously been largely diluted with Avater to preArent the precipitation of chloride of lead; or by heating the solution containing both metals Avith cyanide of potas- sium, which precipitates the lead in the state of carbonate, retaining the silver in solution, as argento cyanide of potas- sium. The silver is subsequently precipitated in the form of cyanide of silver by the addition of nitric acid. Estimation of Silver in Alloys by a Standard Solution of Common Salt.—This method, Avhich was introduced several years ago by Gay Lussac, and which is extensively employed in France, consists in dissolving a certain knoAvn weight of 308 QUANTITATIVE ANALYSIS. the alloy in pure nitric acid, and in determining the exact quantity of a standard solution of common salt, which is required completely to precipitate the silver, the proportion of silver is determined by the volume of the standard solu- tion used. A burette, similar to that shown in fig. 6, is employed for measuring the volume of the test liquor, which is added, drop by drop, to the nitric solution of the alloy, until no further precipitation takes place. The number of diArisions of the burette required to precipitate a certain weight of pure sihTer is previously determined. The pre- sence of copper and lead does not, in the least, interfere with the accuracy of the process; there is, however, one metal which may introduce error, though its presence in silver alloys is very rare, viz., mercury, which might be precipi- tated by the test solution, together with the chloride of silver, in the form of calomel. To avoid this inconvenience, 31. Levol supersaturates the nitric solution of the alloys with caustic ammonia; he then adds the normal test liquor, and supersaturates the excess of ammonia Avith acetic acid; he states that by this modification he is able, either with the presence or absence of copper, to estimate accurately silver containing a tenth part of its weight of mercury. The pre- sence of mercury in the precipitate of the chloride of silver, is rendered evident by its non-coloration under the influence of light. 31. Gay Lussac simplifies this process, by adding to the nitric solution of silver the ammonia and acetic acid at one and the same time, but in sufficient quantity to saturate the whole of the nitric acid, both that in combination with the silver, and that in the free state. He finds acetate of soda to answer quite as well as acetate of ammonia. In pre- paring the standard solution of salt, it is convenient in prac- tice to have it of such a strength that 100 divisions of the burette shall correspond exactly to 10 grains of pure silver; or, if the operator prefer the continental system of weight and measure, it should be of such a strength that 100 cubic centimetres are required to precipitate 1 gramme of pure silver, and the burette employed should be divided into 1000 parts, so that each division may correspond with a thou- sandth part of the saline solution. All trouble of calcula- tion is thus dispensed with, since the number of divisions required to effect the complete precipitation, indicates an equal number of thousandths of silver in the alloy operated QUANTITATIVE ANALYSIS. 309 upon. In preparing the saline solution, Gay Lussac dis- solves common culinary salt in a certain quantity of water, and then determines with the greatest care the quantity re- quired to precipitate 1 gramme of pure silver; this being determined, he dilutes the solution with pure water, and brings it to such a strength that 100 cubic centimetres shall be equivalent to 1 gramme of silver; then, suppose 28 cubic centimetres of the first solution are required, this is mixed with o§ of its volume of distilled water to form the standard liquor: and he finds it convenient in practice to dilute a por- tion of this normal liquor still further Avith 9 times its volume of water, so that, when the solution of the alloy is nearly precipitated, it may be completed Avith a more diluted saline solution, an excess of a feAV drops of which could do no harm, and 10 cubic centimetres of which correspond with one of the first solution. In these determinations by volume, temperature exercises an influence on the result which ought not to be neglected; the dilatation of the two liquors for every variation of temperature may, however, be ascertained once for all, and Gay Lussac has calculated and published tables on the subject, Avhich shoAV the changes of volume for each degree aboA^e and below + 15° Centigrade, as the nor- mal temperature; he has also described a convenient appa- ratus for the whole analytical process.* Berzelius remarks, that this method is susceptible of greater accuracy than that of cupellation; it effects, moreover, a great saving of time, since several assays may be made at once. On the other hand, it is not so applicable to the determination of small quantities of silver as the process of cupellation; its use is, therefore, confined, in a great measure, to the examination of large ingots and silver coin. It may be obserAred that the correctness of the results depends not only on the dexterity of the operator, but also upon the exact observation of the moment Avhen the complete precipitation has been effected. Among the various other methods of separating silver from c&pper, two\ may be specially noticed. The first consists in * Ann de Chim. et de Phys.. vol. lviii. p. 218; and vol. lxiii. p. 334. ■J- Haidlen and Fresenius separate silver from copper by adding cyanide of potassium to the solution of the two metals until the precipitate redissolves. A current of sulphuretted hydrogen is then passed into the liquor, the excess of gas expelled by heat, and a little more cyanide added. The silver is thus pre- cipitated while the copper remains in solution. 310 QUANTITATIVE ANALYSIS. fusing the argentiferous copper with 2J parts of lead, and cooling the fused mass in thick round cakes. These cakes are then introduced into a furnace of peculiar construction, and the heat is raised sufficiently high to fuse the alloy of silver and lead, but not to fuse the copper. On cooling, the whole of the silver is found combined Avith the lead, from which it is separated by cupellation. The second 3Iethod consists in dissolving the argentiferous copper in sulphuric acid, in a platinum vessel, and in precipitating the silver from the solution by means of plates of copper; the precipi- tated silver, which is in the form of a gray metallic poAvder, is washed and fused with a mixture of nitre and borax; it is thus purified from the copper which may have been precipi- tated Avith it. The method has tAvo advantages; first, the copper is recovered in a marketable form (that of blue vitriol); and, second, the gold, amounting to from j^q to y-o^th part, is saved, this metal remaining undissolved by the sulphuric acid. Analysis of Alloys of Silver by Cupellation.—This method, which is the one usually adopted at the mint, and by refiners, and Avhich, as above observed, is Avell adapted for the exami- nation of very small quantities of silver alloys, where no very great accuracy is required, consists essentially in this. The noble metals silver, gold, and platinum are capable of Avith- standing the action of the air, even at high temperature; the base metals, on the other hand, become, under similar circum- stances, oxidized. It is not possible, however, entirely to re- move the oxidable metals from silver by heat alone, in conse- quence of the protective action of the latter; the alloy is, there- fore, mixed Avith a certain quantity of pure lead, and heated in a small vessel formed of bone earth, called a cupel; now the oxide of lead is fusible, and possesses the property of dissolving the oxides of the base metals. On heating the mixture, there- fore, to bright redness, the foreign metals present in the alloy become oxidized, are dissolved by the fused oxide of lead, and absorbed by the cupel; Avhile, if the operation has been care- fully conducted, a button of pure silver remains. The cupel, which is best made of a mixture of finely levi- gated ashes of birch Avood and calcined bones, is thus pre- pared:—The ash, slightly moistened, is laid in a brass mould somewhat deeper than that of the cupel intended to be made; in this is placed a curved and polished steel pestle, which is QUANTITATIVE ANALYSIS. 311 then struck smartly Avith a hammer. The operator must be care- ful to put as much ash into the mould as is required to make the cupel at once; it is otherwise apt to separate in layers Avhe«n it comes to be heated. The little vessel thus made is dried with great care, and heated to redness before it is used. One part, by weight, of the cupel, absorbs, during the process of cupel- lation, the oxide formed by two parts of lead. The assayist is thus furnished with a guide to the size of the cupel required for any particular experiment. In mixtures of lead and cop- per, only one part of copper is reduced to scoriae by six parts of lead; but Avhen the copper is alloyed Avith silver, a much larger quantity of lead is required. The quantity of lead necessary for different proportions of copper and silver has been determined. The results of the experiments made on this subject are thus given by Berzelius;* 1 part of copper alloyed with 30 parts of silver, requires 128 parts of lead; Avith 15 parts of silver, 96 of lead; with 7 of silver, 64 of lead; with 4 of silver, 56 of lead; with 3 of silver, 40 of lead; with 1 of silver, 30 of lead; with % of silver, 20 of lead; and Avith Jg of silver, 17 of lead. It is scarcely neces- sary to mention that the lead employed in assaying must be perfectly free from silver, or, if it does contain any of that metal, the quantity must previously be determined with the greatest care. The alloy to be examined is beat to a thin leaf by a polished hammer on a polished anvil, and being cut into small square pieces and accurately Aveighed, it is enveloped in a piece of thin lead, the weight of which is also known. The muffle is placed in one of the apertures of the assay furnace, and as soon as one- half of the bottom is red hot, the empty cupel is introduced, and advanced gradually into the muffle till it is itself red hot; a weighed piece of lead is then introduced, and, Avhen it is melted, the assay, enveloped in its covering of lead, is care- fully introduced; the heat is then someAvhat diminished, taking care, however, not to reduce it below the melting point of the vitrified lead; all the imperfect metals are gradually dissolved, and the fluid glass, which they form with the oxide of lead, soaks into the cupel, producing an appearance called circula- tion, by which the operator judges Avhether the process be going on well. As soon as a play of colors is perceived on * Traite de Chimie, vol. ii. p. 488. 312 QUANTITATIVE ANALYSIS. the melted metallic button, the mouth of the muffle is partially closed with a piece of charcoal, until it is perceived that the surface of the molten globule is clear and brilliant. It is al- lowed to remain for some minutes in the cupel, in order that the AA'hole of the oxide of lead, &c, may be absorbed by the bone ash, after Avhich it is allowed gradually to solidify; it is then removed, and, having been cleansed from all adhering oxide of lead, is weighed. The loss of weight indicates of course the quantity of copper and other oxidable metals origi- nally present in the alloy. The instant of the disappearance of the last traces of the oxidable metals is knoAvn by the melted silver globule becoming suddenly Avhiter, or flashing, as it is technically termed. In this manner the silver which ac- companies the lead in galena is extracted; but, previous to submitting the sample to the operation of cupellation, advan- tage is taken of the remarkable fact, that the quantity of silver may be concentrated in a comparatively small quantity of lead by crystalization. It has been ascertained that the silver is not diffused uniformly through all the lead, but com- bined in atomic proportions with a certain quantity of it form- ing an alloy, which is then mixed with an excess of lead. This alloy is more fusible than lead, so that Avhen a large basin of lead containing a small quantity of silver is melted, and allowed to cool very slowly, so as to crystalize, the por- tions which first solidify are pure lead; and these portions being removed with iron colanders, all the silver remains in the mother liquor. The process must be stopped, however, before this begins to congeal. By a succession of crystaliza- tions of this sort, the great excess of lead is gradually got rid of, and the quantity to be oxidized at the cupel diminished in a corresponding degree.* Dr. Percy proposes to separate both silver and gold from their ores by means of hyposulphite and chloride of lime. Ch. Gaz. 6.354. Mercury. This metal is in general most conveniently weighed in its metallic state. It may also be estimated in the form of calo- mel (subchloride), and as sulphuret. * Kane's Chemistry. QUANTITATIVE ANALYSIS. 313 Quantitative Estimation as 3fetattic Mercury. 1. Reduction by the dry way.—The solid mercurial com- pound is heated in a tube of hard glass, with an excess of soda lime, precisely in the same manner and with the same precautions as are observed in the analysis of ammoniacal salts (see page 249). The open end of the combustion tube is drawn out, and bent at a somewhat obtuse angle, in order that it may be inserted into a flask containing water, into which the mercury is received; Avhen the analysis is over, the fluid metal is collected into one large globule, by agitating the flask; it is then decanted into a porcelain capsule, and the adhering water having been removed by blotting paper, it is dried in vacuo over sulphuric acid, without the application of heat. In their experiment for the determination of the atomic weight of mercury, Erdmann and Marchand adopted the following somewhat complicated method of reducing the oxide, their object being the attainment of the greatest accu- racy.* A combustion tube about 3 feet long, was drawn out in front to an open point, from 9 to 10 inches in length, and curved downwards. A loose stopper of copper shavings, Avhich had been first oxidized by heating them while exposed to the air, and then reduced in a current of hydrogen, Avas introduced through the other end, and thrust forward to near the point. This copper was folloAved by a stratum five to six inches in length, of small fragments of strongly ignited sugar charcoal, from which every trace of dust had been care- fully removed by sifting, and then the oxide (which had pre- viously been strongly ignited in a current of air so as to re- move every trace of mercurial vapor) was introduced. To adArance to the front every trace of oxide which might have remained adherent to the hinder portions of the tube, it was finally rinsed with pulverulent copper: the tube, thus ar- ranged, was treated precisely in the same manner as in organic analysis, and then placed in a long furnace. To the hinder extremities a broad tube, filled Avith chloride of cal- cium, was fixed by means of a caoutchouc tube; to this was applied a Liebig potash apparatus, filled with sulphuric acid, and at last a large gasometer filled Avith carbonic acid. The * Journal fur Praktische Chimie, xxxi. p. 385. 314 QUANTITATIVE ANALYSIS. point in front of the tube was connected by a caoutchouc tube Avith a Aveighed recipient, destined to receive the mer- cury, and in the arm proceeding from the last bulb of the latter there ay as placed some gold leaf, to retain any trace of mercurial vapor Avhich had not been condensed in the bulb. A gentle stream of the dry carbonic acid gas was first alloAved to pass from the gasometer through the apparatus, the tube Avas then immediately surrounded Avith incandescent charcoal, proceeding from the front tOAvards the hinder part in the same manner as in an organic analysis. The carbon in the anterior portion of the tube is seen to burn at the expense of the libe- rated oxygen, and the mercury, which distils over in the cur- rent of carbonic acid, collects perfectly bright in the recipient. On the combustion of the charcoal some Avater is formed, which passes over along with the mercury. This Avater is en- tirely removed, as Avell as the carbonic acid contained in the apparatus, by a current of atmospheric air at the close of the operation. By this mode of analysis these chemists obtained from four experiments the following numbers:—92.594, 92.596, 92.598, and 92.596, the mean of which, 92.596, gives as the equivalent number of mercury the figure 100.07. A modification of this process, consisting in the employment of a current of hydrogen gas to assist in the reduction of the mercurial compound, has been adopted by 31. 3Iillon.* Hydrogen gas, he observes, is more easily obtained in a regular current than most other gases, and it greatly facili- tates the decomposition of all mercurial compounds: it favors the expulsion of the water Avhich accompanies the reduction, and likewise the condensation of the mercury in the expansion of the tube in which it is to be collected and Aveighed. The process is conducted as folloAVS:—The dry gas is passed through a tube containing copper turnings heated to redness— a plan Avhich Avas found the most efficacious for preserving the perfect metallic lustre of the mercury, Avhile it also insured the purification of the hydrogen. On leaving the tube with the copper turnings, the gas enters the tube containing the mercurial salt. This tube should be from fourteen to sixteen inches long, and of the diameter of an ordinary tube for organic analysis. At a small distance from its free extremity, it is contracted, and then again contracted and drawn out at the * Ann. de Chim., 1846. QUANTITATIVE ANALYSIS. 315 point and curved upwards: it thus presents a space of from three to four inches between the tAvo contractions. A little asbestos is first placed in the tube next the first contracted part; then caustic lime in small fragments to the extent of from six to eight inches : the mercurial compound is next introduced, the quantity of Avhich may vary from 15.5 to 62 grains, and then the tube is filled Avith caustic lime similar to the other. The tube is noAV placed in the furnace used for organic analysis: it receives the current of hydrogen at its Avider and uncontracted extremity, and heat is applied in the usual manner. The ignited charcoal is gradually ap- proached to the part of the tube containing the mercurial compound, and then a feAV pieces are placed behind it to pre- vent the condensation of the metal there. The Avater is first seen in the portion of the tube betAveen the contractions: it is dissipated by gently heating it. This part of the tube is then allowed to cool, and the mercury now makes its appear- ance, condensing in its turn Avithout any difficulty. At the end of the operation the part of the tube containing the mer- cury is separated by slightly moistening the heated tube ;the pqrtion of the tube is weighed with the mercury it contains; the metal is then poured out, the tube is rinsed out by nitric acid; it is then Avashed, dried, and Aveighed again. The dif- ference between the tAvo weights gives the Aveight of the mer- cury. The author states that by this mode of operating he has been able to propel 45 to 60 grains of mercury from one extremity of the tube to the other, condensing it between the contracted parts Avithout the smallest loss. Two analyses of chloride of mercury yielded 73.87 and 73.82 per cent, of mercury, figures Avhich give as the atomic weight of mercury 100.07, the same as that obtained by Erdmann and Mar- chand. 2. Reduction in the 3Ioist Way.—The best reducing agent for this purpose is protochloride of tin. The process is con- ducted as folloAVS:—The mercurial compound, if a solid, is digested with strong hydrochloric acid, a concentrated solu- tion of protochloride of tin, Avhich has been rendered perfectly clear by the addition of a feAV drops of hydrochloric acid, is then added. The whole is boiled, but only for a feAV minutes, to avoid the risk of the volatilization of a portion of the mer- cury in company Avith the aqueous vapors- On cooling, the mercury is usually found deposited in the form of a black 316 QUANTITATIVE ANALYSIS. precipitate, the supernatant fluid is removed by a syphon, and the precipitate is boiled Avith Aveak hydrochloric acid, on which it generally loses its pulverulent appearance, and becomes converted into running globules. It is washed, first Avith very dilute hydrochloric acid, and finally Avith distilled Avater; it is then received into a porcelain crucible, dried, first with bibulous paper, and lastly over sulphuric acid in the manner already directed. When mercury has to be estimated in a liquid con- taining nitric acid, it is necessary to destroy this acid, before a correct determination can be made: this is done by adding hy- drochloric acid gradually to the solution and concentrating by evaporation. The nitric acid is thus destroyed, free chlorine being at the same time disengaged, and the addition of the hydrochloric acid must be continued as long as the odor of chlorine is perceptible: protochloride of tin is then added, and the remainder of the operation is conducted in the manner already described. It is very difficult to obtain correct results when the solution contains much nitric acid. Wherever it is admissible, therefore, it is advisable to precipitate the mer- cury as sulphuret by sulphuretted hydrogen, or colorless hy- drosulphuret of ammonia, having previously nearly neutralized the solution Avith potassa, and mixed it Avith excess of cyanide of potassium. Other reducing agents, such as phosphorous or sulphurous acids, may be employed in the place of protochloride of tin, and Rose remarks, that the former Avould be preferable to the tin salt, could it be procured easily in sufficient quantities. It may be added at once to a mercurial solution containing nitric acid, which it destroys, with the aid of heat, more effectually than hydrochloric acid. It is, moreover, easier to obtain mercury in large globules by these acids than when protochloride of tin is employed. Quantitative estimation as Subchloride. — This method, which is extremely tedious, and which is only employed in certain cases where other methods are inadmissible, is directed by Fresenius* to be applied in the following manner :—The solution of the mercurial compound is mixed with hydro- chloric acid in excess, potassa is then added until the excess of acid is nearly neutralized, and then excess of formiate of soda, after which it is allowed to remain for four days at rest * Quantitative Analysis, p. 212. QUANTITATIVE ANALYSIS. 317 at a temperature of from 140° to 176°. It is then collected on a filter which has been dried at 212°, and weighed. The filtrate is again allowed to stand for twenty-four hours, and should any fresh precipitate form, it is added to the first; the same process is repeated until the filtrate remains perfectly clear. The whole is then washed, dried at 212°, and weighed. Care must be taken to confine the temperature to 170°, since otherwise metallic mercury might separate; should this be the case, the precipitate will exhibit a grayish appearance, and the experiment must, under such circumstances, be con- sidered a failure. The composition of subchloride of mercury is Two equivalents of Hg ... 200.14 . . . 84.97 One do. ofCl ... 35.50 ... 15.03 One do. of Hg2Cl 235.64 100.00 Quantitative estimation as Sulphuret.—A stream of washed sulphuretted hydrogen is transmitted through the acid solu- tion of the salt; in solutions of the suboxide, the precipitate formed is black at once; but, Avhen a compound of oxide of mercury is under examination, in the beginning of the experi- ments AA'hite-colored compounds of mercurial salts, with sul- phuret of mercury, are produced: the addition of larger quantities of the gas causes the precipitate to assume various colors, but it ends in becoming pure black. If the Avhole of the mercury exists in the original solution as oxide, it may be determined in the state of sulphuret, with which view the precipitate, occasioned' by sulphuretted hydrogen, is re- ceived on a weighed filter, quickly washed with cold Avater, dried at 212°, and weighed; but if the mercury, or any por- tion of it, existed as suboxide, it is inadmissible to estimate it as subsulphuret, because it is liable to be partly decomposed, even by a gentle heat, into sulphuret of mercury and metallic mercury; and as the latter may be partly volatilized by a very gentle heat, an error of greater or less amount would be intro- duced (Rose). The sulphuret containing a minimum of sul- phur must, therefore, undergo further treatment, as follows:— It is collected on a filter, and transferred, filter and all, into a wide-mouthed flask, capable of being closed by a glass stopper. A small quantity of dilute hydrochloric acid is then poured into the flask, and a slow current of chlorine conducted 318 QUANTITATIVE ANALYSIS. into the solution; the sulphuret is hereby decomposed into chloride, sulphuric acid, and free sulphur, as soon as the latter is observed to have a clear yellow color; the stream of chlorine is stopped, and the flask is exposed to a gentle heat to expel the free chlorine; it is then filtered off from the sulphur, and the mercury in the filtrate is estimated by protochloride of tin. Mercury may also be separated from neutral or alkaline solutions by hydrosulphuret of ammonia; an excess of the precipitant does not dissolve the precipitate in the cold; the sulphuret must, subsequently, be treated with chlorine, and the metal estimated in the manner just described. It must be observed that, in the presence of sesquioxide of iron or of chromic acid, oxide of mercury cannot safely be weighed as sulphuret, in consequence of the free sulphur with which it would be accompanied: it must be treated with chlorine and protochloride of tin, and estimated in the metallic state. The composition of sulphuret of mercury is One equivalent of Hg ... 100.07 . . . 86.21 One do. of S ... 16 ... 13.79 One do. of HgS . . . 116.07 100 Separation of Oxides of Mercury from Oxide of Lead. 1. By Sulphuretted Hydrogen Gas.—The two metals are first precipitated together as sulphurets from a diluted solu- tion; the mixed sulphurets are dried, and introduced into a bulb blown in a tube of hard glass, the weight of which, be- fore and after the introduction of the sulphurets, is accurately taken. The tube is connected with an apparatus for generat- ing chlorine, and a stream of the gas, dried by passing through a tube filled with chloride of calcium, is sent through the tube. When the whole apparatus is filled with chlorine, the bulb containing the sulphurets is gently heated, upon which the chloride of mercury volatilizes, and is completely separated from the chloride of lead. The sublimed chloride of mercury is driven forward by the flame of a small spirit lamp, and re- ceived in a vessel containing water. As soon as all appear- ance of sublimation ceases, the tube leading from the bulb to the receiver is cut off with a file, and any crystals Avhich may have collected in it are washed into the flask. The chloride QUANTITATIVE ANALYSIS. 319 of mercury dissolved in the receiver is precipitated by proto- chloride of tin, and the chloride of lead remaining in the bulb is determined by first weighing it together with the bulb, and then dissolving it out and weighing the bulb alone. 2. By Cyanide of Potassium.—This method, which is far more simple and easy of execution than the one just described, is conducted as follows:—The diluted solution of the two oxides is mixed with carbonate of soda, and then heated with excess of cyanide of potassium; the whole of the lead is pre- cipitated in the state of carbonate, while the mercury remains in solution in the form of double cyanide of mercury and po- tassium. The solution is filtered off from the insoluble lead salt and precipitated by sulphuretted hydrogen. 3. By Hydrochloric Acid.—All the mercury present in the compound must be in the form of oxide. The dry mix- ture is treated with hydrochloric acid, and eAaporated to dry- ness at a gentle heat. Alcohol, mixed with ether, is added to the residue, and the whole is digested: chloride of mercury alone dissolves. The insoluble chloride of lead is received on a filter, washed with alcohol, dried, and weighed. The alco- holic solution of chloride of mercury is evaporated to expel the alcohol and ether, and the mercury is then precipitated by protochloride of tin. 4. By Sulphuric Acid.—The solution is concentrated, and mixed Avith excess of sulphuric acid: after the lapse of several hours, it is filtered. The precipitated sulphate of lead is washed first with dilute sulphuric acid, and then Avith alcohol. The mercury in the filtrate is precipitated by protochloride of tin. Separation of Oxides of Mercury from Oxide of Silver. 1. By Hydrochloric Acid.—For this purpose the mercury must be in the state of oxide, suboxide of mercury being pre- cipitated by hydrochloric acid. To insure this, the compound is digested with nitric acid, hydrochloric acid is then added in slight excess, and the precipitated chloride of silver is col- lected and weighed with the precautions prescribed (page 306). The mercury in the solution is precipitated by protochloride of tin, the nitric acid having been previously destroyed by chlorine. 2. By Cyanide of Potassium.—The solution is nearly neu- tralized with potassa; excess of cyanide of potassium is then 320 QUANTITATIVE ANALYSIS. added, by which the precipitate which first forms is entirely redissolved, and the solution contains the double cyanides of silver and potassium, and of mercury and potassium. On adding nitric acid the cyanide of potassium is decomposed, the silver is precipitated in the form of cyanide of silver, while the cyanide of mercury remains in solution; the former is separated by filtration, and from the filtrate the mercury is precipitated by sulphuretted hydrogen. 3. By Chlorine.—This is effected precisely in the same manner and with the same apparatus as is employed in the separation of oxide of mercury from oxide of lead; chloride of silver remains in the bulb, in which it is weighed, the bent tube, through which the volatilized chloride of mercury makes its escape into the receiver having been cut off. The fused chloride of silver must, after weighing, be removed from the bulb by zinc and sulphuric acid, in order that the weight of the latter may be taken. Separation of Suboxide of 3Iercury from Oxide of 3Iercu- ry.—The solution is diluted considerably with water, and the suboxide is precipitated as subchloride by hydrochloric acid: heat must be avoided. The subchloride, after standing for some time, is received on a weighed filter, and dried at a gen- tle heat. The oxide of mercury in the filtrate is precipitated by protochloride of tin. If the substance be a solid and in- soluble, it is acted upon at a low temperature, with diluted nitric acid, until it is completely dissolved: hydrochloric acid is then added as before. Analysis of Amalgams.—If the metal or metals with which the mercury is combined be not volatile, or oxidizable by heat with excess of air, the amount of mercury in the amalgam may be ascertained in the simplest manner by igniting it in a porcelain crucible. If, however, the metals are liable to alteration by exposure to heat in an open vessel, the ignition must be performed in a retort, the neck of Avhich, after the volatilization of the mercury, must be closed up by the blow- pipe, while the retort is still ignited. Bismuth. This metal is almost invariably weighed as oxide. It is precipitated from its solution in nitric acid by carbonate of ammonia; the solution should be diluted, and it should be heated nearly to boiling for a few minutes before it is filtered, QUANTITATIVE ANALYSIS. 321 otherwise a portion of the oxide will be retained in solution by the. precipitant. Neither carbonate of potassa nor carbon- 'ate of soda can be substituted for carbonate of ammonia; a portion of the former is carried down with the precipitate, and is not easily removed by subsequent washing, and the latter fails to effect a perfect precipitation. The carbonate of bismuth, having been washed, is separated from the filter and ignited in a porcelain crucible, by which it loses carbonic acid, and becomes converted into protoxide of a yelloAV color. The filter is burnt on the cover of the crucible, and its ashes added to the oxide. The composition of protoxide of bismuth is One equivalent of Bi ... 70.95 One do. of 0 . . . 8 One do. of BiO . . . 78.95 In the presence of sulphuric or hydrochloric acids bismuth cannot be effectually precipitated by carbonate of ammonia, as in the former case a basic sulphate, and in the latter a basic chloride, is at the same time precipitated, and neither of these salts can be subsequently decomposed eAren by pro- tracted digestion with excess of carbonate of ammonia. In such cases it is necessary, in the first place, to mix the solu- tion of the bismuth salt with acetic acid (Avater will not do, as it would cause the formation of an insoluble basic salt), and then to precipitate the bismuth in the form of sulphuret by sulphuretted hydrogen, or by hydrosulphuret of ammonia, ha\Ting previously rendered the solution alkaline by the addi- tion of caustic ammonia. The precipitated sulphuret, having been washed, is decomposed by digesting it, filter and all, with nitric acid; the solution is diluted with weak acetic acid, filtered, the filter washed with the same diluted acid, and the filtrate finally precipitated by carbonate of ammonia. Separation of Oxides of Bismuth from Oxides of Lead. 1. By Sulphuric Acid.—An excess of sulphuric acid is added to the solution containing the two oxides, and heat is applied till the sulphuric acid begins to volatilize: it is then quickly filtered, and the sulphate of lead is washed with Avater acidulated with sulphuric acid. The sulphate of bismuth in 21 322 QUANTITATIVE ANALYSIS. the filtrate is precipitated by carbonate of ammonia. The results are not very accurate, since sulphate of lead is not altogether insoluble even in dilute sulphuric acid. 2. Ullgren's Process.—The two oxides are together preci- pitated with carbonate of ammonia, and redissolved in acetic acid. A strip of clean lead, of knoAvn weight, is then put into the solution, so that the whole of it is covered. The vessel is closed, and allowed to stand for some hours. The bismuth is separated in the metallic state, and that which remains on the strip of lead is washed off, and the strip dried and weighed. It is brought on a filter and washed with wa- ter that has been boiled and allowed to cool; it is then dis- solved in nitric acid, evaporated to dryness, ignited, and the oxide weighed. The solution of lead is precipitated with car- bonate of ammonia, and the Aveight of the oxide determined from this is to be deducted, the oxide corresponding to the loss which the strip of lead has suffered during the operation. 3. By Heat.—The process is the same as that employed for the separation of silver from mercury and lead from mer- cury, namely, by converting the metals into chlorides by heat- ing them in an atmosphere of chlorine, and expelling the volatile chloride of bismuth by heat. Too high a temperature must be avoided, othenvise a portion of the chloride of lead may be also volatilized. The proportion of bismuth may be calculated from the loss of weight which the compound under examination experiences. 4. Liebig's Method.—To a cold solution of the nitrates of the two oxides carbonate of lime is added, which precipitates the.bismuth, but not the lead. Separation of Oxide of Bismuth from Oxide of Silver. 1. By Hydrochloric Acid. — Nitric acid is added to the solution, and then hydrochloric acid, which precipitates the silver as chloride. The bismuth in the filtrate is precipitated by sulphuretted hydrogen, the sulphuret decomposed by nitric acid, and, finally, precipitated by carbonate of ammonia. 2. By Cyanide of Potassium.—This reagent is added to the solution of the two oxides, whereupon the bismuth is pre- cipitated as carbonate; the silver remains in solution as double cyanide of silver and potassium; it is separated by filtration from the carbonate of bismuth, and is, finally, precipitated as cyanide by the addition of nitric acid. QUANTITATIVE ANALYSIS. 323 Separation of Oxide of Bismuth from Oxide of Mercury.— This also is effected by cyanide of potassium; the soluble argento-cyanide of potassium is decomposed by sulphuretted hydrogen, and the mercury may be determined as sulphuret. Cadmium. This metal may be quantitatively estimated as oxide or as sidphuret. Estimation as Oxide.—The solution under examination is precipitated by carbonate of potassa, and the resulting white carbonate of cadmium is decomposed by ignition into carbonic acid and water which escape, and oxide of cadmium Avhich re- mains behind in the form of a broAvn powder. Ammoniacal salts interfere with the complete precipitation of oxide of cad- mium by alkaline carbonates; carbonate of ammonia cannot, therefore, be employed as the precipitant. In precipitating oxide of cadmium by carbonate of potassa in the presence of ammoniacal salts, the same precautions must be taken as in the precipitation of carbonate of zinc under similar circum- stances. The composition of oxide of cadmium is One equivalent of Cd ... 55.74 . . . 87.45 One do. of 0 . . . 8 ... 12.55 One do. of Cd 0 ... 63.74 100 Precipitation as Sulphuret.—This may be effected either by sulphuretted hydrogen, or by hydrosulphuret of ammonia; in acid solutions the former reagent is employed. It should be largely diluted, and the gas allowed to pass sloAvly through the liquid for a long time; the resulting sulphuret is of a yel- low or orange color, according as the solution has been more or less diluted. It is collected on a Aveighed filter, Avashed with distilled water, and dried at 212°. The composition of sulphuret of cadmium is One equivalent of Cd ... 55.74 ... 77.78 One do. of S ... 16. ... 22.22 One do. of Cd S ... 71.74 100 When hydrosulphuret of ammonia is employed as the pre- cipitant, the sulphuret should be decomposed by digestion 324 QUANTITATIVE ANALYSIS. Avith hydrochloric acid, and the solution precipitated with carbonate of potassa. It has been observed by Br. H. Reinsch, * that Avhen a salt of cadmium is dissolved in hydrochloric acid, and then treated with sulphuretted hydrogen, no precipitate takes place till after the gas has been passed through the so- lution for a long time, and that then the precipitate is a com- bination of sulphuret of cadmium with chloride. On edulco- rating Avith Avater the chloride is dissohred, and the yellow sulphuret is left on the filter. This observation sIioavs the necessity of diluting the solution before passing the gas through it. I have observed, also, that in precipitating a hydrochloric solution containing copper, lead, bismuth, and cadmium by sulphuretted hydrogen, the three former metals are completely throAvn doAvn before the chloride of cadmium is at all decomposed; the filtered liquor gives no traces of either of the three first metals, but on continuing to pass the gas sloAvly through it for a long time the cadmium is precipi- tated of its characteristic yelloAV color. Separation of Oxide of Cadmium from Oxides of Lead. 1. By Cyanide of Potassium.—The diluted solution of the tAvo oxides is first rendered slightly alkaline by carbonate of soda; cyanide of potassium is then added, and heat applied. The lead is precipitated as carbonate, the cadmium remains in solution as double cyanide of cadmium and potassium, and maybe precipitated, from the filtered solution by sulphuretted hydrogen. 2. By Sulphuric Acid.—The solution is concentrated, and excess of dilute sulphuric acid added; sulphate of lead pre- cipitates, which is received on a filter and Avashed, first Avith dilute sulphuric acid, and, finally, Avith alcohol; the cadmium in the filtrate is precipitated by carbonate of potassa; the former method Avith cyanide of potassium gives the best re- sults, in consequence of the partial solubility of sulphate of lead, even in dilute sulphuric acid. Separation of Oxide of Cadmium from Oxide of Silver. 1. By Hydrochloric Acid.—To the diluted solution nitric acid is added, and then slight excess of hydrochloric acid, the * Jahrb. fur Prakt, Pharm., xiii. p. 72; and Chem. Gaz , vol. v. p. 167. QUANTITATIVE ANALYSIS. 325 liquor filtered from the precipitated chloride of silver contains the cadmium, and is precipitated by carbonate of potassa. 2. By Cyanide of Potassium.—The nitric solution of the two metals is rendered neutral by the addition of potassa; cyanide of potassium is then added in such quantity that the precipitate, which is at first formed, is entirely re-dissolved. To the clear solution excess of nitric acid is next added, whereupon the Avhole of the silver is precipitated as cyanide: the cadmium remains in solution, and may either be precipi- tated by hydrosulphuret of ammonia, having previously ren- dered it slightly alkaline by the addition of potassa, or the hydrocyanic acid may be expelled by evaporating with sul- phuric acid, and the cadmium precipitated as carbonate by carbonate of potassa. Separation of Oxide of Cadmium from Oxide of 3Iercury.— This may be effected by formiate of soda, but the process is tedious, and requires considerable care. Hydrochloric acid is added to the solution, which is then nearly saturated with potassa; excess of formiate of soda is then added, and the solution is set aside for some days at a temperature not above 170°. The mercury precipitates in the form of calomel: the solution filtered from the subchloride of mercury contains the cadmium, which is then precipitated by carbonate of potassa. Cyanide of potassium may also be employed to separate these tAvo oxides in the following manner:—The clear solution is rendered neutral by potassa, and an excess of cyanide of po- tassium is then added. To the solution- of the two cyanides very dilute nitric acid is added, and the whole is boiled; the mercury salt is not decomposed: the cyanide of cadmium, on the other hand, is converted into nitrate, and may, conse- quently, be decomposed by carbonate of potassa: the filtrate, from the carbonate of cadmium, containing the oxide of mer- cury, may be precipitated by sulphuretted hydrogen. Separation of Oxide of Cadmium from Oxide of Bismuth.— This likewise is effected by cyanide of potassium, an excess of the cyanide is added, and heat applied, the Avhole of the bis- muth is separated as carbonate, and the cadmium is precipi- tated either by sulphuretted hydrogen, or by carbonate of potassa, having previously boiled the solution, filtered from the carbonate of bismuth, with hydrochloric acid. 326 QUANTITATIVE ANALYSIS. Copper. In AA'hatever manner copper may be precipitated from its solutions, it is invariably weighed as oxide. If the salt to be examined be soluble in Avater or in nitric acid, proA'ided no organic substance be present, it is best precipitated by caustic potassa. The solution is considerably diluted, and raised to the boiling temperature in a capacious porcelain basin, and the caustic alkali gradually added as long as a brownish black precipitate is produced; the boiling is continued for a few minutes, and the precipitated oxide is then received on a filter, and washed Avith boiling Avater. The greater part of it is then removed from the filter and transferred to a platinum crucible, in which it is ignited. The filter, with its adhering oxide, is dried, burnt on the coA'er of the crucible, and the ashes added to the main bulk of the oxide. As oxide of copper absorbs moisture rapidly from the atmosphere, it must be weighed as soon as it is sufficiently cold to be placed in the scale of the balance, and it is adArisable to allow the crucible to cool under- neath a receiver by the side of a vessel containing concen- trated sulphuric acid. If the solution be not dilute, the pre- cipitation by caustic potassa is incomplete, as is rendered eA'ident by the filtrate becoming discolored when mixed with sulphuretted hydrogen water: the same is the case if any organic matter be present; in either of these cases the filtrate must be concentrated by evaporation, precipitated by sulphur- etted hydrogen, and the precipitate treated as will be pre- sently described. The oxide on the filter must be well Avashed with boiling water, to remove all traces of the alkali, which is invariably carried down in company with the oxide during its precipitation. The composition of oxide of copper is One equivalent of Cu ... 31.66 . . . 79.73 One do. of 0 ... 8 ... 20.27 One equiv. of CuO .. . 39.66 100 Precipitation as Sulphuret.—The solution is acidified with hydrochloric acid, diluted with water, and a stream of washed sulphuretted hydrogen gas passed through it till it is perfectly saturated. The precipitated sulphuret is received on a filter and washed as quickly as possible with water impregnated QUANTITATIVE ANALYSIS. 327 with sulphuretted hydrogen; it is removed as completely as possible, from the filter, which is then dried and ignited, and its ashes mixed Avith the bulk of the precipitate. The copper cannot be estimated as sulphuret, as that salt becomes par- tially oxidized during drying; it is therefore decomposed by digestion Avith dilute nitro-hydrochloric acid, and, the sulphur being separated, the solution is eAraporated with sulphuric acid until the nitric acid is entirely expelled; a large quantity of water is then added, and the oxide is precipitated by caus- tic potassa at the boiling temperature. If the solution be neutral or alkaline, hydrosulphuret of ammonia may be em- ployed as the precipitating agent. Levol's Method of determining Copper.—This is a modifi- cation of the method proposed by Fuch for the quantitative estimation of iron (see page 292). The cupreous solution is introduced into a flask that can be accurately closed with a glass stopper; ammonia is added till the liquid assumes a trans- parent blue color, and the flask is then filled with water, from which all atmospheric air has been expelled by boiling; a clean and accurately weighed slip of copper is introduced into the bottle, which is immediately closed: when the liquor has become perfectly colorless, the slip is removed, washed, dried, and weighed; the diminution in weight which it has undergone, indicates the amount of copper originally present in the so- lution. The result which, Avhen properly conducted, is very accurate, depends on the abstraction of one equivalent of copper from the slip by every equivalent of oxide of copper in the solution to form an equivalent of suboxide of copper, which forms with ammonia a colorless solution, thus— CuO, + Cu = Cu20 It requires a considerable time to complete the process, which is obviously altogether inapplicable in the presence of foreign metals, which are capable of being precipitated by copper. Cassaseca's Method.—This consists in dissolving the copper compound in an acid, adding an excess of ammonia to the solution, and comparing the tint furnished by this solution with those which a knoAvn Aveight of pure copper yields like- wise in the state of ammoniuret. Pelouzes Method of Estimating Copper by Standard So- lutions.*—This mode of analysis Avas suggested to the author, * Comptes Rendus, Feb. 2, 1846. 328 QUANTITATIVE ANALYSIS. by the accuracy and rapidity Avith which alloys of silver are analyzed by the process discovered by 31. Gay-Lussac (page 308). He succeeded in effecting his object in several different ways, all based principally on the phenomena of precipitation and simultaneous decoloration. The following Avas the mode of proceeding which he finally adopted: a certain quantity of very pure copper is dissolved in nitric acid, the solution is diluted Avith Avater, and excess of ammonia added: a deep blue solution is obtained. On the other hand, some sulphuret of sodium (colorless crystalized hydrosulphate of soda of com- merce) is dissolved in water and poured into a tube graduated and divided into tenths of cubic centimetres, the ammoniacal solution is heated to boiling, and the solution of the sulphuret gradually added. If we suppose that it required 31 cubic centimetres to decolorize 1 gramme of copper, Ave have a standard solution of knoAvn strength. To apply this to the analysis of copper alloys, a certain known Aveight is dissolved in aqua regia, the solution is supersaturated Avith ammonia, heated to boiling, and the standard solution of the sulphuret added until it is decolorized, taking care to add from time to time a little dilute ammonia to replace that which is evapo- rated. The decrease in the depths of the blue tint points out that the end of the experiment is more or less near, and when it is requisite to add the last portions of the sulphuret in drops. When the operation is supposed to be finished, the number of divisions employed for the decoloration is read off and compared with the number required to decolorize an equal weight of pure copper. It must be remarked that the am- moniacal liquor from which the copper has been precipitated does not long remain colorless, but gradually becomes blue in consequence of the sulphuret of copper becoming partially converted into sulphate, by the absorption of oxygen. This mode of operating is not, according to the author, liable to an error amounting to more than five or six thousandths, though still greater accuracy is obtained by completing the decoloration of the blue liquid with a very weak solution of sulphuret, precisely in the manner recommended by Gay- Lussac in his Analysis of Silver Alloys by Standard Solu- tions of Common Salt. Neither tin, zinc, cadmium, lead, antimony, iron, arsenic, nor bismuth, in any way interfere with the success of this process, not being in the least affected by the sulphuret of sodium while a trace of copper remains QUANTITATIVE ANALYSIS. 329 to be precipitated; indeed the author found that when the sulphuret of zinc, cadmium, tin, lead, bismuth and antimony are placed in contact with an ammoniacal solution of sulphate of copper, they decolorize it, some in the cold, others with the assistance of heat, which proves very evidently that these sulphurets cannot exist, except, perhaps, for an instant, in a solution of copper. Their formation subsequently to the de- coloration has no influence on the result of the analysis, as the termination of this is judged of by the decoloration of the liquid, without paying the least attention to the precipitates Avhich subsequently form; or, if any attention is paid, it is only with a view to obtain some knoAvledge of the nature of the metals which accompany the copper. Thus, if any alloy consists of copper, lead, tin, and zinc, the presence of zinc is readily detected by the Avhite precipitate which succeeds the black precipitate of sulphuret of copper, the lead and tin being precipitated at the outset by ammonia. Cadmium, like zinc, is precipitated immediately after the copper. The very moment the liquid is observed to be decolored, a beautiful pure yellow precipitate of sulphuret of cadmium is formed if the addition of sulphuret be continued. If the alloy contains silver, that metal is previously precipitated from the nitric solution by hydrochloric acid. In this method of estimating copper, an important property of the ammonia, besides that of heightening the color, is, that it prevents the salts of cop- per being precipitated by sulphites and hydrosidphites, with- out which it would probably have been impossible to estimate the copper by means of solutions of the alkaline sulphurets, since these salts almost ahvays occur in the alkaline sulphur- ets, and are, moreover, produced from them by contact with the air. A solution of sulphuret of sodium becomes Aveaker by contact with the air, but the alteration is very slow, nor is it necessary to change the liquid as long as any remains in the flask in which a quantity has been prepared. The only precaution to be taken—and it is one which applies to all standard solutions—is to determine previous to each assay the actual strength of the sulphuret with a known weight of pure copper. 31. Pelouze states, in conclusion, that this method applied to the analysis of copper ores, yields results of the greatest accuracy, and that he entertains no doubt that it will render great services in the administration of the 330 QUANTITATIVE ANALYSIS. Mint, the government foundries, and other metallurgical works. Separation of Oxide of Copper from Oxide of Lead. 1. By Cyanide of Potassium.—To the diluted solution of the two oxides carbonate of soda is added in slight excess, and then cyanide of potassium, and heat applied. The lead precipitates as carbonate; the copper remains in solution in the form of double cyanide of copper and potassium: it is evaporated with sulphuric acid till all the hydrocyanic acid is expelled, then largely diluted with water, and precipitated at the boiling temperature by caustic potassa. 2. By Sulphuric Acid.—The solution is concentrated, and the oxide of lead precipitated by dilute sulphuric acid, the sul- phate of lead is collected on a filter, and washed first with di- lute sulphuric acid, and then with spirits of wine. The filtrate is boiled for some time, to drive off the alcohol, and finally precipitated by caustic potassa. Separation of Oxide of Copper from Oxide of Silver. 1. By Hydrochloric Acid.—Nitric acid is added to the so- lution, the silver is then precipitated as chloride by hydro- chloric acid, and the oxide of copper is thrown down from the filtrate by caustic potassa. 2. By Cyanide of Potassium.—The solution is neutralized with potassa, cyanide of potassium is then added till the pre- cipitate which is first formed is entirely redissolved. To the clear solution nitric acid is added, Avhich precipitates the sil- ver completely as cyanide. The filtrate is evaporated with sulphuric acid till all the hydrocyanic acid is expelled, and the copper is finally precipitated by caustic potassa. Fresenius gives another method of treating the solution of the oxides of these two metals in cyanide of potassium. Sulphuretted hydrogen is passed into the solution, Avhich precipitates only the silver, provided sufficient cyanide of potassium be present. The solution filtered from the sulphuret of silver is heated to expel the excess of sulphuretted hydrogen; cyanide of potas- sium is again added, and then, having completely decomposed this salt by evaporating with a mixture of sulphuric and nitric acids, the copper is precipitated by caustic potassa. For the method of assaying alloys of silver and copper, see " Silver." QUANTITATIVE ANALYSIS. 331 Separation of Oxide of Copper from Oxide of 3Icrcury. 1. By Cyanide of Potassium.—This is effected in the same manner as the separation of oxide of silver from oxide of cop- per; the solution of the tAvo oxides in cyanide of potassium is treated with sulphuretted hydrogen, by which mercury alone is precipitated. 2. By Formiate of Soda.—Hydrochloric acid is added to the solution, Avhich is then nearly neutralized with potassa, and the mercury precipitated as subchloride by formiate of soda, in the manner directed in treating of the separation of oxide of mercury from oxide of cadmium. Separation of Oxide of Copper from Oxide of Bismuth. 1. By Carbonate of Ammonia.—On adding this reagent to the solution of the two oxides, in considerable excess, oxide of bismuth alone is precipitated; it is allowed to remain at rest for some time in a Avarm place, and then filtered, the oxide of bismuth being washed on the filter Avith carbonate of ammo- nia. The filtrate is gently evaporated to expel the excess of carbonate of ammonia, caustic ammonia is then added, and the oxide of copper is finally precipitated by caustic potassa. This method is not to be recommended, it being difficult to remove all traces of oxide of copper from the precipitated oxide of bismuth, even by protracted washing with carbonate of am- monia. 2. By Cyanide of Potassium.—Carbonate of soda is first added in slight excess to the solution, the oxide of bismuth is then precipitated in the form of carbonate, by heating with cyanide of potassium; the copper in the filtrate is determined by precipitating it by caustic potassa, having previously ex- pelled the hydrocyanic acid by eAraporating with sulphuric acid. 3. By Chlorine.—The solution of the two metallic oxides is precipitated by sulphuretted hydrogen, and the mixed sulphu- rets, having been washed and weighed, are introduced into a bulb, blown in a tube of hard glass, connected with an appa- ratus for generating chlorine. A stream of this gas is trans- mitted through the tube, which at the same time is heated by a spirit lamp, first gently, and then to redness; the sulphurets are thus converted into chlorine, and the chloride of bismuth, being Aolatile, is gradually expelled; it may be received into 332 QUANTITATIVE ANALYSIS. a vessel containing water impregnated with hydrochloric acid, or the amount of oxide may be estimated by the loss of weight sustained by the analyzed substance. The apparatus employed may be the same as that used for separating mercury from lead, mercury from silver, or bismuth from lead. The chlo- ride of copper remaining in the bulb is washed out with a little dilute nitric acid, evaporated with sulphuric acid, and finally precipitated by caustic potassa. Separation of Oxide of Copper from Oxide of Cadmium. 1. By Carbonate of Ammonia.—This reagent is added in excess to the solution of the two oxides; carbonate of cadmium is precipitated, while oxide of copper remains in solution. 2. By Cyanide of Potassium.—This reagent is added until a clear solution is obtained, sulphuretted hydrogen is then pas- sed through the mixture, by which the cadmio-cyanide is com- pletely decomposed, sulphuret of cadmium being precipitated, Avhile the Avhole of the sulphuret of copper remains in solution. The excess of sulphuretted hydrogen is expelled by heat, and a little more alkaline cyanide added. The copper may then be precipitated as sulphuret by the addition of an acid, or the double cyanide may be decomposed by evaporating Avith sul- phuric acid, and the metal precipitated as oxide by caustic potassa. Separation of Oxide of Copper from Oxide of Zinc.— Analysis of Brass.—Although oxide of zinc is, when alone, completely soluble in caustic potassa, this reagent cannot safely be employed to separate zinc from copper, since the oxide of copper invariably carries down with it a greater or less quantity of oxide of zinc. Sulphuretted hydrogen is, however, an effectual reagent for this purpose. The alloy, being dissolved in nitric acid, is treated with a current of the gas; sulphuret of copper alone precipitates, and from the fil- trate the oxide of zinc may be completely thrown down, by boiling with carbonate of potassa, or by evaporating it to dry- ness, and igniting in a platinum crucible. Analysis of Phosphate or Arseniate of Copper.—Berthier's method is to dissolve the compound in hydrochloric acid, and to boil the solution with sulphite of ammonia, Avhereupon the copper is thrown down as a red subsulphite, a minute trace only remaining in the solution. The same chemist has also proposed sulphite of ammonia as a means of separating oxide QUANTITATIVE ANALYSIS. 333 of copper from the oxides of iron, manganese, nickel, and zinc; he adds excess of this salt, and boils; copper alone is precipitated. In analyzing brass he first separates the cop- per in this manner, and then precipitates the zinc by hydro- sulphuret of ammonia. Palladium. This metal is remarkable for its great affinity for cyanogen, on which property is founded a method of separating it from its solutions; cyanide of mercury is added, the solution having previously been neutralized with soda; a bright yelloAV preci- pitate is produced, which, by drying, becomes yelloAvish gray, and by ignition is decomposed, metallic palladium of a blue color remaining in the crucible. From all metals which are not precipitated by sulphuretted hydrogen, palladium may be separated by that reagent; the resulting sulphuret is convert- ed by heat into basic sulphate, which, being dissolved in hy- ■ drochloric acid and neutralized with soda, is precipitated by cyanide of mercury. Separation of Palladium from Copper.—In crude platinum ores palladium occurs in combination with copper. Berzelius giAres the following process for separating these two metals.* Both metals are precipitated from an acid solution by sul- phuretted hydrogen. The precipitated sulphurets are exposed to heat, while still moist, and roasted as long as they give off sulphurous acid; they are thereby converted into basic sul- phates of oxides. These salts are dissolved in hydrochloric acid, the solution is mixed with chloride of potassium and ni- tric acid, and then evaporated to dryness. The dark saline mass thus produced contains chloride of potassium, chloride of copper and potassium, and chloride of palladium and po- tassium. The first two of these salts are to be extracted by alcohol, specific gravity 0.833; the palladium salt, being insoluble therein, remains behind. It is brought on a weighed filter, and Avashed with alcohol; it is then dried and weighed; it contains 28.84 per cent, of palladium. The saline mass may also be dissolved in Avater, and precipitated with cyanide of mercury. The alcoholic solution of the copper salt is eva- porated to expel the spirit, the saline mass is redissolved in Avater, and the copper precipitated by caustic potassa. * Poggendorf's Annalen, B. xiii. p. 561; and Rose's Manual of Analytical Chemistry, translated by Griffin, p. 135. 334 QUANTITATIVE ANALYSIS. Palladium has of late years been imported into this country from Brazil, alloyed Avith gold, some specimens containing 5 or 6 per cent, of palladium. The operation of refining is thus described by 3Ir. Cock.* The gold dust is fused, in charges of about 7 lbs. troy, with its own Aveight of silver, and a cer- tain quantity of nitre; the effect of this fusion is to remove all earthy matter, and the greater part of the base metals contained in the gold dust and in the silver melted with it. The fused mixture is cast into ingot moulds, and when cooled the flux or scoria is detached. Tavo of the bars thus obtained are then remelted in a plumbago crucible, with such an addi- tion of silver as Avill afford an alloy, containing one-fourth its Aveight of pure gold, and Avhich, first being well stirred to insure a complete mixture, is poured through a perforated iron ladle into cold water, and thus very finely granulated. It is then ready for the process of parting. For this purpose about 25 lbs. of the granulated alloy is placed in a porcelain jar upon a heated sand bath, and subjected to the action of about 25 lbs. of pure nitric acid, diluted with its OAvn bulk of Avater; after the action of this quantity of acid, the parting of the gold is \*ery nearly effected; but, to remove the least portions of silver, &c, about 9 or 10 lbs. of strong nitric acid are boiled upon the gold for two hours. It is then completely refined, and, after being washed Avith hot water, is dried and melted into bars containing 15 lbs. each. The nitric acid gas, and the vapor of nitric acid arising during the above process, are conducted by glass pipes (con- nected with the covers of the jars) into a long stoneAvare pipe, one end of which slopes downwards into a receiver for the condensed acid, the other end being inserted into the flue for the purpose of carrying off the uncondensed gas. The nitrate of silver and palladium, obtained as above, is carefully decanted into large pans, containing a sufficient quantity of solution of common salt to effect the precipitation as chloride of the whole of the silver, the palladium and cop- per remaining in solution in the mother liquor, Avhich is draAvn off, and, when clear, run off, together with the subsequent washings from the chloride of silver, into wooden vessels, and the metallic contents are then separated in the form of a black poAvder, by precipitation Avith sheet zinc, assisted by sulphuric * Proceedings of the Chemical Society, vol. i. p. 162. QUANTITATIVE ANALYSIS. 335 acid. The chloride of silver, when washed clean, is reduced by the addition of granulated zinc and dilute sulphuric acid, washed on the filter with boiling water, dried and melted in plumbago crucibles without the addition of any flux. From the black powder obtained as above, the palladium is extracted by resolution in nitric acid and supersaturation with ammonia, by which the oxides of palladium and copper are first precipi^ tated and then re-dissolved, Avhile those of iron, lead, &c, remain insoluble. To the clear ammoniacal solution, hydro- chloric acid in excess is then added, which occasions a copious precipitation of the yellow ammonia—chloride of palladium, from Avhich, after sufficiently washing it Avith cold Avater and ignition, pure metallic palladium is obtained. The niother liquor and washings contain all the copper and some palladium, which are recovered by precipitation with iron.* Rhodium. This metal is, according to Berzelius,f best estimated by the folloAving process:—The solution is mixed with excess of carbonate of soda, and evaporated to dryness; the dry residue is then ignited in a platinum crucible. Upon dissolving the mass in water, peroxide of rhodium remains behind, which is brought upon a filter and washed, first with hydrochloric acid, and finally with water. It is then ignited with the filter, and subsequently reduced by hydrogen gas. The reduction is so easily effected that it is scarcely necessary to assist the action of the gas by the application of heat. Separation of Rhodium from Copper.—Berzelius% directs to pour the solution into a flask which is furnished with a glass stopper, and to saturate it with sulphuretted hydrogen gas. The flask is then closed and allowed to remain for twelve hours in a Avarm situation. The sulphuret of copper is, in that time, fully, and the sulphuret of rhodium, for the most part, preci- pitated. The solution is filtered, and, being heated and eva- porated, yields a fresh portion of sulphuret of rhodium, which * Palladium being precipitated from its acid solutions by sulphuretted hydro- gen, it can thus be separated from iron and other metals not precipitable by this gas. The resulting sulphuret is roasted into basic sulphate, and dissolved in HCl acid. Upon the addition of a solution of cyanide of mercury to the solution, previously neutralized by soda, cyanide of palladium falls and may then be ignited. t Poggendorf's Annal., B. xiii. p. 454; and Rose's Manual of Analytical Chemistry, translated by Griffin, p. 131. £ Berzelius' Traite de Chimie. 336 QUANTITATIVE ANALYSIS. is added to the other sulphurets. These are placed, while still moist, in a platinum crucible, and roasted as long as sulphurous acid exhales. When the roasting is finished, the mass is sub- jected to the action of concentrated hydrochloric acid, peroxide of rhodium remains undissolved, and is reduced by hydrogen. gas, the copper in the solution is precipitated by caustic potassa. Rhodium exists together with iridium, palladium, osmium, &c, in platinum ores. It is extracted from the liquor from which the palladium has been precipitated by cyanide of mer- cury by the folloAving process. Hydrochloric acid is added, and the solution is evaporated to dryness, the excess of cyanide of mercury is decomposed, and transformed into chloride. The dry saline mass is reduced to a very fine powder and washed Avith alcohol, sp. gr. 0.837. The double chlorides of sodium and platinum, sodium and iridium, sodium and copper, and sodium and mercury, are dissolved, but the double chloride of sodium and rhodium remains behind in the form of a fine red poAvder. It is Avashed with alcohol and decomposed by gently heating in a current of hydrogen gas, by Avhich the chloride of rhodium is reduced, and the metal is subsequently separated from the chloride of sodium by water. Another method of treating the saline mass is to mix it with about twice its weight of carbonate of potassa, and to calcine the mixture. The residue is treated Avith water, and the copper dissolved out by hydrochloric acid. The residual mass is next mixed carefully with five times its weight of anhydrous bi- sulphate of potassa and heated to redness in a well-covered platinum crucible; the heat is continued till the mixture is about to solidify. The oxide of rhodium dissolves in the bi- sulphate of potassa. The saline mass is extracted with boiling water, and the process is repeated with fresh bisulphate as long as the salt continues to receive color; excess of carbonate of soda is poured into the aqueous extract, the whole is evapor- ated to dryness, and the residue is calcined; the residue is again treated with boiling water. Oxide of rhodium remains undissolved, and is then in a state to be reduced by hydrogen gas. Osmium and Ruthenium. The first of these metals, which is found in combination with iridium in platinum ores, is extracted by the following QUANTITATIVE ANALYSIS. 337 process.* The grains of osmium-iridium, which are exceed- ingly hard, are reduced to a very fine powder, which is then digested with hydrochloric acid, to remoA7e the iron which has become rubbed from the mortar during the operation of tritu- ration : it is then dried, mixed Avith nitre, and heated gradually to redness in a porcelain retort connected with a receiver con- taining caustic ammonia. During this operation, both metals become oxidized, and a portion of the oxide of osmium, or osmic acid, which is volatile, is carried forward Avith the nitric oxide gas, and condensed in the ammonia, to which it commu- nicates a yellow color. Another portion is condensed on the sides of the receiver in the form of a crystaline mass. All disengagement of gas haAring ceased, the apparatus is allowed to cool, the receiver containing the ammonia is then removed, and the mass Avhich remains in the retort is dissolved in water. The solution is of a deep brown color, and contains a com- bination of the two oxides with potassa. It must not be fil- tered, since the organic matter of the paper decomposes it. It is therefore at once distilled, at a gentle heat, in a retort connected with a receiver, and the greater part of the liquor drawn over. This liquor, which is colorless, and possessed of a strong and disagreeable odor, contains the osmium in the form of osmic acid. The following method of extracting iridium and osmium from the pulverulent residue, after di- gesting platinum ore with aqua regia, was proposed by WiShler. The residue is mixed with an equal weight of dry and finely pulverized common salt, heated to redness in a long glass tube, and a stream of chlorine sent through, as long as it continues to be absorbed. In this operation the titanate of iron is not attacked, but there are formed compounds of iridium and osmium with chloride of sodium; much osmic acid is also dis- engaged, being expelled with the aqueous vapor introduced with the chlorine gas; this is condensed in a receiver contain- ing ammonia, which is adapted to the tube. When no more chlorine is absorbed, the contents of the tube are treated with water, Avhich dissolves the double salts of iridium and osmium. The solution has a deep red-broAvn color. The titanate of iron and other matters remain undissolved. The solution is then distilled, by which much osmic acid, arising from the decomposition of the chloride of osmium, is removed, and is * Berzelius's Traite de Chimie. 22 338 QUANTITATIVE ANALYSIS. condensed in a recehrer containing ammonia; when no more osmic acid passes OA^er, the distillation is stopped, and the residual liquor, after being filtered, is mixed Avith excess of carbonate of soda, evaporated to dryness, and the residue feebly calcined. It consists of a mixture of suboxide of iri- dium with chloride of sodium; the latter is dissolved out by water. The suboxide of iridium is not, however, pure, it still contains a notable quantity of iron and of osmium; the former is removed by reducing the oxide to the metallic state in a current of hydrogen gas, and then acting on the residue with concentrated hydrochloric acid. Under this treatment the platinum residue loses in general from 25 to 30 per cent, of its Aveight: it is not, however, exhausted; and, by a second treatment with chloride of sodium, a farther amount of 5 or 6 per cent, of a mixture of osmium, iridium, and iron may be extracted. From the residue a small quantity of platinum may generally be dissolved out by aqua regia: it not unfre- quently, also, contains chloride of silver, which may be sepa- rated by ammonia. The following modification of this process has been recom- mended by Fritzsche.* Equal portions of caustic potassa and chlorate of potassa are melted together in a very spacious porcelain crucible over a spirit lamp, and into the fused mass is conveyed about three times its weight of osmium-iridium, AA'ithout first reducing it to powder. As soon as, on farther heating, the chlorate of potassa liberates oxygen, the fused mass begins to act on the osmium-iridium. The mass froths violently, so that the heat must be moderated when it becomes more tenacious ; the action at last proceeds Avithout any further heating, the mass becomes nearly black, and the operation is discontinued as soon as the frothing has ceased. During the Avhole operation, not a trace of osmium vapors is perceptible, but a slight evolution commences on the solidification of the mass, which is increased by farther heating; this, however, is unnecessary, so that there is scarcely any trouble Avith the Arapors of osmic acid. Six hundred grammes of osmium-iri- dium may be fused Avith ease in a porcelain crucible capable of holding 2 lbs., with 100 grains of caustic potassa and chlo- rate of potassa, over a spirit lamp. The operation scarcely lasts an hour, and at least 50 grains are decomposed. On * Journ. fur Prakt. CheriL xxxvii. p. 483; and Chem. Gaz., vol. iv. p. 319. QUANTITATIVE ANALYSIS. 339 treating the fused mass with water, an orange-colored solu- tion, containing osmium and ruthenium, is obtained, and a blackish-blue precipitate, which may very easily be separated by suspension from the undecomposed iridium-osmium. By the above process of Berzelius, iridium cannot be com- pletely separated from osmium, for, on heating the former while exposed to the air, vapors of osmic acid are always dis- engaged. In order to complete the separation of these two metals, the following method is employed by Fremy:* 100 grammes of the residue of the platinum workings are mixed Avith 300 grammes of nitre; the mixture is introduced into a large crucible and kept for an hour at a red heat in a wind furnace. After this calcination the mass is poured out on a metallic plate, wdiich operation should be performed in the open air, and it is even indispensable to cover the face, for without this precaution, the vapors of osmic acid would act violently on the skin. During the calcination with nitre, a certain quantity of osmic acid is lost, but it was found that the proportion of this acid which might be condensed would never repay the inconveniences of calcining in a porcelain crucible. The decanted mass, which contains the osmiate and iridiate of potassa, is treated in a retort with nitric acid, which liberates the osmic acid, which is condensed in a con- centrated solution of potassa. The residue is treated with Avater, Avhich removes the nitre, and it is then acted upon with hydrochloric acid, which dissohres the oxide of iridium. In this manner the osmium is obtained in the state of osmiate of potassa, and the iridium in that of soluble chlo- ride. Into the solution of osmiate of potassa Fremy pours a small quantity of alcohol; the liquid becomes heated, ac- quires a red tint, and deposits a crystaline powder of osmite of potassa; in this case the osmium is frequently precipitated entirely from solution. The salt may be washed with alcohol, which does not dissolve it, and it then may be preserved with- out alteration. All the compounds of osmium may be pre- pared from it. On treating it with a cold solution of sal-am- moniac, it dissolves at first, and is then decomposed, giving rise to a new yelloAV salt, scarcely soluble in cold water. This salt, which is so easily prepared, affords, on calcination in a current of hydrogen, osmium perfectly pure. * Comptes Rendus, Jan. 22, 1844; and Chem. Gaz., vol. ii. p. 107. 340 QUANTITATIVE ANALYSIS. To extract the iridium, Fremy treats the chloride obtained as above with sal-ammoniac, a reddish-brown precipitate is formed, consisting of a combination of the bichlorides of os- mium and iridium with sal-ammoniac. To separate these two double salts a stream of sulphurous acid is passed into the water in Avhich they are suspended, the double salt of iridium is decomposed, chloride of iridium is formed, which is very soluble in water; the double salt of osmium undergoes no change, it remains in the state of a red salt. The soluble salt of iridium crystalizes in large brown prisms out of solu- tions in sal-ammoniac; it is, therefore, easy to purify it when calcined in a current of hydrogen; it affords metallic iridium in a state of purity. Besides iridium and osmium, another metal has been found in the platinum residues by Professor Clauss.* It is called by its discoverer ruthenium. He prepared it in the following manner:—The residue, which had been once fused with nitre and extracted with water and acids, was mixed with an equal quantity of nitre, and kept at a white heat in a Hessian cru- cible for two hours. The mass was taken out while still red hot with an iron spatula, and, after cooling, Avas reduced to a coarse powder, which Avas extracted with distilled Avater, leaving it to stand with it till it became clear; the perfectly clear liquid, which was of a dark yellow color, was then de- canted. It could not be filtered, since it was decomposed by the action of the organic matter of the paper. It contained rutheniate, chromate, and silicate of potassa, not a trace of either rhodium or iridium, and only a very minute trace of osmiate of potassa. Nitric acid was cautiously added to this solution, until the alkaline reaction of the liquid had disap- peared: oxide of ruthenium and potassa, and some silicic acid, were hereby precipitated in the form of a velvet black powder, while chromate of potassa remained undissolved. After edulcoration the oxide of ruthenium and potassa was dissolved in hydrochloric acid, and the solution was evaporated till the silica separated as a gelatinous mass. It was then diluted with water and filtered. It could not be evaporated to dryness for the more complete separation of the silica, because the chloride of ruthenium was thereby decomposed * Bullet, de la Classe Physico-Math. de 1'Acad. de St. Petersburg, t. iii. p. 311; and Chem. Gaz., vol. iii. p. 49. QUANTITATIVE ANALYSIS. 341 into an insoluble protochloride. The filtered solution, Avhich is of a beautiful orange yellow color, was eAraporated down to a very small volume, and mixed with a concentrated solution of chloride of potassium, when the salt KC12+ RuCl4 separated in reddish-brown crystals. A further quantity was obtained by evaporating the liquid decanted from the crystals. The salt was further purified by recrystalization. Clauss has hitherto only been able to obtain the metal as a blackish-gray powder, Avhich is considerably lighter than iridium: the aqueous solution of its chloride is precipitated in the form of a black oxide by ammonia, by which it is distinguished from all the other platina metals, none of which are precipitated by ammonia at the ordinary temperature. If a slip of zinc be inserted in a solution of the orange-colored chloride acidified Avith hydrochloric acid, a black metallic powder is after a time deposited, the liquid acquires a dark indigo blue color, but subsequently, after the Avhole of the metal is deposited, be- comes colorless. Analysis of a mixture of Oxides of Lead, Bismuth, Silver, Copper, 3Iercury, and Cadmium.—To a diluted solution car- bonate of potassa is first added and then excess of cyanide of potassium; the oxides of lead and bismuth are precipitated in the form of carbonates, they are received in a filter, washed, dissolved in nitric acid, and the oxide of lead separated from the oxide of bismuth by dilute sulphuric acid, as directed (p. 321). The washing from the precipitated carbonates being mixed with the filtrate, excess of diluted nitric acid is added, the silver is precipitated as cyanide, in the form of which salt it is estimated. The filtrate from the cyanide of silver, to- gether Avith the Avashings, are again neutralized by carbonate of potassa, a fresh quantity of cyanide of potassium is added, and a stream of sulphuretted hydrogen gas is passed through the solution, the mercury and the cadmium are precipitated as sulphurets: the AA'hole of the sulphuret of copper is retained in solution by the cyanide of potassium, provided a sufficient quantity of that reagent has been added; to insure this, it is advisable to add a fresh portion after the action of the sul- phuretted hydrogen. The precipitated sulphurets of mercury and cadmium, after being well Avashed on the filter, are de- composed by digestion with aqua regia, the solution is filtered off from the sulphur, nearly neutralized Avith potassa, and the mercury estimated as subchloride by formiate of soda, aa 342 QUANTITATIVE ANALYSIS. directed p. 316. The cadmium in the solution, filtered from the subchloride of mercury, is precipitated by carbonate of soda. The sulphuret of copper, which remains dissolved in the cyanide of potassium, is mixed with nitric acid and eA'apo- rated Avith the addition of sulphuric acid, until the Avhole of the hydrocyanic acid is expelled, the sulphate of copper re- tained in solution is finally precipitated at a boiling tempera- ture by caustic potassa. GROUP 6. Antimony, Arsenic, Tin, Platinum, Iridium, Gold, Selenium, Tellurium, Tungsten, Vanadium, 3Iolybdenum. Antimony. This metal is quantitatively estimated as sulphuret, as an- timonious acid, and as pure metal. Precipitation as Sulphuret.—The solution is diluted with water, and tartaric acid added only until the resolution of any basic salt which the addition of AA'ater may have precipitated. A stream of washed sulphuretted hydrogen gas is then con- ducted through the solution until it smells strongly of it, it is allowed to remain at rest for some time in a moderately warm situation till the excess of sulphuretted hydrogen has been expelled. If the solution under examination contain antimony in the state of oxide only, the precipitated sulphuret may be then collected on a Aveighed filter, Avashed thoroughly with distilled water, dried at 212°, and weighed. Its composi- tion is One equivalent of Sb ... 129.03 . . . 72.88 Three do. of S ... 48 ... 27.12 One do. ofSbS3... 177.03 100 But if any of the higher oxides of antimony are also pre- sent, which will always be the case when the compound under examination is dissolved in aqua regia, correct results cannot be obtained by simply weighing the precipitated sulphuret, its composition being A'ariable. In this case the sulphuret must be decomposed by nitric acid, and the amount of sulphur pre- sent determined by converting it into sulphuric acid in the QUANTITATIVE ANALYSIS. 343 following manner:—The sulphuret is collected on a filter, dried at 212°, and its weight, filter included, accurately determined; a portion is then removed for analysis, the weight of this por- tion is noted; it is digested in a flask Avith fuming nitric acid, carefully added at first, the action generally being very ener- getic; hydrochloric acid is then added, and heat applied and continued for some time if a clear solution be obtained; it is diluted with water, tartaric acid being added to redissolve any basic salt which may be thereby precipitated. The sulphuric acid formed by the oxidation of the sulphur is precipitated in the form of sulphate of baryta by chloride of barium: it is received on a filter, well washed with boiling distilled water, ignited, and weighed: from the weight obtained the amount of sulphur is calculated, which, being deducted from the weight of the sulphuret of antimony operated on, gives the quantity of metal; should it happen that a portion of the sul- phur escaped oxidation by the nitric acid, the solution will not be clear; in this case, the solution, having been diluted with water with the requisite addition of tartaric acid, is passed through a weighed filter, and the weight of the sepa- rated sulphur, after being Avell Avashed and dried on the filter at 212°, is added to that calculated from the sulphate of baryta. It may be observed, that it is easy to see Avhether sulphuret of antimony precipitated from the original solution by sulphuretted hydrogen is the sulphuret corresponding to Sb03: a small weighed portion of it is boiled in a test tube with hydrochloric acid; if a clear solution is obtained, the sul- phuret is SbS3, and the remainder may at once be weighed and calculated; but if it does not completely dissolve, it con- tains a mixture of one or more of the higher sulphurets, and the residue must be treated as above directed. Two other methods have been proposed for treating the mixed sulphu- rets: one is to decompose them at a gentle heat in a current of dry hydrogen gas, by Avhich operation the sulphur is re- moved partly as sulphur and partly as sulphuretted hydrogen, metallic antimony being left behind; the other is to heat the mixture in a small retort out of contact of air, by which all the higher sulphurets are converted into the loAvest; neither of these methods, however, gives such correct results as the first. When the reduction process is adopted, it is impossible to regulate the heat so as to prevent the volatilization of a small portion of the antimony, and, in the process of heating 344 QUANTITATIVE ANALYSIS. the sulphurets out of contact of air, a portion of SbS3 is vola- tilized, and another portion is reduced to oxide, which is sub- limed together with the sulphur. Quantitative estimation as Antimonious Acid.—The com- pound under examination is evaporated Avith nitric acid, and the residue ignited as long as it continues to lose weight. Its composition is One equivalent of Sb ... 129.03 . . . 80.12 Four do. ofO ... 32 ... 19.88 One do. of Sb04 .. 161.03 100 Separation of Antimony from 3Ianganese, Iron, Zinc, Co- balt, Cadmium, Lead, Bismuth, Copper, Silver, and Mer- cury.—This may be effected by hydrosulphuret of ammonia, in which the sulphuret of antimony alone is soluble. The concentrated solution of the oxides is first saturated with am- monia, and, disregarding the bulky precipitate Avhich is thereby produced, hydrosulphuret of ammonia, containing excess of sulphur, is added, and the whole digested at a gentle heat: water is then added, and it is alloAved to cool, the vessel being closed. When quite cold, it is filtered; the whole of the anti- mony is contained in the filtrate, from which it may be pre- cipitated by hydrochloric acid. If the compound to be ana- lyzed be a solid, it may frequently, according to Fresenius, be analyzed by fusing it with sulphuret of potassium, and treating the fused mass with water, Avhen sulphuret of anti- mony alone will be dissolved. It is necessary, however, to observe, that sulphuret of mercury is not altogether insoluble in sulphuret of potassium, neither is sulphuret of copper alto- gether insoluble in hydrosulphuret of ammonia. Arsenic. This metal, whether in the form of arsenious acid or in that of arsenic add, may be quantitatively estimated by com- bining it with protoxide of lead; when in the form of arsenious acid, it is generally most conveniently weighed as sulphuret. Quantitative estimation by Protoxide of Lead.—To insure the metal being in the state of arsenic acid, the compound under examination (which must contain no other acid) is digested with aqua regia, and carefully evaporated to dry- ness; the residue, after being somewhat more strongly heated QUANTITATIVE ANALYSIS. 345 in a platinum crucible, is dissohved in Avater, and a known weight of recently ignited and pure protoxide of lead added; the mix- ture is carefully evaporated to dryness, and gently ignited: the amount of arsenic acid present is learned from the in- crease in weight, and from this the quantity of arsenic is cal- culated. Estimation as Sulphuret.—For this purpose the arsenic must be in the form of arsenious acid, to insure which the so- lution of the compound should be mixed with a concentrated aqueous solution of sulphurous acid, and gradually heated to gentle ebullition in a flask; the heat must be maintained till the Avhole of the excess of sulphurous acid is expelled; hydro- chloric acid is noAv added, and a stream of washed sulphuretted hydrogen is conducted through the liquid, till it smells strongly of it. It must not be immediately filtered, because the sul- phuretted hydrogen liquor may hold in solution a portion of sulphuret of arsenic. It is set aside in a warm place, until the excess of sulphuretted hydrogen gas is expelled. Frese- nius recommends that this be done by transmitting through the solution a stream of washed carbonic acid gas. The liquid, being freed from sulphuretted hydrogen, is passed through a weighed filter, washed with hot distilled water, dried at 212°, and weighed. Its composition is One equivalent of As ... 75 ... 60.97 Three ditto of S ... 48 ... 39.03 One ditto of As,S3 . .. 123 ... 100 Should the process of treating the solution with sulphurous acid not have been adopted, and if there is reason for sup- posing that a portion of the arsenic may have been in a higher state of oxidation than that of arsenious acid, and if, more- over, there should be present certain other substances capable of decomposing sulphuretted hydrogen, such as chromic acid, peroxide of iron, &c, then the sulphuret of arsenic cannot be Aveighed for the purpose of estimating the metal, until after the excess of sulphur has been removed: this is done precisely in the same manner as has been directed in the case of sulphuret of antimony, with excess of sulphur, viz., by converting the free sulphur into sulphuric acid, and deter- mining its amount in the form of sulphate of baryta. Levol's Method of Estimating Arsenic in the Copper and 346 QUANTITATIVE ANALYSIS. Tin of Commerce, and in Bronzes.—The arsenic is thrown down, in company Avith peroxide of tin, by nitric acid, and the arseniferous oxide of tin thus produced is reduced by hy- drogen gas. The author found the reduction to take place readily at a dark red heat, the greater part of the arsenic being separated by sublimation, the small quantity still re- maining with the tin is received by hydrochloric acid. The arseniuretted hydrogen yields on decomposition the whole of the arsenic retained by the tin. The best state for employing the tin for the purpose of collecting the arsenic, appeared to be that of a solution in cold weak nitric acid; the protoxide which is thus formed, remaining dissolved, readily comes into contact Avith the molecules of the arsenic; and, Avhen the temperature is raised to convert it into peroxide, it seizes on the arsenic and carries it down Avith it. Arsenic and anti- mony oxidized with nitric acid likewise enter into combination, but the product is not entirely insoluble. M. Levol has also published a method for the quantitative separation'of the arsenic and arsenious acids; it is founded on the insolubility of the bi-basic arseniate of ammonia and magnesia (2NH3,2 MgO,AsOs + lOAq.), a salt corresponding to the double ammonio-phosphate of magnesia, and which he obtained in the same Avay as the latter, viz., by adding a soluble ammonio- magnesian salt to the liquid containing arsenic acid, having previously rendered it ammoniacal; it is deposited in the form of very minute crystals on the sides of the vessel; its solu- bility is such that one part of arsenic acid, diluted Avith 56818 parts of Avater rendered ammoniacal, is made apparent shortly after the addition of a feAV drops of the concentrated solution of ammonio-sulphate of magnesia. Arsenious acid does not yield an insoluble double salt with ammonia and magnesia. The precipitate, on being dried and ignited, becomes 2MgO, As05 = 55.74 per cent, of the neAV salt which represents 41.02 per cent, of arsenic acid. M. Levol suggests the use of ammonio-magnesian salts in cases of poisoning by arsenic acid. The separation of arsenious from arsenic acid may, also, according to Fresenius, be effected satisfactorily in the folloAving indirect manner:—The solution containing the tAvo acids is divided into two equal portions; in one, the arsenic acid is reduced to arsenious acid by sulphurous acid, and the Avhole then precipitated by sulphuretted hydrogen: the pre- cipitated sulphuret of arsenic is washed, dried at 212°, and QUANTITATIVE ANALYSIS. 347 weighed. The arsenious acid in the other half of the solution is converted into arsenic acid by chlorine, for Avhich purpose it is mixed with hydrochloric acid and solution of indigo, added till the fluid acquires a blue color. Chloride of lime, containing a knoAvn amount of chlorine, is then added from a Aveighed solution, until the blue color disappears: from the quantity consumed, the amount of chlorine used is calculated. This operation depends on the circumstance that every equiva- lent of arsenious acid requires tAvo equivalents of chlorine to convert it, in the presence of water, into arsenic acid, thus— As03 + 2C1 + 2HO = As05 + 2HC1. By calculating the resulting quantity of arsenious acid upon sulphuret of arsenic, and subtracting the weight of this from the total weight obtained from the first portion, of the analyzed solution, the amount of arsenic, originally contained in the latter, is found. Separation of Arsenic from the metals of the 5th Group. —This may be effected by hydrosulphuret of ammonia, hav- ing first precipitated the solution by sulphuretted hydrogen, the sulphuret of the metals of the 5th Group being insoluble in hydrosulphuret of ammonia. The dissolved sulphuret of arsenic is precipitated from its alkaline solution'by acetic acid; but it must be remembered, that in this case it contains free sulphur, which must be removed and estimated in the manner already described. The separation of arsenic from the members of the 5th Group may likewise be effected by fusing the mixture with twice its weight of carbonate of soda, and twice and a half its weight of nitre; the arsenic is hereby converted into arsenic acid, which combines with the alkali, and may thus be dissolved out from the remaining metallic oxides; from lead, arsenic acid is separated by dissolving the compound in nitric acid and precipitating the lead by sul- phuric acid, with the addition of alcohol. Separation of Arsenic from Antimony.—When the com- pound of the two metals is in the reguline state, the arsenic may be expelled by heating out of contact of air; Avhen, hoAveArer, other metals are also present, this process cannot be adopted, since most other metals retain a part of the arsenic Avhen at a red heat. In this case several methods have been proposed:— 1. The substance is dissolved in aqua regia, tartaric acid is added, and the antimony and arsenic are together precipi- 348 QUANTITATIVE ANALYSIS. tated by sulphuretted hydrogen; the sulphurets are intimately stirred together, collected on a filter, dried at a very gentle heat, and weighed. From a weighed portion the amount of sulphur is determined by dissolving it in aqua regia, and hav- ing added tartaric acid and diluted Avith Avater, precipitating the sulphuric acid formed by chloride of barium. Another weighed portion of the mixed sulphurets is heated in a tube, through which a stream of hydrogen gas is passing: the ex- cess of sulphur and the sulphuret of arsenic are expelled, leaving the sulphuret of antimony, which may then be weighed. This method, when carefully performed, is capable, according to Rose, of affording a result only about a half per cent, from truth: the proportion of arsenic present is calculated from the loss, the united weight of both metals having by the first experiment been determined in the state of sulphuret. 2. Behren's Method.—The arsenic and antimony are com- bined into sulphurets, and to the mixture is added, while still moist, an equal volume of neutral nitrate of lead, and about as much water. The mass is boiled in a porcelain dish, being stirred without interruption, and the water which eA'aporates being renewed until the whole has acquired a dark brown color, it is then filtered. The residue contains the entire amount of antimony, and a portion of the arsenic. The so- lution contains the arsenic in the state of arsenious acid, nitric acid, and oxide of lead; it is heated with carbonate of am- monia as long as a precipitate is formed. To the liquid filtered from the carbonate of lead some hydrochloric acid is added, until it has an acid reaction; sulphuretted hydrogen gas is then transmitted through the solution, and the sulphuret of arsenic thus obtained has no trace of antimony. To se- parate the arsenic contained in the state of sulpho-arseniuret of lead, in the mass which remained on the first filtration, M. Behren digests it at a gentle heat with caustic ammonia, which converts the sulpho-arseniuret of lead into sulphuret of lead and sulphuret of arsenic, which latter dissolves in am- monia. To the filtered solution hydrochloric acid is added, and the sulphuret of arsenic precipitated is added to that first obtained. Fresenius objects to the precipitation of the lead in the solution containing the arsenic by carbonate of ammonia; he prefers separating the tAvo metals by hydrosulphuret of am- QUANTITATIVE ANALYSIS. 349 monia, or by evaporating the solution to dryness, and fusing the residue with carbonate of soda and nitre. 3. Antimony and arsenic in alloys may, according to Fre- senius, be separated, though not in a very accurate manner, by heating the mixture coArered Avith common salt and car- bonate of soda, in a glass tube, through which a current of dry carbonic acid gas is passing; the tube is heated gently at first, but the heat is gradually increased to the highest degree of intensity; by this means the arsenic is driven off, while the volatilization of the antimony is prevented by the common salt and carbonate of soda. 4. The method proposed by Fresenius, to distinguish be- tween the metallic mirrors formed by antimony and arsenic, under similar circumstances, and which has already been de- scribed,* may be employed in the quantitative estimation of these tAvo metals; when carefully performed, it yields results which are tolerably accurate. Rose has recentlyf described a method of separating the acids of arsenic and antimony, as likewise that of the perox- ide of tin from bases by the use of chloride of ammonium. Great inconvenience, he observes, are attached to the method generally employed for analyzing these compounds, particu- larly such as are sparingly soluble in water and in hydro- chloric acid: all these difficulties may, however, in many cases, be avoided, by adopting the following process:—Sup- pose Ave have a salt of one of these metallic acids, with an alkaline base to examine; after having ignited and weighed it, it is to be mixed in a finely pulverized state with from five to eight times the quantity of finely powdered chloride of ammonium, and heated in a small porcelain crucible, which may be covered with a concave platinum lid, over an argand lamp, until the whole of the chloride of ammonium is volatil- ized. The alkali is left behind in the state of chloride, the quantity of Avhich may be with great accuracy determined. So long as chloride of ammonium continues to be volatilized, the temperature is so low that none of the alkaline chloride can escape. As soon as the ammoniacal salt is driven off, the temperature is moderated, so that the residue in the por- celain crucible does not fuse. After weighing, it is mixed * See Part I., p. 101. f Chem. Gaz, April 15th, 1848. 350 QUANTITATIVE ANALYSIS. with a fresh quantity of chloride of ammonium, and again heated, in order to see whether the weight of the residue re- mains constant or is diminished; in Avhich latter case, the treatment Avith chloride of ammonium must be repeated. Sometimes, owing to the access of air, the platinum lid is covered with a film of the metallic acid, especially with per- oxide of tin Avhen stannates are examined. In this case, the lid, in the subsequent ignition, is covered Avith a little of the ammoniacal salt. The use of chloride of ammonium in ana- lytical chemistry is not, Rose observes, restricted to the com- pounds here mentioned, but is capable of considerable exten- sion, as he purposes hereafter to point out. 5. Meyer's method of separating arsenic from antimony is founded on the insolubility of antimoniate of soda and the conArersion of arseniferous antimony into arseniate and anti- moniate of soda. Chem. Gaz., 6, 375. Tin. This metal is weighed as peroxide: it has also been attempt- ed to estimate it by a normal solution of iodine. Quantitative estimation as Peroxide.—The compound un- der examination is evaporated nearly to dryness, at a boiling heat, with strong nitric acid to insure the whole of the metal being in the state of peroxide; if any hydrochloric acid be present, it must be completely decomposed and expelled. The peroxide of tin, Avhich by the action of the nitric acid has become converted into the insoluble modification, is fil- tered, washed, ignited, and weighed. Its composition is One equivalent of Sn ... 58.82 . . . 78.61 Tavo do. of 0 ... 16 ... 21.39 One do. of Sn02 . . 74.82 100 Tin may also be precipitated from its acid solution, whether in the state of a proto-salt or of a persalt, by sulphuretted hydrogen; in the former case the resulting sulphuret is brown, in the latter case it is yellow; the gas must be passed through the solution till it smells strongly of it, and a gentle heat must afterwards be applied, by which a small quantity of sulphuret, which is dissolved in the saturated liquor, becomes again deposited; the sulphuret of tin must not be Aveighed as such, but converted into peroxide, which may be done by heat- QUANTITATIVE ANALYSIS. 351 ing it, first gently and then intensely, in a porcelain crucible, till all the sulphur is remoAred in the form of sulphurous acid, the expulsion of which is facilitated by adding a small frag- ment of carbonate of ammonia. Rose recommends to con- vert the sulphuret of tin into peroxide by nitric acid, observ- ing that, Avhen the quantity of sulphuret is at all considerable, its conversion into peroxide takes place by heat alone with extreme sloAvness. Quantitative estimation of Tin by Volume.—This method was proposed by M. Gaultier de Claubry.* As a normal solution, he employs 1 grm. (about 15 grs.) of iodine dissolved in a decilitre (about 6 cubic inches) of alcohol, sp. gr. 0.932, and the solution of tin is prepared with one gramme of this metal dissolved in hydrochloric acid, and diluted with water freed from air, so as to form a litre (61 cubic inches). By means of a graduated pipette, a demi-decilitre (about 3 cubic inches) of the tin solution is measured off, and the burette, divid- ed into tenths of a cubic centimetre, is filled Avith the normal solution; the latter is poured into the first until it is no longer decolorized; half a decilitre of the tin solution, containing 5 decigrammes (about 7.5 grs.) of tin, decolorizes 100°, or 10 cubic centimetres of the normal solution. If the tin ore under examination is soluble in hydrochloric acid, the operation is perfectly simple; if it does not dissolve in it, it is acted on with aqua regia, containing much hydrochloric acid; and, when the tin is become converted into perchloride, an excess of hydrochloric acid is added, and it is then boiled Avith some iron, by which it becomes reduced to protochloride; the pro- cess is now conducted in the same manner as in the preceding case. If it happens to be an alloy containing only 20 per cent, of lead, hydrochloric acid will dissolve it; beyond that, however, only imperfectly; but, as aqua regia scarcely acts on the compounds of lead, the alloy must be dissolved in nitric acid, evaporated to expel the excess of acid, and then treated with hydrochloric acid and iron. Stannic acid, espe- cially when it has not been dissolved, is readily converted into protochloride in the presence of an excess of hydrochloric acid and protochloride of iron, so that the assay is brought to the same state as A\hen the product could be acted upon im- mediately with hydrochloric acid. When the compound to * Comptes Rendus, July 13, 1846; and Chem. Gaz., vol. iv. p. 455. 352 QUANTITATIVE ANALYSIS. be analyzed contains arsenic, antimony, bismuth, copper, or lead, the iron precipitates it, and again reduces the assay to the state of a tin solution. To precipitate the whole of the copper, and not to leave any of the protochloride of that me- tal in solution, a considerable excess of hydrochloric acid must be employed, and the boiling with iron continued for some length of time. The analysis of a salt of tin can be made with the same ease, and if a mixture of a per and proto- salt is examined, or any of the corresponding haloid com- pounds, the relative proportions can be determined by ana- lyzing the substance itself, and then making a second analysis of the product boiled Avith hydrochloric acid and iron. Zinc and iron do not interfere with the analysis by iodine, while the protosalts of iron and the corresponding haloid compounds decolorize the sulphate of indigo, Avhich M. Pelouze had at- tempted to employ for the estimation of tin, and renders this process impracticable. Iodine may, according to the author, be used to determine the quantity of tin in a solution containing various metals; but if there be present an arsenite, sulphite, or hyposulphite, phosphite, or hypophosphite, the normal solution will be de- colorized as with protochloride of tin. It will be -requisite, therefore, to oxidize these salts by nitric acid or by chlorine, and to reduce the tin to protochloride by means of iron. Separation of protoxide of tin from peroxide of tin.—Rose's method is the following:—The solution is divided into two portions; in one the amount of the metal is determined by precipitating it by sulphuretted hydrogen, and then convert- ing it into peroxide in the manner described above. The other portion is dropped into solution of chloride of mercury, and the subchloride of mercury precipitated is filtered, Avashed, dried at a gentle heat, and Aveighed. From this weight it is easy to calculate how much protoxide or protochloride of tin was contained in the solution, since the quantity of chlorine contained in the subchloride of mercury is the same as that contained in the protochloride of tin, by which it was precipi- tated; or, on the other hand, the quantity of chlorine in the subchloride of mercury is equivalent to the quantity of oxygen in the protoxide of tin, Avhich acted as a precipitant. Separation of Oxides of Tin from the Members of the Fifth Group.—This may be effected by supersaturating the con- centrated solution with ammonia, and then precipitating by QUANTITATIVE ANALYSIS. 353 hydrosulphuret of ammonia the sulphuret of tin retained in solution, while the sulphurets of the other metals remain un- dissolved. From most other metals tin may also be separated by nitric acid; the alloy is boiled with the acid, which oxidizes all the metals, and dissolves everything but tin, which remains in the form of insoluble peroxide. To separate tin from iron, Berthier employs sulphite of am- monia, which he adds to the hydrochloric solution; having previously diluted it with water, and neutralized with ammo- nia, the Avhole of the tin is precipitated, Avhilg the iron re- mains in the liquid. Analysis of Alloys of Tin and Copper.—The process of 31. Cottereau* is founded on the principle that copper is pre- cipitated from its solutions by zinc before tin. The alloy is reduced to a fine powder, a certain quantity weighed off and digested with boiling hydrochloric acid. Into the resulting solution of the protochlorides of copper and tin a plate of zinc is introduced. By a previous assay of the copper con- tained in the alloy by the cuprometric process of 31. Pelouze (p. 328), the quantity of copper is determined, and conse- quently an equivalent amount of zinc may be added to the solution ; or the plate of zinc may be immediately introduced into the solution, and left there until a bright iron blade does not acquire a red tint on being immersed in the liquor. The strip of zinc is then removed, and the precipitate collected on a filter. Whichever plan be adopted, the filtered liquor is % acted on just as if it were pure protochloride of tin. The protochloride of zinc formed does not in the least interfere with the reaction. Separation of Tin from Antimony.—This is attended with very great difficulties. The following methods have been pro- posed:— 1st. Berthier's Method.—The two metals being dissolved in concentrated hydrochloric acid, tartaric acid is added to the solution, which is then diluted Avith water, sulphite of am- monia added, and the whole boiled. The tin is precipitated while the antimony remains dissolved. 2d. Levol's Process.^—The alloy being reduced to a thin plate is heated with hydrochloric acid; after some minutes' * Comptes Rendus, June 29th, 1846; and Chem. Gaz., vol. iv. p. 348, | Ann. de Chim. et Phys., Jan. 1845 ; and Chem. Gaz., vol. iii. p. 52. 23 354 QUANTITATIVE ANALYSIS. boiling a saturated aqueous solution of chlorate of potassa is added in small quantities at a time, until the alloy entirely disappears. The two metals are then throAvn down together by means of a bar of distilled zinc ; the precipitate is removed from the zinc with the greatest care, a quantity of concen- trated hydrochloric acid, about equal to Avhat was employed at first, is added, and the Avhole is boiled so as to redissolve the tin Avithout previously removing the chloride of zinc; when the action has terminated, that is, when nothing remains but the antimony, which is ahvays the case after an hour's boiling, this rSetal then forms a very fine blackish powder: it is collected on a weighed filter, and the tin may now be immediately obtained from the liquors by sulphuretted hy- drogen. According to Br. L. Eisner* the above process has no claim to accuracy. He found, on repeating the experiment Avith a mixture of 7J grains of tin and as much antimony, exactly according to the directions giA'en by Levol, that the acid liquid filtered from the black powder, on being treated Avith sulphuretted hydrogen, yielded a precipitate which con- sisted evidently of tAvo differently colored layers ; the inferior layer Avas clearly the orange-red precipitate of sulphuret of antimony, above which was the chocolate-brown protosul- phuret of tin. It is certain, therefore, that some antimony had dissohred with the tin. Br. Eisner convinced himself that antimony is partly dissolved on being boiled Avith hydro- chloric acid, and that, consequently, no quantitative method of separating it from tin can be founded on its insolubility, in that acid. Rose's 3Ietliod.\—Strong nitric acid is cautiously poured upon the metals, and Avhen the violent oxidation has ceased the whole is evaporated at a gentle heat, and the dry powder of the oxides fused in a silver crucible over an argand lamp with an excess of hydrate of soda. The fused mass is soft- ened with a large quantity of water, gently warmed, and the antimoniate of soda allowed to subside. When perfectly cold, the clear solution is passed through a filter: if this is done while it is still warm, the solution will contain some antimo- niate of soda. The insoluble salt is again treated once or * Journ. fur Prakt. Chem., vol. xxxv. p. 313. f Chem. Gaz., vol. v. p. 313. QUANTITATIVE ANALYSIS. 355 twice with water, allowed to settle and cool, and the liquid, when perfectly clear, passed through the filter. When the whole of the stannate of soda has been dissolved in this man- ner, the liquid which has been warmed with the antimoniate of soda remains opalescent; it must not be poured on the filter, as it would pass through turbid. A small quantity of a dilute solution of carbonate of soda may be added to it, which renders it clear; but the edulcoration must not be con- tinued for any length of time, as otherwise some antimoniate would be dissohred. The moist antimoniate of soda is now treated in a beaker with a mixture of hydrochloric and tartaric acids, in which it readily dissolves; and the filter, upon Avhich mere traces of the salt should have collected, washed with the same mixture. The antimony is then precipitated from the solution by sul- phuretted hydrogen, and the amount of antimony estimated from the quantity of sulphuret obtained. Rose reduces the sulphuret of antimony by hydrogen in a porcelain crucible, through the lid of which a thin porcelain tube passes. A gentle heat is carefully applied, until the crucible no longer decreases in weight. After the reduction the inner side of the lid is coated Avith metallic antimony, which, however, in no way interferes with the accuracy of the experiment. The solution of stannate of soda is acidified with hydro- chloric acid. It is not necessary to add so much acid that the whole of the eliminated oxide of tin is again redissolved. It is merely necessary that the solution should strongly red- den blue litmus paper. Upon this, sulphuretted hydrogen is passed into it. The sulphuret of tin is converted by roasting into oxide. When it has been dried, it frequently decrepi- tates, which, by want of care, may occasion a very consider- able loss. It is, on this account, preferable to place it with the filter, while still moist, in a porcelain crucible, and to heat it for a long time very gently, and with access of air, in order to expel the sulphur at the lowest possible temperature. If a strong heat be given at the commencement, Avhite fumes of oxide escape, especially when the air has free access. The higher sulphuret of tin has the property of subliming some- what at certain temperatures; the vapors are oxidized by contact Avith the air, and form oxide of tin. This is also the cause of a white sediment of oxide of tin being formed upon the charcoal, Avhen sulphuret of tin is heated on charcoal 356 QUANTITATIVE ANALYSIS. before the blowpipe. A strong heat should not be applied until there is no longer any perceptible odor of sulphurous acid. After being strongly ignited, a piece of carbonate of ammonia is placed in the crucible, and, after its volatilization, a strong heat applied, with access of air, in order to expel the whole of the sulphuric acid formed; a small decrease of weight will be perceived. The oxide of tin thus obtained never appears perfectly white: and the sulphuret of tin, precipitated by sulphuretted hydrogen, does not possess a purely yellow color, which Rose attributes to melting the metallic oxides with hydrate of soda in the silver crucible, traces of oxide of silver being removed by the alkaline solution. The results do not attain the high- est degree of accuracy. Although stannate of soda contain- ing an excess of hydrate of soda does not become turbid by boiling, as stated by Fremy, and the solution may even be evaporated until crystals separate, which, on the addition of water, entirely dissolve, yet the antimoniate of soda contains a small quantity of oxide of tin. Consequently the sulphuret precipitated by sulphuretted hydrogen from the acid solution of the antimoniate of soda contains a small amount of sul- phuret of tin, which does not part with the whole of its sul- phur at the temperature at which the sulphuret of antimony is reduced by hydrogen. For this reason a somewhat smaller amount of tin, a larger quantity of antimony, and a slight excess, is found in the analysis. Separation of Tin from Arsenic.—The following process is given by Fresenius.* The solution is perfectly freed from nitric acid by evaporating it to dryness at a gentle heat, with the addition of hydrochloric acid. A weighed portion of the dry mass is digested with hydrochloric acid, and solution of chlorate of potassa added until it is completely dissolved. The solution is introduced into a flask, together with a strip of clean zinc; the flask is provided with a bent tube, through which the disengaged hydrogen is conveyed, first through a bottle half full of water, and then into a Liebig's potash ap- paratus filled with a solution of neutral nitrate of silver. As soon as the evolution of gas has ceased, the apparatus is taken asunder, the zinc is removed from the flask and carefully washed, the washings being added to the contents of the * Instruction in Quantitative Analysis, p. 341. See also Appendix. QUANTITATIVE ANALYSIS. 357 flask, the precipitate in which is allowed to subside, and the clear supernatant fluid cautiously decanted. The flask con- tains the Avhole of the tin, it may also contain a portion of the arsenic, but the greater part of the latter metal will have been volatilized in the form of arseniuretted hydrogen, and have become condensed in the solution of nitrate of silver in the state of arsenious acid. The precipitated metal in the flask is treated Avith hydrochloric acid; if it completely dissolves, it is free from arsenic, and may at once be precipi- tated as sulphuret of tin by sulphuretted hydrogen, but, if a black powder remains, it consists of metallic arsenic, and must be separated, Avashed, dried, and weighed, and the weight added to that of the arsenic found in the silver solution. This method is troublesome, but it appears to be the best known of separating these two metals. When antimony, tin, and arsenic have to be separated from one another, the process just described is adopted; the greater portion of the antimony and arsenic is transferred to the silver solution, and, if the metal precipitated by the zinc does not completely redissolve in hydrochloric acid, the in- soluble residue may contain both antimony and arsenic: it is separated by filtration from the tin solution, and after having been well washed, first Avith dilute hydrochloric acid and then Avith pure Avater, it is submitted to one of the processes al- ready described for the separation of antimony from arsenic. The tin in the filtrate is precipitated by sulphuretted hydro- gen. The contents of the potash apparatus are filtered, the insoluble antimoniuret of silver is collected upon a filter, Avashed, and the antimony determined by nitric acid. The weight found is added to that obtained from the insoluble black powder. The arsenic Avhich remains in the solution, filtered from the antimoniuret of silver, is separated from the silver by hydrochloric acid, and finally precipitated, with the proper precautions, by sulphuretted hydrogen. The following equations, given by Fresenius, illustrate the nature of the decompositions and transpositions in this process : 6(AgO,N05) + AsII3= 6 Ag+AsOs+3HO + 6NOs 3(AgO,N05)-r-SbH3=Ag3Sb + 3HO-f3N05 Six equivalents of nitrate of silver and one of terhydride of 358 QUANTITATIVE ANALYSIS. arsenic react in such a manner as to produce six equivalents of silver, one of arsenious acid, three of Avater, and six of nitric acid; again, three equivalents of nitrate of sih^er and one of terhydride of antimony, giAre rise to one equivalent of antimoniuret of silver, three of Avater, and three of nitric acid. Platinum. In whatever form this metal may be precipitated, it is in- variably weighed in the reguline state. It may be precipi- tated from its solution as ammonio-chloride of platinum, as potassio-chloride of platinum, and as sulphuret of platinum. 1. Precipitation as Ammonio-Chloride of Platinum.—The acid solution is concentrated; it is then mixed with a con- centrated solution of muriate of ammonia, and a sufficient quantity of spirits of wine added to effect the complete pre- cipitation of the double salt: the precipitate is allowed to subside perfectly,* it is then collected on a filter and washed with spirits of Avine till the fluid passes through quite colour- less, dried, and ignited, by which it is completely decomposed, metallic platinum in the form of a gray spongy powder, re- maining in the crucible. The ignition requires to be per- formed with great care; the dried double salt is transferred, filter and all, into a weighed platinum crucible, and is heated gently, the cover of the crucible being laid loosely on, as long as fumes of sal-ammoniac are seen to escape; the cover is then removed, and a stronger heat applied till the organic matter of the filter is consumed; the crucible is finally ex- posed to an intense heat. The reason Avhy a gentle heat must be applied at first is, because a portion of the unde- composed double salt might otherwise be carried off with the fumes of the sal-ammoniac. Precipitation as Potassio-Chloride of Platinum.—The so- lution is mixed with chloride of potassium in excess, and alco- hol added; the precipitated double salt is collected on a filter, dried at 212°, and Aveighed. It would not be safe, however, to estimate the platinum from the weight of the double salt, and, indeed, after ignition, it is not completely decomposed * If the solution is very acid, it should be nearly neutralized with ammonia previous to the addition of the sal-ammoniac; and, to ensure entire deposition of the precipitate, a repose of twenty-four hours is recpaired before filtering. QUANTITATIVE ANALYSIS. 359 into metallic platinum and chloride of potassium; where accuracy is required, therefore, a knoAvn portion of the dou- ble salt dried at 212° must be introduced into a weighed bulbed tube, and heated to redness, while a stream of dry hydrogen gas passes through it. It thus becomes completely reduced, hydrochloric gas being evolved; Avhen this has ceased, which is known by white fumes ceasing to be formed on bringing a glass rod or a feather dipped in ammonia Avater near the end of the tube, the apparatus is allowed to cool, the chloride of potassium is then dissolved out with water, and the reduced platinum well Avashed. It is then again heated to low red- ness in a stream of hydrogen gas, and weighed; the weight obtained calculated upon the Avhole precipitate on the filter gives the result. Precipitation as Sulphuret.—This is sometimes practiced to separate platinum from such metals as are not precipitated from their acid solutions by sulphuretted hydrogen, as well as from others whose sulphurets are insoluble in alkaline sul- phurets ; in the former case, the gas is passed into the acid solution. No precipitation frequently takes place till heat is applied, when the solution turns broAvn, and sulphuret of platinum is precipitated; it is not weighed as such, but after being washed is ignited, by Avhich it becomes reduced, and is then estimated in its metallic state: in the latter case, the solution is rendered either neutral or alkaline, and hydro- sulphuret of ammonia added in excess, in Avhich the sulphu- ret of platinum dissolves. Separation of Platinum from Antimony, Arsenic, and Tin.—This is readily effected by taking advantage of the volatility of the chlorides of the three last metals; all four are first precipitated together by sulphuretted hydrogen ; the mixed sulphurets are introduced into a bulbed tube, and heated in a stream of chlorine gas. Platinum alone remains. Separation of Platinum from the metals which accompany it in its Ores, namely, Iridium, Osmium, Rhodium, and Palladium.—Berzelius directs to proceed as folloAVS :*—The mineral is introduced into a tubulated retort connected with a receiver, and gently heated with hydrochloric acid, to which a little nitric acid has been added; as the action slackens, fresh portions of nitric acid are added. When the acid is * Traite de Chimie, vol. ii. p. 429, et seq. 360 QUANTITATIVE ANALYSIS. saturated, the liquor is eAraporated to the consistence of syrup. It is then alloAved to cool, diluted Avith a little water, and de- canted from the undissolved residue. The product of the distillation contained in the receiArer has generally a yellow colour, in consequence of the spirting OA*er of a portion of the contents of the retort. Spangles of osmium-iridium are also sometimes found there. The distillate is returned to the .retort, and the greater portion redistilled. If the mineral is not noAV decomposed, a fresh quantity of aqua regia must be added. It frequently happens that a residue still remains, which, on examination, is found to consist of grains of osmi- um and iridium, Avhich had escaped detection before submit- ting the ore to the action of the acid, or of brilliant plates of the same alloy, or of iridium itself in a black and pulve- rulent state; fragments of hyacinth, quartz, chrome iron, titanium, iron, &c. &c, are also frequently formed in the in- soluble residue. The acid from the second distillation should be colorless. Should it not be so, it must be a third time distilled. This distillate contains osmic acid, the method of separating Avhich has been already described. The solution in the retort has usually a deep red color; if it disengages an odor of chlorine, it is a proof of the presence of bichloride of palladium, Avhich must be decomposed into chloride by boiling. Into the clear liquor, a saturated solution of chloride of potassium is poured, as long as a precipitation takes place. This precipitate, the color of Avhich varies from a clear yelloAV to a cinnabar red, consists of the double chloride of platinum and potassium, mixed with a greater or less quantity of the double chloride of iridium and potassium, to which it owes its red color. It is receiA7ed on a filter and Avashed Avith a dilute solution of chloride of potassium until the Avash liquor ceases to strike blue with ferrocyanide of potassium. The filtrate contains rhodium, palladium, a little platinum and iridium, iron and copper. The double salt on the filter is dried, inti- mately mixed with double its weight of carbonate of potassa, and heated gradually till the mass begins to fuse in a plati- num crucible. The carbonate of potassa decomposes the double platinum salt, chloride of potassium is formed, the platinum is reduced to the metallic state, while the iridium remains in the state of suboxide. The mass is washed first with water, then with Avarm hydrochloric acid ; the residue is finally digested, first with dilute, and then with concentrated QUANTITATIVE ANALYSIS. 361 aqua regia, in Avhich the suboxide of iridium is insoluble. The solution contains the Avhole of the platinum, still, how- ever, mixed Avith a certain quantity of iridium. It is, there- fore, again precipitated Avith chloride of potassium, and the precipitate decomposed as before by ignition Avith carbonate of potassa ; should the solution in aqua regia still have a red tinge, it must undergo a third treatment. The solution of platinum, Avhen pure, has a pure golden yelloAV color. It is necessary to bear in mind, however, that there exists a chlo- ride of platinum the aqueous solution of Avhich has a dark broAvn color, though this is only formed by evaporating and gently heating the bichloride, during which chlorine is dis- engaged. It cannot, therefore, be formed by dissolving the chloride of platinum directly. Into the solution of pure chloride of platinum, solution of chloride of ammonia is poured; a clear yellow precipitate is formed, consisting of double chloride of platinum and ammonium; this precipitate furnishes, by gentle ignition, pure metallic platinum. For details of the processes for conArerting the metal as thus ob- tained, in what is termed its spongy form, into a malleable state, works on general chemistry must be consulted. Gold. This metal, like the preceding, is always weighed in the metallic state, in Avhich it is precipitated from its solutions by protosulphate of iron or by oxalic acid. A method of es- timating the metal indirectly by means of standard solutions has also been published by 0. Henry. Gold may also be precipitated from its acid solution by sulphuretted hydrogen. The sulphuret is readily reduced by heat alone. Precipitation by Protosulphate of Iron.—If the solution contains nitric acid, it must be evaporated nearly to dryness, with the addition of successive portions of hydrochloric acid, the residue is dissolved in Avater, acidulated with hydrochloric acid, and mixed Avith an excess of a clear solution of proto- sulphate of iron. It is set aside for some time in a Avarm place till the reduced gold has completely subsided in the form of a fine broAvn poAArder, which is then filtered, gently ignited, and weighed. The object in expelling the nitric acid is to prevent the formation of aqua regia, which might redis- sohTe a portion of the precipitated gold. Solution of proto- nitrate of mercury may be employed in the place of proto- 362 QUANTITATIVE ANALYSIS. sulphate of iron; the latter, howeA^er, is preferable as the reducing agent. Reduction by Oxalic Acid.—In certain cases it is not con- venient to introduce another metal into the solution from which gold is to be precipitated, oxalic acid is then employed as the reducing agent. The solution, as before, is freed from nitric acid, and oxalate of ammonia added; if the solution does not already contain free hydrochloric acid, a quantity is next added, and the mixture set aside in a warm place ; the whole of the gold is deposited in the form of yelloAV scales, which are collected on a filter, Avashed, gently ignited, and weighed. In cases where gold is the only fixed substance present, its quantity may be estimated by simply evaporating the solution to dryness and igniting the residue, and, Avhen in combination Avith other substances Avhich are incapable of precipitating from acid solutions by sulphuretted hydrogen, gold may be separated by that reagent, and the resulting sulphuret decomposed by ignition in a platinum crucible. The rationale of the reduction of terchloride of gold by protosulphate of iron is this: AuC]3+6(FeO,S03)=2(Fe203,3S03) + Fe2Cl3-r-Au. One equivalent of terchloride of gold and six of protosulphate of iron giA^e rise to two equivalents of persulphate of iron, one of sesquichloride of iron and one of gold. The rationale of the reduction by oxalic acid is as follows: AuCl3+3(HO,C203)=Au+3HC1 + 6C02. One equivalent of terchloride of gold and three of oxalic acid give rise to one equivalent of gold, three of hydrochloric acid, and six of carbonic acid. M. Henry's method of estimating Gold by Standard Solu- tions.*—This process, which Avas devised by the author in consequence of the difficulty which he experienced in appre- ciating very minute quantities of gold, either by weighing or by cupellation, in certain investigations, in Avhich he Avas en- gaged relative to the neAV processes, of gilding and silvering, of Elkington and Ruolz, is founded on the principle, that in a mixture of terchloride of gold, a basic salt, and copper, a quantity of the latter metal, equivalent to that of the gold, separated either in powder or upon the objlct to be gilt, is dissolved. When the amount of gold upon a gilt object, or • Journ. de Pharm., Jan. 1847; and Chem. Gaz., May 15th, 1847. QUANTITATIVE ANALYSIS. 363 in a bath which has been, or is to be employed in gilding has to be ascertained, the folloAving plan may be adopted. The objects, weighed with care, are digested with hot pure nitric acid; as soon as the copper forming the basis is dissolved, the solution is diluted with distilled Avater, and the gold is soon seen to settle at the bottom of the vessel in small brilliant scales. These are collected, and, after washing, dissolved in aqua regia, the solution evaporated Avith great precaution nearly to dryness, so as to obtain a ruby red product, soluble in Avater; this is terchloride of gold with a little acid. This product is now dissolved in distilled Avater, and mixed with five or six times its weight of pure bicarbonate of potash or soda, dissolved in distilled water; the mixture is heated, con- veyed into a ground-stoppered flask, and a somewhat large amount of finely divided copper, which has been previously heated in a current of hydrogen, added to it; the mixture is noAV and then shaken, and after about an hour the liquid assayed. A very minute quantity of the liquid is poured upon a watch glass and treated with protosulphate of iron; if the liquid does not yield a black or gray precipitate, it is a sign that it contains no gold in solution; should the contrary occur, more copper must be added and again agitated. When the whole of the gold has been precipitated upon the copper, the liquid is carefully saturated Avith pure sulphuric acid so as to be slightly acid. By this means all the copper preci- pitated in the state of carbonate is dissolved without the gold or metallic copper being at all acted upon. It is filtered, and a solution of pure ferrocyanide of potassium of known strength carefully added by means of a graduated burette, until a pre- cipitate ceases to be formed; the number of divisions of the instrument employed to precipitate the copper is noted, and in this manner the quantity of the metal dissolved in the liquid is ascertained. When it is a solution which is to be, or has been, used for gilding, the author advises to precipitate the diluted acid so- lution by a current of sulphuretted hydrogen, to collect the precipitate and strongly calcine it after washing. The sul- phuret of gold being reduced to the metallic state, the calcined residue is redissolved in nitric acid, and the gold which has remained unattacked, dissolved in aqua regia, and treated as aboA^e described. The use of the ferrocyanide of potassium, to determine the 364 QUANTITATIVE ANALYSIS. amount of copper which represents the gold in a compound, is founded on the fact, that this reagent is still very sensitive when sulphuret of sodium has no longer any perceptible action. The conditions requisite for the success of the operation are: 1st, to take care that the copper employed is perfectly free from oxide; 2d, to be certain that, after contact with the copper, no'gold remains in solution ; 3d, to saturate the mix- ture exactly Avith pure sulphuric acid after the reaction; 4th, to mix as quickly as possible, at a gentle heat, the copper and the bicarbonate Avith the solutions of the terchloride of gold; 5th, to add to the test liquid, Avhich has been made shortly before use with precaution, and only by drops, Avhen but a slight chestnut or dark red precipitate is produced. M. Henry quotes a number of experiments, the results of which prove the exactness of the process, as Avell as the ease and quickness with which it may be performed. Separation of Gold from Platinum.—The alloy is boiled in aqua regia, and the gold reduced by oxalic acid; from the filtered solution the platinum may be throAvn doAvn in the metallic state by formic acid; or the platinum may first be precipitated from the concentrated hydrochloric solution (diluted with 60 per cent, its bulk of alcohol) by chloride of potassium, and the gold in the filtrate may then be reduced by protosulphate of iron. Separation of Gold from Antimony, Tin, and Arsenic.— This may be effected in the same manner as the separation of platinum from these metals, viz., by heating the mixed sul- phurets in a stream of chlorine gas. The chlorides of tin, antimony, and arsenic distil over, while the gold remains behind. Br. Eisner employs metallic zinc as the precipitant for gold, which he finds to remove the metal from a solution of its chloride more effectually than protosulphate of iron. For the quantitative determination of gold, ho\veArer, in a mixture of platinum, gold, and tin, he prefers protosulphate of iron, on account of the greater simplicity of the operation. He first precipitates the platinum by a concentrated solution of chloride of ammonium, and afterwards the gold from the filtrate by a recently prepared solution of protosulphate of iron. He found that, when an excess of this reagent was employed, the filtrate from the precipitate still gave a beauti- ful dark red coloring with protochloride of tin, though no precipitate was observed. QUANTITATIVE ANALYSIS. 365 Analysis of Alloys of Gold.—Several methods are em- ployed. In the first place, an approximation to the relative proportions of the constituents is obtained by the touch-stone and the assay-needle: the former is a black and polished ba- salt; black flint and pottery will serve the same purpose. The assay-needles are small fillets of gold, alloyed with dif- ferent and known quantities of silver or copper: the sets may consist of pure gold; pure gold, 23 J carats, with half a carat of silver;* 23 carats of gold, with one carat of silver; 22 J carats of gold, with 1^ carat of silver, and so on till the silver amounts to four carats, after which the additions may proceed by whole carats. Other needles may be made in the same manner, with copper instead of silver, and other sets may have the addition, consisting either of equal parts of silver and copper, or such proportions as the occasions of business re- quire. When a specimen of gold is about to be examined, it is rubbed on the touch-stone, and the color which it leaves is compared with that communicated to the stone by the assay- needles taken successively; that which leaves a mark most nearly resembling that produced by the specimen is in com- position most nearly allied to it, and, as the composition of the needle is known, so the operator is enabled to judge of the quantity of silver necessary to be added for the quartation proof. The alloy is next cut into small thin plates, and fused in the cupel (see Silver), with 3J times as much pure silver as it contains gold, and with three or four times its weight of lead. After the operation, the gold and the silver remain, the oxide of copper being absorbed with the oxide of lead by the cupel. This process is termed quartation, because the gold forms one-fourth part of the cupelled alloy, a proportion which admits of the complete subsequent extraction of the silver by the action of nitric acid. The alloy of gold and silver is next reduced to thin plates, weighed, and gently heated with nitric acid, diluted, and quite free from nitrous and hydrochloric acids; the silver dissolves, the gold remain- ing untouched. The acid being saturated, a stronger acid is * In estimating or expressing the fineness of gold, the whole mass spoken of is supposed to weigh twenty-four carats of twelve grains each, either real or merely proportional like the assayer's weights; and the pure gold is called fine. Thus, if gold is said to be twenty-three carats fine, it is to be understood that, in a heap weighing twenty-four carats, the quantity of pure gold amounts to twenty- three carats.—Dr. lire's Chemical Dictionary. 366 QUANTITATIVE ANALYSIS. added, and the solution is gradually brought to boil, by which the perfect separation of the silver is accomplished, the gold retaining still the form of the original plate. It is, therefore, easily weighed; previous to which, however, it must be washed Avith distilled Avater, as long as any traces of silver appear, by the test of common salt, and then heated to redness. The loss which the mass experiences by the process of cupellation indicates the quantity of copper contained in the alloy, and the proportion of silver is afterwards found by the action of the nitric acid. It must particularly be borne in mind, that if the nitric acid be not free from nitrous acid, and especially from hydrochloric acid, a portion of the gold, sufficient to affect seriously the result of the assay, may be dissolved. Purification of Gold by Cementation.—The alloy is reduced to a thin plate, and surrounded in a crucible with a pulverulent mixture of four parts of brick-dust, one of calcined vitriol, and one of common salt. It is then exposed for 16 or 18 hours to a strong red heat. The vapors of hydrochloric and sul- phuric acids which are formed attack the metals mixed with the gold, and the mass is prevented from fusing by the brick- dust. If the first cementation has not been found sufficient to purify the gold, the operation is repeated, but, in the place of common salt, nitre is used. The same method is employed to refine the surface of gold articles after they are polished. The cementation here produces the same effect as tartar and salt, in which silver goods are boiled to give them a white color. Purification by Fusion with Sulphuret of Antimony.— Some borax is fused in a crucible, so that the walls become lined with the vitrified flux; a mixture of two parts of sul- phuret of antimony and one of the gold to be assayed is then introduced. The sulphur combines with the foreign metals, and the antimony unites Avith the gold; the alloy being re- moved, the scorise are a second time fused, with the addition of two parts more of sulphuret of antimony, and, when the whole of the gold is extracted, the various alloys are mixed together and heated in an open vessel, with tAvo parts of sul- phur. The sulphuret of antimony volatilizes, leaving the gold pure; to increase the action, a current of air from a pair of bellows may be directed on the surface of the melted mass, or, Avhat is perhaps still better, the mixture of the two metals QUANTITATIVE ANALYSIS. 367 may be fused in a large crucible, with three times its weight of nitre, by which the antimony becomes oxidized and dis- persed, the gold remaining untouched. Another method is to fuse the gold alloy with a mixture of oxide of lead and sulphur, and to add to the fused mass charcoal in the state of fine powder ; the gold is thus obtained alloyed with the lead only, from which it may be separated by cupellation. Selenium. When existing in solution in the form of selenious acid, it is reduced by sulphite of ammonia, which separates selenium in the form of a cinnabar red powder, Avhich, if boiled, be- comes black; it is collected on a filter, and dried at a very gentle heat: nitric acid, if present in the solution, must be decomposed and expelled by hydrochloric acid, previous to the addition of the sulphite of ammonia. When, however, selenium is contained in a solution, as selenic acid, it must first be reduced to selenious acid by boiling with hydrochloric acid, if it be intended to precipitate it by sulphite of ammonia. As, however, it is difficult entirely to convert selenic into selenious acid by hydrochloric acid, Rose recommends that the estimation of selenic acid be effected by precipitating it in the form of seleniate of baryta, by nitrate of baryta, which, when washed, dried, and ignited, has the following compo- sition : One equivalent of Se03 ... 63.57 . . . 45.34 One do. of BaO ... 76.64 ... 54.66 One do. ofBaO,Se03 140.21 100 As selenium is precipitated from its solution when in the form of selenious acid by sulphuretted hydrogen, it may thus be separated from all those substances which are not pre- cipitated by that reagent. Selenic acid does not, however, possess the property of being precipitated by sulphuretted hydrogen; when selenium, therefore, exists in this state, and has to be separated from other substances, it must either be precipitated as seleniate of baryta, or reduced to selenious acid. From the metals of the Fifth Group selenious acid may be separated by hydrosulphuret of ammonia, in which sul- phuret of selenium is soluble; and from the other metals of 368 QUANTITATIVE ANALYSIS. the Sixth Group it may be separated by converting it into selenic acid, which remains, as before observed, unaltered by sulphuretted hydrogen gas. Analysis of Seleniate of Lead.—It is reduced to a fine state of division, and diffused in water, through Avhich a cur- rent of sulphuretted hydrogen is passed; the liquor filtered from the sulphuret of lead is boiled, to expel the excess of sulphuretted hydrogen, and the selenic acid precipitated as seleniate of baryta ; in this way selenic acid may be separated from other metals which are capable of precipitation by sul- phuretted hydrogen. Tellurium. Like selenium, this metal is best precipitated from its solu- tion when in the state of oxide, by sulphite of ammonia ; the precipitation must be effected at a boiling temperature, and the solutions should contain free hydrochloric, but not nitric acid. From these oxides which are not precipitated by sul- phuretted hydrogen, it may be separated by that reagent. The sulphuret of tellurium is decomposed by digestion with aqua regia, and subsequently reduced by sulphite of ammonia. From the metals of the Fifth Group, tellurium is separated by hydrosulphuret of ammonia. From gold and platinum it may be separated by ignition in a glass tube through which a stream of chlorine is passing. Chloride of tellurium is vola- tilized, and may be received into a vessel containing very dilute hydrochloric acid, in which it dissolves, and out of which it may be precipitated by sulphite of ammonia. From arsenic, tellurium may, according to Berzelius, be separated by distillation, reguline tellurium remaining behind. Tungsten. The method proposed by Berzelius for quantitatively esti- mating tungstic acid, was to precipitate it from its neutral or alkaline solution in the form of sulphuret of tungsten by hy- drosulphuret of ammonia, and then to add excess of the re- agent, by which the sulphuret is dissolved; from this solution it is reprecipitated by nitric acid, and, having been washed and dried, it is roasted by a gentle heat, whereby it becomes converted into tungstic acid, in which state it is weighed. The composition of tungstic acid is QUANTITATIVE ANALYSIS. 369 One equivalent of W (Wolfram) . . . 94.64 . . . 79.77 Three do. of 0 ... 24.00 ... 20.23 One do. of W03 . . . 118.64 ... 100 A method of determining the quantity of tungstic acid in neutral salts, by nitrate of mercury, has also been described by Berzelius. The folloAving is the plan proposed by 31. 3Iarhate of alumina (if present) will be precipitated. Collect and wash the precipitate, and label the solution C. Treat the precipitate with solution of caustic potassa, which will redissolve the phosphate of alu- mina, and leave the phosphate of iron: separate, wash, dry, and weigh the latter; add ammonia to the potash solution to throw down the phosphate of alumina, Avhich is, in like man- ner, to be collected and weighed. It must not be inferred that the phosphates of iron and alumina obtained in this manner existed as such in the soil; the phosphoric acid may have been, at least in part, in com- bination with lime or magnesia, while the iron may have been in the state of peroxide, and the alumina uncombined; but, on dissolving these ingredients in the hydrochloric acid, the * Or rather the crucible should be allowed to cool underneath a receiver close to a vessel containing sulphuric acid, and weighed with the cover on. QUANTITATIVE ANALYSIS. 493 phosphate of lime or magnesia would be decomposed, and phosphate of iron and alumina formed. As this decomposi- tion would ahvays take place under the circumstances indi- cated, it next becomes a question whether the equivalent pro- portions of peroxide of iron, or alumina, or of phosphoric acid existed in excess. To determine this point, divide the solution c into tAvo parts; to one add a feAV drops of solution of perchloride of iron, which, if any earthy phosphates still remain undecomposed, will occasion a precipitate of phosphate of iron, in which case it may be concluded that the whole of the iron originally in the solution has been obtained in the state of phosphate of iron. Continue the addition of per- chloride of iron as long as a precipitate is formed, and treat this precipitate the same as that first obtained from solution A. If, on the other hand, no precipitate be formed from the perchloride of iron, it will be necessary to try whether there be more iron or alumina in the solution. In this case, add to the other half of the solution c liquid ammonia, so as to ren- der it slightly alkaline; then add hydrosulphuret of ammonia, which will throw down peroxide of iron, oxide of manganese and alumina, if present; collect and wash this precipitate, and label the solution D. Dissolve the precipitate in hydrochloric acid and boil the solution, add caustic potassa in excess, Avhich will throw doAvn peroxide of iron and oxide of manganese, but will retain alumina in solution; the tAvo former being thus separated, add hydrochloric acid to the filtered solution in slight excess, and finally precipitate the alumina by am- monia. VII. The quantity of manganese contained in soils is usually so small as to render its separation from the iron unnecessary. Its presence may be indicated by the black color which the iron precipitate assumes on being exposed to the air, or by the smell of chlorine, which is afforded on add- ing a few drops of hydrochloric acid to the precipitate. If thought desirable to separate the two oxides, dissolve them in hydrochloric acid and add precipitated carbonate of lime, Avhich Avill throw doAvn the oxide of iron. Separate the precipitate, and add to the filtrate ammonia and oxalate of ammonia, by which the lime is removed; then add caustic soda. Collect, dry, and Aveigh the precipitate, which may be estimated as oxide of manganese. VIII. The solution d may still contain lime, magnesia, and 494 QUANTITATIVE ANALYSIS. salts of potassa and soda. Boil, to drive off any sulphuretted hydrogen Avhich it may contain, then add oxalate of ammonia as long as a precipitate of oxalate of lime is formed. Collect, dry, and weigh this precipitate, and label the solution e ; if the precipitate be dried at 212°, it will contain one atom of water. IX. Add hydrochloric acid to the solution E; eAraporate to dryness, and heat to dull redness. Redissolve in water, and * add red oxide of mercury; treat the residue with Avater, pure magnesia (if present) will remain, Avhich is to be collected and weighed. X. The chlorides of potassium and sodium, as well as the sulphate of lime, have yet to be determined. Boil 200 grains of the dried specimen in ten ounces of distilled water; filter the solution and wash the insoluble part; divide the solution into tAvo equal parts; to one add nitric acid, and then chloride of barium as long as any precipitate occurs. Collect, wash, and dry this precipitate, which is sulphate of baryta, obtained from the decomposition of sulphate of lime. To the other half of the solution add nitric acid, and then nitrate of silver as long as any precipitate occurs, which treat as in the former case. This will be chloride of silver, obtained from the decomposition of the chlorides of potassium and sodium. The above process, though it has no pretensions perhaps to great accuracy, is sufficiently exact for most practical purposes. When a complete analysis is to be made, Br. Ure adopts the following method.* A knoAvn Aveight (about 100 grains) of the soil is introduced into a large glass flask Avith a thin concave bottom, capable of holding at least a quart of water, and over it is poured a sufficient quantity of dilute hydrochloric acid. The flask is placed on the ring of a retort- stand and exposed to a gentle heat, while the beak of a large glass funnel, having its mouth covered Avith a porcelain basin filled Avith distilled water, is inserted into its neck. By this arrangement, a continuous ebullition may be maintained in the mixture of soil and acid, without loss of acid or nuisance from its fumes, because the vapors are condensed whenever they reach the cold basin above the funnel; and in this Avay a boiling heat may be kept up till every constituent of the soil, except the silica, becomes dissolved. The funnel and * Pharm. Journ., June, 1845. QUANTITATIVE ANALYSIS. 495 porcelain basin should be properly supported on the rings of the retort-stand. Br. Ure maintains the action for six or eight hours, at the end of which time he throws the contents of the matrass on a filter, and supersaturates the filtered liquor with ammonia. The silica which remains on the filter having been washed, is dried and weighed. The alumina, oxide of iron, and phosphate of lime thrown down by the ammonia being washed on the filter, and dried to a cheesy consistence, are removed with a bone spatula into a silver basin, and digested with heat in a solution of pure potassa, whereby the alumina is dissolved; the alkaline solu- tion is passed through a filter and saturated with hydro- chloric acid; ammonia is then added, pure white alumina falls, Avhich is collected on a filter, washed, ignited, and weighed. The iron and phosphate of lime on the filter may be dried, gently ignited and weighed, or otherwise directly separated from each other without that step, by the action of dilute alcohol, acidulated with sulphuric acid at a gentle heat. Thus the oxide of iron will be dissolved, and its solution may be passed through a filter, while the sulphate of lime will remain undissolved, and may be dried, ignited, and weighed; five parts of it correspond with four of phosphate. The iron is obtained in the state of sesquioxide by precipitation with ammonia. The first filtered liquor, with excess of ammonia, contains the carbonate of lime and the magnesia. The former is sepa- rated by solution of oxalate of ammonia, and digestion, at a gentle heat, for a feAV hours; it is then filtered, washed, dried, and gently ignited, by which it is converted into carbonate, in which form it is weighed. The magnesia in the filtrate is precipitated with phosphate of soda. For some refractory soils in which the alumina exists as a double or triple silicate, it becomes necessary to fuse about fifty grains of the sample in fine powder, mixed with four times its weight of dry carbonate of soda, the mixture being put into a platinum crucible, and into a cavity in the centre fifty grains of hydrate of potassa being laid. The crucible is slowly raised to a red Avhite heat, Avhen its contents fuse into a homogeneous liquid, of a gray or brown color, accord- ing to the metals present in it. Manganese gives a purple tint: and iron a red broAvn. The fused matter should be poured out into a shallow platinum basin, and, as soon as it 496 QUANTITATIVE ANALYSIS. is cold, it should be pulverized, dissolved in dilute hydrochloric acid, the solution evaporated to dryness, the dry mass again digested with hot water acidulated with hydrochloric acid, and the Avhole thrown down upon a filter. Pure silica remains, which is Avashed, dried, ignited, and weighed. The filtered liquor, Avhich contains the remaining constituents of the soil, is treated as already described. Besides these systematic investigations, Br. Ure directs researches to be made for certain peculiar substances, and especially for the so-called neutro-saline constituents, in the folloAving manner. One hundred grains of the soil are tritu- rated with twenty times their weight of distilled water, placed in a *beaker till the clayey matter subsides, and the clear liquor is then decanted into a filter. A little of the filtered solution should be tested Avith nitrate of baryta, and also with oxalate of ammonia. If precipitates are afforded, the presence of sulphate of lime is indicated, and the following steps must be taken to eliminate it entirely.—Tavo hundred grains of the soil are triturated with a quart of distilled water, holding in solution fifty grains of sal ammoniac. The mixture should be allowed to clarify itself by subsidence, when the super- natant clear liquor should be evaporated doAvn to tAvo ounce measures, and then mixed with an equal bulk of strong whisky (11 per cent, over proof). The Avhole of the sulphate of lime will then be separated from the fluid, and, after being drained on a filter, may be dried, ignited, and weighed. For determining the alkaline salts, the water filtered from the one hundred grains of soil should be evaporated doAvn to one-fifth of its bulk, and then treated, 1st, with nitrate of baryta for the sulphates; 2d, with nitrate of silver for the chlorides; 3d, Avith oxalate of ammonia for the nitrate of lime, or chloride of calcium, provided no sulphate of lime is indi- cated by the first test; 4th, with litmus paper for the alkaline or acid reaction; 5th, with soda chloride of platinum for potassa, salts which are very valuable for the vigorous growth of many plants. The portions of the soil tested for potassa salts should, before being digested in water, be gently cal- cined, to insure the expulsion of every particle of ammonia- cal salt; otherwise the precipitate afforded by soda chloride of platinum would be fallacious. Another peculiar research to which Br. Ure directs espe- cial attention, is that which determines the amount of ammo- QUANTITATIVE ANALYSIS, 497 nia in a soil, which may exist either ready formed, or in its elements, capable of affording a portion of that azotic food so indispensable to vigorous vegetation. The actual ammonia is easily obtained, by distilling the soil along with milk of lime; the distillate will contain all the volatile alkali, Avhich may be estimated by a standard solution of sulphuric acid, according to Peligot's method, described page 468. What Br. Ure calls the potential ammonia, slumbering, so to speak, in its embryo elements, may be estimated by igniting 200 grains of the soil Avith its oavu weight of a mixture of hydrate of soda and quicklime. Br. Ure gives also the following simple method of testing for phosphoric acid in a soil:—Digest it for an hour or so, at a moderate heat, with dilute nitric acid (free from hydro- chloric acid). ThroAv the mixture on a filter; to the filtered liquor add potassa water cautiously, till the instant that a precipitate begins to appear; then drop into it a weak solution of nitrate of silver. If any phosphoric salts be present, a yelloAvish precipitate will immediately fall, which is resoluble in an excess of nitric acid. Whatever is not thus dissolved is chloride of silver, and ought to be separated by filtration. On adding then weak potassa water cautiously to the filtered liquor, pure phosphate of silver will be obtained, without any alumina or iron, provided the liquor be still acidulous in a slight degree. The portion of soil should be fresh, not cal- cined, because the phosphates, Avhen ignited, afford a white precipitate with nitrate of silver. The stronger the solution of the phosphoric compound is, the more characteristic is the yellow precipitate with silver; and then ammonia may be used to effect the partial separation of the excess of acid. A solution of sulphate of magnesia, containing a little sal ammoniac, is probably the best test liquor for detecting phos- phates in faintly acidulous, but still better in neutral, solu- tions. The determination of phosphoric acid in soils is best effect- ed by the following process, proposed originally by Schulze, and modified by Liebig. It is founded on the insolubility of phosphate of peroxide of iron and phosphate of alumina in acetic acid:__The hydrochloric solution of the soil is evapo- rated to dryness, nitric acid being added during the evapora- tion, the dry mass is treated with dilute hydrochloric acid, and'the solution filtered off from the insoluble silica. To the 32 498 QUANTITATIVE ANALYSIS. acid solution ammonia is added, and then acetic acid; the mixture is boiled, filtered while hot, and the precipitate, which contains the whole of the phosphoric acid, in combination with iron and alumina, is collected on a filter, washed, dried, weighed, and digested with caustic potassa, which dissolves the latter. This is the process as originally proposed by Schulze. According to Liebig's modification,* ammonia is added to the hydrochloric solution of the soil, till a precipi- tate begins to form; acetic acid is then added, and, finally, acetate of soda in excess; the mixture is boiled and filtered. The precipitate, having been Avashed with hot water, is dis- solved in hydrochloric acid, ammonia added to alkaline re- action, and then hydrosulphuret of ammonia. The fluid is filtered off from the precipitated sulphuret of iron, and the latter is washed with water mixed with hydrosulphuret of ammonia. The filtrate is concentrated by evaporation, sul- phate of magnesia added, and the mixture stirred ; the forma- tion of a crystaline precipitate indicates phosphoric acid; this precipitate consists of basic phosphate of magnesia and am- monia. It is collected on a filter, washed with water con- taining a little ammonia, dried, and ignited; the phosphoric acid is estimated as pyrophosphate of magnesia. According to Mr. Nesbif\ this process is inapplicable where phosphate of alumina is contained in the solution, the phos- phoric acid being kept back in the precipitate formed by am- monia and hydrosulphuret of ammonia, and cannot be obtain- ed in the filtrate. Although the quantity of soluble saline matter extracted from a moderate quantity of any of our soils is rarely so great as to admit of a rigorous quantitative examination, it is, nevertheless, very desirable that a qualitative analysis of the aqueous extract should be made, in order to furnish informa- * tion as to the ingredients which are supplied directly to the plant with the water which they imbibe from the soil. In some soils, those, for instance, of Egypt and India, and of other warm countries, soluble saline matter in the form of chlorides, sulphates, and nitrates, to the amount of 14 per cent., has been found.! The qualitative examination will * Fresenius—Quantitative Analysis, p. 516. t Quarterly Journ. of the Chemical Society, No. 1, p. 45. J See Johnstone's Lectures on Agricultural Chemistry and Geology, p. 43, Appendix. QUANTITATIVE ANALYSIS. 499 always inform the operator whether or not a quantitative analysis is required. The most convenient plan, therefore, is to digest a large quantity (from two to three pounds) of the soil with distilled water, and, having thrown it on a moist filter and thoroughly washed the insoluble matter, to divide the filtrate into two parts, using one part for the qualitative, and setting aside the other for the quantitative examination, should such be found necessary. As the analysis of soils is a subject which is likely early to occupy the attention of the student in analytical chemistry, we have, with a view of assisting him in his labors, collected in a tabular form the different steps of the treatment of the hydrochloric solution. The substance of this Table is taken from the article on the analysis of soils, in Johnstone's Agri- cultural Chemistry, a work which we take the liberty of strongly recommending to the attention of the agricultural student. To the hydrochloric solution Add ammonia in excess. The solution contains Lime, magnesia, oxide of manganese, potassa, and soda. Add oxalate of ammonia, and cover from the air. The solution contains Oxide of manganese, magnesia,potassa, and soda. Add hydrosulphuret of ammonia. The solution contains Magnesia, potassa, and soda. Acidify with hydrochloric acid, boil, filter, evapo- rate to dryness, and heat to incipient redness, to drive off the ammoniacal salt. Redissolve in water, mix with a little pure red oxide of mer- cury : evaporate again to dryness, heat to redness, and treat with water. The solution contains the chlo- rides of potassium and sodium. Evaporate to dryness, weigh, redissolve in water, and add bi- chloride of platinum. The residue is caustic magne- sia. Wash, ig- nite, and weigh. The solution contains The precipitate is the chloride of sodium, the'double chloride of pla- weight of which is found|tinum and potassium. by deducting from the Wash with dilute al- weight of the mixed chlo-!cohol, dry at a gentle rides that of the chloride heat, and weigh. of potassium. The precipi- tate is Sulphuret of manganese. Dissolve in hydrochloric acid, precipi- tate by car- bonate of soda. Wash, heat to redness in the air, and weigh. Every 100 grains may be considered to indicate the presence of 93.84 grains of protoxide of manganese. The precipitate is Oxalate of lime. Wash, heat to redness to convert into carbonate, and weigh. The precipitate contains Oxide of iron, alumina, and the phosphates of iron and alumina. Digest in acetic acid. The solution contains Alumina and oxide of iron. Add ammonia, and digest the precipitate in a solution of caustic potassa. The solution contains Alumina. Add hydro- chloric acid till the solu- tion is sour, and then excess of ammonia ; alumina is precipitated, which collect, wash, dry, ignite, and weigh. The precipi- tate is Oxide of iron, which wash, dry, ignite, and weigh. The precipitate contains alumina and oxide of iron in the state of phosphates. It may be treated according to Liebig's plan; or, where great accuracy is not particularly desired, it may be fused in a platinum crucible with three times its weight of carbonate of soda: the fused mass is extracted with water. The solution contains The insoluble Alkaline phosphate. residue con- Neutralize with nitric acid, sists of alumi and add nitrate of silver, when phosphate of silver will fall; or with hydro- chloric acid, and add chlo- ride of calcium and am- monia, when bone earth will fall : every 100 grains of phosphate of silver are equal to 23.51 of phospho- ric acid or 4S.50 of bone earth, and every 100 grains of bone earth contain 48.45 of phosphoric acid. na and oxide of iron. Dissolve in hydrochloric acid, and add the solution to that con- taining the rest of the iron and alumina. QUANTITATIVE ANALYSIS. 501 In reference to the detection of minute quantities of phos- phoric acid in soils, rocks, &c, we may allude to the method adopted by 3Ir. Fownes, by Avhich he succeeded in obtaining evidence of the existence of this important acid in several rocks of igneous origin, such as white porcelain clay from Bartmoor, green basalt from Berbyshire, and various lavas, &c. &c. The minerals were finely poAvdered in a porphyry mortar, and boiled with dilute hydrochloric acid: the solutions contained large quantities of alumina and oxide of iron. The liquids were separated from the insoluble part by decantation, evaporated nearly to dryness, water added, and then an excess of ammonia. The copious bulky precipitate obtained was washed and digested in dilute acetic acid. The undissolved residue was dried, ignited, and fused with silica and carbonate of soda ; when cold, the melted mass was acted on with boiling water, and the soluble and highly alkaline portion was sepa- rated by filtration from the insoluble silicate of alumina. The solution was mixed with excess of nitric acid, evaporated to dryness, Avater added, and the product filtered. The liquid thus obtained was divided into two portions; one of these was carefully neutralized with a little ammonia, and then mixed with a few drops of nitrate of silver, a distinct yellow preci- pitate appeared, which was freely soluble in dilute nitric and acetic acids. The other portion was mixed with excess of ammonia, sal ammoniac added, and then a few drops of solu- tion of sulphate of magnesia; after a short time a distinct crystaline precipitate appeared, which increased on agitation. It was found necessary to add silica to the undissolved residue previous to fusion with carbonate of soda, in order to retain the whole of the alumina in an insoluble condition. Betermination of the Specific Gravity of a Soil.—A por- tion is dried in the water bath until it ceases to lose weight; a small bottle is filled up to a mark made in its neck with dis- tilled or rain water, and the weight accurately taken. Part of the water is then poured out of the bottle, and 1000 grains of the dry soil introduced in its stead, the bottle is well shaken to expel all the air from the pores of the soil, filled up to the mark in the neck with water, and again weighed. The weight of the soil divided by the difference between the weight of the bottle with soil and water, and the sum of the weights of the bottle of water and soil together gives the specific gravity. 502 QUANTITATIVE ANALYSIS. Example.—Suppose the bottle with the water to weigh 2000 grains, and with water and soil 2600, then— Grains. Weight of bottle with water alone 2000 Do. with dry soil 1000 Sum, being the weight which the bottle and the soil ~\ would have had could the soil have been introduced V 3000 without displacing any of the water J Actual weight of bottle and water 2600 Difference, being the weight of water taken out to ad- mit 1000 grains of dry soil. Therefore 1000 grains of soil must have the same bulk as 400 grains of water, or the soil must be 2 J times heavier than 1000 „ , ., .- water, since---- = 2.5 = its specific gravity. '400 t & j Betermination of the Relative Proportions of Gravel, Sand, and Clay.—A certain quantity, (say four or five hundred grains) of the soil is well agitated with hot water in a large flask, the whole is then poured into a Phillip's precipitating jar, and allowed to stand for a couple of minutes; the Avater, to- gether with the fine floating matter, is then poured off into another vessel, and the process is repeated several times, till nothing but sand and gravel remain; these are now dried and weighed, and then sifted through a gauze sieve more or less fine, when the gravel and coarse sand are separated and may be weighed, and their respective proportions estimated. These separated portions of gravel and sand should now be moistened with water and examined carefully with the aid of a microscope, with the view of ascertaining if they are wholly silicious, or if they contain also fragments of the different kinds of rock, sand-stones, slates, granites, traps, lime-stones, or iron-stones. A few drops of strong hydrochloric acid should also be added, when the presence of limestone is shown more distinctly by an effervescence, which can be readily perceived by the aid of a glass—of peroxide of iron, by the brown color which the acid speedily assumes; and of black oxide of manganese, by the distinct smell of chlorine, which is easily recognized. QUANTITATIVE ANALYSIS. 503 Betermination of the absorbing Power of the Soil; its Power of holding Water; and the Rapidity with which it Bries.— Johnston gives the following directions for determining these several points. A thousand grains of the perfectly dry soil are spread over a sheet of paper, and exposed to the air for twelve or twenty-four hours, and then Weighed. The increase of weight shows its power of absorbing moisture from the air. If it amounts to 15 or 20 grains, it is so far an indication of great agricultural capabilities. This same portion of soil may now be put into a funnel on a double filter, and cold Avater poured upon it drop by drop, till the whole is wet, and the water begins to trickle down the neck of the filter. It may now be covered with a piece of glass, and allowed to stand for a few hours, occasionally adding a feAV drops of water, until there remains no doubt of the whole soil being perfectly soaked. The two filters and the soil are then to be removed from the funnel, the filters opened and spread for a few minutes upon a linen cloth, to remove the drops of water Avhich adhere to the paper. The wet soil and inner filter being noAV put into one scale and the outer filter into the other, and the whole carefully balanced, the true weight of the wet soil is obtained. Suppose the original Avet soil now to weigh 1400, then the soil is capable of holding 40 per cent, of Avater; for— As 1000 : 400 : : 100 : 40 The wet soil, Avith its filter, may now be spread out upon a plate and exposed to the air, in what may be considered or-. dinary circumstances of temperature and moisture for 4,12, or 24 hours, and the loss of weight then ascertained. This will indicate the comparative rapidity with which such a soil would dry, and the consequent urgent demand for draining, or the contrary. As great a proportion of the water is said to evaporate from a given weight of sand saturated with water, in 4 hours, as from an equal part of pure clay in 11, and of peat in 17 hours, when placed in the same circumstances. The Organic Constituents of the Soil.—We have already in the last chapter alluded to the observations of Mulder* on this subject, and have stated that he reduces the number of organic substances as at present known to exist in the soil to seven. The varieties would indeed be incalculable but for the * Chemistry of Vegetables and Animal Physiology. Translated, with Notes, by Johnston, pp. 143 et seq. 504 QUANTITATIVE ANALYSIS. existence of a general cause which reduces them to a small number. This cause is the transformation and decomposition which vegetables undergo at their death, by Avhich they are converted chiefly into a substance called humus. This change is remarkably uniform, since from the innumerable organic combinations which exist in plants and animals the same few constituents of the black layer of soil are derived; and if we exclude those substances which are mixed accidentally Avith the black soil, as Avell as those substances Avhich have not yet undergone sufficient decomposition, its constituents are limited to a small number of organic substances—substances existing in it everywhere, and on the decomposition of which the growth of plants depends. These substances have the fol- loAving properties:—Some of them are soluble in water, others in alkalies; others again are insoluble in both, Avhile some dissolve more or less readily in alcohol and ether. The latter are of a resinous nature, and do not appear to have any share whatever in vegetation. If a soil be exhausted by means of water, a great many salts may be extracted from it, among which may be men- tioned the alkalies, lime, magnesia, and ammonia, in combi- nation Avith formic, acetic, carbonic, crenic, apocrenic, and humic acids. From the soils thus treated with Avater, alkaline solutions extract substances Avhich may be precipitated by acids. In different kinds of soils the substances thus extracted ■are sometimes different. They all consist, hoAvever, of one or more of the following: Geic acid C40H12014 Humic acid C40H12O12 Ulmic acid C40H14O12 The latter is that which, in neutral vegetable substances un- dergoing decay, is formed first. From it, by absorption of oxygen from the air, humic acid is produced, and finally, by a further absorption, geic acid. The substances Avhich are in- soluble in alkalies, ulmin and humin, can be rendered soluble, and so converted into ulmic and humic acids respectively, by the decomposition which is ahvays going on in the constituents of the soil. The base by which Mulder supposes these acids to be ren- dered soluble in water, is ammonia. He does not adopt the idea of Liebig, that this ammonia is carried down to the soil from the atmosphere, by means of rain water, but he accounts for its QUANTITATIVE ANALYSIS. 505 presence in the following manner:—Nitrogen, in the state of pure gas, and also atmospheric air are possessed of one com- mon property, namely, that when in contact within an enclosed space with putrefying substances, from which hydrogen is in consequence given off, the nitrogen combines ivith the hydrogen, and forms ammonia. This property of nitrogen is well known. It is the principle on which saltpetre is formed, the production of that substance being always preceded by that of ammonia. Now, air is contained in the soil, and is in continual contact with moist and decomposing substances. This air could pro- duce saltpetre, if there Avere only a sufficient abundance of bases, and that even without the presence of putrefying or- ganic substances. There are in Ceylon 22 natural saltpetre grottos, where there are no organic substances from Avhich nitrogen might be supplied. Nitrogen is derived from the air contained in these caverns, and in favorable circumstances even the Avater is decomposed, and ammonia at the same time produced, which afterwards is oxidized into nitric acid by the oxygen _ of the air, in places where it has more easy access; this acid then combines again with the bases from the walls of the grottos, and forms "nitrates. All this would happen in the soil if organic substances were not present to absorb the oxygen, and thus to prevent the oxidation of the nitrogen in the^ am- monia, and the formation of saltpetre. In a porous soil in Avhich moist air is contained, nitrogen is combined with the hydrogen of the organic bodies only into ammonia, the oxygen of the°water, and from the air, being consumed in the higher oxidation of the organic substances themselves. ^ In this way the first product of the decomposition of organic substances, namely, ulmic acid (C40H140X,), is converted into humic acid (C40H12O12), and this again into geic acid (VJisOu)'w"lch- in its turn is further oxidized into apocrenic acid (C481124032), and, finally, into crenic acid (C24H120]6). It is to this formation of ammonia from the constituents ot atmospheric air and water that Ave must look, according to the Dutch chemist, for the cause of one of the most important peculiarities in the growth of plants. It is owing to this slow formation of ammonia, that the organic substances of the soil insoluble in Avater are rendered soluble, and can be offered to plants as organic food, even without a supply of ammoniacal manure to the soil. In other words, it is owing to this cause 506 QUANTITATIVE ANALYSIS. that the five acids already mentioned can be converted into soluble ammoniacal salts. It is particularly worthy of remark, and a fact of great interest, that these humic substances, Avhich can be extracted from the soil by alkalies, and precipitated by acids, have a great uniformity, from whatever kind of soil they may have been prepared; and they are remarkably simi- lar to those substances Avhich by the action of several chemical agents may be obtained from the materials Avhich are generally diffused through the animal and vegetable kingdoms. The manner in which sugar is changed into ulmin, humin, and geic acid, by a simple transposition of its elements, is thus suggested by Mulder:— C. H. 0. J of 7 equiv. of sugar+02 . . . 42 35 37 2 equiv. of carbonic acid 19 do. of water 1 do. of ulmin J of 7 equiv. of sugar + 04 2 equiv. of carbonic acid 23 do. of water 1 do. of humin J of 7 equiv. of sugar+06 . 2 equiv. of carbonic acid 23 do. of Avater .... 1 do. of geic acid .... 42 35 41 In the same manner the conversion of cellulose, starch, gum, pectin, and other analogous substances, which are so very much diffused through plants into the humic substances, may be represented; and the way in which his protein even may be converted into humic acid, by the influence of hydrochloric acid and oxygen, is shown in a very ingenious manner by Mulder.* 2 4 19 19 40 16 14 42 35 37 42 35 39 2 4 23 23 40 12 12 42 35 39 42 35 41 2 4 23 23 40 12 14 * Chemistry of Vegetable and Animal Physiology, p. 159. QUANTITATIVE ANALYSIS. 507 The crenic and apocrenic acids, like the humic acids, exist in the soil in the state of salts of ammonia, potassa, and soda, combined Avith lime, magnesia, and oxide of iron; they never exist in the soil uncombined. They unite intimately with am- monia, which, however, can be completely separated from them by caustic potassa. Apocrenic acid, when artificially prepared, is a five-basic acid. It is produced in the form of apocrenate of ammonia when humic acid in whatever way prepared, or wood charcoal, is exposed to the action of nitric acid. Its value in the soil is very highly estimated by 3Iulder, as in consequence of its five-basic character it may supply plants either with several bases at once, or these bases may be alternately exchanged according as the proportion of a more poAverful base in the soil is less, and that of a more feeble one temporarily greater; in consequence of these pro- perties he assigns to it a much higher rank than the humic class of acids. The formation of apocrenate of ammonia, by the oxidation of humate of ammonia, is continually going on in the soil during the warmth of summer (except on the very surface which is directly exposed to the air). Each minute portion produced can be taken up by the roots of plants, in the form of double apocrenates of ammonia and various fixed bases, provided there be a sufficient supply of water at hand; and, while in this Avay the soil loses its apocrenates, a new portion of apocrenate of ammonia is formed from the humic acid or humin, which is present in large excess. We may thus call the production of apocrenic acid in one respect an organic nitrification. The series of organic acids present in the soil is, according to the views of Mulder, concluded by a fifth important sub- stance, a final product of the oxidation of organic substances before they are entirely changed into carbonic acid and water, namely, crenic acid, the composition of which is C24H12Ol6. It also is combined with ammonia in the soil, and forms double salts, which are soluble in Avater. These exist, along with the apocrenates, in all kinds of water* which have been in contact with organic substances in the soil. They Avere first found by Berzelius in spring water; they exist also in the waters of ditches, marshes, and bogs. Crenic acid is four- * See last Chapter. 508 QUANTITATIVE ANALYSIS. basic. By the continual tendency to nitrification in the soil, apocrenic acid must always be converted into crenic acid, the series of ulmic, humic, geic, and apocrenic acids thus termi- nating Avith crenic acid. In the upper layer of the soil, Iioav- ever, Avhere the air is not inclosed, and consequently no tend- ency to nitrification exists, crenic acid must conversely be changed into apocrenic acid. Johnston* thinks that to the five acids, mentioned by 3Iul- der, several others may be added, as occurring in certain circumstances in the soil. Thus, from a sample of compressed peat, he extracted by ammonia a substance, from Avhich hy- drochloric acid threw doAvn a dark brown acid, having the composition C24H12012; the same peat, Avhen digested Avith solutions of caustic potassa, or of carbonate of potassa, or carbonate of soda, and precipitated by an acid, gave a sub- stance, having the formula C24H14Og; agreeing, therefore, with the ulmic acids of 3Iulder, in containing an excess of hydrogen, but not reducible to his ulmic group, the excess of hydrogen being very much greater than in ulmic acid, and the equiva- lent containing only twenty-four instead of forty equivalents of carbon. These acids agree with those of Mulder in their tendency to unite with several bases at once, and to combine with oxygen and nitrogen from the air, producing ammonia and acids containing more oxygen than the humic and ulmic acids. Again, from a substance called Pigotite, found on certain parts of the rocky coasts of Cornwall, Avhere caves occur, Johnston extracted an acid, represented by the formula C12H508. This acid Avas obviously formed from the decaying vegetable matter of the soil, and was combined with alumina. It approaches very closely in composition to the crenic acid of Mulder, and is called by its discoverer Mudeseous acid; on treating its compound Avith alumina, with nitric acid, Johnston obtained still another acid, the formula of which is The above is a very brief and imperfect outline of the present state of our knowledge regarding the nature of the organic constituents of the soil. It will be seen that the subject is still quite in its infancy, and that no attempt can as yet be made to point out a method of analyzing a soil with a vieAV of isolating any particular acid. The following mode of examination must, therefore, for the present suffice. * See his translation of Mulder's work, p. 184. QUANTITATIVE ANALYSIS. 509 Beterminatian of the total Amount of Organic 3Iatter.— From 100 to 200 grains of the soil thoroughly dried, at a tem- perature not higher than between 250° and 300° Fahrenheit, are burned in a platinum crucible till all blackness disappears. The earth is then moistened with carbonate of ammonia, dried, and again gently ignited. The difference in weight furnishes a close approximation to the amount of organic matter present. It is not absolutely exact, because it is impossible thoroughly to expel the whole of the water from some soils, without par- tially decomposing the organic matter. Betermination of the Acids of the Humic Group.—About 500 grains of the soil are digested for several hours at about 200° Fahrenheit, with a solution of carbonate of soda; the fluid is then filtered off, an operation which, with soils con- taining much alumina, frequently takes a considerable time;* the filtrate is mixed with slight excess of hydrochloric acid, whereupon the humic acid separates in the form of light broAvn flakes; these are collected on a tared filter, washed, dried, and Aveighed; the dry mass is then burned, and the weight of the ashes subtracted from that of the dry flakes; the remainder is the amount of humic acid. Betermination of the Humus.—About 500 grains of the soil are digested for some hours with caustic potassa in a por- celain basin; the alkaline ley is diluted with water, filtered, the undissolved matter washed, and the filtrate precipitated by hydrochloric acid. The whole of the humus_ is by this treatment converted into humic acid; and the difference in weight between the precipitate thus obtained and that of the former experiment, when carbonate of soda Avas employed as the solvent, represents the quantity of organic matter existing in the soil in the form of humus; and the two weights added to- gether, and deducted from the amount which the soil lost by ignition, shows the quantity of the other organic ingredients not belonging to the humic group. _ Should the operator Avish to determine the amount of resinous and waxy matters in the soil, he may extract them by digesting about 2000 grains Avith strong alcohol, precipitating them from the alcoholic solution by water; and, should he _ desire to know the quantity of nitrogen Avhich the soil contains, he * Should the first nitrate be still muddy, it should be concentrated by evapo- ration, and again passed through the filter, when it will, in most cases, be ob- tained quite clear. 510 QUANTITATIVE ANALYSIS. may burn a known quantity with soda lime in the manner described in detail at page 250. CHAPTER VI. ON THE ANALYSIS OF COMPOUNDS CONTAINING THE OXIDES OF IRON AND MANGANESE, ALUMINA AND ALKALINE EARTHS IN COMBINATION WITH PHOSPHORIC, ARSENIC AND SILICIC ACIDS. BY. R. FRESENIUS. Journ. fur Prakt. Chem., 1848, and Chem. Gaz. 7-22. I. Separation of the Peroxide of Iron from Phosphoric Acid in the presence of Alkaline Earths. a. Many chemists have hitherto assumed, that by fusing the perphosphate of iron with carbonated alkali and exhaust- ing the mass with boiling Avater, the perphosphate of iron may be completely separated from phosphoric acid (Berzelius, Ram- melsberg); nay, that even when alkaline earths are present, the phosphoric acid passes entirely to the alkali, and is dis- solved on treatment with water (Rose). I had formerly convinced myself that phosphate of lime and phosphate of magnesia could not be perfectly decomposed with carbonate of soda; but now I have found that even the peroxide of iron cannot be wholly deprived of phosphoric acid by this treatment. In fact, if the residue, after being most carefully washed, is dissolved in muriatic acid, precipitated with ammonia and sulphuret of ammonium, filtered, and the solution mixed with chloride of ammonium and sulphate of magnesia, there is always obtained a very perceptible preci- pitate of ammonio-phosphate of magnesia; it consequently re- quires no further proof that all the methods based upon the above principle are inaccurate. b. When a muriatic solution containing phosphoric acid, per- oxide of iron and lime, is mixed with carbonate of soda until the free acid is nearly saturated, then mixed with an excess of acetate of soda and boiled, the whole of the phosphoric acid is precipitated with the peroxide of iron, whilst the lime remains QUANTITATIVE ANALYSIS. 511 in solution. The peroxide of iron and phosphoric acid may then be separated by sulphuret of ammonium. This method is not inaccurate, but it is extremely inconvenient, especially when mere traces of phosphoric acid have to be estimated and the amount of peroxide of iron is very great, a case which very frequently occurs in the analysis of iron ores, soils, kc. With respect to the other method, which is given in my In- troduction to Quantitative. Analysis, of separating phosphoric acid from peroxide of iron (it consists in adding tartaric acid, and then ammonia, to the solution, and lastly a mixed solution of chloride of ammonium and sulphate of magnesia), I must observe that it has now been found to lead to erroneous re- sults ; as a mixture of a solution of tartaric acid, sulphate of magnesia, chloride of ammonium and ammonia deposits after a short time, when of a certain degree of concentration, a crystaline precipitate, which has entirely the appearance of the ammonio-phosphate of magnesia. The employment of citric acid, sugar, &c, instead of the tartaric acid, has not yielded satisfactory results. c. The method which I now employ is based upon an en- tirely new principle. The solution, which we will suppose to contain much peroxide of iron, lime and some phosphoric acid, is heated to boiling, removed from the lamp, and a solution of sulphite of soda added until the color has become pale green, and carbonate of soda produces a white precipitate ; it is then boiled until the smell of sulphurous acid has disappeared, any excess of free acid neutralized with carbonate of soda, a few drops of chlorine water mixed with it, and lastly an excess of acetate of soda. The smallest quantity of phosphoric acid is immediately detected by the production of a white flocculent precipitate of perphosphate of iron.* [This reaction is so sensitiA^e because the perphosphate of iron is insoluble both in acetic acid and in the acetate of the protoxide of iron, whilst it dissolves abundantly in a solution of the peracetate of iron. It is owing to this circumstance that no precipitate is ever ob- tained when a nearly neutral solution of the peroxide of iron, containing only a small amount of phosphoric acid, is mixed with acetate of soda; the blood-red liquid remains clear in the * When the solution contains silicic or arsenic acid, a precipitate is formed in the absence of phosphoric acid. These two acids must therefore be first sepa- rated, before the phosphoric acid can be detected with certainty by the above reaction. 512 QUANTITATIVE ANALYSIS. cold, and the Avhole of the iron, Avith the phosphoric acid, is only deposited on boiling.] Chlorine Avater is now added gradually until the liquid appears reddish; it is then always turbid. It is boiled until it has become clear, which soon re- sults, filtered hot, and the precipitate washed with hot Avater. This precipitate contains the whole of the phosphoric acid as perphosphate of iron mixed Avith a minute quantity of basic peracetate of iron; the solution contains nearly the Avhole of the iron and the lime, which are easily separated by sulphuret of ammonium. The precipitate containing the phosphoric acid and iron may be readily and completely decomposed, after solution in muriatic acid, by the addition of ammonia and sulphuret of ammonium. But perfect decomposition may also be effected in the following manner, avoiding the use of sulphuret of ammonium. It is dissolved in muriatic acid, re- duced with sulphite of soda as above, an excess of caustic potash or soda added, boiled until the precipitate has become black and granular, and then filtered through very close paper.* This precipitate is protoperoxide of iron free from phosphoric acid : it is dissolved in muriatic acid, and united with the other solution of iron. The filtered solution contains the phosphoric acid, which is precipitated in the usual manner as ammonio-phosphate of magnesia. II. Separation of Iron from Alumina. One of the most frequent operations of analytical chemistry is the separation of peroxide of iron from alumina by caustic potash ; it is, however, very inaccurate. It had already been noticed by seA'eral persons, that the separation of these tAvo oxides by caustic potash was not complete; and Knoppf has in consequence proposed precipitating the solution with sul- phuret of ammonium, and then boiling with potash. This latter method is, however, extremely inconvenient, as the liquid, even though yellow and free from iron at the commencement, almost always passes through green and ferruginous in the washing, whether pure water or water containing sulphuret of ammonium is employed. The following experiment will shoAV * When the filter is too porous, very often some of the fine precipitate passes through, especially when washed. Should this happen, the nitrate is suffered to stand, the clear liquid decanted, and the remainder filtered through a separate little filter. f Chem. Gaz., vol. v. p. 14. QUANTITATIVE ANALYSIS. 513 the inaccuracy of the usual method. A solution of chloride of aluminum, containing 1.000 grm. alumina, was mixed with a solution of perchloride of iron, an excess of caustic soda added to it, boiled, filtered hot, the filtrate acidified with mu- riatic acid, and carefully precipitated Avith ammonia. After standing several hours in a warm place, it was filtered. The alumina upon the filter was yelloAV, and led me to suspect the presence of iron, which Avas subsequently confirmed. The hydrated peroxide of iron also contained alumina, since although completely washed it gave a precipitate, although a very small one, on being again boiled with caustic soda and treating the filtrate as above. Instead of 1.000 grm. alumina, only 0.909 (which moreover contained iron) was obtained; there was consequently a loss of 10 per cent. After standing for eight days, the filtered solution deposited some alumina ; consequently the Avhole of the lost alumina had not remained with the iron, but a portion had not been precipitated by the ammonia. After some experiments the cause of it was found out. It is owing to the circumstance, that, on filtering the liquid containing the caustic alkali through paper, organic matter is dissolved, which prevents the precipitation. This was proved by the following experiments:— A solution of pure chloride of aluminum, containing 1.320 grms. alumina, was precipitated Avith potash, the precipitate redissolved in an excess of potash, the liquid heated to boiling filtered, acidified with muriatic acid, and precipitated with ammonia. The alumina obtained amounted only to 1.290, that is 97.72 per cent. In a second experiment, made in the same manner, instead of 2.640 grms. only 2.590 or 98.48 per cent, were obtained. This evil is avoided by filtering through asbestos instead of paper; but far more simply and better by heating the liquid acidified with muriatic acid, and boiling with a little chlorate of potash (upon the addition the flask is remoA'ed from the fire). By this means the organic substance, preventing the complete precipitation of the alu- mina, is destroyed, as the following experiments will show. A solution containing 0.3420 alumina was treated as above described ; after being acidified with muriatic acid, boiled with chlorate o'f potash, it gave 0.3418 grm. alumina, that is 99.94 per cent. In a second experiment, instead of 0.150, 0.1495 or 99.67 per cent, was obtained. The other source of inaccuracy, which in the first experi- 33 514 QUANTITATIVE ANALYSIS. ment had raised the loss of alumina to 10 per cent., and which is owing to its not being possible to free the hydrated per- oxide of iron completely from alumina by caustic potash, may be aAroided Avithout the application of Knop's inconvenient method. The acid solution, containing the alumina and per- oxide of iron, is heated to ebullition in a flask, removed from the fire, and reduced Avith sulphite of soda. The liquid, after being kept boiling for some time, is neutralized Avith carbonate of soda, an excess of caustic soda added, and, after being well shaken, boiled until the liquid has become black and granular. [The succussion which precedes the boiling may be avoided by inserting a coil of platinum wire, and also by constant agitation. As soon as it really boils the thumping ceases.] It is now removed from the fire and allowed to sub- side, the clear liquid passes through a close filter, and the precipitate washed with hot water, at first by decantation, and then upon the filter. The filtered solution, treated in the above-mentioned manner with muriatic acid and chlorate of potash, furnishes, upon precipitation with ammonia and several hours' standing, the whole of the alumina in a perfectly pure state. III. Separation of Alumina from Phosphoric Acid. To make an accurate analysis of a compound containing alumina, peroxide of iron, lime, magnesia and phosphoric acid, it is necessary, in the first place, to separate the alumina from the other bases. This is readily effected by precipitating the liquid, after the peroxide of iron has been reduced by sul- phite of soda, with carbonate of soda, and then boiling with the addition of an excess of caustic soda. It must be borne in mind, in this case, that, on boiling, the carbonic acid which had been combined with the protoxide of iron passes to the soda, which it converts into carbonate; consequently, to retain the alumina in solution, it is requisite to add from time to time some caustic soda, and especially A\Then the precipitate has become black and granular. In this way the alumina, together with a portion of the phosphoric acid, is obtained in solution (when alumina and peroxide of iron are the only bases present, the whole of the phosphoric acid is in the filtered solution), and we have now to seek for a simple method of separating the two. The following furnishes perfectly satisfactory results:—The QUANTITATIVE ANALYSIS. 515 alkaline solution is rendered acid, boiled with some chlorate of potash, precipitated with ammonia (avoiding a large excess), and chloride of barium added as long as a precipitate appears. After digesting for some time, it is filtered. The precipitate, which contains the whole of the alumina and phosphoric acid (the latter combined in part with alumina and in part with baryta), is collected upon a filter, washed with a little water, and dissolved in as little muriatic acid as possible. The solu- tion is saturated with carbonate of baryta with the assistance of heat, an excess of caustic soda added, and heat applied. Any baryta contained in the solution is precipitated by car- bonate of soda and filtered. The whole of the alumina is now in the solution, and the whole of the phosphoric acid in the precipitate. The solution is rendered acid with muriatic acid, boiled with chlorate of potash, precipitated with ammonia, allowed to stand for some hours in a warm spot; the alumina filtered, washed, dried, calcined and weighed. The precipitate is dissolved in muriatic acid, and the baryta precipitated with dilute sulphuric acid, separated by filtration, and the phosphoric acid determined as ammonio-phosphate of mag- nesia as usual. IV. Course of Analysis. The compound, the analysis of which we will^ describe, I will suppose to contain a large amount of peroxide of iron, protoxide of manganese, alumina, lime, magnesia, phosphoric acid, sulphuric acid, arsenic acid, silicic acid and sand, as is the case with iron ores. A weighed quantity (which should not be too small) of the finely-pulverized mineral is digested with moderately-dilute muriatic acid in a flask, at a temperature near to boiling point until all that is soluble has passed into solution, lhe liquid is diluted, passed through a filter of known weight of ash, and the residue washed. With brown iron ore the quantity is m general very small. It is dried with the filter, carefully separated from it, calcined and weighed ; it is then transferred into a boiling solution of carbonate of soda, allowed to boil for some time, filtered through the filter first employed, washed dried, calcined and weighed. The difference between this weight (sand, alumina, &c.) and the one first obtained gives the amount of insoluble residue, or silicic acid. The ferruginous muriatic solution is filtered from the resi- 516 QUANTITATIVE ANALYSIS. due, carefully evaporated to perfect dryness, and kept for some time at a temperature slightly above that of boiling water. After it has been moistened with muriatic acid, and kept for some time with it at a gentle heat, water is added, and any silica separated by filtration. Its weight, added to that above obtained, gives the total amount of silicic acid in combination. The ferruginous solution is heated to boiling in a flask, and reduced Avith sulphite of soda as described under I. When the Avhole of the sulphurous acid has been expelled by boil- ing, sulphuretted hydrogen is passed into the liquid until it is saturated with it. The precipitate produced is the proto- sulphuret of arsenic. The amount of arsenic contained in it is ascertained, after deducting the sulphur in it, which has been previously determined as sulphate of baryta, from its weight determined at 212°. If the precipitate does not ap- pear yellow, but brown or black, there is reason to suspect some other metallic oxides, and it must be further examined in the ordinary manner. The liquid filtered from the protosulphuret of arsenic is boiled to expel the whole of the sulphuretted hydrogen, then precipitated with carbonate of soda, and boiled with an excess of caustic soda (as directed in II.) until the precipitate appears black and granular. It is allowed to subside, the clear liquid poured off, the precipitate washed by decantation with hot water, and finally brought upon a filter of close texture, and washed with hot water. a. Treatment of the Precipitate.—The precipitate (which contains proto and peroxide of iron, protocarbonate of manga- nese, carbonate and phosphate of magnesia) is again trans- ferred, together with the filter, into the flask, and digested Avith muriatic acid. After standing for some time in a warm place, it dissolves entirely, although not so readily as the hydrated peroxide of iron. When no more black particles are per- ceptible, it is filtered; the filter is left whole, a little hot water poured over it, the flask inclined so that it remains hanging to the side, and the liquid runs off, &c. In this manner it may be quickly and completely washed. The fil- tered solution is reduced with sulphite of soda, nearly neu- tralized with carbonate of soda, heated to boiling, mixed with a feAV drops of chlorine-water, then with an excess of acetate of soda; and when the liquid or the precipitate has not a red- QUANTITATIVE ANALYSIS. 517 dish tint, chlorine water is added until this is the case. The whole is boiled until the precipitate has separated, filtered hot, and the precipitate, consisting of phosphate and some basic acetate of the peroxide of iron, washed. a. The filtered solution is precipitated, after the addition of ammonia and while hot, with sulphuret of ammonium, fil- tered quickly, the precipitate consisting of protosulphuret of iron and manganese, washed uninterruptedly Avith hot water, and the lime in the solution determined by oxalate of am- monia; and, after removing the oxalate of lime, the magnesia thrown down by phosphate of soda. The precipitate of the sulphurets is dissolved in muriatic acid, oxidized with chlorate of potash or nitric acid, boiled until all the chlorine is ex- pelled, allowed to cool to about 140°, nearly neutralized with carbonate of soda, the peroxide of iron precipitated with car- bonate of baryta, and the other oxides estimated in the usual manner. 13. The precipitate, containing the perphosphate of iron, is dissolved in muriatic acid, reduced with sulphite of soda, boiled for some time with an excess of caustic soda, and filtered. The solution containing the phosphoric acid is supersaturated with muriatic acid, and placed aside. The precipitate of proto- peroxide of iron is also dissolved in muriatic acid, oxidized with nitric acid, the solution added to the principal solution of the iron, separated from the manganese and baryta, and the whole precipitated with ammonia. b. Treatment of the filtered Alkaline Solution.—This liquid, which contains the alumina, is treated exactly as described under III. The alumina is consequently weighed in a pure state. The solution, freed from baryta and containing phos- phoric acid, is united with the above-mentioned liquid con- taining the other portion of phosphoric acid, supersaturated with ammonia, and precipitated with sulphate of magnesia, with the addition of chloride of ammonium if necessary. The sulphuric acid in the mineral is determined in a sepa- rate portion by dissolving it in muriatic acid, filtering the dilute solution, and precipitating with chloride of barium. How far the course of analysis is simplified when one or the other of the substances in question is not present, I have not considered necessary to mention, nor the mode in which the qualitative examination should be conducted. 1 will only observe with respect to the latter, that the course of analysis 518 QUANTITATIVE ANALYSIS. proposed cannot be deviated from without disadvantage; and further, that it is of great importance, before commencing the qualitative analysis, to ascertain the presence or absence of alumina, manganese and alkaline earths; for when no alumina is present, the first precipitation with carbonate of soda and the boiling with caustic soda may be omitted; the Avhole of the phosphoric acid is contained in the alkaline liquid hold- ing the alumina in solution when no alkaline earths are pre- sent; and the residue which had remained undissolved by the potash may be at once treated for the separation of the iron from manganese; or, when no manganese is present, precipi- tated at once with ammonia from the muriatic solution after previous oxidation, calcined, and calculated as peroxide of iron. In proof of the accuracy of this method, the author pre- pared a liquid containing known quantities of peroxide of iron, alumina, lime, magnesia and phosphoric acid, and divided it into two equal portions, each of Avhich was analyzed pre- cisely according to the preceding directions. Each half of the liquid contained— Found. ,--------*--------N Grms. I. II. Phosphoric acid . . 0.100 0.0993 0.0995 Lime......0.133 0.1328 0.1327 Magnesia .... 0.103 0.1020 0.1029 Peroxide of iron . . 1.443 1.4426 1.4424 Alumina .... 0.150 0.1495 0.1495 Or in 100 parts— Phosphoric acid Lime .... Magnesia . . Peroxide of iron Alumina . . 1.929 1.9262 1.9270 5.18 5.14 5.16 6.89 6.88 6.88 5.34 5.29 5.33 74.81 74.78 74.77 7.78 7.75 7.75 100.00 99.84 99.89 QUANTITATIVE ANALYSIS. 519 CHAPTER VII. ON THE ANALYSIS OF ASHES OF PLANTS. The method recommended by Brs. Will and Fresenius is the following:—* First Preparation.—Plants in a normal and healthy con- dition should be selected, unless the design be to study dis- eases and their causes. All foreign matter, such as dirt, dust, &c, should be carefully removed; but the plants should not be washed, or certain soluble salts might be extracted. Plants which have been exposed to moist Aveather should, for the same reason, be rejected. The design of analyzing the ashes of plants may be—1st, simply to ascertain the amount and nature of their inorganic constituents; or, 2dly, the operator may have in view the discovery of the presence or absence of certain substances in the soil, such as alkalies, alkaline earths, and phosphates: For the latter purpose an examination of the ashes of all the va- rieties of plants growing upon the soil must be undertaken ; and Avhen a knowledge is hereby obtained of the composition of the inorganic constituents of both Aveeds and of cultivated plants, and AAThen to this is added an acquaintance with the nature of the soluble constituents of the soil itself, the analyst is in a position to determine for what crops the soil in question is best adapted. Woods, herbs, and roots, after being per- fectly dried, may be burned upon a clean iron plate; leaves, fruit, and seeds will be best burned in a Hessian crucible, by means of charcoal or coke: the crucible should be placed somewhat obliquely in the fire, in order to favor the access of air. Sometimes the ashes are left perfectly white, but some seeds require a higher temperature than others to rid the ashes entirely of charcoal: care must, however, be taken not to allow the heat to rise sufficiently high to fuse the alkaline salts, or it will be found afterwards almost impossible thoroughly to burn away the charcoal. During the operation of burning, and especially towards the end of the process, the ashes should be allowed to lie as lightly in the crucible as possible, in order * Memoirs of the Chemical Society, vol. ii. p. 179, et seq. 520 QUANTITATIVE ANALYSIS, that air might circulate freely through them; they should not, therefore, be stirred together: by attending to this, a much Avhiter ash is procured than Avould otherAvise be the case. After the ashes have been well burnt in the crucible, it is ad- visable to transfer them to a platinum dish, and to heat them to low redness over a gas or spirit lamp, Avith constant stirring; they should then be rubbed to a fine powder, and transferred while Avarm to a well stoppered bottle. Rose objects to this mode of preparing the ash for analysis; his important obser- vations on this subject will be referred to at length further on. The ash being prepared, the first step is to determine, by means of a qualitative examination, to Avhich class the ashes belong:—Avhether to the silicious, or to the phosphoric, or to the carbonic class. A small portion is treated with con- centrated hydrochloric acid, Avhich generally dissolves it com- pletely, unless the ash abounds in silica; if a strong effervescence accompany the solution in hydrochloric acid, carbonates of the alkalies or alkaline earths predominate, and the whole of the phosphoric acid present is probably combined with peroxide of iron; if no (or only moderate) effervescence attend the solution, phosphates predominate; and, if complete solution in hydro- chloric acid cannot be obtained, the ash belongs to the silicious class. To the clear hydrochloric solution acetate of ammonia is either at once added, or it is first neutralized by means of caustic ammonia, and free acetic acid afterwards added. In most cases a yellowish white gelatinous precipitate is formed, consisting of phosphate of peroxide of iron. This precipitate is collected on a filter, and ammonia added in excess to the clear filtrate, by which means a fresh precipitate may be ob- tained: if it be red, it is peroxide of iron. The solution is well protected from the air, and allowed to stand for some time; if no further precipitation take place, then it is known that the ash contains no other phosphate than that previously precipitated; but, should a white deposit gradually form, it consists of phosphates of lime and magnesia, and shows that the ash under examination contains more phosphoric acid than is combined with the peroxide of iron. It is not necessary to proceed further with the qualitative examination, unless the operator should wish to test for fluorine, oxide of manganese, iodine, bromine, or any other peculiar substance, the presence of which may be suspected, and in such cases separate por- QUANTITATIVE ANALYSIS. 521 tions of the ash must be used for each experiment, as also for determining quantitatively the amounts of carbonic acid in the ashes abounding in that principle, and of the alkalies in the ashes belonging to the silicious class. I. Betermination of the Quantity of Ashes yielded by a given weight of the Plant.—This is a problem, the solution of which is of considerable importance: a quantity of solid mat- ter is annually removed from the soil in the crop taken from it, which loss should be repaired as nearly as possible by the judicious addition of manure. It is the nature of the manure to be furnished Avhich the farmer seeks from the analytical chemist; but the farmer must take his share in the inquiry by informing the analyst as to the weight of the crop which a given surface of soil should yield, and this he can in most cases do with sufficient accuracy. The vegetable substance under examination should be dried in the water bath, or still better in a current of dry air produced by the efflux of water till it ceases to lose weight.* The quantity of substance employed in this experiment depends on the proportion of its inorganic con- stituents. Of herbs and seeds, which are in general rich in these matters, from 30 to 50 grains will be sufficient, whilst of woods ten times that amount must be taken. The combustion succeeds best in a platinum crucible, which should at first be covered, and a gentle heat only applied, but a stronger heat must aftenvards be employed, the lid of the crucible being removed to ensure the perfect combustion of the charcoal. Those ashes which do not effervesce with acids, as the ashes of seeds, may be treated with nitric acid, and again ignited, by which treatment they will speedily be rendered quite white. If a very strong heat has been employed, the carbonic acid in those ashes which effervesce with hydrochloric acid will be ex pelled, but it may be restored by moistening the ashes with solution of carbonate of ammonia, and afterwards again ex- posing them to gentle ignition: so also, at a high temperature in contact with charcoal, the sulphates (if any be present) may be converted into sulphurets, but the reconversion of those compounds into the original salts may be effected by heating the ashes intensely, and for a considerable time, to- gether with pure peroxide of mercury. Although the above method of estimating the amount of ashes yielded by a plant * See Fig. 283 "Morfit's Manipulations." 599 QUANTITATIVE ANALYSIS. is not altogether free from objection, it is, nevertheless, a sufficiently close approximation to truth to answer every prac- tical purpose; indeed, it is doubtful whether more accurate methods Avould really be more valuable, since it is found that the amount of ashes yielded by the same plant is not constant. II. Analysis of Ashes, rich in Carbonates and Sulphates. —Betermination of the Silica, Charcoal, and Sand.—About 60 grains of the ashes, which have been found to be soluble in hydrochloric acid, are treated with concentrated acid in a matrass, held obliquely so as to avoid any loss of the liquid during the evolution of the carbonic acid; a gentle heat is then applied, until it is evident that everything is dissolved excepting the carbonaceous and sandy particles. The whole is now carefully removed into a porcelain basin, evaporated to dryness over a water bath, and then heated somewhat more strongly, as is usual in separating silica (see page 395). The mass when cold is moistened with strong hydrochloric acid, digested for half an hour with a sufficient quantity of water, and boiled; after Avhich the acid liquor is poured upon a stout filter, which has previously been dried at 212°, and weighed. The silica remains on the filter; and, if the ashes were not perfectly white and pure, some sand and charcoal also. The filter is Avashed and dried, and the substance carefully removed from it into a platinum or silver crucible without injury to the paper. This is effected without difficulty if the matters be perfectly dry, the paper in most cases only retaining so much as to be slightly colored by the charcoal. The powder is now boiled for half an hour with pure potash ley (free from silica), by which the whole of the silica, natural to the ash, will be gradually dissolved, leaving the sand and charcoal unacted upon. The insoluble matter is again collected on the same filter, and after being well washed it is dried at 212°, till it no longer loses weight. The increase upon the weight of the dried filter is to be estimated as charcoal and sand. The silica in the alkaline solution is determined by adding hydro- chloric acid in excess, whereby it is precipitated; the whole is evaporated to dryness, and the further treatment conducted in the manner directed at page 395. The acid solution originally filtered from the silica, sand, and charcoal, after being well mixed, is divided into three, or more conveniently into four equal portions, one portion being reserved in case of an accident happening with either of the QUANTITATIVE ANALYSIS. 523 other quantities. The division is best effected by means of an accurately graduated tube or cylinder; the A\liole of the fluid is collected into the tube or cylinder, the measure of which thus represents the weight of ash experimented upon. The solution is now divided into three or four equal or known portions, the volume of each is noted, and they are labeled respectively with the letters a, b, c, and d. In a the peroxide of iron (oxide of manganese) and the alkaline earths are estimated. In b the alkalies. In c the phosphoric and sidphuric acids. a. Estimation of the Peroxide of Iron, Oxide of Manganese, and Alkaline Earths.—To the solution ammonia is added until the precipitate thereby produced no longer entirely redissolves; acetate of ammonia is next added, and sufficient acetic acid to render the solution strongly acid. From the form and ap- pearance of the precipitate, it can easily be judged whether it still contains phosphate of lime; if this be the case, more acetic acid must be added. The yellowish white precipitate which remains consists of phosphate of peroxide of iron 2Fe 0 +3P05; its separation from the fluid is assisted by gently heating; it is then well washed on the filter with hot water, ignited, and weighed. To the filtered solution neutral oxalate of ammonia is added as long as a precipitate continues to be formed, and the amount of lime is determined in the usual manner (see page 256). When it has been shown by the qualitative analysis that, besides phosphate of iron, the ash contains peroxide of iron or oxide of manganese (in which case the presence of the earthy phosphates is very rarely de- tected), the solution, previous to the separation of the lime, should be supersaturated with ammonia, and precipitated by means of sulphuret of ammonium, the two oxides being after- wards separated according to one of the methods given at page 292. If the ashes under examination contained earthy phosphates, the solution filtered from the oxalate of lime will contain free acetic acid; if otherwise, there will be free am- monia; it is next somewhat concentrated, rendered ammoniacal, treated with a solution of phosphate of soda, and the precipi- tate formed collected and estimated as pyrophosphate of mag- nesia. (See page 257.) ... , b. Estimation of the Alkalies.—The solution is treated with baryta water until it gives an alkaline reaction; it is 524 QUANTITATIVE ANALYSIS. then gently heated and filtered. By this means we get rid of all the sulphuric and phosphoric acids, the peroxide of iron, the magnesia, and part of the lime. The precipitate is washed on a filter as long as the washings render turbid a solution of nitrate of silver. It is next warmed, treated with caustic and carbonate of ammonia, and allowed to stand until the precipitate becomes heavy and granular. The whole is now filtered, and the solid matter Avashed, after which the solution is evaporated to dryness, and the residue heated to redness in a platina capsule to expel the ammoniacal salts. What remains consists of the chlorides of potassium or sodium, or more generally of a mixture of the two. The weight being noted, a little water is added, which generally leaves undis- solved a trace of magnesia; this is collected on a filter, its quantity subtracted from that of the supposed alkaline chlo- rides, and added to that of the magnesia, as previously ascer- tained. The quantity of. potash is determined by means of chloride of platinum in the usual way (see page 236), and that of the soda is calculated from that of the chloride of sodium indicated by deducting the weight of the chloride of potassium from that of the mixed alkaline chlorides; or the amount of the two alkalies may be determined by the indirect method as directed in page 240. c. Estimation of the Sulphuric and. Phosphoric Acids.— From the acidulous solution the sulphuric acid is first separated by chloride of barium; the filtered liquor is nearly neutralized by ammonia; acetate of ammonia is added, and then a solu- tion of perchloride of iron until the liquor begins to turn red in consequence of the formation of acetate of iron. Care must here be taken that sufficient acetate of ammonia be added to convert the whole of the chlorine of the perchloride into sal- ammoniac. The solution is now boiled until it becomes color- less, all the iron being then precipitated. The precipitate, after being washed with hot water, consists of phosphate of iron and a quantity of basic acetate of iron. It is dried, ignited in a platinum crucible, treated with a few drops of nitric acid, re-ignited and weighed. It is next digested with concentrated hydrochloric acid, by which it is speedily dis- solved. The solution is diluted with hot water mixed with tartaric acid, and ammonia added until the yellowish white precipitate, which is at first formed, disappears. A clear solution of a dingy green color is thus obtained, from which QUANTITATIVE ANALYSIS. 525 the iron is precipitated by hydrosulphuret of ammonia. The precipitate and supernatant fluid are digested together in the water bath until the latter loses its green tinge, and is of a clear yellow color, resembling that of hydrosulphuret of am- monia with excess of sulphur. It is now rapidly filtered, access of air being prevented, and the precipitate is washed with hot Avater containing a little hydrosulphuret of ammonia, until a drop of the filtered liquid, dried upon a platinum spatula and ignited, no longer gives any acid reaction. The sulphuret of iron is dissolved from the filter by means of hot and dilute hydrochloric acid; the solution is boiled, treated with a few drops of nitric acid to peroxidize the iron, and ammonia is then added in excess. The precipitate is pure peroxide of iron, the weight of which, deducted from that of the basic phosphate, gives the quantity of phosphoric acid. (See page 385.) The perchloride of iron used in this experi- ment must be quite free from sulphuric acid. Estimation of the Chlorine.—A fresh portion (about 15 grains) of the ashes is Aveighed out and exhausted with hot water, slightly acidulated with nitric acid; the solution is pre- cipitated with nitrate of silver, following the directions given at page 306. If the ashes should contain appreciable quan- tities of iodine and bromine these bodies will be found in the precipitated silver salt; for their quantitative estimation, how- ever, a larger quantity of the ashes must be employed. Estimation of the Carbonic Acid.—The amount of this acid is determined Avith the apparatus of Drs. Fresenius and Will, described at page 245. III. Analysis of Ashes abounding in Silica.—Ashes of this kind are in general only partially soluble in acids. Their alkalies must, therefore, be determined in a separate portion of the ash. The chlorine and carbonic acid are determined in the same manner as when the ash is entirely soluble in acids. The quantity of chlorine found in ashes of this class is however, probably always somewhat less than it should be, since the alkaline chlorides, when ignited with silica and carbon, undergo a partial decomposition. Estimation of the Silica.— Pure potassa or soda ley is poured upon about sixty grains of the ashes, and evaporated to dryness in a platinum or silver dish. The silicic acid com- pounds are, by this treatment, dissolved, leaving the sand unaffected. The heat should not be so great as to fuse the 526 QUANTITATIVE ANALYSIS. mass, or some of the charcoal might be oxidated at the ex- pense of the Avater of the hydrated alkali. Diluted hydro- chloric acid is poured upon the mass, the whole evaporated, and the silica, charcoal, &c. determined in the manner already described. The acidulous solution filtered from the insoluble matter is divided into two parts; one is employed for the determination of the sulphuric and phosphoric acids, and the other for that of the peroxide of iron and the alkaline earths by the methods detailed above. Estimation of the Alkalies.—A second portion of the ash (about fifty grains) is ignited in a platinum crucible with four times its weight of hydrated baryta. The acid solution which remains after separating the silica, &c. is precipitated suc- cessively with baryta water and carbonate of ammonia, the alkalies being then obtained in the state of chlorides. The further treatment has already been described. Arrangement of the Results.—Since the analysis of the ashes of a plant can convey no preeise information as to the manner in which the several acids and bases found are actu- ally combined in the living vegetable, the method recom- mended by Fresenius and Will* namely, that of enumerating the per centage weights of the acids and bases found is pro- bably the best which the present state of our knowledge admits of; but, whether this or any other method be adopted, it is highly desirable that there should be uniformity on the subject, for it is only thus that the results of different analyses can be compared together, and so applied to the solution of certain interesting questions in physiology and in agriculture. The chlorine found in the analysis is always calculated as chloride of sodium, and the manganese as manganoso-man- ganic oxide (Mn304). As an illustration of this method, we may quote Messrs. Rowney and How's analysis of the ashes of the orange-tree.f Amount of ash left by— 100 parts of the root . . 4.48 100 parts of the stem . 2.74 100 parts of the leaves . 13.73 100 parts of the fruit . . 3.94 100 parts of the seeds . 3.30 * Fresenius1 Quantitative Analysis, p. 507. f Mem. Chem. Soc, vol. iii. p. 370. QUANTITATIVE ANALYSIS. 527 Per Centage Composition of the Ashes of the Root. Potassa . 15.43 Soda . 4.42 Lime . 49.89 Magnesia . . 6.91 Sesquioxide of iron . 1.02 Chloride of sodium . 1.18 Phosphoric acid . . 13.47 Sulphuric acid . 5.78 Silicic acid . 1.75 Per Centage Composition of the Ashes of the Stem. Potassa Soda Lime Magnesia . Sesquioxide of iron Chloride of Sodium Phosphoric acid . Sulphuric acid Silicic acid 11.69 3.07 55.13 6.34 0.57 0.25 17.09 4.64 1.22 Per Centage Composition of the Ashes of the Leaves. Potassa Soda Lime Magnesia * Sesquioxide of iron Chloride of sodium Phosphoric acid Sulphuric acid Silicic acid 16.51 1.68 56.38 5.72 0.52 6.66 3.27 4.43 4.83 528 QUANTITATIVE ANALYSIS. Per Centage Composition of the Ashes of the Fruit. 36.42 jroiassa Soda 11.42 Lime . 24.52 Magnesia . 8.06 Sesquioxide of iron 0.46 Chloride of sodium 3.87 Phosphoric acid 11.07 Sulphuric acid 3.74 Silicic acid . 0.44 100 Per Centage Composition of the Ashes of the Seed. 40.28 Soda 0.92 Lime 18.97 Magnesia . Sesquioxide of iron Chloride of sodium 8.74 0.80 0.82 Phosphoric acid . Sulphuric acid Silicic acid 23.24 5.10 1.13 100 In the above calculations the unessential constituents, viz : carbonic acid, sand and charcoal, are deducted.* Rose's Method of examining the Ashes of Organic Bodies. —It has been mentioned above, that the method of preparing the ashes of plants for analysis, by igniting the vegetable in Hessian crucibles, and continuing the heat until all the organic matter is destroyed, has been objected to by Rose, who obsenresf that, if the fixed constituents of plants are * The reader is referred to a paper, by Mr. Watts, on the "Analysis of the Ash of the Hop," published in the third volume of the "Memoirs of the Che- mical Society,'' p. 392, et seq. In this analysis an entirely different system from that above detailed was pursued; separate examinations of the aqueous and the hydrochloric solutions were made, and the acids and bases are arranged as they were supposed to exist in the plant. The analysis itself is remarkable as point- ing out the unusual presence of phosphate of alumina. t In a paper read before the Royal Academy of Berlin; Chem. Gaz., vol. v., p. 158. et seq. QUANTITATIVE ANALYSIS. 529 examined according to the process which he adopted in ex- amining the ashes of ox-blood, results differing entirely from those yielded by the ash analyses hitherto published may be obtained. The process adopted by the Berlin chemist in his analyses of the ashes of blood Avas this. The blood Avas exposed in a covered platinum crucible to a very faint red heat, then ex- tracted with cold water, and the colorless liquid evaporated to dryness. It was found to consist of alkaline chlorides and carbonates, Avith very minute quantities of alkaline sulphates and phosphates. The charred mass, extracted with water, was now treated with hydrochloric acid : the filtered solution did not yield, with ammonia, a very considerable precipitate, which, though it looked almost like pure hydrated oxide of iron, contained some phosphoric acid as well as lime and magnesia. In the filtered solution a pretty considerable quantity of oxalate of lime Avas obtained with oxalate of am- monia, proving the presence of carbonate of lime in the char- red blood; and in the liquid separated there was also a small quantity of magnesia. The cinder, after treatment with water and hydrochloric acid, yielded a very considerable quantity of a red-colored ash, on being burnt in an atmosphere of oxygen. It Avas in a semifused state, and contained per- oxide of iron (which formed the chief part) and earthy and alkaline phosphates. These results differ considerably from those of if. Enderlin, Avhose method was* to evaporate fresh blood to dryness, and then to powder and incinerate the re- sidue. The ash thus obtained dissolved in hydrochloric acid without effervescence, whence he concluded that the alkalinity of blood cannot be caused by an alkaline carbonate, and that there cannot exist in the blood any alkaline salts with organic acids. The salts found by M. Enderlin in the ashes of blood he states to be tribasic phosphate of soda (3NaO,P05), chlo- rides of sodium and potassium, sulphate of soda, phosphate of lime, phosphate of magnesia and oxide, with some phosphate of iron, the alkalinity of the blood being produced by phos- phate of soda (3NaO,P05). If the phosphate of soda in the blood were the ordinary phosphate (2NaO,HO,POi), it would, according to 31. Enderlin, be converted by a red heat into the pyrophosphate (2NaO,P05), the third atom of base (HO) » See Liebig's Annalen, and Chem. Gaz., vol. iii. p. 229. 34 530 QUANTITATIVE ANALYSIS. escaping; but, according to Rose, the ordinary phosphate of soda (2NaO,HO,P05) would, at a high temperature, decom- pose carbonate of soda and be converted into tribasic phosphate (3NaO,P05); and that, in consequence, the conclusions of if. Enderlin are erroneous. It has been shown, also, by Mar- chand* that the circumstance of no carbonates being found in the ash does not in the least prove that they are not con- tained in the blood, and that we are as little justified in ad- mitting unconditionally the presence of tribasic phosphate of soda (3NaO,P05) because that salt is found in the ash. In- deed Marchand declares that the admission of the presence of 3NaO,P05 in the blood absolutely requires the admission of that of carbonate of soda, since it has been proved that 3NaO,P05 is converted, on exposure to a moist atmosphere containing carbonic acid, into 2NaO,HO,POs, and NaO,C02. The same objections Avhich have been urged against the conclusions drawn by Enderlin with regard to the salts exist- ing in the blood, from the analysis of the ashes prepared at high temperatures, have been also applied by Rose to the con- clusions drawn from the results of the analysis of the ashes of plants prepared in the usual manner. It had previously been remarked by Erdmannf that the mode of preparation of the ashes for analysis has great influence on their apparent composition. His method was to burn the plant or seeds in a muffle furnace, in which, in the course of three or four hours, upwards of 200 grains of the most beautiful ash of corn may be obtained. The ashes so prepared, especially in those seeds that are difficult to reduce to ash, generally contain the phos- phoric acid in a lower state of saturation than those prepared in a crucible. Thus the ash of rye, which usually contains an alkaline phosphate, yielding, with oxide of silver, a white precipitate, gives a yellow one when it has been prepared by long-continued ignition in a covered crucible; and biphosphate of potassa, when ignited for a long time with carbonized sugar, is converted into a bibasic, and finally even into a tribasic salt. It is evident, therefore, that a reduction of the phos- phoric acid has taken place, and the same is the case with the sulphuric acid. These facts induced Rose to undertake * Journ. fur Prakt. Chem., April 6th, 1846; and Chem. Gaz., vol. iv. p. 210. t See Liebig's Annalen, liv. p. 341—356, 360—363; lvi. p. 122; lvii. pp. 67, 68; and Chem. Gaz., vol. iv. p. 230, et seq. QUANTITATIVE ANALYSIS. 531 an examination of the fixed constituents of certain plants by the same method Avhich he had adopted in the analysis of ox- blood, a method which, although it may be objected to in that it takes more time, furnishes (he says) far more correct results, and gives satisfactory answers to several questions as to how, or in what combinations, the constituents found in the ash were contained in the organic substance. His method is as follows.* The organic substance is charred at a very faint red heat, so that the Avater with which it is extracted is not colored yellowish or brownish. At this temperature, which, OAving to the volatilization of so many substances, is much lower .than would appear, no alka- line chlorides are volatilized, nor can chlorine be expelled from them, in the form of hydrochloric acid, by acid phos- phates. The alkaline and earthy phosphates are not able to expel the carbonic acid from the alkaline carbonates, either contained in the organic substance or formed by charring; nor can phosphoric acid be eliminated, from its combination's, from silica, reduced by carbon, and volatilized in the form of phosphorus. The charring is effected either in a spacious covered platinum crucible, over a spirit lamp; or, with larger quantities of the organic substances, in a spacious covered Hessian crucible, especially if they do not fuse. When there is no longer much empyreumatic odor perceptible, the heating is discontinued, the cold mass left for some time in contact with water, and the solution of the salts furthered by heating. The edulcoration requires considerable time and much hot water; but, if the highest degree of accuracy is not desired, the edulcoration may be discontinued when several drops of the wash-water leave a scarcely perceptible residue on evapo- ration upon a slip of platinum foil: this point is very soon attained. The aqueous extract contains the alkaline salts. The alka- line chlorides were contained as such in the organic substance previous to the charring, as well as at least a part of the alkaline sulphates and phosphates. If, as in most cases, car- bonated alkali is found in the aqueous extract of the charred * For the report of Prof. Rose's important paper on the " Examination of the Ashes of Organic Bodies," given in the text, the author is indebted to the " Chemical Gazette;" he has preferred transcribing the paper almost in full to giving any abstract of it, to avoid the possibility of any misconception in any of the details of the operation. 532 QUANTITATIVE ANALYSIS. mass, it either pre-existed in the organic substance, or the alkali in it was combined with an organic acid, or some other organic body which acted the part of an acid towards the alkali. If the organic substance contain sulphate of lime, this, when carbonated alkalies are present in sufficient quan- tity in the charred mass, is converted, on treating the latter with water, into carbonate of lime and alkaline sulphate. In the same way, when phosphate of lime is present, a certain quantity of alkaline phosphates is formed from it, in the aqueous extract, by the alkaline carbonates. Carbonated alkali and phosphate of lime are not perfectly decomposed even by fusion at very high temperatures. The decomposition in presence of much water is likewise imperfect; and, the more alkaline phosphate is obtained in the aqueous extract, the more concentrated the solution, the more carbonated alkali it contains, and the longer the charred mass has been digested at an elevated temperature. Alkaline sulphates and phosphates will, however, be found in far smaller quantities in the aqueous extract of the charred mass than was to be expected from the ash analyses that have hitherto been published. Frequently the two, and especially the latter, are present only when too high a temperature has been em- ployed in the charring. From this, however, it is evident that the nature of the salts in the aqueous extract may vary some- what, according to the temperature employed and the longer or shorter digestion of the mass with water. When the char- ring is effected at too high a temperature, the greater portion of the carbonated alkalies are decomposed by the earthy phos- phates. The accurate examination of the salts in the aqueous extract is not accompanied with any great difficulties. One circum- stance, however, renders it somewhat less easy. Carbonate and phosphate of lime and magnesia frequently dissolve to a considerable extent in neutral solutions of alkaline salts, par- ticularly of alkaline carbonates and phosphates; in the course of time they are deposited from the solutions, especially after the application of heat. When, therefore, the aqueous extract is evaporated, it frequently becomes somewhat turbid, and deposits small quantities of earthy salts. It should conse- quently be evaporated nearly to dryness, diluted with water, and the solution set aside for some time; when the earthy salts have subsided, it is filtered, the filtered solution evapo- QUANTITATIVE ANALYSIS. 533 rated to dryness, and its weight determined. When there is no alkaline sulphate or phosphate present, the examination is very easy. The quantity of carbonic acid is determined in a suitable apparatus, by decomposition with nitric acid; and, upon this, that of the chlorine by a solution of silver: upon which, after removing the excess of silver by hydrochloric acid and concentrating the liquid, the potash may be sepa- rated from the soda by chloride of platinum. With the pre- sence of alkaline sulphate or phosphate, it is advisable to divide the quantity of the alkaline salts, and in the one-half to determine the quantity of the chlorine and the alkalies, and in the other that of the carbonic acid by decomposition with hydrochloric acid; that of the sulphuric acid by a salt of barytes; and, after removing the baryta by means of sulphuric acid, and supersaturating with ammonia, to ascertain the quantity of phosphoric acid by means of a solution of a salt of magnesia, to which chloride of ammonium has been added. The charred mass, exhausted with water, is now digested with hot hydrochloric acid for some length of time, and then washed with water. This operation requires considerably more time and water than in the treatment of the charred mass with water; and, if the washing were to be continued until some drops of the filtered liquid no longer produced any opalescence in a solution of silver, an enormous length of time, several months, would be required, especially in operating upon large quantities. The edulcoration, therefore, is only continued until a considerable quantity of the wash-water does not exhibit a trace of a precipitate when treated with ammonia; it will then also be seen that a large quantity of the wash-water, when evaporated upon platinum, no longer leaves any perceptible residue; this does not require much time, especially when hot water is used. The acid solution contains the earthy phosphates which existed as such in the organic substance, and the peroxide of iron. It is precipitated by ammonia, and, after having de- termined the weight of the precipitate, the bases are separated from the phosphoric acid. On separating the earthy phos- phates by means of ammonia, a small quantity remains dis- solved in the filtered liquid, owing to the presence of chloride of ammonium; consequently, upon adding oxalate of ammonia, a precipitate of oxalate of lime is obtained, but its quantity is usually larger than corresponds to the phosphate of lime 534 QUANTITATIVE ANALYSIS. dissoh'ed by the chloride of ammonium; consequently, a por- tion of the lime existed as carbonate of lime in the charred mass, or avhs formed by the decomposition of the sulphate or phosphate of lime by the alkaline carbonates. The liquid fil- tered from the oxalate of lime indicates, on the addition of a solution of phosphate of soda, the presence of some magnesia. The insoluble earthy salts, which separated from the aqueous extract, may be examined conjointly with those in the acid extract. With respect to the charred mass which has been exhausted with water and hydrochloric acid, it might be imagined that it could contain only silica or silicates, undecomposable by dilute hydrochloric acid; but it yields a very large amount of ash on complete combustion, even Avhen the organic substance contains no silica or mere traces. Rose effects the complete combustion of the charred mass in a thin porcelain crucible, provided with a platinum cover, which is perforated in the centre, and into which there passes a curved silver tube about eight inches long, through which dry oxygen gas is conveyed into the crucible. The crucible is half filled with the sub- stance and heated over a spirit-lamp, and, with proper care, not a particle of the ash is carried away, and the combustion proceeds with great rapidity: a further quantity of the sub- stance is conveyed from time to time into the crucible. The ash thus obtained may be weighed with great accuracy. Its weight added to that of the evaporated aqueous extract of the charred mass, and to that of the insoluble earthy salts dis- solved by the hydrochloric acid, gives the correct quantity of fixed constituents in the organic substance employed. The ash obtained, especially when derived from vegetable substances, consists of the same constituents as were found in the aqueous and acid extracts; if alkalies were present in them, we likewise find them in the ash of the exhausted charred substance; otherwise, it consists principally of earthy phosphates. When the subject of the analysis is the blood, nearly the whole of the iron is met with in this ash. Only about a tenth part of it is found in the acid extract of the charred mass, and indeed the less the more carefully the charring was effected with exclusion of the air. When the organic substance contains no silica, various views may be entertained respecting the origin of the ash from the charred mass which has been exhausted with water and acid. The QUANTITATIVE ANALYSIS. 535 most probable is, perhaps, to derive it from an imperfect exhaustion of the two solvents. When an organic substance is destroyed by heat, the charcoal formed may contain such cavities that the inorganic salts surrounded by them are pro- tected from the action of the solvents. The globules of the blood, those of yeast, and the cells of plants, form, perhaps, after charring, extremely minute vesicles, with such small apertures that no liquid can penetrate into them. That the vessels of wood are capable of forming extremely thin fila- ments Avith minute apertures by charring is known from the investigations of Begen. The charred mass of an organic substance (yeast), after it has been most carefully exhausted by water and hydrochloric acid, was ground to the finest powder upon a plate of agate; the two solvents now extracted only imperceptible traces of fixed constituents, and, after burning the exhausted charred mass, Rose obtained the same large amount of ash as from the non-pulverized charcoal. It may, nevertheless, be supposed that the extremely minute vesicles were not destroyed and torn by the friction upon the agate plate. The microscope threw no light upon the subject. It is known that charcoal is capable, by a weak kind of affinity, of remoAdng certain salts from their solutions. Rose found it almost impossible, also, to remove entirely by wash- ing the whole of the hydrochloric acid from the charred mass which had been digested in hot acid; but the quantity of ash is too considerable for us to ascribe this origin to it, since it is known that the salts which the charcoal has combined with may be entirely separated by long treatment with water at different temperatures. If sulphate of potash and phosphate of lime are mixed Avith sugar and the whole charred, water, and after this hydrochloric acid, will extract the two salts completely, so that, on subsequently burning the charred mass in an atmosphere of oxygen, not a trace of ash is ob- tained. Rose then discusses the several views which might be advanced to account for the ashes obtained from the charred mass. The following is remarkable from the curious con- siderations it involves with respect to the combinations of the organic with the inorganic materials in the living vegetable. The salts found in the ashes may, perhaps, not have pre- existed as such in the organic substances, but were first formed by oxidation after the burning of the coal. It has long been known that the protein compounds, of both animal and vege- 536 QUANTITATIVE ANALYSIS. table origin, contain sulphur and phosphorus in an unoxidized state; but the supposition has never been advanced, that the radicals of the earths and alkalies may likewise be contained in organic substances, in an unoxidized state, perhaps com- bined with those elements. These would certainly constitute a very peculiar class of combinations, such as at present we are not acquainted Avith. If they are really combined with organic substances in the living body,* they cannot have been essentially altered on destroying the organic body by char- ring, or they have entered into combination with carbon and nitrogen, which are insoluble both in water and in hydro- chloric acid. The salts found in the ashes of the charred mass exhausted with Avater and acid, especially when derived from vegetable substances, are similar to those which occur in the aqueous and acid extract. If this be really true, then those salts found in the ash after the destruction of the living plants are probably contained in them only in part as such, and in part in a deoxidized state. The inorganic salts, therefore, which are taken up from the soil by the living plant are partially deoxidized by it, and in this state form combinations with organic substances contained in the plant. This view (observes Rose) is far more probable with respect to several animal substances, especially the blood, than in reference to plants. It has long been suspected that the iron in the blood was contained in it in an unoxidized state: and, according to the recent investigations of Mulder, the iron is actually extracted by acids from hsematine with evolution of hydrogen gas. On the other hand, it is very remarkable that iron cannot be extracted from the charred blood by hydro- chloric acid. This subject deserves investigation. With respect to plants, the view above advanced can evidently only be confirmed or refuted by following the method of ana- lysis above described, and thus it is that Rose has pronounced it by far the most rational mode of investigation. It has been shown by Rose that frequently very consider- able quantities of alkaline carbonates are extracted by water from several organic substances by charring, in the ashes of which no carbonic acid was found by former investigators. But all organic substances do not yield alkaline carbonates when treated in this manner, even though considerable quan- tities of alkali are contained in their ash. Highly remarkable QUANTITATIVE ANALYSIS. 537 in this respect is yeast, the ashes of which, according to Mit- scherlich, contain no carbonic acid and no metallic chlorides; and Rose's experiments show that they are likewise not to be found in the aqueous extract of the charred yeast. Yeast diffuses, on being charred, an odor similar to that of the pro- tein compounds: the aqueous extract did not turn litmus paper blue—became turbid on evaporation, and deposited a large quantity of earthy phosphates. The mass evaporated to dry- ness yielded, on filtration, a clear solution which faintly red- dened litmus-paper, and contained, therefore, not a trace of alkaline carbonates; the only substances that could be found in it were alkaline phosphates, with very minute traces of alkaline sulphates and chlorides. The charred mass gave, on treatment with hydrochloric acid, a solution from which am- monia threw down a considerable precipitate of earthy phos- phates. The cinder, exhausted with water and acid, furnished on combustion a very large quantity of ash, which contained the same constituents which had been extracted from the charred mass. CHAPTER VIII. ON THE ANALYSIS OF URINE AND URINARY CALCULI. Fkom the following analysis of this important secretion by Berzelius, it will be seen that its composition is very compli- cated ; indeed the Chemistry of Urine is as yet very imperfect, for in no complete analysis which has hitherto been published has any account been taken of the hippuric acid, or the krea- tine, or kreatinine, which Liebig has announced to be constant constituents, while, according to the same chemist, normal urine contains no lactic acid; so that in the subjoined analysis the 17.14 parts which are set down to this acid and its salts are, in reality, something else, the nature of which has yet to be discovered. 538 QUANTITATIVE ANALYSIS. Analysis of Urine by Berzelius. Water , 933.00 Urea ... 30.10 Uric acid . . 1.00 Lactic acid, lactates, and animal matter 17.14 Mucus of the bladder . . . 0.32 Sulphate of potash . . . 3.71 Sulphate of soda . . 3.16 Phosphate of soda . . . 2.94 Phosphate of ammonia . . 1.65 Chloride of sodium . 4.45 Hydrochlorate of ammonia . 1.50 Earthy matters, with a trace of fluoride of calcium 1.00 Silicious earths . . 0.03 1000 Urine may be acid, neutral, or alkaline, even in a healthy condition of the body, its reaction to test paper as Avell as the nature of the salts which it contains depending in a great measure on the nature of the food, so that the physician has the saline condition of this secretion greatly under his control, a fact of great value in the treatment of calculous diseases. When the food contains salts of potassa and soda with organic acids, the urine becomes alkaline; these acids becoming ox- idized in the circulation yield carbonic acid, which combines with the alkalies, and the alkaline carbonates appear in the urine. When the food contains but very little of such salts of organic acids, the urine may be neutral, and Avhen it con- tains none at all it becomes acid from the solution of uric or hippuric acid, or both, in phosphate of soda.* The specific gravity of healthy urine may vary from 1.012 to 1.030, and contain about 7 or 8 per cent, of solid matter, the remainder being water. In certain diseases, hoAvever, the density of the secretion may be considerably greater, as well as its proportion of solid ingredients. The following table, showing the quantity of solid matter in diabetic urine of different specific gravities between 1.020 and 1.050, Avas drawn up by Br. Henry, and assuming its correctness, Br. Frampton\ has given the folloAving simple method of deter- * Turner's Chemistry, by Liebig and Gregory. Eighth edition. ■J- Medical Gazette. QUANTITATIVE ANALYSIS. 539 mining, without haAring recourse to actual experiment, the amount of solid matter voided in a given time in urine of any specific gravity. If Br. Henry's table be examined, it will be found that there is an increase of solid matter in each wine pint of urine, corresponding to the increase of one degree of specific gravity of exactly 12.2 grains, or of 1.2 grains of solid matter in each ounce for every one degree of specific gravity. Hence, to determine the amount of solid contents in urine, say specific gravity 1.025, we have only to multiply the constant quantity 1:2 grains, by 25j making 30 grains, to give us the solid contents of one ounce, Avhose specific gravity is 1.025, and this again by the number of ounces voided in a given time, say 40 ounces (making 1200 grains), to give us the whole contents of solid matter dissolved in the urine passed in that time. This rule will be found, on trial, to give results so nearly coinciding with those of the table (the error is con- stantly just 1.6 grains in excess in the wine pint), it is so easy both to recollect and to apply, and so much more convenient than a table not always at hand, that it is well worthy of the notice of medical men. In the experiments, which furnished the following table, the urine Avas evaporated at a steam heat till it ceased to lose weight, and till it left an extract which, on cooling, became quite solid. In reference to such tables, Br. Bence Jones* obserA'es, that though they may be true for the total quantity of water passed in twenty-four hours, they are not so for the urine made at any one period of the day. The Avater made before and after dinner, for instance, may have the same specific gravity, but the total quantity of solid residue in each case may be entirely different. Br. Henry's Table of Solid Matter in Urine of different Bensities. Specific gravity of the Quantity of solid Quantity of solid extract in a urine, water being extract in a wine wine pint in 1000. pint in grs. oz. dr. scr. grs. 1020 . . 382.4 . . 0 6 1 0 1021 . . 401.6 . . 0 6 2 1 1022 . . 420.8 . . 0 7 0 0 1023 . . 440.0 . . 0 7 1 0 1024 . . 459.2 . . 0 7 1 19 * Phil. Trans., Part iv., for 1846. 540 QUANTITATIVE ANALYSIS. Specific gravity of the Quantity of solid Quantity of solid extract in a urine, water being extract in a wine wine pint in 1000. pint in grs. oz. dr. scr. grs. 1025 . . . 478.4 . . . 0 7 2 18 1026 . . . 497.6 . . 10 0 17 1027 . . . 516.8 . . 10 1 16 1028 . . . 536.0 . . 10 2 16 1029 . . . 555.2 . . . 110 15 1030 . . . 574.4 . . . 111 14 1031 . . . 593.6 . . . 112 13 1032 . . . *612.8 . . . 12 0 12 1033 . . . 632.0 . . . 12 1 12 1034 . . . 651.2 . . . 12 2 11 1035 . . . 670.4 . . . 13 0 10 1036 . . . 689.6 . . . 13 1 9 1037 .. . 708.8 . . 13 2 8 1038 . . . 728.0 . . 14 0 8 1039 . . . 747.2 . . 14 1 7 1040 . . . 766.4 . . 14 2 6 1041 1042 . . . 804.8 . . 15 1 4 1043 1044 . . . 843.2 . . .16 0 3 1045 1046 .. . 881.6 . . 16 2 1 1047 1048 . . . 920.0 . . .17 1 0 1049 1050 . . . 958.4 . . 17 2 15 It is no part of our plan, neither would it be at all suited to the design of the present work, to give any detailed account of the numerous and important investigations which have been made within the last few years on the urine, both in health and in disease. To the physiologist and pathologist it cannot be doubted that the subject must be one of the highest interest; but it is not to a general treatise on chemical ana- lysis that the cultivator of medical science would refer for such imformation as he might require in this department of his studies. We have, nevertheless, thought that it might add to the usefulness of our work to bring together some of the later methods, AA'hich have been adopted by chemists for QUANTITATIVE ANALYSIS. 541 the detection and quantitative estimation of certain of the ingredients of this complicated secretion. Quantitative Estimation of Urea.—Two methods have long been in use, viz: separating it as nitrate, and calculating its proportion; or as oxalate, this being subsequently decomposed by carbonate of lime, and the urea weighed in its pure state. Both these methods are fallacious, on account of the solubility of both the salts; the following have, therefore, been proposed as substitutes. 1. Rabsky's Method.*—Concentrated sulphuric acid, in the quantity of half that of the urine used, is added to the latter, and the mixture kept in a moderate state of ebullition ; much water is thus vaporized, and the fluid becomes black. The temperature continues to rise, until at about 392° (it should not very much exceed this temperature) carbonic acid is evolved in small bubbles; the cessation of this disengagement of gas indicates that the urea is completely decomposed. The black residue is then thoroughly exhausted with water, and the solution filtered: the clear yellow filtrate is then evapo- rated in the water bath, and the generated sulphate of am- monia treated with alcohol and chloride of platinum. Since urine contains salts of potassa and ammonia, which will like- wise be precipitated upon the addition of chloride of platinum, their exact proportion must be determined from a separate weighed portion by precipitation with chloride of platinum, and the corresponding amount must be subtracted from the first quantity. The author found this method to give accu- rate results, which were not interfered with by mixing the urea with sugar previous to analysis: in applying it, however, it is necessary to remove all those substances which might introduce error, such as uric acid, hippuric acid, albumen, &c. In many instances it may be advisable to separate the urea previously by oxalic acid, and to decompose the oxalate subsequently with sulphuric acid. In calculating the amount of urea, one part of ammonia-chloride of platinum corresponds • to 0.134498 of urea. The conversion of urea into carbonate of ammonia, which also takes place when the urine is left to itself, will be under- stood from the following equation, in which it is seen that by * Lancet, Dec. 6, 1845. 542 QUANTITATIVE ANALYSIS. the addition of the elements of water all its carbon is con- verted into carbonic acid, and all its nitrogen into ammonia. 1 equivalent urea C2N2H402 ) 2 do. water H202 ) C2N2H604 ( 2 equivalents carbonic acid C2 02 ( 2 do. ammonia N2H6 ^C^N^O^ The carbonate of ammonia thus formed is of course instantly decomposed in the above experiment by the sulphuric acid, sulphate of ammonia being generated, and carbonic acid set free. 2. Heintz's Method.*—Estimation of the Potassa and Am- monia.—A weighed quantity (from 100 to 120 grains) of the urine is treated with about 30 drops of hydrochloric acid, and set aside in a cool place for 24 hours; it is then filtered through a very small filter into a large platinum or porcelain crucible; the filter and glass are Avashed Avith a small quantity of Avater; the filtrate is treated with about 100 grains of sulphuric acid, and the liquid evaporated over a small spirit lamp, taking care that it does not boil, until the evolution of carbonic acid com- mences. The crucible is then covered with a Avatch glass, and heated until the evolution of carbonic acid ceases, the tem- perature not being allowed to exceed 180°. The contents of the crucible are then filtered into a porcelain dish, the cru- cible and the watch glass are Avell washed, and the filtrate is evaporated until almost all the Avater has passed off. About 20 drops of hydrochloric acid are then added to the residue, and afterwards a sufficient quantity of chloride of platinum and alcohol mixed with aether. If the liquid from which the precipitate has subsided is of a very pale color, more chloride of platinum must be added. After 8 or 10 hours the preci- pitate is separated by filtration, washed, dried, and heated to redness in a crucible, which is at first covered, but subse- quently open. The residue is treated with boiling dilute hy- drochloric acid, the solution filtered, and this is repeated until the liquid which drops from the filter leaves no residue when evaporated upon platinum foil; the crucible and filter are dried at a gentle heat: the latter is burnt in the former, and * Poggendorff's Annalen, No. 9, 1845: and Chem. Gaz., vol. iv. p. 17. QUANTITATIVE ANALYSIS. 543 weighed. Thus the amount of platinum, which corresponds to that of the potassa, ammonia, and urea, is obtained. Another weighed quantity of the fresh urine is treated at once with chloride of platinum, 3 volumes of alcohol and 1 of ether: at the end of 10 or 12 hours the mixture is filtered, and the precipitate heated to redness in a well covered and weighed platinum crucible. The residue is treated as above with dilute hydrochloric acid, and the filter is burned and weighed. We thus obtain the weight of platinum which cor- responds to the potash and ammonia contained in the urine; its per-centage is calculated, and then deducted from that ob- tained in the first experiment: the difference gives the amount of platinum which corresponds to the urea. In estimating the urea, if perfect accuracy be not required, the separation of the lithic acid may be avoided, the error hereby introduced amounts to about 0.7 part per 1000, placing the average amount of lithic acid in the urine at 1.0 per 1000. The filtration of the residue after the action of the sulphuric acid may be avoided, and it may be mixed at once with the chloride of platinum, alcohol, and ether. The estimation of the amount of potash and ammonia in the urine should not be neglected, as it is liable to considerable variation: the author found it 1.0 to 11.6 parts per 1000. These two alkalies are precipitated together by treating fresh urine with chloride of platinum, alcohol, and ether. To sepa- rate them, the yellow precipitate is heated to redness, and the residue repeatedly extracted with boiling dilute hydro- chloric acid: the solution is filtered, and the filter burnt. The platinum remaining corresponds to the quantity of ammonia and potash in the urine. On evaporating the filtered liquid with chloride of platinum and alcohol, a precipitate of platino- chloride of potassium is obtained, which is treated as above to estimate the potash it contains. Separation of Albumen.—To estimate the urea in albu- minous urine, a carefully Aveighed portion is treated with bi- chloride of mercury and boiled in a capacious dish. The liquid is then filtered, the precipitate slightly broken up and washed with water. When this is perfectly effected, a slow current of sulphuretted hydrogen is passed through the filtrate, and the liquid is filtered from the sulphuret of mercury formed. The separation of the mercury may also be omitted, if care be taken to guard against the vapors of mercury which escape 544 QUANTITATIVE ANALYSIS. on heating it with sulphuric acid. The filtrate is evaporated with the addition of sulphuric acid until the urea is com- pletely decomposed. The fluid thus obtained is treated as above described. Another weighed portion of the urine is also precipitated with bichloride of mercury, the precipitate washed with alcohol, and the filtrate treated with bichloride of platinum and ether. The platinum obtained enables us to calculate the amount of potash and ammonia present. The author found that albumen is not perfectly precipitated by boiling even from acid urine, neither indeed is it admissible to use nitric acid when the urine is subsequently to be treated for the estimation of urea, since, by the action of sulphuric acid, nitrous acid would be formed, Avhich decomposes the urea so as to liberate part of the nitrogen in the gaseous state. He also found that with alcohol a considerable amount of al- bumen may, in many cases, remain unprecipitated; and that, moreover, the albumen precipitated by alcohol is very difficult to wash. The above process has been shown by Heintz to be applicable to the estimation of the urea in urine containing blood, milk, and bile. In the latter case, should the urea amount to one-ninth of that of the urine (which could hardly occur), the error would not exced 0.16 per 1000. Bunsen's method of estimating Urea*.—It is founded on the fact, that aqueous solutions of urea are readily decom- posed into carbonate of ammonia Avhen heated above 212° jn hermetically closed vessels. The metamorphosis begins even below 248°, but proceeds so slowly at this temperature that it is not completed in three or four hours; Avhile, if the temper- ature is kept between 428° and 464°, three or four hours suf- fice for perfect decomposition. To apply this reaction to the determination of the amount of urea in liquids, it suffices to heat them, in strong glass tubes, with an ammoniacal solution of chloride of barium up to 428°—464°, a precipitate of car- bonate of baryta equivalent to the amount of urea is ob- tained. The author found that none of the different nitrogenous substances present in the urine interfered with the accuracy of this method, and he proved, by direct experiment, that it possesses sufficient accuracy even in the presence of sub- stances the most widely diffused in the animal body. In order * Leibig's Annalen, March, 1848; and Chem. Gaz., vol. vi. p. 222. QUANTITATIVE ANALYSIS. 545 to avoid the influence which the so-called extractive substances of the urine may exert, Bunsen determines the urea from two separate portions of the urine, one of which has been pre- viously deprived of its extractive substances by basic acetate of lead, and he gives a formula for facilitating the calculation from the results of the analysis.* Estimation of the Uric Acid.—A weighed quantity of the fresh urine is precipitated by strong acetic acid; the preci- pitate is collected on a Aveighed filter, and washed Avith water acidified with acetic acid. According to Liebig, the uric acid in the urine is held in solution by phosphate of soda; it has been proved, however, by Heintz, that this in nowise interferes with the accuracy of the method. The uric acid, during its precipitation, carries with it a certain quantity of the coloring substances of the urine; but, according to Heintz, the increase of weight from this cause is about compensated for by the loss which the uric acid sustains by washing. Lastly, the same chemist has proved, by .direct experiment, that neither sugar, albumen, nor blood, have any essential influence upon the quantitative estimation of uric acid, provided acetic acid be employed as the precipitant. Estimation of the Hippuric Acid.\—A weighed or mea- sured quantity of fresh urine is evaporated over the water-bath to the consistence of a thin syrup, and, on cooling, one- twentieth part of strong hydrochloric acid added to it, then shaken with ether, this dissolves the hippuric acid which has separated. It frequently happens that the ethers, as in an emulsion, separate with difficulty from the resin; but this is instantly effected by the addition of a few drops of alcohol. In this case the ethereal solution of the hippuric acid should be shaken, previous to evaporation, with some water, in order to remove the urea taken up by the ethereal solution through the intermediation of the alcohol. When this is done, crystals of pure hippuric acid are obtained on evaporation of the ethereal solution. In stale urine the hippuric acid gives place to benzoic acid, and, when concentrated and distilled, a large quantity of acetic acid is also obtained. Another method of separating the hippuric acid from normal urine, is to evaporate * For this formula, and for the reasoning on which, it is founded, the reader is referred to the original paper, which is too lengthy for our limited space. + Liebig, in Archiv. der Pharm. for March, 1844. 35 546 QUANTITATIVE ANALYSIS. until the salts are deposited, and then to add strong alcohol and apply heat; uric acid remains undissolved. The clear solution is eA'aporated nearly to dryness, the residue redis- solved in hot Avater, and the urea decomposed by passing a current of chlorine through the solution; a small quantity of a mineral acid is then added, and the solution concentrated, when the hippuric acid is obtained in a crystaline state. Betection of Bile in Urine.—A spirituous extract of the secretion is evaporated nearly to dryness on the water-bath; the residue, when cold, is transferred to a test tube. When quite cold, sulphuric acid and a very small quantity of a solution of one part of cane-sugar to four or five of water is added, the temperature of the solution being kept as low as possible. In the course of a feAV minutes, if the most minute trace of bile be present, a violet red color, of more or less dis- tinctness, is produced. Concentrated hydrochloric acid, heated with bile and sugar, likewise produces a red color, but it is much lighter and less beautiful than that with sulphuric acid. The following precautions, in the application of this test, are prescribed by its author* (M. Pettenkofer). 1st. The temperature must not exceed 144° Fahr., other- wise the color may be destroyed; 2d, the quantity of sugar must not be too large, or sulphurous acid may be formed, whereby the color may be concealed; 3d, the sulphuric acid must be free from sulphurous acid; 4th, if the fluid should contain albumen, it should be previously coagulated; 5th, great excess of chlorides convert the color to a brownish red; they should, therefore, be separated. To detect the consti- tuents of the bile in urine, M. Schwertfegerf recommends precipitating with basic acetate of lead. When bile is present, a yellow precipitate is formed, from which a green solution is obtained with alcohol containing some sulphuric acid, and from which pure alcohol extracts, with the assistance of heat, bilate of lead. It is impossible to conclude from the color of the urine as to the presence of bile, since similar colors mav likewise originate from other causes. Betection and Separation of Kreatine.—Pettenkofer and Heintz give the following as the most advantageous method.J To the alcoholic extract of the urine an alcoholic solution of * Ann. der Chem. und Pharm., Oct. 1844. f Jahrb. fur Prakt. Pharm., ix. p. 375. % Comptes Rendus, March 22, 1847. QUANTITATIVE ANALYSIS. 547 chloride of zinc is added; in a short time a deposit is formed, which contains the kreatine in combination with chloride of zinc, together with a small quantity of phosphate of zinc. These two substances are separated by boiling water, which dissolves the first, but which is without action upon the latter. The pure kreatine is obtained from the aqueous solution of its combination Avith chloride of zinc, by precipitating the zinc with hydrosulphuret of ammonia; after having evaporated the filtered liquor as far as possible without a precipitate being formed from the boiling solution, absolute alcohol is added to it, when the kreatine is immediately deposited in the form of small crystals resembling those obtained in ope- rating upon the alcoholic solution of the aqueous extract of meat. The composition of these crystals, according to Heintz, leads to the formula C8H9N3044- 2HO, which is the same as that advanced by Liebig. Betection of Oxalate of Lime.--The following process is recommended by Br. Golding Bird* Allow a portion of the urine passed a few hours after a meal to repose in a glass vessel; if this be done in winter, or during the prevalence of frequent and rapid alterations of temperature, a more or less dense deposit of urate of ammonia will generally make its appearance, arising either from the sudden cooling of the urine, or from interference with the functions of the skin prior to excretion. In warm weather, however, or when the functions of the skin are tolerably perfect, the urine, albeit it may be loaded with oxalate of lime, may still appear limpid, or, at furthest, its lower layers only be rendered opaque by the deposition of a cloud of vesical mucus. Decant the upper nhs of the urine; pour a portion of the remainder into a watch glass, and gently warm it over a lamp; in a few seconds the heat will have rendered the fluid specifically lighter, and induced the deposition of crystals of oxalate, if any were pre- sent; this maybe hastened by gently moving the glass to and fro so as to give the fluid a rotatory motion, which will col- lect the oxalate to the bottom of the capsule. The applica- tion of warmth serves also to remove the obscurity arising from the presence of urate of ammonia, which, as is well known, is readily dissolved by exposing the urme containing it to a gentle heat. * Lond. Med. Gaz., 1841-2, p. 638. 54s QUANTITATIVE ANALYSIS. Having allowed the urine to repose for a minute or two, remove the greater portion of the fluid Avith a pipette, and replace it by distilled water. A white poAvder, often of a glittering appearance, will now become visible, and this, un- der a low magnifying power, as by placing the capsule under a microscope furnished with a half-inch object-glass, will be found to consist of splendid crystals of oxalate of lime, in beautifully formed octohedra, with sharply defined edges and angles. It sometimes occurs that the oxalate is present in the form of exceedingly minute crystals: it then resembles a series of minute cubes, often adhering together like blood- discs ; these, however, are readily and rapidly resolved into octohedra under a high magnifying power. Betermination of the Alkaline and Earthy Phosphates.— Br. Bence Jones,* in his investigations relative to the amount of phosphates in the urine of a healthy man, adopted the following method:—The specific gravity of the urine was first taken, and if ever it was not strongly acid, a drop or two of hydrochloric acid Avas added. Then, from a weighed quantity, usually about 1000 grains, the earthy phosphates were pre- cipitated by means of pure ammonia, filtered, washed with ammoniacal water, and then heated to redness; a drop or two of nitric acid being added at last. The alkaline phosphates were estimated by taking usually about 500 grains of the urine, adding an excess of chloride of calcium and then pure ammonia; by this means all the phosphoric acid was precipi- tated as phosphate of lime; this Avas filtered, well washed, and heated to redness with nitric acid; by deducting the previously determined earthy phosphates, the difference was considered as alkaline phosphates. The results, though they answered well for purposes of comparison, are somewhat too high, in consequence of the formation of a small quantity of carbonate of ammonia and the precipitation of some sulphate of lime, which even long washing cannot entirely remove. Betection of Sugar in Urine. 1. Hunefeld's Test.f—Place four ounces of the suspected urine in a glass exposed to the sun's rays, and add about six drops of. a tolerably strong solution of chromic acid. In a * Contributions to the Chemistry of the Urine, Phil. Trans., Part 2, 1845. t Journ. fur Practische Chemie, vii. 42. QUANTITATIVE ANALYSIS. 549 few minutes the mixture, previously orange red, becomes brownish, and soon after assumes a bistre-brown color, if sugar be present. These changes take place much more quickly if the mixture of urine and chromic acid be gently warmed before exposure to light. This test depends for its action upon the deoxidizing power of the sugar, by which the chromic acid is reduced to oxide of chromium; for, after warming the mixture, the addition of a few drops of liquor potassse produces a copious deposit of green oxide. There is an important objection to this test, which renders all its indica- tions liable to serious fallacy, depending upon the fact, that all urine containing a normal proportion of coloring matter deoxidizes chromic acid; and consequently urine, whether saccharine or not, will partially convert this acid into oxide. This change certainly does not occur so readily in non-sac- charine urine as in a diabetic state of that fluid, but still it is sufficiently marked to prevent HiXnefeld's test being re- garded in any other light than a fallacious one. 2. Runges Test.*—Allow a thin layer of the suspected urine to evaporate on a white surface, as the bottom of a white plate; and, whilst warm, drop upon the surface a few drops of sulphuric acid, previously diluted with six parts of water. With healthy urine the part touched with the acid becomes merely of a pale yellow color, from the action of the latter on the coloring matter of the urine; whilst if sugar be pre- sent the spot becomes deep brown, and soon black from the decomposition of sugar by the acid, and consequent evolution of carbon. This test is stated to be so delicate that 1 part of sugar dissolved in 1000 of urine can be readily detected; and even when mixed with 2000 parts the indications are tole- rably distinct. According to Br. Golding Bird,f the pre- sence of albumen introduces a fallacy into the application of this test, the acid assuming a tint nearly resembling that pro- duced by sugar. 3. Trommer's Test.%—This is a very trustworthy test, and much superior to either of the preceding. Add to the sus- pected urine contained in a large test-tube a few drops of a solution of sulphate of copper. A very inconsiderable trou- bling generally results, probably from the deposition of a lit- * Poggendorff's Annalen, Band 33, s. 431. f London Medical Gazette. % Phil. Mag., March, 1842. 550 QUANTITATIVE ANALYSIS. tie phosphate of copper. Sufficient liquor potassse should then be added to render the Avhole strongly alkaline; a gray- ish green precipitate of hydrated oxide of copper falls, which, if sugar be present, wholly or partly redissoh'es in an excess of the solution of potassa, forming a blue liquid not very un- like the blue ammoniuret of copper. On gently heating the mixture nearly to ebullition, the copper falls in the state of sub-oxide, forming a red and copious precipitate. If sugar be not present, the copper is deposited in the form of black oxide. This test is founded on a fact long known, but not previously applied to the detection of sugar, of the power possessed by some organic matter of reducing oxide of copper, as well as some other oxides, to a lower state of oxidation. It is important that no more of the solution of sulphate of cop- per be used than is sufficient to afford a decided precipitate on the addition of the liquor potassse. If this precaution be not attended to, a part only of the black oxide will be reduced to red oxide, unless a very large quantity of sugar be present, and thus the indications of the test will be rendered indistinct. 4. Test of Fermentation.—The development of the vinous fermentation, on the addition of a little ferment or yeast to a fluid, has long been applied to the detection of sugar. When a little yeast is added to healthy urine, and exposed to a tem- perature of about 80°, no other change occurs for some time, except the development of a portion of carbonic acid mecha- nically entangled in the yeast. When sugar is present in the urine thus treated, it soon becomes troubled, a tolerably free disengagement of bubbles of carbonic acid takes place, and a frothy scum forms on the surface of the fluid, which evolves a vinous odor. These changes take place with great rapidity, even when the quantity of sugar present is very small. If the evolved carbonic acid be collected, the quantity of sugar in the urine may be determined by measuring it, as a cubic inch of the gas very nearly corresponds to a grain of sugar. In the great majority of specimens of diabetic urine it is not necessary to add yeast to excite fermentation, provided a sufficient temperature be employed. 5. Test afforded by the Growth of Torulse.—If the smallest proportion of sugar exists in urine, exposed for a few hours to a temperature above 70°, and a drop of the fluid (taken from the surface) be examined under the microscope, nume- rous very minute ovoid particles will be discovered. In the QUANTITATIVE ANALYSIS. 551 course of a few hours more these become enlarged, and appear as distinct oval or egg-shaped vesicles, which soon become developed into a confervoid or fungoid vegetation, identical with that which appears in ordinary saccharine fluids when un- dergoing the vinous fermentation. The advantages of this test are the facility with which its indications are observed by the microscope with an object-glass of one-seventh or one-eighth inch focus, and the certainty of any possible fallacy being corrected by the subsequent development of fermentation. It is, however, less convenient than Trommer's, in conse- quence of the time required before its indications can be observed. 6. Lowig's Method.—Evaporate the urine to the consist- ence of a syrup, then exhaust the residue with alcohol. The alcoholic urinary solution is then mixed with an alcoholic solution of potash, when, if sugar be present, a white precipi- tate, a compound of sugar and potash, is formed, which, when washed with alcohol, and then dissolved in water, yields a saccharine solution, which is fit for any further examination, and from which the amount of sugar may be ascertained quan- titatively, if necessary. Urinary Calculi. Uric Acid.—These, which are the most abundant, are known by their solubility in caustic potassa, and their precipi- tation from the alkaline solution by acid. In nitric acid, with the aid of heat, they are soluble, and the solution, Avhen eva- porated to dryness, leaves a residue, which, on the addition of ammonia, assumes a purple red color (murexide). Before the blowpipe the uric acid calculus is consumed, leaving a small quantity of a white ash, which has an alkaline reaction. Urate of Ammonia.—This calculus is distinguished from the last by its solubility in carbonate of potassa, and by its evolving ammonia when digested with caustic potassa. ^ Bone Earth.—This also is a common calculus. It is insolu- ble in caustic alkalies, and does not burn when heated.^ In a strong heat it fuses. It is insoluble in acetic acid, but is solu- ble in the mineral acids even when diluted. Ammonia-Magnesian Phosphate.—-This calculus is soluble in acetic acid, and again precipitated by ammonia It evolves ammonia when digested with caustic potassa, and also when heated alone. It has frequently a crystaline appearance. 552 QUANTITATIVE ANALYSIS. Fusible Calculus.—This is a mixture of the two preceding. It is partly soluble in acetic, and wholly in hydrochloric acid. It melts easily before the blowpipe into a pearly bead. Oxalate of Lime.—Insoluble in acetic acid: converted by heat into carbonate of lime, which dissolves in acids with effervescence. It is also decomposed by boiling with car- bonate of potassa. It is very hard, and has a dark-colored rough surface. Xanthic Oxide.—This calculus is rare. It is soluble in potash, but is reprecipitated by carbonic acid. It dissolves in nitric acid without effervescence. It is distinguished from uric acid in not furnishing murexide when ammonia is added to the residue on evaporating the nitric solution. The above are the most frequently occurring calculi. It is not uncommon, however, to meet with calculi in which layers of uric acid alternate Avith layers of phosphate of lime, am- monia-magnesian phosphate, and fusible calculus. 'TftNOcqq'^eNqoq co Tf im o oo to tj< e* o oo co •*!• cn © oq q •* # e* © oq q •>* e* oci^&t^&~ttoci^to lOiOlOlOOlOCOCOCOCOCOt— f^t^C-r-t-00C0G000C005050505C75O5OOOOO — •—«"—i -h ^- .—UNCJOtM cM'*tD'vioi'-miot-ooo(N^|cot-oi'-Mioo)^n nmmmmn't^Tf5«mSoioiO>o»j^£^£^COCX)C»COOOOOCOCOCOCOOT030i05C^ iOT)iwooo»^«oM»^MOKte^«ooo(e^«qoq»^«qoqw^iNqoq»^«ooqc9^«q<»o co' oo' © ci tp" b r»" 05 —' co ^ cd cd b c< co u^ r^ 05 ^ 00COTtt©00COTt^vniomiomiocococDcocoi>t-)>r-r-t-ooGOOoooooo5030505a50i©©©oo (NWN«(MMM«(N0C0t-00C5©^t-C-t-C000X)C0C»COCX3b->^Ot-o^ ^-g5^^§S"SoScoCOCOCOCOCOC-r-l?PScOOOCCCOM0003050^05C35© o-rH ioco^(Km©i^(Mco^vocDt-oo(^©--cNco^iocor^ooc^©^cNmTt«cot^ooo5©^(Mco^iocor-o^ D^«»^*OT°~£2S.22rtS2cN0©CNTt0^,M«iHO'iMM ITTTTTTT M17771777177 m m m n" MTT1TT77T7 i i i i i i i i i + ©COCO~105Wl4^COtOf— OCOCO-JOiOlil^COtOi-'© ^- ~"re o- 3 re Q--3 £.09 5 g S £ en ^ re ■JOjCiifcWhOM t-OC0C000-J-3O5C505_0l0liU*. cococo^-tnbco^-'i^^-J-- bibio-coj^bb'tobobi t£5^0i©»-.~lGOCOtOOltOt005COCO~lCO— COOitO O50\--COCO~JtO©--^-05Cn*>.O3COi— tOCO^-~!Ol ^2 ►o o t?o » K"< o re i ro 33!> re 0, ^ « re c O- re — o 3 c ^cocooJcoooweotocototototoVotototototo ©COOoSo5W*.COtO.-©COOO~105 0i^COtO-- ,~S-re °o 3 re a~j m"^; ft) .-.ere i-i •J- re e re CJlC^^^ifc^WCOCOtOtOtOtOtOtOtOtOtO.-''-' ii to co & £ — co-3wco>-cDoop50icoto©qai b-co^'toGcb'^^^bbo^O'bbitocobg 05©050>03COCO-J—'O5©CO^>&.t0CO—'O-JO CCWCOCOC ti » o IK Ere? re ^ re £ re >j» 2 8.5 • CD C - o 5 g o <-. totototototototototototototoKototototototo ^COCOCOCOCOCOCOCOCOCOtOtOtOtOtOfcOtOtOtOtO ©COOO-J050lif*.tOtO~©COOO-3050li^COtOi— ©° ffiOlOlOiOiUlOtUi^i^iKibi&^UCOUWUKIbS ^^OC005CneO-">CO~1054*K>OpO-JOiCO--CO 00^ ©Voii^bbobuiiubbobUi'^bboo'torf^bsbo© 0 re 3 TI p 3- tototototototototototototototototototototo I— ©CO00 *k tS ■- CO-JOlCOtO©00O5*»CO — CO -1 O' bo © io *>. os bo b "to >&. 05 bo b to '&* 05 bo © to it*. 05 bo 0 re 3 TI =r tototototototototototototototototototototo to— ©CO00-aO5O>i(>-tOtOi-'©CO00-JO3Ol*.CO too OiOiOiOiOi&OlOiOlOlOlOiOiOlOlOlOlOlOlOlOl cocococococotototohoto — — — — — --©oo© co-J05>l^60©oo-lOico>—coooosi^tooco-Jtnco bbo©toi^bbobk>^05bobtoii.bbobto*.b5 Cent. Fahr. cococototototototototototototototototototo ©©©©cocococococococococococooooocnoooo WtO-®t3O)'JO)0\4»W>SH.OCP00-JO5 0\* COO cjic^oic>oi&oicnc^wc>c>c>oic>oiO>Oioioioi MOicoto©coo34^coH-q^oi>t».joocopoico --^bbo©k>^bbo©K>i^b5bo©to*-b5bo©toii. O re 3 TI p S" uuuuuuucjcococouuucowcc io _ _ _- ___«-.»-»-»-©©©©©o ©COCO-J05C!l4i-COlOH-©COOO<103t» i^-O 050)CD05C350iOiC310iCnOiOlCnO-tO©CD~ltnCO.-©GC05>t*.tO-- CO © to '.^ 05 bo © to i* b bo '© io '*. b> bo © to° O re 3 TI S- QUANTITATIVE ANALYSIS. 555 TABLE III. Showing the Quantity of Oil of Vitriol of Specific Gravity 1.8485, and of Anhy- drous Acid in 100 Parts of dilute Sulphuric Acid, of different Densities, accord- ing to Dr. Ure. Liquid. Specific Gravity. Dry. Liquid. Specific Gravity Dry. 100 1.8485 81.54 50 1.3884 40.77 99 1.8475 80.72 49 1.3788 39.95 98 1.8460 79.90 48 1.3697 39.14 97 1.8439 79.09 47 1.3612 38.32 96 1.8410 78.28 46 1.3530 37.51 95 1.8376 77.46 45 1.3440 36.69 94 1.8336 76.65 44 1.3345 35.88 93 1.8290 75.83 43 1.3255 35.06 92 1.8233 75.02 42 1.3165 34.25 91 1.8179 74.20 41 1.3080 33.43 90 1.8115 73.39 40 1.2999 32.61 89 1.8043 72.57 39 1.2913 31.80 88 1.7962 71.75 38 1.2826 30.98 87 1.7870 70.94 37 1.2740 30.17 86 1.7774 70.12 36 1.2654 29.35 85 1.7673 69.31 35 1.2572 28.54 84 1.7570 68.49 34 1.2490 27.72 83 1.7465 67.68 33 1.2409 26.91 82 1.7360 66.86 32 1.2334 26.09 81 1.7245 66.05 31 1.2260 25.28 80 1.7120 65.23 30 1.2184 24.46 79 1.6993 64.42 29 1.2108 23.65 78 1.6870 63.60 28 1.2032 22.83 77 1.6750 62.78 27 1.1956 22.01 76 1 6630 61.97 26 1.1876 21.20 75 1.6520 61.15 25 1.1792 20.38 74 1.6415 60.34 24 1.1706 19.57 73 1.6321 59.52 23 1.1626 18.75 72 1.6204 58.71 22 1.1549 17.94 71 1.6090 57.89 21 1.1480 17.12 70 1.5975 57.08 20 1.1410 16.31 69 1.5868 56.26 19 1.1330 15.49 68 1.5760 55.45 18 1.1246 14.68 67 1.5648 54.63 17 1.1165 13.86 66 1.5503 53.82 16 1.1090 13.05 65 1.5390 53.00 15 1.1019 12.23 64 1.5280 52.18 14 1.0953 11.41 63 1.5170 51.37 13 1.0887 10.60 62 1.5066 50.55 12 1.0809 9.78 61 1.4960 49.74 11 1.0743 8.97 60 1.4860 48.92 10 1.0682 8.15 59 1.4760 48.11 9 1.0614 7.34 58 1.4660 47.29 8 1.0544 6.52 57 1.4560 46.48 7 1.0477 5.71 56 1.4460 45.66 6 1.0405 4.89 55 1.4360 44.85 5 1.0336 4.08 54 53 1.4265 44.03 4 1.0268 3.26 1.4170 43.22 3 1.0206 2.446 52 51 1.4073 42.40 2 1.0140 1.63 1.3977 41.58 1 1.0074 0.8154 556 QUANTITATIVE ANALYSIS. TABLE IV. Showing the Quantity of Real or Anhydrous Nitric Acid in 100 Parts of Liquid Acid, at different Densities, according to Dr. Ure. Specific Gravity. Real Acid in 100 parts of the Liquid. Specific Gravity. Real Acid in 100 parts of the Liquid. 1.5000 79.700 1.2947 39.850 1.4980 78.903 1.2887 39.053 1.4960 78.106 1.2826 38.256 1.4940 77.309 1.2765 37.459 1.4910 76.512 1.2705 36.662 1.4880 75.715 1.2644 35.865 1.4850 74.918 1.2583 35.068 1.4820 74.121 1.2523 34.271 1.4790 73.324 1.2462 33.474 1.4760 72.527 1.2402 32.677 1.4730 71.730 1.2341 31.880 1.4700 70.933 1.2277 31.083 1.4670 70.136 1.2212 30.286 1.4640 69.339 1.2148 29.489 1.4600 68.542 1.2084 28.692 1.4570 67.745 1.2019 27.895 1.4530 66.948 1.1958 27.098 1.4500 66.155 1.1895 26.301 1.4460 65.354 1.1833 25.504 1.4424 64.557 1.1770 24.707 1.43S5 63.760 1.1709 23.910 1.4346 62.963 1.1648 23.113 1.4306 62.166 1.1587 22.316 1.4269 61.369 1.1526 21.519 1.4228 60.572 1.1465 20.722 1.4189 59.775 1.1403 19.925 1.4147 58.978 1.1345 19.128 1.4107 58.181 1.1286 18.331 1.4065 57.384 1.1227 17.534 1.4023 56.587 1.116S 16.737 1.3978 55.790 1.1109 15.940 1.3945 54.993 1.1051 15.143 1.3882 54.196 1.0993 14.346 1.3833 53.399 1.0935 13.549 1.3783 52.602 1.0878 12.752 1.3732 51.805 1.0821 11.955 1.3681 51.068 1.0764 11.158 1.3630 50.211 1.0708 10.361 1.3579 49.414 1.0651 9.564 1.3529 48.617 1.0595 8.767 1.3477 47.820 1.0540 7.970 1.3427 47.023 1.04S5 7.173 1.3376 46.226 1.0430 6.376 1.3323 45.429 1.0375 5.579 1.3270 44.632 1.0320 4.782 1.3216 43.835 1.0267 3.985 1.3113 43.038 1.0212 3.188 1.3110 42.241 1.0159 2.391 1.3056 41.444 1.0106 1.594 1.3001 40.647 1.0053 0.797 QUANTITATIVE ANALYSIS. 557 TABLE V. Showing the Quantity of Absolute Alcohol in Spirits of different Specific Gravities, according to Lowitz. 100 Parts. Specific Gravity. 100 Parts. Specific Gravity. Alcohol. Water. At 68°. At 60O. Alcohol. AVater. At 68°. At 60°. 100 0 0.791 0.796 49 51 0.917 0.920 99 1 0.794 0.798 48 52 0.919 0.922 98 2 0.797 0.801 47 53 0.921 0.924 97 3 0.800 0.804 46 54 0.923 0.926 96 4 0.803 0.807 45 55 0.925 0.928 95 5 0.805 0.809 44 56 0.927 0.930 94 6 0.808 0.812 43 57 0.930 0.933 93 7 0.811 0.815 42 58 0.932 0.935 92 8 0.813 0.817 41 59 0.934 0.937 91 9 0.816 0.820 40 60 0.936 0.939 90 10 0.818 0.822 39 61 0.938 0.941 89 11 0.821 0.825 38 62 0.940 0.943 88 12 0.823 0.827 37 63 0.942 0.945 87 13 0.826 0.830 36 64 0.944 0.947 86 14 0.828 0.832 35 65 0.946 0.949 85 15 0.831 0.835 34 66 0.948 0.951 84 16 0.834 0.838 33 67 0.950 0.953 83 17 0.836 0.840 32 68 0.952 0.955 82 18 0.839 0.843 31 69 0.954 0.957 81 19 0.842 0.846 30 70 0.956 0.958 80 20 0.844 0.848 29 71 0.957 0.960 79 21 0.847 0.851 28 72 0.959 0.962 78 22 0.849 0.853 27 73 0.961 0.963 77 23 0.S51 0.855 26 74 0.963 0.965 76 24 0.853 0.857 25 75 0.965 0.967 75 25 0.856 0.860 24 76 0.966 0.968 74 26 0.859 0.863 23 77 0.968 0.970 73 27 0.861 0.865 22. 78 0.970 0.972 72 28 0.863 0.867 21 79 0.971 0.973 71 29 0.866 0.870 20 80 0.973 0.974 70 - 30 0.868 0.872 19 81 0.974 0.975 69 31 0.870 0.874 18 82 0.976 0.977 68 32 0.872 0.875 17 83 0.977 0.978 67 33 0.875 0.879 16 84 0.978 0.979 66 34 0.877 0.881 15 85 0.980 0.981 65 35 0.880 0.883 14 86 0.981 0.982 64 36 0.882 0.886 13 87 0.983 0.984 63 37 0.885 0.889 12 88 0.985 0.986 62 38 0.887 0.891 11 89 0.986 0.987 61 39 0.889 0.893 10 90 0.987 0.988 60 40 0.892 0.896 9 91 0.988 0.989 59 41 0.894 0.898 8 92 0.989 0.990 58 42 0.896 0.900 7 93 0.991 0.991 57 43 0.899 0.902 6 94 0.992 0.992 56 44 0.901 0.904 5 95 0.994 55 45 0.903 0.906 4 96 0.995 54 46 0.905 0.908 3 97 0.997 53 47 0.907 0.910 2 98 0.998 52 48 0.909 0.912 1 99 0.999 51 49 0.912 0.915 0 100 1.000 50 50 0.914 0.917 s S3-T3 m* en p g p <-t a c+- en P ^ ^E o M P^ h5 CD ^ P* O ° P p CD O i.H>0 >-*s O o* o P i-s tr p ^» ^ 4 f B h "" ST cr S- p ,- © ^ - •« p" rs &^ m ^ 4 ° S, p 2 O CD TJ P 2 P «-" < l P^ COCOCOCOCOCDCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCDCOCOCOCOCOO CDCOCDCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCDCOCOcecOCOCDCOCDCOCOCOCDCOO 050505050505a5050505-4-J-J-J-3-3-J^-J^GOOOGOOOG©OOOOOOOOOCCOCOCOCOCOCOCOCOCOCO© Oh-t003^0i05^C»CO©--tOC04^W05_• © co co oo oo -j -a b b "en bi ">&. in co to to "— *— b © co co bo bo '-3 b b h\ bi "*» V to to to to "—'"—bo £.OCCO-4tO-Jtoa5--Oi»-'Ol© 3 o « re re o COCOCDCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCO COCOCOCOCOCOCOCDCOCOCOCOCOCOCDCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCDCOCOCOCO M(atsi4(atoNi(o(a6aN)CowcoucocouwwcoAA>^**.ifi*^jiitoiOiCiiOio\OiaoioiOi CO©»-tOCO^Oi05-!.*_. 00CO©H-tOCO*-CnC5nCnO5-JG0CO©»- tOCO*.OlO5^100CD©i-i tO CO i£- CJ< C5 -1 00 0-J-J^050lC^050505C5C^05C^0505050^05C^C5lC^C>OlOlOlC^C>C^C^OiOlOlC>C^M^ to — b b b bo no o b bs oi V In co to to'— bbbbobo^jlobbbi'#>.cocototo — bbcoboboUiVjb C005COtOO re 2 o. COCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCDCOCOCOCOCOCOCOCOCOCOCOCOCOCDCOCOCD 00 00 00 00.00 CX)CZ)C»00CCCOCOCO00C0CCCOCC0000COCOCOCB00COCOCOC»C»C»C»COC»CCCO cow^^j^*i&^it^ifcfc»»oi»oi0ioio\oicj>o)0)oi«ffi0)0)0)0)aj.j^»ioooo 00 CO © — tOCO^»O5^CBCO©^tOCO1^WO5-JC»CO©H-t300inOlOJ-J00CO©>--toCOi(>.OiO5^ re g o offlp!0»pwppffltotoffl!Offlooai»(»ooaiaiMa'oooooooooO'jvi^^«j^.coco -JtOtOO>C»©W05CO--^^©tOOlC>0--i^ SIS ^*i 55 «3 CO QUANTITATIVE ANALYSIS. 559 pulverized and added to ordinary alcohol of specific gravity .850 at 60° Fahr. till it ceased to dissolve any more: the whole was then allowed to digest 24 hours, being frequently agitated, when the alcohol was carefully poured off. As much fresh-burned quicklime as was considered sufficient, when powdered, to absorb the whole of the alcohol, was introduced into a retort, and the alcohol added to it; after digesting 48 hours, it was slowly distilled in a water-bath, at a tempera- ture of about 180° Fahr. The alcohol thus obtained was carefully redistilled, and its specific gravity at 60° Fahr. was found in two experiments to be .7946 and .7947. It was subse- quently digested a second and a third time for several days with recently ignited quicklime, and redistilled at 172° Fahr. The mean of several determinations gave the number .79381, which the author thinks may be regarded as expressing the true specific gravity of absolute alcohol at 60° Fahr. TABLE VII. In the following table the figures are all calculated on the equivalent numbers assigned to the elementary substances in the table inserted at page 233, and which is from the latest authorities; few of the numbers differ very considerably from those given in similar tables in other works on Chemical Ana- lysis; but, with the accuracy which is now introduced into the science, it was thought that the advantages of having a series of numbers in accordance with the atomic weights, as at pre- sent received, were sufficiently great to justify the time con- sumed in the recalculation. The application of these tables, and their great convenience in quantitative analysis, may be illustrated by the following example: 1. Suppose, as the result of an experiment to determine the amount of sulphuric acid in a certain substance, 37.45 grains of sulphate of baryta are obtained: on turning to the table we find under the head of "required" sulphuric acid, "found" sulphate of baryta, a series of figures arranged in nine columns, those in the first column representing the quan- tity of sulphuric acid in a unit of sulphate of baryta, and 560 QUANTITATIVE ANALYSIS. those in the other columns the multiples of that number by 2, 3, 4, 5, 6, 7, 8, and 9. In the case we are considering we require to learn the amount of sulphuric acid in 37.45 grains of sulphate of baryta; we turn to column 3, where we find the number 1.02872; we put down this number, therefore, shifting the decimal point one figure further to the right; we next turn to column 7, where we find the number 2.40058; we place this number under the former, preserving the deci- mal point unaltered; we have thus filled up the tens' and the units' place; the next number is 4, under which column we find the number 1.37176; but as this in our experiment is the first place of decimals, in writing down the number we shift the decimal point one figure further to the left; in like manner, the last number being 5, and in the second place of decimals, we shift the decimal point of the number found under column 5, viz: 1.71470 two places further to the left; the whole will consequently stand thus:— 10.2872000 2.4005800 .1371760 .0171470 12.8421030 37.49 grains of sulphate of baryta contain, therefore, 12.842 grains of sulphuric acid. TABLE VII. col Oil Required. Aluminum A I, Ammonia NH3 Ammonia NH3 Antimony Sb Oxide of Anti- mony Sb03 Oxide of Anti mony Sb03 Oxide of Anti mony Sb03 Arsenic As Arsenic As Arsenious Acid AsOs Arsenious Acid AsO, Found. Alumina A1203 Chloride of Am- motiium NH4C1 Ammonio-chloride of Platinum NH4ClPtCl, Oxide of Antimony Sb03 Antimony Sb Sulphuret of Anti- mony SbSs Antimonious Acid Sb04 Arsenious Acid AsOs Arsenic Acid As05 Arsenic Acid As05 Sulpharsenious Acid AsS, 1 0.53289 0.31776 0.07611 0.84317 1.18600 0.86443 0.95032 0.75757 0.65217 0.86087 0.80488 1.06578 0.63552 0.15222 1.68634 2.37200 1.72886 1.90064 1.51514 1.30434 1.72174 1.60976 1.59867 0.95328 0.22833 2.52951 3.55800 2.59329 2.85096 2.27271 1.95651 2.58261 2.41464 4 5 6 7 2.13156 2.66445 3.19734 3.73023 1.27104 1.58880 1.90656 2.22432 0.30444 0.38055 0 45066 0.53277 3.37268 4.21585 5.05902 5.90219 4.74400 5.93000 7.11600 8.30200 3.4577-2 4.32215 5.18659 6.05101 3.80128 4.75160 5.70192 665224 3.03028 3.78785 4.54542 5.30299 2.60868 3.26085 3.91302 4.56519 3.44348 4.30435 5.16522 6.02609 3.21952 4.02440 4.82928 5.63416 TABLE VII.—CONTINUED. Required. Baryta BaO Baryta BaO Baryta BaO Bismuth Bi Boron B Bromine Br Cadmium Cd Calcium Ca Lime CaO Lime CaO Carbon C Carbonic Acid CO, Chlorine Cl Found. Sulphate of Baryta BaOS03 Carbonate of Ba- ryta BaOCO, Silico-fluoride of Barium BaFl,SiFla Oxide of Bismuth BiO Boracic Acid B03 Bromide of Silver AgBr Oxide of Cadmium CdO Lime CaO Sulphate of Lime CaOS03 Carbonate of Lime CaOCO, Carbonic Acid CO, Carbonate of Lime CaOC02 Chloride of Silver AgCl 0.65706 0.77696 0.52460 0.89867 0.31241 0.42016 0.87449 0.71429 0.41176 0.56000 0.27273 0.44000 0.24729 1.31412 1.55392 1.04720 1.79734 0.62483 0.84032 1.74899 1.42857 0.82353 1.12000 0.54545 0.88000 0.49458 1.97118 2.33088 1.57380 2.69601 0.93724 1.26043 2.62348 2.14286 1.23529 1.68000 0.81818 1.32000 0.74188 2.62824 3.10784 2.09440 3.59468 1.24966 1.68064 3.49797 2.85714 1.64706 2.24000 1.09091 1.76000 0.98917 3.28530 3.88480 2.64300 4.49335 1.56207 2.10080 4.37246 3.57143 2.05882 2.80000 1.36364 2.20000 1.23646 3.94236 4.66176 3.14760 5.39202 1.87449 2.52096 5.24696 4.28571 2.47059 3.36000 1.63636 2.64000 1.48375 7 8 ' . 4.59942 5.28648 5.91354 5.43872 6.21568 6.99264 3.67220 4.18880 4.72140 6.29069 7.18936 8.08803 2.18690 2.49932 2.81173 2.94112 3.36128 3.78144 6.12145 6.99594 7.87044 5.00000 5.71429 6.42857 2.88235 3.29412 3.70588 3.92000 4.48000 5.04000 1.90909 2.18181 2.45455 3.08000 3.52000 3.96000 1.73104 1.97834 2.22563 Cn OS Hydrochloric Acid HCl i Chromium Cr Chromic Acid 2Cr03 Chromic Acid Cr03 Protoxide of Co- balt CoO Copper Cu Fluorine Fl Fluorine 3F1 Hydrogen H Iodine I Iron Fe2 Protoxide of Iron 2FeO Lead Pb Chloride of Silver AgCl Oxide of Chro- mium Cra03 Oxide of Chro- mium Cr203 Chromate of Lead PbOCr03 Cobalt Co Oxide of Copper CuO Fluoride of Cal- cium CaFl Fluoride of Silicon SiFI3 Water HO Iodide of Silver Agl Oxide of Iron Fe„0 2^3 Oxide of Iron Fe203 Oxide of Lead PbO TABLE VII.—CONTINUED. Required. Oxide of Lead PbO Oxide of Lead PbO Lead Pb Oxide of Lead PbO Magnesium Mg Magnesia MgO Magnesia 2 MgO Manganese Mn Manganese Mn3 Protoxide of Manganese MnO Protoxide of Mercury H?20 Found. Sulphate of Lead PbOS03 Chloride of Lead PbCl Chloride of Lead PbCl Sulphuret of Lead PbS Magnesia MgO Sulphate of Mag- nesia MgOS03 Pyrophosphate of Magnesia 2MgO,P05 Protoxide of Man ganese MnO Manganoso-man- ganic Oxide MnO-fMna03 Protosulphate of Manganese MnO,S03 Mercury Hg2 1 0.73608 0.80250 0.74495 0.93309 0.61204 0.34015 0.36468 0.77571 0.72176 0.4713S 1.03997 2 3 4 5 6 7 8 9 1.47216 2.20823 2.94431 3.68039 4.41647 5.15255 5.88862 6.62470 1.60500 2.40749 3.20999 4.01249 4.81499 5.61749 6.41998 7.22248 1.48990 2.23485 2.97980 3.72475 . 4.46970 5.21465 5.95960 6.70455 1.86618 2.79926 3.73235 4.66544 5.59853 6.53162 7.46470 8.39779 1.22407 1.83611 2.44815 3.06018 3.67222 4.28426 4.89630 5.50833 0.68030 1.02046 1.36061 1.70076 2.04091 2.38106 2.72122 3.06137 0.72936 1.9404- 1.45872 1.82340 2.18808 2.55276 2.91744 3.28212 1.55142 2.32713 3.10284 3.89855 4.65426 5.42997 6.20568 6.98139 1.44352 2.16528 2.88704 3.60880 4.33056 5.05232 5.77408 6.49584 0.94276 1.41414 1.88552 2.35690 2.82828 3.29966 3.77104 4.24242 2.07994 3.11991 4.15988 5.19985 6.23983 7.27980 8.31977 9 35974 QUANTITATIVE ANALYSIS. 565 00 i> cn o CO i> »rt •<* i> 00 ^ 00 CO •«* o CO CO CO CO o m CN CN CO 00 1ft OS o cn «n 00 CO 01 CO OS 1> t> ■* o 00 CO l> CO ■*!" -* ■*f o CO t- cq f; p o CN q l> l> q 1> .-< Os i> r-^ r-' d ** ■* ^ " ^ ■^ \ri vft •<* CO ■«* o ,H o O CN ■* CN CN CO CO o o CN t> 00 CO CO 00 CN cn l> o CO os o t- ■* CN CO CO CN ■<* CO CN CO co os cn cn o CO o CN O O o 00 OS to t> 00 CN o »H r> 00 o o o o o 00 cd CO CO d *■• CO cn" r* ~ CO vft Tji cn to 00 ^ CO CN o cn ^ 1ft CO Tj< o> o o o cn cn U0 CO O CN o CN o CO o i^ cn ■<* o •* 00 o CN t~ cn o TJ> CO o CO cn ■<* cn o CO CO o OS q o ■<* OS CN o CO CO i-^ ■*. p r»' lri CD o d d CO 00 ~ ~ CO ■* ■ft O^ o en r> OJ t- CN r> CO Tl< co I> 1ft t> OS t- CN I- O r^ CO co eo CO ■t ■^ o -* l> co 00 i> CO »-* CD CO ■ d ** CN CO CO rt ■q> t> CN o 1> o co m CN O o >ft 1> o I> CN CN CO 1^ CO cn O) CO 00 en c^ o ■* 00 O CN co o en •* CO CO i> i> CN 1> l> CO CN CO cn CO I- CO »-H CT> cn CN •—; 00 \ri ■* ■* CO d d CN CO d d CN CO CN t- CO CN 00 o o o ^ CN CO CO 00 00 t- o CO CO ■fl> CO 00 a. m CO CN CD en 00 00 i> CO O CO i> 00 CO cn TT >>J> no CO o r> i> l> ■^ OS CO CO "cr f-H CN o CO OJ r~ l> t> 1ft CN •>*' co" CO CO d d -* ■t' d d ^ CN CN CO CN CO CO m CN o 00 CJi cn l> CO —1 00 o 1" o Ift CN CO ^H o O t> cn o en 00 CO o 00 CO CO CO CN CO CO >ft CN CO ■<* 00 CO 00 CN CO 00 00 oo CO o CN CN o o CO — ■* CO CO_ o o CO q r-_ CO cn CN CN d d ^ CO d d *" rt '" 00 CN ^ cn o o o o CO CO 00 - Ol ■<* o c- CO CO o cn ■f CO ift ■«t lO o 00 00 cn o 00 o cn CN c- OJ 00 CN o 00 00 00 t> ■"f CO l> o •^ CN OJ >* CO CO oo CN '—[ cn -< " ** d d d CN d d d "" 1-1 TT ,_, o -* o i> o CO CO CO cn CN r~ en 1ft 00 00 o cn r~ © CO o CO en cn CN CD CN CM CN l> "* •<* •* 1ft ■* i> n< CO 00 CO TP CO CN 03 05 «* CO o 00 00 t> o ^H ■V CN — ^* ■* CD -< © d d d d d -< d d d d d *-\/^*^< /^^.^^/^^^^ f%s**r> /^**^\ /^N^N C-i O cu 'C b ° 9 ,rj o §^ oS u cu c_ .a Ch o cu S S -C 3 V c O '2 c-S O Oh §<-B o y fe o B Ui So m O" a, "a W3 3 cu > 0 <* M cu > -a 'o < o 2 a.'a o" fe o" JSfe Hg2< Sulphide cury HgS Protoxide NiO SB |fe s oO O CN o ■%< a Bi ^2 o-fe o J3 , i» cu 2 c ■S M — ss SI S3 CN CCN in o J3 s 1-1 fe < fe o O o fe fe fe o '3 'o <1 noxide of Mercury HgO >> SB £» Sfl a 0) .___ "2 *2 'S ,o'3 VI •> §1" cfe o Q.fe O -S3 ceo cn 0 J3 ja 2 s g £ 55 Z, ^ U H5 fe fe fe TABLE VII.—CONTINUED. Required. Found. 1 2 3 4 5 6 7 8 9 Phosphoric Acid Phosphate of Sil- } po5 ver 3AgO,P05 i 0.17146 0.34292 0.51438 0.68584 0.85730 1.02876 1.20022 1.37168 1.54314 Phosphoric Acid Pyrophosphate of } ™5 Silver 2AgO,P05 £ 0.23689 0.47378 0.71067 0.94756 1.18445 1.42134 1.65823 1.89512 2.13201 Potassium K Potash KO I 0.83020 1.66041 2.49061 3.32081 4.15101 4.98122 5.81142 6.64162 7.47183 Potash KO Sulphate of Potash KO,S03 I 0.54084 1.08168 1.62251 2.16335 2.70419 3.24503 3.78587 4.32670 4.86754 Potash KO Nitrate of Potash KO,N05 I 0.46586 0.93173 1.39759 1.86346 2.32232 2.79518 3.26105 3.72691 4.19278 Potassium Chloride of Potas- s K sium KC1 V 0.52454 1.04908 1.57362 2.09816 2.62270 3.14724 3.67178 4.19632 4.72086 Potash Chloride of Potas- ^ KO sium KC1 S 0.63182 1.26364 1.89546 2.52728 3.15909 3.79091 4.42273 5.05455 5.68637 Potash Potassio-chloride \ KO of Platinum KClPtCl2 \ 0.19297 0.38593 0.57890 0.77186 0.96483 1.15780 1.35076 1.54373 1.73669 Chloride of Po- Potassio-chloride i tassium of Platinum V 0.30541 0.61083 0.91624 1.22166 1.52707 1.83429 2.13790 2.44332 2.74873 KC1 KClPtCl2 S Silicon Si Silicic Acid Si02 I 0.47078 0.94156 1.41234 1.88312 2.35390 4.82468 3.29546 3.76624 4.23702 Silver Ag Chloride of Silver AgCl I 0.75271 1.50542 2.25812 3.01083 3.76354 4.51625 5.26896 6.02166 6.77437 Oxide of Silver AgO Chloride of Silver AgCl I 0.80850 1.61701 2.42551 3.23402 4.04252 4.85103 5.65983 Sodium Na Soda NaO I 0.74172 1.48343 2.22515 2.96686 3.70858 4.45030 5.19201 Soda NaO Sulphate of Soda NaO,S03 I 0.43641 0.87282 1.30923 1.74564 2.18205 2.61846 3.05487 Soda NaO Soda NaO Nitrate of Soda NaO,N05 Chloride of Sodium NaCl I 0.36442 0.53010 0.72805 1.06020 1.09327 1.59030 1.45769 2.12040 1.82211 2.65050 2.18654 3.18061 2.55096 3.71071 Sodium Na Chloride of Sodium NaCl I 0.39318 0.78637 1.17955 1.57274 1.96592 2.35910 2.75229 Soda NaO Carbonate of Soda NaO,C02 I 0.58470 1.16940 1.75410 2.33880 2.92349 3.50819 4.09289 Strontium Sr Strontia SrO I 0.84567 1.69134 2.53701 3.38268 4.22835 5.07402 5.91969 Strontia SrO Sulphate of Stron-tia 0.56446 1.12892 1.79338 2.25784 2.82230 3.58676 3.95122 Strontia SrO SrO,S03 Carbonate of Stron tia SrO,COa \ 0.70205 1.40410 2.10615 2.80420 3.51025 4.21230 4.91435 Sulphur S Sulphate of Baryta BaO,S03 I 0.13717 0.27434 0.41151 0 54868 0.68585 0.82302 0.96019 Sulphur S3 Sulphuret of Ar-senic I 0.39024 0.78048 1.17072 1.56096 1.95130 2.34144 2.73168 As03 s Sulphuric Acid S03 Tin Sn Sulphate of Baryta BaO,S03 Oxide of Tin SnO,, I 0.34294 0.78616 0.68588 1.57233 1.02872 2.35849 1.37176 3.14466 1.71470 3.93082 2.05764 4.71698 2.40058 5.50315 Protoxide of Tin SnO Oxide of Tin SnOa \ 0.89308 1.78616 2.67924 3.57232 4.46543 5.35848 6.25156 Zinc Zn Oxide of Zinc | ZnO I 0.80260 1.60520 2.40781 3.21041 4.01301 4.81561 5.61821 APPENDIX. ON SOME NEW APPLICATIONS OF SULPHURETTED HYDROGEN IN CHEMICAL ANALYSIS. BY M. EBELMEN. Hitherto sulphuretted hydrogen has rarely been employed in analysis, ex- cept to precipitate certain metals from their solution in acids. In many cases this substance is one of the most accurate and handy reagents known. The facts contained in the present paper will show that it may likewise be used with considerable advantage for separating certain substances one from the other by converting them iD the dry way into sulphurets. It may then happen that one of the sulphurets formed is not acted upon by acids, while the other is; it may also happen that one of the sulphurets is volatile, and is separated from the other by the employment of a somewhat elevated temperature. I have employed this method in solving several problems of chemical analysis, the solution of which by our present means was not quite satisfactory. I shall now proceed to give the results obtained. 1. Separation of Manganese from Cobalt.—A considerable number of methods have been proposed for the separation of these two metals. The most accu- rate, according to Rose, would consist in converting the two oxides into proto- chlorides, by heating them in a current of hydrochloric acid gas, and treating the protochlorides at an elevated temperature with hydrogen. The protochloride of cobalt is alone reduced to the metallic state, so that water merely dissolves the protochloride of manganese. This method is complicated and not quite accurate; a little oxide of manganese always remains with the cobalt. It has recently been proposed to treat the solution of the two oxides in hydrochloric acid with an excess of carbonate of baryta, and then to pass into the neutral- ized liquid a current of sulphuretted hydrogen, which was said to precipitate only the cobalt in the state of sulphuret. I found that the cobalt was pre- cipitated, it is true, before the manganese, but that the latter metal was en- tirely thrown down in the presence of carbonate of baryta by the sulphuretted hydrogen; it is consequently impossible to separate these two metals by this process. The method which I have employed to solve the question is simple and very expeditious ; it is founded on the fact, that the sulphuret of cobalt prepared in the dry way is not in the least acted upon by cold dilute hydrochloric acid, which does not apply to the sulphuret of manganese. I proceed as follows:— After having weighed the mixture of the two oxides to be separated, it is placed in a platinum or porcelain tray, and heated in a current of sulphuretted hydrogen. The action begins at the ordinary temperature. The mixture of the two oxides gives off considerable heat in the gas. The tube containing the two oxides is then raised to a dark red heat; the sulphuret is allowed to cool in a current of the gas, the tray drawn out of the tube, and digested in cold water containing a little hydrochloric acid. The sulphuret of manganese alone is dissolved. After some hours' digestion, it is filtered, the liquid boiled, pre- cipitated with potash, and the oxide of manganese determined. The black residue of sulphuret of cobalt is redissolved in nitric acid, and this solution also precipitated by potash. The following experiments will serve to show the ac- curacy of the process:— 570 APPENDIX. First Experiment.—A mixture of Red oxide of manganese .... 0.300 grm. Protoxide of cobalt . . . . 0;300 ... was dissolved in hydrochloric acid, the whole precipitated with potash, and the precipitate washed carefully and calcined; it weighed with the ash of the filter 0.611. It was then heated on a porcelain tray in sulphuretted hydrogen, the sulphurets digested for twelve hours in cold very dilute hydrochloric acid, and then filtered; the filtered liquid was perfectly colorless, and on treatment with potash gave 0.302 red oxide of manganese. The residue of sulphuret of cobalt was decomposed with nitric acid, and the filtered solution precipitated with potash, it gave 0.303 protoxide of cobalt. The red oxide of manganese, on examination before the blowpipe, gave with borax a perfectly colorless bead in the reducing flame, which proved that it contained no cobalt. The oxide of cobalt, treated with nitre and potash in a silver crucible, did not exhibit the least sign of the presence of manganese. Second Experiment.—A mixture of Red oxide of manganese .... 0.481 grm. Protoxide of cobalt.....0.090 ... treated as in the preceding experiment, gave Red oxide of manganese .... 0.486 grm. Protoxide of cobalt.....0.092 ... Both the oxides were ascertained to be free from each other. Third Experiment.—A mixture of 0.023 grm. red oxide of manganese and 0.980 protoxide of cobalt gave, on similar treatment, 0.028 oxide of manga- nese ; the cobalt was not estimated. The oxide of manganese gave a perfectly colorless bead with borax in the reducing flame of the blowpipe. Dissolved in a small quantity of hydrochloric acid, it furnished a perfectly colorless liquid which gave with hydrosulphuret of ammonia an orange colored precipitate. The least trace of cobalt would have blackened it. The slight excess found in the estimation of the manganese, and which is apparent in all the experiments, appears to be attributable to a small quantity of foreign substances in the alkaline solution used to precipitate the cobalt and manganese. The difficulty of obtaining alkalies absolutely free from silica or alumina is well known. It was also found that the cobalt and manganese from the preceding experiments always left a slight insoluble residue when treated with hydrochloric acid after having been calcined and weighed. Fourth Experiment.—A mixture of 0.963 grm. red oxide of manganese and 0-012 protoxide of cobalt afforded on similar treatment 0 012 oxide of cobalt- the manganese was not determined. The oxide of cobalt did not contain a trace of manganese. The two last experiments show that the process may be employed for the accurate separation of cobalt and manganese, even in the case where one of the metals greatly preponderates over the other. It may be applied directly in examining ores of manganese for oxide of cobalt. It would suffice to heat them in a current of sulphuretted hydrogen and then act upon them with very dilute hydrochloric acid. The whole of the cobalt will be contained in the insoluble residue. Separation of Manganese and Nickel.—This is effected by the same method as that for manganese and cobalt. A mixture of Protoxide of nickel ..... 0.179 grm. Red oxide of manganese .... 0.321 ... was dissolved in hydrochloric acid, precipitated with potash, the precipitate calcined, heated in sulphuretted hydrogen, and treated with cold very dilute hydrochloric acid. There was found— APPENDIX. 571 Oxide of nickel • • • • 0-178 grm. Red oxide of manganese • • • 0320 • • • The results are consequently as precise in this case as in the separation of co- balt from manganese. Separation of Manganese and Zinc.—I have attempted to apply the above pro- cess to the separation of zinc and manganese. As the sulphuret of zinc dissolves with time in dilute hydrochloric acid. I treated the mixture of the two sulphu- rets prepared in the dry way with acetic acid, the action of which was assisted by heat. In this way only the manganese is dissolved, but the sulphuret of zinc retains a small quantity of manganese which cannot be separated by this method. When operating with weighed quantities of zinc and manganese, I have always obtained too large an amount of oxide of zinc, and have found it to contain a certain quantity of oxide of manganese. Separatum of Iron and Cobalt.—When a mixture of peroxide of iron and co- balt is heated in sulphuretted hydrogen, and then acted upon even with concen- trated hydrochloric acid, scarcely any iron is removed; the sulphuret of cobalt retains nearly the whole of the sulphuret of iron. As the sulphuret of iron, which is obtained by heating peroxide of iron to a nascent red in sulphuretted hydrogen, is not acted upon by dilute cold hydro- chloric acid, I imagined that this property might be turned to account for sepa- rating iron from manganese; but experiment has shown that the sulphuret of iron always contains a considerable proportion of sulphuret of manganese. The volatility of certain sulphurets furnishes a means of separation which may be turned to account in some cases. I will mention two examples, the one relative to the separation of iron and arsenic, the other to the separation of arsenic and tin. Separation of Iron and Arsenic.—When arseniate of iron is heated in a current of sulphuretted hydrogen, both the iron and arsenic are completely sulphurized ; but the latter body is entirely volatilized. The separation is very accurate. A mixture was made of Metallic iron . . 1-330 grm., corresponding to peroxide, 1-900 Arsenious acid • " 1-380 grm., corresponding to arsenic acid, 1-711 3-611 The two bodies were dissolved in aqua regia, the solution precipitated with ammonia in excess; the precipitate, dried and carefully removed from the filter, weighed after calcination 3-315; the filter and adherent matter were calcined separately in a porcelain crucible, and gave 0055=3-370, which number is con- siderably lower than that which ought to have been obtained if the whole of the arsenic had been precipitated with the peroxide of iron. I found that a very considerable quantity of arsenic remained in the ammoniacal solution, but not a trace of iron. It amounted to 0241 grm. or 14 per cent, of the total quantity. 3*370 arseniate of iron must therefore contain— Peroxide of iron . . 1-900 grm. 56-4 in 100 parts Arsenic acid . . . 1'470 . . . 436 • • ■ 3-370 100-0 which composition corresponds very nearly to the formula As05,2Fe303. 0-788 grm. of this arseniate was heated to a faint red heat in sulphuretted hydrogen. A large quantity of sulphuret of arsenic was volatilized. The sulphuret'of iron which remained was of a greenish-yellow color, and possessed a certain metallic lustre; it weighed 0-6065. On dissolving it in nitromuriatic acid, precipitating with ammonia, it gave 0444 peroxide of iron, which proves that the arseniate contained— 572 APPENDIX. Peroxide of iron .... 0444 grm. 563 per cent. Arsenic acid (from the loss) • ■ 0-344 ■ • • 43-7 • • ■ 0788 The peroxide of iron was dissolved in hydrochloric acid; the solution, boiled with sulphurous acid and treated with sulphuretted hydrogen, gave not a trace of sulphuret of arsenic. Second Experiment.—1-050 grm. of the same arseniate of iron, treated as above, gave— Peroxide of iron . 0-594 grm. 56.5 per cent. Arsenic acid .... 0-456 • • ' 435 ■ • • 1-050 The peroxide of iron, examined as in the preceding experiment, did not give a trace of arsenic. It is seen that the results of these two experiments agree very well with each other, and with those deduced synthetically; they perfectly establish the accu- racy of the method. The native arseniates of iron may be directly analyzed by this method. It may also probably be applied without modification to the direct analysis of the arseniates of cobalt, nickel, zinc, copper and lead. When a current of sulphuretted hydrogen is passed over heated perphosphate of iron, it is merely changed into the protophosphate, which dissolves without residue in hydrochloric acid, and without exhibiting any disengagement of sul- phuretted hydrogen. Separation of Arsenic and Tin.—The separation of arsenic and tin is considered to be one of the most difficult problems of analytical chemistry. Professor Rose states in his work on Analytical Chemistry, that he is not acquainted with any good method of separating these two substances. The plan recently proposed by M. Levol* is very complicated. I have applied the method above given for the separation of iron from arsenic to the separation of arsenic from tin; and the following experiments will show that the process is susceptible of very great accuracy. I weighed off 0495 grm. of fine tin, corresponding to 0629 stannic acid, and 0'233 arsenious acid. The two substances were treated with hot nitric acid, evaporated nearly to dryness, then mixed with water. The oxide of tin weighed after calcination 0-746; it consequently contained 0-117, or 15.7 per cent, of its weight of arsenic acid; the rest of the arsenic had remained in solution. Of this 0-746 grm. arseniate of the oxide of tin I took 0-347, and heated it upon a porcelain tray in a current of sulphuretted hydrogen. A con- siderable quantity of sulphuret of arsenic sublimed; the residue appeared to be a mixture of bisulphuret of tin and of a lower sulphuret. Roasted and then strongly calcined in a platinum crucible, this residue of sulphuret left 0 286 stannic acid, or 82-4 per cent. According to synthesis 84-3 should have been found; but this slight difference is readily explained from the difficulty of ob- taining absolutely pure tin. I assured myself, by reducing the 0-286 stannic acid and treating the tin obtained with hydrochloric acid, that the sulphuret of tin had not retained a trace of arsenic. The arsenic was not determined, but it would have been easy to have done so, as the whole of the sulphuret of arsenic was contained either in the tube or in the water into which the tube dipped. This method therefore appears applicable to the analysis of the arsen- iates of tin, and it may probably also be applied to the direct analysis of the arseniuret of tin. This substance, when exposed to the action of sulphuretted hydrogen, parts with the arsenic in the state of sulphuret; and the sulphuret of tin which remains is readily converted into stannic acid by roasting.—Ann. de Chim. et de Phys., Jan. 1849, p. 92, and Chem. Gaz. vii. 82. * Chem. Gaz., vol. iv. p. 159. EEEATA. 1GE 117, 2d line from bottom, for M02, read Mo02. " 118, 21st top, for Mo3, read Mo03. " 159, 8th bottom, for soluble, read insoluble " 370, 6th top, for M03, read Mo03. " 371, 6th " MO, read Mo. " «« 8th " MO,S2, read MoS2. " 168, 17th " baryta, read lime. " barium, read calcium.