iohtvt ^tm^ ^hm^tm ^ mn to 1303 .Cornell University Library Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031257821 A COMPENDIOUS MANUAL QUALITATIVE CHEMICAL ANALYSIS. CHAELES W: 5LI0T, ?IiOrESSOIi OF ANALYTICAL <;HEMISTET AND METALLUKGY, FEANK H STOEEE, PKOFESSOB OF GENERAL AND INDUS- IBIAL CHEMISIKT, IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. NEW YORK: D. VAN NOSTEANB, PUBIyISHEE, 23 MuRRAT Street and 27 Wasreh Street. 1869. Eutorod according to Act of Congress, in the year IStj^s. by FRANK IT. STOKER and CHARLES W. ELIOT, in the Clerk's OIDce of tbo District Court of the District of MnssacLusctt?. PRE FACE. The aiithors have endeavored to include in this short treatise enough of the theory and practice of qualitative analysis, " in the wet way," to bring out all the reasoning involved in the subject, and to give the student a firm hold upon the general principles and methods of the art. It has been their aim to give only so much of mechani- cal detail as is essential to an exact comprehension of the methods, and to success in the actual experiments. Hence, the multiplication of different tests or processes, having essentially the same object, has been purposely avoided. For the same reason, none of the rare ele- ments are alluded to. The manual is intended to meet the wants of the general student, to whom the study is chiefly valuable as a means of mental discipline, and as a compact example of the scientific method of arriving at truth. To professional students who wish to make themselves expert analysts, this little book offers a logical introduction to the subject — an outline which is trust- worthy as far as it goes, but which needs to be filled in and enlarged by the subsequent use of some more elaborate treatise as a book of reference. Prof. Johnson, of Yale, has supplied this need with his excellent edition of Freseniiis's comprehensive manual. The authors beHeve that they have put into the follow- ing pages as much of inorganic quaUtative analysis as is useful for training, and also as much as the engineer, physician, agriculturist, or liberally educated man needs to know. The book has been written for the use of classes in the Institute of Technology, who have already studied the authors' "Manual of Inorganic Chemistry." It is simply an implement devised to facilitate the giving of thorough instruction to large classes in the laboratory. It is the authors' practice to examine their classes orally every four or five exercises, in order to secure close at- tention to the reasoning of the subject. With this excep- tion, the art is studied exclusively in the laboratory, tools in hand. Fifty laboratory exercises of two hoiirs each have proved sufficient to give their classes a mastery of the subject as it is presented in this manual. It is scarcely necessary to say that this httle work is a compilation from well-known authorities, among which may be particularly mentioned the works of Galloway, WiU, Freseniiis, and Northcote ifc Chiu-ch. Boston, Ajn-il, 18G9. TABLE OF CONTENTS. Page. Introduction. Qualitative analysis defined. Scope of this manual. Identifying compounds. Division of tlie subject 9-12 PAUT I. Chapter I. Example of tlie separation of two elements. Division of twenty-four metallic elements into seven classes 13-26 Chapter II. Class I. Chlorides insoluble in water and acids. Lead. Silver. Mercury 2G-29 Chapter III. Class II. Sulphides insoluble in water, dilute acids, and alkalies. Mercury. Lead. Bismuth. Copper. Cadmium. The precipitation of Classes II and III 29-B7 Chapter IV. Class III. Sulphides insoluble in water or dilute acids, but soluble in alkaline solutions. Arsenic. Antimony. Tin. [Gold and Platinum.] 38-44 Chapter V. Class IV. Hydrates insoluble in water, ammonia- water, and solutions of ammonium-salts. Simultaneous precipi- tation of some salts which require an acid solvent. Treatment of the precipitate, produced by ammonia water, with oxalic acid. Iron. Manganese. Chromium. Aluminum. Separation of Class IV from Classes II and III. ^The original condition of iron. The use of chloride of ammonium. Interference of organic matter. . 43-54 Chapter VI. Class V. Sulphides insoluble in water, and in saline or alkaline solutions. Manganese. Zinc. Nickel. Cobalt. Sepa- ration of Class V from Class IV 54-60 b TABLE OF CONTENTS. Page. Chapter VII. Class VI. Carbonates insoluble in water, ammonia- water, and saline solutions. Barium. Strontium. Calcium. Separation of Class VI from the preceding classes 61-GG Chapter VIII. Class VII. Three common metallic elements not comprised in the preceding classes. Magnesium. Sodium. Pot- assium. Table for the separation of the seven classes of the me- tallic elements 67-72 Chapter IZ. General tests for the non-metallic elements. The classes of salts treated of. General reactions for acid.^. Metallic elements to be first detected. The barium test. The calcium test. The silver test. Nitrates, chlorates, and acetates 72-^:^ Chapter X. Special tests for the non-metallic element?. Efferves- cence. Carbonates. Cyanides. Sulphides. Sulphite.-. Hypo- sulphites. Chromates. Arscnites and Arseniates. Sulphates, Pho.^phates. Oxalates. Tartrates. Borates. Silicates. Fluo- rides. Chlorides. Bromides. Iodides. Nitrates. Chlorates. Acetates 83-97 PAET II. Preliminary Treatment. Order of Procedure. 1. Treatment of a salt, mineral, or other non-metallic body. 2. Treatment of a metal. 3. Treatment of a liquid. Husbanding material 09-100 Chapter XI. Treatment of a salt, mineral, or other non-metallic solid. . . . Preliminary examination in the dry war. Closed-tube test. Destruction of organic matter. Ga-es "or vapors to bo recognized. Sublimates. Koduction tcft. Metallic glotiules Dissolving a salt, mineral, or other non- metallic solid, free from organic matter. Dissulving in water. An aqueous solution. Dissolving in acid*. An acid solution. . . . Treatment of insoluble substance,*. List of such sulistances. Preliminarj' dri--way tests. Fusions. Treat- ment of the fused mass. Fusion for alliali-metals. Dcfla-ra- "°" !".!. 100-lJ,i Chapter XII. Treatment of a pnro metal or alloy. Action of nitric acid on metals. Gold tost. Plutiuum test 126-130 Chapter XIII. Preliminary examination of a liquid. Kvaporatiou tvM. Toitnij; with litmus. Tostiii;,' for ammonia 1.10-132 TABLE OF CONTENTS. 7 PART ni. Page. Chapter XIV. Eeagents. Acids. Sulphuretted hydrogen. Ammonia- water. Ammonium-salts. Caustic soda. Sodium salts. Potas- sium salts. Nitrate of silver. Calcium salts. Barium salts. Acetate of lead. Lead paper. Sulphate of magnesium. Ferric chloride. Nitrate of cobalt. Sulphate of copper. Protochloride of tin. Oxide of mercury. Chloride of mercurj'. Bichloride of platinum. Solution of indigo. Litmus paper. Turmeric paper. Starch paste. Water 133-145 Chapter XV. Utensils. List of utensils. Reagent Bottles. Test- tubes. Test-tube rack. Flaslf!. Beakers. Funnels. Filtering. Filter-stand, Porcelain dishes and crucibles. Lamps. Blast- lamps and blowers. Iron-stand. Tripod. Wire-gauze. Triangle. Water-bath. Sand-bath, Platinum-foil and wiie Pincers. Platinum crucibles. Wash-bottle. Glass tubing. Slirring-rods. Cutting and cracking glas.'^. Bending and closing gla.-.s tubes. Blowing bulbs. Caoutchouc. Corks. Gas-bottle. Self-rfgu- lating gas-generator. Mortars. Spatulse 145-186 QUALITATIVE ANALYSIS. INTEODUCTION. 1. Qtiajlitative Analysis, in the widest sense of the term, is the art of finding out the elements contained in compound substances. This general definition has im- portant limitations in practice. In the first place, the art, as commonly taught, applies almost exclusively to miner- al, or inorganic, substances, and touches only incidentally upon the multifarious compounds of carbon with hydro- gen, oxygen, nitrogen, and a few other elements, which form the subject-matter of that branch of chemical science called organic chemistry. Again, the analysis of gases constitutes a distinct branch of analysis, requiring methods and apparatus of its own, and therefore to be most ad- vantageously studied by itself. These deductions made, there remains the analysis of inorganic sohds and Hquids, which is in fact the main subject of qualitative analysis in the present technical sense of the term. Of the sixty-five recognized chemical elements, only the thirty-four most important are embraced in the systematic course of this manual. Means of detecting a few other less common elements are incidentally given ; but the ele- ments which are so rare as to be at present of little in- 10 IDEKTIFYING COMPOUNDS. §§ 2, 3 terest except to tlie professional chemist or mineralogist, are not alluded to. 2. Some preyious knowledge of general chemistry is essential to the successful study of qualitative analysis. Ifc is assumed that the student knows something of the common elements and of their most important combina- tions, that he is familiar with the principal laws which govern chemical changes, and that he possesses a certain skiU in the simplest manipulations. The tools and opera- tions employed in qualitative analysis are few and simple ; but neatness, method in working, and a vigUant attention even to the minutest details, are absolutely essential. As the various substances used or produced in the operations of analj'sis wHl not be particularly described, the careful student will keep at hand some text-book on general chemistry, to which he can constantly refer to refresh his recollection of the formulae and physical and chemical projjerties of the substances referred to. It should be observed that it is often very difficult — -in fact, impossible in the present state of knowledge — to express in exact equations the involved or obscure reactions whic-h occur ia complex mixtures during the operations of aniilysis. It is a useful exorcise for students to write out in equa- tions the simpler chemical changes which occur in analy- sis ; but when the attempt is made to put a complex reaction into numerical symbols, the equations are apt to express either more than we know, or less. 3. Although the detection of the elemoTits contained in csiupound substances is the ultimate object of aualvsi.s, it is only l)y exception that the clcmouts themselves are isolated, and rcci>;4uizod in tlioir uuoombincd condition. An element is generally recognized through some familiar § 3 IDENTIFYING COMPOUNDS. 11 compound, whose apparition proves the presence of all tlie elements it contains, just as the presence of any word upon this page makes it sure that the letters with which it is spelt are imprinted there. If, as the result of a defi- nite series of operations upon some unknown body, the hydrated oxide of iron be produced, no iron having been added during any stage of the process, the proof of the presence of iron in the original body is quite as certain as if the gray metal itself had been extracted from it. If some well-known sulphate, like sulphate of lead, or of barium, for example, result from a series of experiments upon some unknown mineral, it is certain that the mineral contained sulphur ; pro^aded only that no sulphur has been introduced in any of the chemical agents to whose action the mineral has been submitted. The compounds through which the elements are recog- nized are necessarily bodies of known appearance, deport- ment, and properties. They are, in fact, bodies of various, though always definite, composition ; oxides, sulphides, chlorides, sulphates, and many other salts, are thus made the means of identifying one or more of the elements which they contain. The object of the analyst is to bring out, from the unknown substance, by expeditious processes and under conditions which admit of no doubt as to their testimony, these identifying compounds, with whose ap- pearance and quahties he has previously made himself ac- quainted. As he follows the course of experiments laid down in this manual, the student will gTadually acquire, with the aid of frequent references to a text-book of general chemistry, that stock of information concerning the identifying compounds which must be always ready for use in his mind, and at the same time he will be made familiar with the character of the methodical pro- cesses which secxu'e a prompt and siu-e testimony to 12 IDENTIFYING COMPOUNDS. § i the elementary composition of the substances lie ox- amines. 4. The subject is treated in two parts or divisions, of which the first contains a systematic course of examina- tion for substances in solution, when once that solution has been made ; and the second treats chiefly of the pre- liminary examination of solids and the means of bringing them into solution. PART FIRST, CHAPTEE I. DIVISION OF THE METALLIC ELEMENTS INTO CLASSES. 5. Example of the Separation of two Elements. Put a small crystal of nitrate of silver and a small crystal of sulphate of copper into a test-tube (§ 155), and dissolve them in two teaspoonfuls of water, warming the water at the lamp to facilitate the solution. Add to this solution a few drops of dilute chlorhydric acid (§ 98). Shake the contents of the tube violently, wait until the curdy precipitate, which the acid produces, has separated from the liquid, and then add one more drop of chlorhydric acid. If this drop pro- duces an additional precipitate, repeat the operation until the new drop of acid produces no change in the partially clarified liquid. Then, and not till then, has all the silver which the original solution contained been precipitated in the form of chloride of silver, an unemployed balance or excess of the reagent, chlorhydric acid, remaining in the clear liquid ; this liquid can be readily separated by fil- tration from the curdy chloride. Shake the contents of the test-tube, and transfer them as completely as possible to a filter (§ 160), supported in a very small glass funnel (§ 159), which has been placed in the mouth of a test-tube. "With the wash-bottle (§ 170) rinse into the filter that 2 li THE TERM CLASS. § 6 portion of the precipitate whicli has adhered to the sides of the first test-tube. When the filtrate has drained com- pletely from the precipitate, set the test-tube which has received it aside. Wash the precipitate together into the apex of the filter by means of a wash-bottle with a fine outlet ; and, in order to wash out the soluble sulphate of copper which adheres to the precipitate, fill the filter full of water two or three times, throwing away this wash- water when it has passed through the filter. The complete separation of the silver and copper which were mixed in the original solution is already accom- plished ; the silver is on the filter in the form of chloride ; the copper is in the clear, bluish filtrate. This speedy and effectual separation of the two elements is based up- on the fact that chloride of sHver is insoluble, while chlo- ride of copx^er is soluble, in water and acid liquids. Such differences of solubUity are the chief reliance of the analyst. Q^(^f\o^, .: ;-,> C / " -'^' --■-' ' ~ 6. Definition of the tenn " Class." Class I. In this ex- periment only two elements have been separated. It might obviously be very difiicult, if not impossible, to find a special reagent for every element, which would always precipitate that single element and never any other. Chlorhydric acid, for example, which precipitates silver so admirably from any sohition containing that element, is capable of eliminating two other elements under like con- ditions. The lower chloride of mercury (calomel) is in- soluble in water and weak ai'ids. Chloride of lead is sparingly soluble in cold water, and is stOl less soluble in water acidulated with i-hlorhydric acid. Tho chlorides of the other motallio elinnentw are all soluble in water and acids under tho conditions of the analytical process. There are embraced in the scope of this manual twenty- § 6 THE TEEM CLASS. 15 two common elements of the sort ordinarily called metal- lic, most of which form those oxides relatively poor in oxygen which are collectively designated as hoses. If chlorhydi-ic acid were added in proper quantity to a solu- tion imagined to contain all these elements, three, and only three, of the twenty-two elements would be precipi- tated as chlorides. After filtration and washing, a mix- ture of chloride of silver, chloride of lead, and subchloride of mercury, would remain upon the filter, and all the other elements would have passed into the filtrate. Silver, lead, and mercury, the three elements thus separated from the rest by this weU-marked reaction with chlorhydric acid, constitute a class, the first of several classes into which the metallic elements are divided for the ends of quahtative analysis. Each class is characterized by some clear re- action which suffices, when intelligently applied, to separ- ate the members of any one class from the other classes. The chemical agent, by means of which this distinctive re- action is exhibited, is called the general reagent of the class. Thus, chlorhydric acid is the general reagent of the first class. This division of the elements into classes renders it un- necessary to find means of separating each individual ele- ment from all the others. In the systematic course of an analysis, the classes are first sought for and separated ; afterwards each class is treated by itself for the detection of its individual members. It is an incidental advantage of this division of the elements into classes, that, when the absence of any whole class has been proved by the failure of its peculiar general reagent to produce a precipitate, it is unnecessary to search farther for any member of that class. Much time is thus saved ; for it is as easy to prove the absence of a class as of a single element. The full treatment of the first class of elements, comprising, as we 16 CLASSES. §§ 7, 8 have seen, silver, lead, and mercury, is the subject of Chap- ter II. 7. E rperiment to illustrate the Division of the Metallic Elements into Classes. We proceed to demonstrate ex- perimentally the chemical facta upon which rests the division of the other metallic elements into convenient classes. Prepare a complex solution, by mixing together in a small beaker (§ 158) the following solutions, A-iz. :— a so- lution of chloride of copper (CuClj) prepared by dissolv- ing a few grains of oxide of copper in chlorhydric acid ; a solution of arsenious acid in chlorhvdi'ic acid ; a solu- tion of ferrous chloride prepared hj dissohing a httle fine iron wire or filings in chlorhydric acid ; an aqueous solu- tion of chloride of zinc ; an aqueous solution of chloride of calcium ; an aqueous solution of chloride of magne- sium ; an aqueous solution of chloride of sodium. If the solutions be all moderately strong, a smaU teaspoonful of each solution will be enough. Dilute the mixture thus prepared with its ovm bulk of water. Should any tui'bid- ity or precipitate appear, add chlorhydric acid, httle by little, until the solution becomes clear. This solution is representative ; it contains at least one member of each of the classes of elements which remain to be defined. It contains no member of the first class, which may be con- sistently supposed to have been previously precipitated, as in the foregoing experiment (§ 5), an excess of chlor- hydric acid remaining in the liquid. 8. Tirjinifion of Classes TTaiid ITT. Pass a slow current of sulphydric acid gas (§ 107) from a gns-bottle or gener- ator through the acid liquid in tho beaker. This opera- tiiiii must lie performed imdor a hood. A dense, dark- § 8 CLASSES II AND III. 17 colored precipitate will immediately appear, and gradu- ally increase in bulk. When the gas has flowed continu- ally for five or ten minutes through the liquid, stop the stream, stir the liquid well, and blow out the sulphydric acid which lies in the beaker. If after the lapse of two or three minutes the hquid smells distinctly of sulphydric acid, it is saturated with the gas, and it is sure that the reagent has done its work. If the hquid does not retain the characteristic odor, the gas must be again passed through it, until saturation is certainly attained. Pour the contents of the beaker, well stirred up, upon a filter, supported over a test-tube or second beaker. Kinse the first beaker once with a teaspoonful of water, and transfer this rinsing water to the filter, allowing the filtered Hquid to mix with the original filtrate. Label* this filtrate "Filtrate from II and III" (classes), and preserve it for later study. If any considerable quantity of precipitate has adhered to the sides of the original beaker, it may be detached and washed into the filter by means of a sharp jet of water from the wash-bottle. The precipitate, as it lies upon the filter, must then be washed once or twice with water ; the wash-water is thrown away. The washed precipitate consists of a mixture of sulphide of copper (CuS) and ter- • The student should at once make it a rule to label every filtrate or precipitate which he has occasion to set aside, even for a few moments, A hit of paper large enough to carry a descriptive symbol or abbreviation should be attached to the vessel which contains the liquid or precipitate. Paper gummed on the hack is con- venient for this use. This habit, once acquired, will enable the student to carry on simultaneously, without error or confusion, several operations. He may be throwing down one precipitate, washing another, filtering a third, and dissolving a fourth, at the same time, and the four processes may belong to as many different s tages of the analysis. There will be uo danger of error, if labels are faithfully used ; and a great deal of time will bo saved. The unaided memory is incapable of doing such work with that full certainty, admit- ting of no suspicion or after-qualms of doubt, which is alone satisfying, or indeed, ad- missible, in scientiilc research. 18 CLASSES II AND III. § 8 sulphide of arsenic (ASjSg). The fact that these sulph- ides are precipitated under the conditions of this experi- ment proves that they are both insoluble in weak acid liquors. They are also both insoluble in water. But an important difference between the two sulphides neverthe- less exists, a difference which affords a trustworthy means of separating one from the other. When the water has drained away from the precipitate, open the filter upon a plate of glass, and gently scrape the precipitate off the paper with a spatula of wood or horn. Place the precipitate in a small porcelain dish (§ 162), pour over it enough sulphydrate of sodium solution (§ 117) to somewhat more than cover it, and heat the mixture cautiously to boiling, stirring it all the time with a glass rod. The quantity of sulphydrate of sodium so- lution to be employed varies, of course, with the bulk of the precipitate ; but in this case two or three teaspoonfuls will probably suffice. It is very undesirable to use an un- necessarily large quantity of the reagent. A portion of the original precipitate remains undissolved ; but a por- tion has passed into solution. Filter the hot Kquid again. The black residue on the filter is sulphide of copper, which is insoluble, not only in water and weak acids, but also in alkaline liquids. To the filtrate, collected in a test- tube, add gradually chlorhydric acid, miiil the liquid has an acid reaction on litmus paper (§ 148). A yellow pre- cipitate of sulphide of arsenic wUl apjiear as soon as the alkaline solvent which kept it in solution is destroyed. The sulphide of arsenic differs from the sulphide of cop- per in that it is soluble in alkaline hydrates and sul- phides. But in this sovica of oxpcrimcnts copper and arsenic stand as rcprosciitativos of classes. The following com- mon elements have sulphides \vlii(_\h are insoluble in § 8 CLASSES II AND III. 19 water, weak acids, and alkaline liquids : — Lead, mercury, bismuth, cadmium and copper. These elements consti- tute Class II in our system of analysis. The following elements have sulphides which are insoluble in water and weak acids, but soluble in alkaline liquids : — ^Arsenic, antimony, tin (and the precious metals, gold and plati- num). These elements constitute Class III. If all the elements of both groups had been present, the analytical process for separating one class from the other would not have been different from that just e;secuted. The question may naturally suggest itself, how it hap- pens that lead and mercury are included in Class II when they were both precipitated in Class I. The chloride of lead which is thrown down by chlorhydric acid, is not wholly insoluble in water ; hence it happens that the lead is not completely precipitated in Class I. That por- tion of the lead which has escaped precipitation as chlo- ride in Class I, wiU be throvm down as sulphide in Class n, for the sulphide of lead is insoluble in water, weak acids, and alkalies. In regard to mercury, it wiU be re- membered that there are two sorts of mercury salts, mer- curous salts and mercuric salts. The mercurous chloride (calomel) is insoluble in water ; but the mercuric chlo- ride (corrosive sublimate) is soluble in water. If, there- fore, mercury be present in the form of some mercurous salt, it will be separated as chloride in Class I. If, on the contrary, it be present in the form of some mercuric salt, it Vidll be separated in Class II as mercuric sulphide (HgS), for this sulphide is insoluble in water, weak acids, and alkaline liquids. If a mixture of mercurous and mercuric salts be contained in the original solution, mer- cury will appear both in Class I and Class II. The treatment of Class II is fully discussed in Chapter TTT - The separation of Class HI and the means of sepa- 20 CLASS IV. § 9 rating the members of the class, each from the others, form the subject of Chapter IV. 9. Definition of Class IV. We now return to the study of the filtrate from Classes 11 and m. Pour the liquid into a small evaporating dish, and boil it gently for five or six minutes, to expel the sulphxiretted hydrogen with which the fluid is still charged. To make sure that all the gas is expelled, hold a bit of white paper moistened with a solution of acetate of lead (§ 138) over the boiling liquid ; when the paper remains white, all the sulphu- retted hydrogen is gone. Next add to the Kquid in the dish ten or twelve drops of strong nitric acid (§ 99), and again gently boil the liquid for three or four minutes, in order that all the iron present may be converted into fer- ric salts. Then pour the liquid into a test-tube, add to it about one-third its bulk of chloride of ammonium (§ 112), and finally add ammonia-water (§ 109), little by little, until the mixture, after being well shaken, smeUs decidedly of ammonia. A brownish red precipitate of hydrated sesqtiioxide of iron will separate from the liquid. Ammonia-water precipitates this familiar iron compound, even in the presence of salts of ammonium, such as the chlo- ride of ammonium which has been expressly added, and the nitrate of ammonium which has been formed during the neutrahzation of the acid Uquid. Pour the contents of the test-tube upon a filter, rinse the tube and the pre- cipitate once with a little water, and preserve the whole filtrate for subsequent operations. Aluminum and chromium are precipitated, as iron has here been, by ammonia-water under the same oouditious and in the same form, namely, as hydrates. These three elements, therefore^, eonstihite the fourth class, whose treatment forms the subject of Chapter Y. The student § 10 CLASS V. 21 may be curious to know why the presence of ammonium- Baits is insisted upon before the elements of this class are thrown down by ammonia-water. The ammonium-salts have nothing to do with the precipitation of iron, alumi- num and chromium; but by their faculty of forming solu- ble double salts, they prevent the partial precipitation of certain other elements which are more conveniently dealt with in classes which are to follow. The ammonium-salts keep in solution certain other elements which otherwise would encumber Class IV. 10. Definition of Class V. We now proceed to the ex- amination of the filtrate from the precipitate of Class IV. Bring this Uquid to boiling in a test-tube (or in a small flask, if there be much liquid), and add sulphydrate of ammonium (§ 110), Httle by little, to the boUing Uquid, as long as a precipitate continues to be formed. To make sure that the precipitation is complete, shake the hot con- tents of the test-tube strongly, and then allow the mix- ture to settle untn the upper portion of the liquid becomes clear. Into this clear portion let fall a drop of sulphy- drate of ammonium ; when this drop produces no addi- tional precipitate, the precipitation is complete. Filter off the whitish precipitate of sulphide of zinc, and preserve the filtrate for further treatment. The element zinc, representing a new class of elements, is precipitated under the conditions of the above experi- ment, because its sulphide, though soluble in dUute acids, is insoluble in alkaUne liquids. The metals manganese, nickel, and cobalt resemble zinc in this respect, and these four elements, therefore, form a new class. Class V, in this analytical method. The representative sulphide of this class was not precipitated by the sulphydric acid when that reagent was employed to throw down the members 2* 22 CLASSES VI AND VII. §§ 11, 12 of Classes II and III, because the solution was at that time acid. Again, it was not precipitated with Class IV by the ammonia-water, because the sulphydric acid gas, with which the solution had previously been charged, was expelled by boiling before the ammonia-water was added. The complete treatment of Class V forms the subject of Chapter VI. 11. Definition of Class VI. Add to the filtrate, from Class V, two or three teaspoonfuls of carbonate of ammo- nium (§ 111), and boil the solution. A white precipitate of carbonate of calcium will be produced. After boiling, aUow the precipitate to settle until the upper portion of the liquid is comparatively clear. To this clarified por- tion add a fresh drop of carbonate of ammonium. If this drop produce an additional precipitate, more carbon- ate of ammonium must be added, and the boiling repeated. To the partially clarified Uquid add again a drop of car- bonate of ammonium. This process of making sure of the complete precipitation of the calcium is essentially the same as that prescribed in precipitating the last class, and is, indeed, of general application. "When the pre- cipitation of the calcium has been proved to be complete, filter the whole liquid, and receive the filtrate in a small evaporating dish. Calcium is separated in the form of car- bonate under these circumstances, because this carbonate is almost insoluble in weak alkaline liquids, when an excess of carbonate of ammonium is present. The allied elements barium and strontium behave in the same way, so that these three elements, \'iz., barium, strontium, and calcium, compose a new class — Class Yl, whose com- plete treatment is set forth in Chapter Vll. 12. Dtfinition o/C/a.ss VI L Of the twenty-two nietaUic elements, which were to be classified (§ 6), only three § 12 CLASS VII. 23 remain, viz., magnesium, sodium, and potassium. It is obvious that these three elements could not have remained in solution through all the operations to which the original Hquid has been submitted, unless their chlorides and sulphides had been soluble in weak acids, and their oxides, sulphides, and carbonates, soluble in dilute am- monia-water, at least in presence of dUute solutions of ammonium-salts. It is a fact that aU these compounds of sodium and potassium are soluble in water, and ia weak acid, alkaline, and saluie solutions ; the magnesium would have been partially precipitated in Classes IV, V, and VI, but for the presence of ammonium-salts in the solution. These three elements constitute Class VII. Evaporate the filtrate from Class VI until it is reduced to one-half or one-third of its original bulk. Pour a small part of the evaporated filtrate into a test-tube ; add a little ammonia-water and a teaspoonful of phosphate of sodium (§ 121), and shake the contents of the tube violently. Sooner or later a crystalline precipitate will appear. This peculiar white precipitate of phosphate of magnesium and ammonium identifies magnesium ; but as we have added a reagent containing sodium, the filtrate is useless for further examination. The liquid remaining in the evap- orating-dish is then evaporated to dryness, and moderately ignited until fuming ceases. All the ammoniacal salts which the solution contained will be driven off by this means, and there will remain a fixed residue, in which are concentrated all the salts of magnesium and sodium which the original solution contained. In this case we have proved the presence of magnesium ; it remains to indicate briefly the nature of the means used to detect sodium. Dissolve the residue in the dish, or a portion of it, in three or four drops of water. Dip a clean platinum wire 24 CLASS VII. §§ 13, 14 (§ 168) into this solution, and introduce this wire into the colorless flame of a gas or spirit-lamp (§ 163). An intense yellow coloration of the flame demonstrates the presence of sodium. A violent coloration would have proved the presence of potassium. Magnesium com- pounds, when present, have no prejudicial effect on these characteristic colorations. The means of detecting each member of this last class in presence of the others will be found described in Chapter VIII. 13. A condensed statement of the classification illus- trated by the foregoing experiments is contained in the table on the next page. All the common metallic ele- ments are embraced in it. The place of the precious metals gold and platinum is also indicated. The classifi- cation itself would not be essentially different, if aU the rare elements were comprehended in it. The general subdivisions would be the same, although some of them would embrace many more particulars. 14. It is essential to success to follow precisely the prescribed order in applying the various general reagents. Class I would go down with Class n, were chlorhydric acid forgotten as the first general reagent. Class II would be precipitated in part with Class IV and in part with Class V, if sulphuretted hydrogen should not be used in its proper place. A large number of the members of the first five classes would be precipitated as carbonates with Class VI, were they not previously eliminated by the systematic application of chlorhydric acid, sulphm-etted hydrogen, ammonia-water, and sulphide of ammonium, in the precise order and under the exact conditions above described. It should be noticed that aU the general re- agents are volatile substances, which can be completely §13 CLASSIFICATION. 25 bfi P-. 1 ^ II i 1 -' bo i 1 •a ® cc (3 a> ® en s ^ W p do" n 6 (§ tg t &% ■a 03 > ^ i i 1 r^ CA ,3 o fc ai •1^:3:2 ci >> to pi 1 5 a [together ^\ tain salts w quire an ac eut.] ^ -s -4J ■3 S CD rJ3 J .g >> „ H 4 1 1 CQ 1 CQ < 03 m <^ Ph 1— 1 i—j g f lead might bo produeed on the addition of the ammonia-water oven wlieu no bismuth was present in the § 20 SEPARATION 01" CADMIUM. 33 solution. To prove the presence of bismuth, the oxychlo- ride must always be carefully tested for. The blue color of the ammoniacal filtrate from the hydrate of bismuth indicates the presence of copper, and when well defined is of itself a sufficient proof of the presence of this element. But in the absence of a marked blue coloration at this stage, copper should be specially tested for in the manner described below. To separate the cadmium from the copper, proceed as foUows : — Transfer the ammoniacal filtrate to a glass flask, heat it to boiling, and drop into the boiling Uquid sulphy- drate of ammonium as long as a precipitate continues to be formed. In order to be sure that the precipitation is complete, remove the flask from the lamp at intervals, shake it strongly, and allow its contents to settle, so that a comparatively clear Uquid may appear at the top, and into this clear liquid pour a drop of the sulphydrate. As a general rule, the operations of boiling and agi- tating tend to increase the coherency of precipitates, and to render them in some sense granular, so that they sepa- rate completely from the Uquid in which they form, leav- ing it clear and susceptible of rapid filtration. Collect the precipitate upon a filter, rinse it once or twice with water, and aUow it to drain ; then open the filter on a plate of glass, scrape the precipitate off the paper and put it in a porcelain dish. Prepare a dilute sulphuric acid by mixing 1 part by measure of the strong acid (§ 103), with 5 parts of water. Cover the precipitate in the dish Uberally with this dilute acid, and heat the mixture until it actually boils ; then pour the boiling liquor upon a filter, and collect the clear filtrate in a beaker. Sulphide of cadmium alone will dissolve in hot dilute acid of the prescribed strength, the black sulphide of copper remaining intact. 34 TESTS FOE CADMIUM AND COPPEB. § 21 To prove the presence of cadmium, pass sulplmretted Test hydrogen gas into the acid filtrate, and observe for that the hquor immediately becomes cloudy from ■ the presence of minute particles of sulphide of cadmium of characteristic yellow color. After some time this precipitate will collect at the bottom of the liquid. To prove the presence of copper, in case no blue colora- tion was visible in the filtrate from, the hydrate of bismuth, transfer the black precipitate, insoluble in dilute sulphu- ric acid, to an evaporating dish, dissolve it in a few drops of boiUng, concentrated nitric acid, remove and wash the the spongy mass of sulphTir which is set free, neutralize the nitric acid with ammonia-water, acidify the solution with acetic acid (§ 105), transfer it to a test-tube, and add one or two drops of a solution of ferrocyanide of potas- jggj slum (§ 125). A peculiar reddish-brown precipi- for tate of ferrocyanide of copper will fall in case *"• much copper be present, and even when the pro- portion of copper in the solution is extremely small, a light brownish-red cloudiness wiU be produced. In the absence of copper, yellow sulphide of cadmixuu would at once be thrown down by the sulphydrate of am- monium, when this reagent is added to the filtrate from the oxide of bismuth; and no further evidence of the pres- ence of cadmium would be requii-ed. 21. The operations above described may be presented in tabular form, as foUows : — §22 TABLE FOK CLASS II. 35 The General Beagent (HzS) of Class II precipitates HgS, PbS, BizSa, CdS, and CuS (as trell as members of Class III, which are snbsequently separated by solution in snlphydrate of sodium). The precipitate is boileS with nitric acid ; — A residue of HgS, plus S, remains. Confirm pres- ence of mer- cury with copper wire. The nitrates of Pb, Bi, Cd, and Cu go into solution. On adding dilute sulphuric acid to the concentrated solution :— PbS04, is thrown down. Confirm the presence of Pb by con- verting PbS04 into PbCr04. The sulphates of Bi, Cd, and Ou remain in solution. On adding an excess of am- monia-water : — Hydrate of Bismuth is thrown down Confirm Bi by precipitating the oxychlo- ride. Compounds of Cd and of Cu remain in solution. Throw down CdS and CuS with (NH4) HS, and boil with di- lute sulphuric acid :^ _ CdS04 goes into solution. Confirm pres- ence of Cd by precipitation of CdS. CuS remains undissolved. Confirm pres- ence of Cu by testing with ferrocyanide of potassium. 22. The method of Separating Class I from Class II has already been particularly described in § 6. It should be observed, however, that even if no member of Class I were present in the mixture to be analyzed, it would still be necessary to acidulate the liquid with chlorhydric acid, before passiag the sulphuretted hydrogen, in order to prevent the precipitation of members of Classes IV and V, and to secure the complete precipitation of the members of Class m. The liquid should be watched attentively when the stream of sulphuretted hydrogen first begins to flow through it, since useful inferences may often be drawn from the various phenomena which present themselves. a. Thus, the formation of a white precipitate which 36 SEPARATION OF CLASSES II AND III. § 22 afterward changes to yellow, orange, brownish-red, and finally to black, as the liquid gradually becomes saturated with the gas, indicates the presence of mercuric chloride. The white precipitate at first formed is a compound of chloride and sulphide of mercury (HgClj; 2HgS), but by the action of successive portions of sulphuretted hydro- gen, the composition and appearance of the precipitate is changed, until it has been completely converted into black sulphide of mercury. b. If the precipitate is of a dull red color at first, after- ward changing to black, the probable presence of lead is indicated ; for sulphuretted hydrogen throws down from solutions which contain much free chlorhydric acid a red compound of chloride of lead and sulphide of lead, which is afterward decomposed, with formation of the black sul- phide, when the solution becomes saturated with the gas. c. A decided bright yellow precipitate would indicate the presence of cadmium, arsenic, or tin ; of these three, cadmium is distinguished by the fact that its sulphide re- mains undissolved when the precipitate is treated with sulphydrate of sodium to separate the members of Class III. But even from solutions which contain no members of Classes II or III, yeUowish-white or mUky-white precip- itates of free sulphur are often thrown down ; for sul- phuretted hydrogen is easily decomposed, with deposi- tion of sulphur, by a variety of oxidizing agents, such as nitric, chromic, and chloric acids, and solutions of ferric salts and of free chlorine. If the solution under examin- ation contained much nitric acid, sulphuretted hydrogen would have to be passed through it for a long time to de- stroy the acid, before tlie liquid could bo satiu-ated with the gas. In this case the sulphur separates as a tenacious mass of dirty yellow color ; biit in most instances, notably § 22 PKECIPITATION OF SULPHUR. 37 when the solution contains a ferric salt, the sulphur is precipitated in the form of exceedingly minute particles, which impart to the solution a peculiar milkiness or opa- lescence. These particles are so fine that they pass through the pores of filter paper ; they cannot be completely re- moved by filtration. If the original solution contains a chromate, its yellow or reddish-yellow color will be changed to green by the action of sulphuretted hydrogen ; for the chromate is reduced to the condition of sesquichloride of chromium : — 2MCrO4+10HCl-|-3H2S=Cr2Cle-(-3S+2MCl2+8H2O. The sulphur is set free in the form of the minute white particles above described, and remains suspended in the green liquid* looking not unlike a green precipitate. A white precipitate of sulphur would be thrown down even before the passage of sulphuretted hydrogen, in case the original solution contained a hyposulphite ; for this class of salts is decomposed, with evolution of sulphurous acid and deposition of sulphur, on the addition of the general reagent (HCl) of Class I. Some sulphides also are decomposed by chlorhydric acid, with deposition of sulphur. A gelatinous white precipitate of hydrated silicic acid might also be formed at this stage in certain circumstances, as will be explained hereafter (§§67, 80, a). d. The immediate formation of a black precipitate in- dicates the presence of copper or bismuth, and it is to be observed that either of these black precipitates woidd ob- scure the colors of the other sulphides of the class, and conceal them if present. e. If no precipitate appears even when the liquid has become saturated with the gas, the absence of every member of Classes II and III is, of course, to be inferred. 3 38 CLASS III. § 23 CHAPTER IV. CLASS III. SULFHIDES INSOLUBLE IN -WATER OB DILTJTE ACIDS, BUT SOLUBLE IN ALKALINE SOLUTIONS. 23. JExample of the Precipitation of the Memhern of Class III. Place in a small beaker six or eight drops of strong solutions of the chlorides of arsenic, antimony, and tin. Pour in enough dilute chlorhydric acid to half fill the beaker, and, if need be, a sufficient number of drops of strong chlorhydric acid to dissolve any cloud of basic chloride of antimony which may appear in the liquor. Pass sulphuretted hydrogen gas through the solution, in the manner described in § 19, until the odor of the gas persists. Then collect the precipitated sulphides upon a filter, and rinse the precipitate once or twice with water. In the analysis of any complex solution of unknown composition which might contain one or all of the mem- bers of Class III, the sulphides of this class would, of course, all be thrown down at the same time as those of Class II. (Compare §§ 8, 21.) It will be well, therefore, for the sake of illustration, for the student to dissolve the present precipitate in sulphydrate of sodium, in order that he may begin the treatment of Class III at the pre- cise point at which this class would be encountered in an actual analysis — namely, with the sulphides of the class in alkaline solution. To this end, allow the washed pre- cipitate to drain, spread out the filter upon a jilate of glass, scrape the precipitate from the paper with a small spatula of platinum, horn, or wood, and transfer it to a porcelain dish. Pour upon the precipitate two or three times as much of a solution of sulpliydrate of sodium as § 24 ANALYSIS OF CLASS IIL 39 would be sufficient to cover it, and boil the mixture very cautiously, so as to avoid spattering. The precipitate wiU soon dissolve, and no soUd matter -will be left sus- pended in the solution, except a few fibres of the filter paper. It is such a solution as this which in an actual analysis is examined for members of Class III. Pour the alkaline solution into a beaker, and stir into it, little by little, dilute chlorhydric acid until the Uquid exhibits an acid reaction. The sulphides of arsenic, anti- mony and tin, are re-precipitated, as such, together with a quantity of siilphur derived from the decomposition of the sulphydrate of sodium. 24. Analysis of the Mixed Sulphides. The method here given of separating arsenic, antimony and tin, depends : — ■ 1st. Upon the solubility of sulphide of arsenic in a dilute aqueous solution of carbonate of ammonium, and the in- solubility, or very slight solubUity of the sulphides of anti- mony and tin in that liquid ; 2d. Upon the oxidation of the sulphides of antimony and tin by fusion with nitrate of sodium ; 3d. Upon the reduction of the compounds thus formed to the metallic state by zinc ; 4th. Upon the solu- bUity of tin in chlorhydric acid. To effect the separation : — Collect upon a filter the pre- cipitate produced by acidifying the sulphydrate of sodium solution, wash it with water to remove the acid and the chloride of sodium which adhere to it, and allow it to drain. Spread out the filter in a small porcelain dish, and cover its contents with a dilute aqueous solution of carbonate of ammonium — obtained by dissolving 1 part of the solid carbonate in 12 parts of water, or by mixing one volume of the strong solution (§ 111) employed as the general reagent of Class VI, with two volumes of water — and stir the mixture. After the lapse of four or 40 SEPAEATION OF AESENIC. § 2-t five minutes, pour the carbonate of ammonium solution upon a new filter, collect the filtrate in a beaker, and stir into it successive drops of dilute chlorhydric acid — tak- ing care to add no more than a single drop of the acid at any one time — until carbonic acid ceases to escape, and the liquid exhibits a strong acid reaction when tested with litmus paper. A bright-yellow precipitate of stdphide of arsenic will separate immediately from the acid liquor, in case much arsenic is present ; or a yellow cloudiness wiU appear at first, if the quantity of arsenic in the solu- tion be minute. In the latter case the mixture must be left at rest for some hours, in order that distinct yellow flocks of the sulphide may collect at the bottom of the vessel. To confirm the presence of arsenic: — Collect the precipi- tated sulphide upon a filter, dry it thoroughly at a gentle heat, scrape it from the paper, place it in a narrow glass tube which has been blown to a bulb at one end (see § 175), and cover it with five or sis times its bulk of a per- fectly dry mixture of equal parts of carbonate of sodium j^gj and cyanide of potassium (§ 127). The bulb of for the tubs must be large enough to hold t^-ice as ■*"' much of the mixture as is really to be placed in it, in order that there may be room for the mass to swell when it is heated and fused. After the bulb has been charged, wipe out the inside of the tube with a tuft of cot- ton fixed to a wire, or with a twisted strip of paper, and heat the contents of the bulb during two or three minutes in the flame of a gas-lamp. A dark, lustrous ring of me- tallic arsenic wUl be deposited upon the cold walls of the tube. The mixed precipitate of sulphide of antimony and sii - phido of tin, insoluble in carbonate of ammonium, is treated as follows : — Scrape and wash all the precipitate § 24 ANTIMONY AND TIN. 41 off the paper into the dish, and add a teaspoonful of strong nitric acid. Evaporate the mixture to the bulk of a teaspoonful without heeding the mass of sulphur which separates ; then add to it two or three teaspoonfuls of a strong solution of nitrate of sodium (§ 120), and evapor- ate the mixture to dryness with constant stirring. Heat the dry mass until it fuses. When the dish has become cold, fill it half fuU of cold water ; when the water has softened the cake of fused salts, stir the contents of the dish, break up the lumps, and finally filter the insoluble tin and antimony compounds from the soluble nitrates which the water has taken up. This insoluble residue must next be placed ia a porcelain dish in contact -with a shp of clean, smooth, platinum foil, and heated with a little chlorhydric acid. Water is then added, and a small fragment of zinc is put into the liquid. Tiu and antimony will be reduced to the metallic state by the ziac. It is found that a part of the reduced anti- ^^^^ mony attaches itself firmly to the platinum foil, for producing a very characteristic black stain upon **''■ the bright surface of the foil. Tin produces no such ef- fect. As soon as the hydrogen has ceased, or nearly ceased, to escape from the liquid, the solution, which con- sists of chloride of zinc, is carefully poured off. The residue, together with the remnant of zinc if any tin adhere to it, is warmed with strong chlorhydric acid, in which the tin dissolves. Pour off this solution of protochloride of tia, and add to it two or three drops of a solution of ^^^^^ mercuric chloride (corrosive sublimate) (§ 145). for A white or gray precipitate of mercurous chloride *"' (calomel), often mixed with gray metallic mercury will be thrown down, for : — 2HgCl24-SnCl2=2HgCl+SnCl^; and 2HgCl+SnCl3=2Hg+SnCl4. 42 TABLE or CLASS in. § 25 To prove that the precipitate really contains calomel, decant the supernatant liquid, cover the precipitate vs^ith ammonia-vi^ater, and heat the mixture to boiling (compare p. 28). The black stain upon platinum is a trustworthy indica- tion of the presence of antimony ; but a verification of its presence may be readily obtained by the following pro- cess : — Wash the residue from the tia solution thoroughly by decantation, and warm it for a quarter of an hour with a solution of tartaric acid (§ 106), adding a few drops of nitric acid towards the close of the digestion. Care must be taken not to heat any part of the dish so hot as to burn or blacken the tartaric acid. Antimony dissolves in this tartaric acid solution ; its presence may be proved by passing sulphuretted hydro- gen through the decanted solution. An orange-red-colored precipitate of sulphide of antimony will be sooner or later thrown down. 25. An outline of the foregoing operations may be re- presented in tabular form, as follows : — The General Keagent (HjS) of Class III precipitates AsoSj, SbjSj, and SnS or SnS,, [AuoSj and PtSj]. (As well as the members of Class II, from which Class III is separated by solu- tion in sulphydrate of sodium and repreeipitation with an acid. ) Digest the precipitate, thrown down by acid from the sulphydmte of sodium solution, in a weak solution of carbonate of ammonium : AsjSa dissolves and may be reprecipitated by neutralizing the solution with HCI. Confirm prcsonoo of As by reducing As.Sj withNii^COj + KCN. SbjSj, SnSaudSuSj [.\UoSj audPtS.], remain undissolved. Treat with HNO3 ; fuse with NaXO , ; ti-eat fused suits with H,,0. llediice the insoluble residue with ziuc and dilute acid in preseuce of platinum tuil. Sb is deposited ou the foil. Tre:it inehillie residue with IICI. Sii .lissolves ; its prosonee is proved by H.rOL,. Sb is I'leii dissolved in tavlario' acid, auJ repre- cipitiiled as orange Sb..Ss. § 25 ALTEENATE METHOD FOE CLASS III. 43 Under some circumstances, acids fail to reprecipitate completely the stdphides which are dissolved in sulphy- drate of sodium. This difficulty is particularly likely to occur when tin is present. It may be avoided by modi- fying the above process, as foUows : add strong nitric acid to the sulphydrate of sodium solution to acid reaction, and without regard to the precipitate which separates, evaporate the acid mixture to the bulk of one or two teaspoonfuls. Then add three or four teaspoonfuls of a strong solution of nitrate of sodium, evaporate to dryness with constant stirring, and heat the mass untU it fuses. Let the dish cool, and then soak the fused salts in three or four teaspoonfuls of cold water, untU they soften and ia part dissolve. Break up the lumps, stir re- peatedly, and finally filter. Arseniate of sodium, together with some nitrate and sulphate of sodiiun, passes into so- lution, while the antimony and tin are to be found in the insoluble residue. This residue is examined for these two metals precisely as above described (§ 24, p. 41). The aqueous solution is tested for arsenic as follows : Acidulate the solution faintly with nitric acid, and warm it ; then add a few drops of a prepared solution of sul- phate of magnesium and chloride of ammonium jest (§ 139), and set the mixture aside for twelve fo^ hours. The formation of a white, crystaUine pre- cipitate of arseniate of ammonium and magnesium ia evidence of the presence of arsenic. Any precipitate supposed to contain arsenic or antimony may be further examined by converting the arsenic or antimony into a hydrogen compound, by the method known as Marsh's test (see the authors' Manual of Inorganic Chemistry, pp. 259, 270). This method is applicable to the detection of very minute quantities of arsenic or antimony. In the case of mixtiu-es containing gold and platinum (see § 13), as well as arsenic, antimony, and tin, the 44 SEPARATION OF CLASSES n AND III. § 26 gold and platinum would remain with the tin, without interfering in any way with the separation or detection of either member of the class. Since the sulphides of gold and platinum are both "black, while those of arsenic and tin are yeUow or brown, and that of antimony is orange, the presence of any considerable quantity of either of the precious metals would be indicated by the black color of the class-precipitate. There are excellent special tests both for gold and platinum, by which these elements may be detected even in the presence of aU the other metals. Hence it is most convenient to make special search for them in the original substance, by methods to be de- scribed hereafter (§ 92 b), whenever the preliminaiy ex- amination has given reason to suspect the presence of either of them. 26. The Method of Separating Glass II from Gl drain. Cut away the superfluous paper, place that portion of tlie filter to which the precipitate is attached upon a piece of Test charcoal, and heat it intensely in the blow-pipe for flame. Moisten the residue with a drop of a so- ■*'■ lution of nitrate of cobalt, and again ignite it Btrongly. The unfusod odinpovmd of aluminum, cobalt §§ 30, 31 TABLE FOE CLiVSS IV. 51 and oxygen, left upon the coal, will exhibit a deejj sky-blue color, when allowed to cool. This reaction is useful in dis- tinguishing the hydrate of aluminum from that of glucinum, an element somewhat similar to aluminum though far less abundant. Hydrate of glucinum when ignited with nitrate of cobalt does not yield a pure blue compound, but only a gray mass. 30. An outline of the foregoing operations may be tabulated as follows : — The General Reagent ([NH4]H0, mixed witli NH4CI) of Class IV preeiijitates the hydrates of Fe, Or, and Al, together with Mn (as a chromite, ferrite or aluminatel, and various phosphates and other compounds of Fe, Cr, Al, Ba, Sr, Ca, and Mg. Boil the precipitate in a solution of oxalic acid : — Ox alates of Ba, Sr, Ca, and Mg separate in the form of a powder, which is col- lected for fu- ture examin- ation in con- nection with Class VI. Oxalates of Fe, Al, Cr, and Mn go into solution. Test a small portion of the solution for Fe with fer- rocyanide of potassium. Evaporate the remainder to dryness and ignite. Test again for Fe. Mix the residue with dry Na-jCOa and KNO3, fuse upon pla- tinum foU, and treat with boiling water : — Test the insoluble residue for Mn. Divide the solution into two portions : — Yellow color of aqueous solu- tion indicates Cr. Confirm Cr b5' precipitation of PbCrOj. Acidulate a portion of the solution with HCl, and add (NH4)H0 :- Colorless flocculent pre- cipitate proves presence of Al. 31. Separation of Class IV from Class III. The methods of eliminating Classes I, II, and III from mixtures which contain members of these classes as well as of Class IV, have already been described in §§ 6 and 8. It is essential to the success of the operation that aU 52 FEEEOUS AND FERRIC SALTS. § 31 the sulphuretted hydrogen in the filtrate from Classes 11 and ni be expelled, and that any iron which may be con- tained in the solution be converted to the state of a ferric salt, before the general reagent (XH^HO) of Class IV is added to the liquid. For sulphuretted hydi-ogen pre- cipitates aU the members of Classes IV and Y from alka- line solutions, and the filtrate now in question is, of course, made alkaline, when ammonia-water is added to it. The iron must be oxidized, because ferrous hydrate is somewhat soluble in ammonium-salts, and could not, therefore, be precipitated completely by ammonia-water from the acid filtrate from Classes H and III. No matter what the condition of the iron may have been in the original solution, it is reduced to the state of ferrous salt by sulphuretted hydrogen. The filtrate from the precipitate produced by sulphuretted hydrogen (the general reagent of Classes II and IH) should, therefore, be placed in a porcelain dish, and boiled, until the steam from it ceases to blacken lead paper (§ 13S). -Vfter the sulphuretted hydrogen has been expelled, thi'ee or four drops of strong nitric acid must be added to the Hquid, and the mixture boiled for a moment longer to oxidize the iron. If much iron be present, the hquid will turn yellow. To determine whether the iron in the suli>tuuee sub- jected to analysis was originally in the state of a ferric or a ferrous salt, test a small quantity of the original solu- tion with a drop of ferricyanide of potassium i^^ 126). The formation of Prussian blue proves the presence of a ferrous salt. Another small portion of the original solu- tion, toslcil with a drop of ferrouyanido of potissitim, would yii'Ul Prussian blue in case the solution i'(>atained a ferric salt. In applying- either of these tests, the blue coloration, indicative of iron, is alone to be looked for ; § 31 CLASS IT. 53 no notice need be taken of other colorations, or of pre- cipitates formed by the action of the ferri- or ferro-cyan- ide upon the various metallic salts which the solution may contain. The possibihty that a ferrous salt may have been changed into a ferric salt during the process of getting the original substance, if a sohd, into solution, must not be lost sight of. After the iron has been oxidized, a small quantity of a solution of chloride of ammonium is added to the boiling liquid, and finally ammonia-water, little by Httle, with constant stirring, until a persistent odor of ammonia is perceptible. A large excess of ammonia must be carefully avoided, for hydrate of aluminum, being somewhat soluble in ammonia-water, might be kept in solution, to the dis- turbance of the analysis of Classes VI and VII. It will be remembered that the object of using chloride of ammonium is to hold in solution magnesium (of Class VII) and the members of Class V. A considerable quan- tity of the ammonium-salt wDl, of course, be formed in any event by the action of the ammonia-water upon the chlorhydric acid in the solution, but it is best always to add a further portion of the chloride, as a precautionary measure. The following inferences may be drawn from the color of the precipitate produced by ammonia-water : — A gelatinous white precipitate indicates aluminum or phosphate of calcium. A grayish-green or grayish-blue precipitate indicates chromium. A reddish-brown precipitate indicates iron. If no precipitate is produced by the ammonia- water, all the members of Class IV are absent, and the solution may at once be tested with sulphydrate of ammonium, the general reagent of Class V. 54 CLASS V. § 32 When the solution contains much chromium, a small portion of this element is apt to remain dissolved at first in the excess of ammonia-water, and to color the solution pink ; but by continuing to boil the solution, the color may be made to disappear, and the whole of the chromium thrown down. Care must be taken to replace, by small portions, the water driven off by boiling, lest some of the members of Class V be rendered insoluble. It is to be observed that the legitimate memlsers of Class IV cannot be completely precipitated by ammonia- water from solutions which contain non-volatile organic substances, like albumen, sugar, starch, and so forth, or organic acids (such as tartaric, citric, oxahc, or even in some eases acetic acid) which form soluble double salts by uniting simultaneously with the ammonium and one or more of the members of the class. The treatment of substances containing organic matter will be explained hereafter. (§ 76, I.) CHAPTER VI. CLASS V. SULPHIDES INSOLUBLE IN WATER AND HT SALINE OR ALKALINE SOLUTIONS. 32. Example of the Precipitation of the Memher.< of CIa.<-< V. Place in a small glass flask six or eight drops of strong aqueous solutions of the sulphates, nitrates, or chlorides of cobalt, nickel, manganese and zinc. Add ta the mix- ture five or six teaspoonfuls of a solution of chloride of ammonium, twice as much water, and ammonia-water to alkaline reaction. Heat the mixture to boiling, and add sulphydrato of § 33 ANALYSIS or CLASS V. 55 ammonium to tlie boiling solution, drop by drop, with frequent agitation, as long as a precipitate continues to be formed. (Compare p. 33.) In the present case there are special reasons why the i3recipitate should be boUed and shaken, in order to make it compact ; for the sul- phides of Class V, when loose and flocculent, are not only easily acted upon by the air and by dilute acids, but are peculiarly Hable to pass through the pores of filter- paper and yield muddy filtrates. At the best, these sulphides oxidize rapidly when moist, with formation of soluble sulphates which are liable to pass through the filters and contaminate the filtrates. The analysis of the sulphides should therefore be pro- ceeded with immediately after the precipitation with sul- phydrate of ammonium, and should be conducted in such manner that no precipitate of a sulphide shall ever be left moist upon a filter more than half an hour. 33. Analysis of the Mixed Sulphides. The detection of the several members of Class V depends, 1st, Upon the almost complete insolubility of the sulphides of cobalt and nickel in cold dilute chlorhydric acid, and the ready solubility of the sulphides of manganese and zinc in that liquid. 2d, Upon the solubility of hydrate of zinc, and the insolubOity of hydrate of manganese, in a solution of caustic soda. 3d, Upon the insolubility of sulphide of zinc in alkaline solutions. 4th, Upon the peculiar colors imparted to borax glass by compounds of cobalt and nickel dissolved in the glass ; and upon certain other spe- cial tests to be described directly. To effect the separation : — Collect the precipitate upon a filter, and rinse it once or twice with water ; spread open the filter in a porcelain dish, and cover it with cold dilute chlorhydric acid. Scarcely any of the sulphide of 56 ANALYSIS OP CLAfSS V. § 33 cobalt, or of nickel, will go into solution, while the sul- phides of manganese and zinc will be completely decom- posed, and dissolved as chlorides. Filter the chlorhydric acid solution, pour the filtrate into a porcelain dish, and boil it, until strips of moistened lead paper held in the steam no longer indicate the pre- sence of sulphuretted hydrogen ; then transfer the liquid to a beaker or test-tube, and add caustic soda (§ 116) to it in shght excess. A whitish gelatinous precipitate of hydrate of manganese, insoluble in caustic soda, will be thrown down, together with small portions of the hydrates of cobalt and nickel (particularly the latter), resulting from the partial decomposition of the sulphides of these metals by the chlorhydric acid, while the hydrate of zinc at first precipitated redissolves completely in the excess of soda. It is to be observed that precipitation should never be effected in a porcelain dish, since a white or transparent precipitate is scarcely visible in a white and opaque dish. To prove the presence of manganese, collect the preci- pitate upon a filter, allow it to drain, and fuse a small portion of it with a mixture of carbonate of sodium and nitrate of potassium upon platiaiim foil in the oxidizing blow-pipe flame, as du-ected on p. 49. Through the alkaline filtrate pass sulphui-etted hydro- gen gas. Sulphide of zinc will be thrown down as white or dirty-white flocculent precipitate. To confirm the presence of zinc : — Collect the precipi- tate produced by sulphuretted hydrogen upon a filter and aUow to drain ; transfer it to a porcelain dish, dis- solve it in dilute chlorhydric acid, and evaporate the solu- tion almost to dryness on a water -bath (§ 166). Dissolve the residue in a few drops of water, and without heeding the milkiness which the presence of particles of free § 33 ZIXC, NICKEL, AND COBALT. 57 sulphur may produce in it, pour this liquid into a test- tube containing two or three teaspoonfuls of a solution of normal chromate of potassium previously heated to boiling. A peculiar yellow, somewhat flocculent j^gt precipitate of basic chromate of zinc will be for formed in the boiling liquid, and will soon sub- ^"' side to the bottom of the tube. The red color of the supernatant fluid is due to the formation of bichromate of potassium. It is to be observed that in the analysis of mixtures which contain no manganese, the precipitate of hydrate of cobalt or of nickel, produced by the caustic soda, is usually small and sometimes hardly perceptible ; but, no matter how minute the precipitate may be, it must always be carefully removed by filtration before testing the solu- tion for zinc with sulphuretted hydrogen. The black residue, insoluble in dilute chlorhydric acid, is washed with water and tested for cobalt and nickel, by heating successive small portions of it in a bead (§ 84, c.) of borax (§ 119) in the oxidizing blow-pipe ^^stg flame. If cobalt alone were present, a bright, for pure blue color would be imparted to the bead. *" ^'' On the other hand, if the precipitate was composed solely of sulphide of nickel, the borax glass would assume a peculiar reddish-brown color. Mixtures of the two sul- phides yield beads of various tints, according to the pro- portions of nickel and cobalt contained in them. By adding the precipitate to the borax by repeated small portions, and fusing the bead anew after each addition, it is often possible to obtain first the characteristic color of one of the elements and afterwards tolerably well defined indications of the other. The blue color of cobalt can usually be made manifest, even in presence of much nickel, by heating the borax 58 SEPARATION OF NICKEL. § 33 bead in the reducing blow-pipe flame (§ 167). In the reduci)]g flame the reddish-brown color imparted by nickel changes to gray, while the cobalt blue remains unaltered. In any event, one of the two metals will be detected by the blow-pipe test, and the subsequent operations can be limited to searching for the other. To prove the presence of nickel, boil the black residue with a few drops of aqua regia in the porcelain dish, and evaporate the solution almost, but not quite, to dryness. Add to the residual acid Uquor, little by little, a strong solution of cyanide of potassium, until the reaction of the solution becomes decidedly alkahne, and boil the mixture for five minutes, taking care to add water by small por- tions to fully replace that lost by evaporation. The cyanides of nickel and cobalt, at first thrown down, both redissolve easily in an excess of cyanide of potassium ; but while the cyanide of nickel undergoes no change when the mixture is boiled, the cyanide of cobalt is aU converted into cobaltioyanide of potassium, and from so- lutions of this compound, cyanide of cobalt is not pre- cipitated on the addition of acids. As soon as the liquid has become cold, pour dilute sul- phuric acid into it, without heeding any precipitate which may have formed during the evaporation, until a drop of the mixture turns blue litmus-paper red. Transfer the acidulated hquor to a large test-tube, fill the latter with water, shake the mixture well, and allow it to stand dur- Tggt ing eighteen or twenty-four houi-s. The soluble for compound of cyanide of nickel and cyanide of potassium is decomposed by the sulphuric acid, and the cyanide of nickel precipitated in the form of a lifiht, dirty greenish-yellow powder, which slowly sub- sides to the bottom of the tube. § 34 8EPAEATI0N OF COBALT. 59 Sometimes a dark layer of dirt, derived from impurities in the reagents, is deposited above or below the stratum of cyanide of nickel, but it seldom happens that the cha- racteristic color of the latter is materially obscured by this contamination. At other times, when the operations have been performed carelessly, and the reagents have been employed in undue quantities, crystals of sulphate of potassium will separate in the tube ; but they can readily be removed by dissolving them in water. To confirm the presence of cobalt in case of doubt : — Dissolve the black residue in a few drops of hot aqua regia, evaporate the solution nearly to dryness, pour into the residual solution two or three times its own volume of a solution of nitrite of potassium (§ 129), and add to the mixture concentrated acetic acid, until the reaction of the liquid is strongly acid. Transfer the mix- jg^t ture" to a test-tube, and leave it at rest during for eighteen or twenty-four hours. A beautiful, yel- low crystalline precipitate of the double nitrite of cobalt and potassium will be deposited sooner or later, accord- ing to the proportion of cobalt which the solution con- tained. On adding caustic soda to the filtrate from the yellow cobalt precipitate, hydrate of nickel would be thrown down if it were present, and the presence of nickel might be confirmed by testing this precipitate with borax in the oxidizing blow-pipe flame. 34. An outline of the foregoing operations may be tabulated as follows : — 60 TABLE FOB CLASS V. ,35 The General Reagent ([NHjlHS) of Class V precipitates CoS, NiS, MnS, and ZnS. Treat the precipitate with dilute HCl : — CoSandNiS remain undis- solved. Test for Co and Ni with borax glass, and, if need be, with KCN or KNO2. MnClj and ZnCl! go into solution, pel HjS, and add NaHO :— Boil, to ex- Hydrate of manganese is precipitated, together with traces of the hy- drates of Co and Ni. Prove presence of Mn by the blow-pipe test Hydrate of zinc goes into solution. Add HjS to throw down ZuS. Confirm presence of zinc by precipitation of the chiomate. 35. Separation of Class V from Cla^s IV. After Classes I, n, in, and IV have been removed in the manner already described (§§ 9, 31), add a single drop of sulphy- drate of ammonium of good quality (§ 110) to the filtrate from Class TV. If no precipitate is produced, none of the members of Class V can be present, and the solution may be immediately tested with carbonate of ammonium, the general reagent of Class YI. If the first drop of the suljshydrate produces a precipi- tate, transfer the mixture to a small flask, heat it until it actually boils, and add more of the sulphydrate, with the precautions enjoined on p. 55 to complete the precipita- tion. In case the precipitate produced by sulphydrate of ammonium be white, the presence of zinc is indicated. If it be flesh-colored or yellovrish-white, and become brown by oxidation when exposed to the air, the presence of manganese is to be inferred. In case the precipitate is black, either cobalt or nickel, or both these elements, are jn-oseut. Both of them must be sought for, whenever the precipitate cxliibits any tinge of black at the moment of its formation. §§ 36, 37 CLASS VL 61 CHAPTEE VII. CLASS VI. CARBONATES INSOLUBLE IN WATER, AMMONIA- WATER, AND SALINE SOLUTIONS. 36. Example of the Precipitation of the Members of Class VI. Place in a test-tube six or eight drops of strong aqueous solutions of the chlorides or nitrates of barium, strontium, and calcium. Add to the mixture two or three teaspoonfuls of a solution of chloride of ammonium, enough ammonia-water to produce an alkaline reaction, and finally a solution of carbonate of ammonium, drop by drop, as long as any precipitate continues to be pro- duced by fresh portions of this reagent. To determine this last point, heat the mixture to boiling at intervals, and after boUing allow it to settle, until a sufficient quan- tity of eomparatively clear liquid has collected at the top of the mixture to permit the application of the test. 37. Analysis of the Mixed Carbonates. The separation of barium, strontium and calcium, one from the other, depends : — 1st, Upon the insolubility of chromate of barium in dilute acetic acid, and the solubility of the chromates of strontium and calcium in that Uquid. 2nd, Upon the fact that sulphate of strontium is almost abso- lutely insoluble in acidulated water, while sulphate of cal- cium, though rather sparingly soluble in water, is still sufficiently soluble to be kept in solution. (See § 123.) Collect the precipitate upon a filter, wash it two or three times with water, taking care to collect the pre- cipitate at the apex of the filter, and dissolve it in acetic acid. The acid may be poured into the filter as it rests 4 62 TEST FOE BABIUM. § 37 in the fimnel, but only a moderate quantity should be used, and the filtrate should be poured back upon the filter, until the acid is saturated. Fiually riase the filter with a little water from a wash-bottle with small orifice, collect the wash-water with the filtrate, and shake the mixture. Pour a small portion of the acetic acid solution into a test-tube, and add to it a drop of a solution of normal chromate of potassium. A pale yeUow precipitate falls Test when barium is present, as in this instance ; for tor chromate of barium is well nigh insoluble in *"■ acetic acid, especially in presence of saline solu- tions. In order to separate the whole of the barium, poux the contents of the test-tube into the reserved portion of the acetic acid solution, heat the mixture to boiling, and add to it chromate of potassium, until no more precipitate falls and the supernatant hquor appears distinctly colored, after having been well shaken and eJlowed to settle. Filter the mixture, and proceed to examine the filtrate for strontium and calcium. If no barium had been present, no precipitate would have been produced by chromate of xx>tas,sium in the small portion of liquid first tested, and it woiild have been unnecessary to mix this reagent with the rest of the acetic acid solution. Trouble would thus be saved, as will ap- pear below. It sometimes happens that chromate of barium is pre- cipitated ia the form of powder so fine that some ^xirticles of it pass through the pores of the paper and contaminate the filtrate. Now, in order to detect strontimu and cal- cium, it is absolutely necessary that this filtrate, althoiigh of a bright yellow color, should be perfectly ti-auspai-eut and fi-ee from suspended particles of the barium salt. If then the filtrate is at all tiu-bid, it must be poured back § 37 TESTS FOB STKONTrUM AND CALCrUM. 63 repeatedly into the filter, and again collected in clean tubes, until the last trace of cloudiness has disap- peared. To the filtrate from the chromate of barium add am- monia-water to alkaline reaction, and carbonate of am- monium as long as a precipitate falls. Heat the mixture to boiUng for a moment, collect the precipitate upon a small filter, and wash it with water, until all the chromate of potassium has been remoTed, and the wash-water runs colorless from the filter. Dissolve the precipitate in the smallest possible quantity of acetic acid, and mix it with three or four times its volume of a solution of sulphate of potassium (§ 123), made of such strength that, though capable of throwing down sulphate of strontium, it cannot precipitate sulphate of calcium. Allow the mixture to stand at rest ^ests for two hours or more, in order that the white for powder of sulphate of strontium may separate "' "' completely. Then filter, and to the filtrate add ammonia- water to alkaline reaction, and half a teaspoonful of a so- lution of oxalate of ammonium (§ 113). A white pre- cipitate of oxalate of calcium will be immediately thrown down. Since sulphate of strontium is somewhat soluble in a solution of chromate of potassium, the filtrate from chromate of barium cannot be examined directly for strontium by means of sulphate of potassium. The strontium and calcium are consequently reprecipitated as carbonates, in order that the excess of chromate of potas- sium may be washed away. The operation serves also to collect the strontium and calcium out of the mass of liquid in which they have become diffused, and to concentrate them to a small bulk. It should be observed that, when the proportion of 64 TABLE rOE CLASS VI. §§ 38, 39 strontium or calcium in a mixture is small, it often happens that the precipitate, produced by carbonate of ammonium in the filtrate from chromate of barium, is held in suspension, and concealed so completely in the yeUow liquor, that an unpractised eye can hardly detect the fact that the liquid has become cloudy. That a precipitate has really been formed in such cases is easily discovered by throwing a portion of the mixture upon a filter, and com- paring the clear filtrate thus obtained with that portion of the mixture which has been left unaltered. 38. An outhne of the foregoing operations may be presented in tabular form, as follows : — The General Reagent ([NHjlsCO,) of Class VI, precipitates the carbonates of Ba, Sr, and Ca. Dissolve in dilnte acetic acid, and add KjCrOi :— BaCrOi is thrown down as a yeUow powder. SrCrOi and CaCrO^ remain in solntion. Add (NH^jjCO,, and (NHiJHO. Collect and wash the precipitate, and dissolve it in acetic acid. Add dilute K2SO4 :— SrSOj is thrown down. CaS04 remains in solution. Add oxalate of ammonium, to precipitate oxalate of cal- cium. 39. Separation of Clas>< VI from the Preceding Classes:. After Classes I, 11, III, lY and V have been sei^arated in the manner ah-eady dosoribid (§§6 to 10), there wQl stUl always remain to be examined the filtrate fi-om C'liiss Y, and sometimes a precipitate (§ 201 composed of oxalates of barium, strontium, calcium and magnesium, — iu case any salt of these cloments, insoluble in ammonia- water, has been thro\\n down with the members of Class IV. § 39 SEPARATION OP CLASS VI. 65 If such a precipitate has been obtained in the analysis of Class IV, the oxalic acid contained in it must now be destroyed, the remainder of the precipitate brought into . solution, and this solution added to the filtrate from Class V, before proceeding to precipitate the members of Class VI. To this end, ignite the dry precipitate carefully upon platinum foil — ^by several successive portions if the precipitate is large, — taking care that none of the powder is left sticking to the paper or lost by dropping it from the foil. At a moderate heat the oxalates suffer decom- position, and only carbonates or oxides are left upon the foil. Place the foil and the residue in a small porcelain dish, and dissolve the residue in boiling dilute chlorhydric acid. Add a few drops of chloride of ammonium to the solution, neutralize the acid with ammonia-water, pour the liquid upon a small filter and add the filtrate to that obtained from Class V. Then add a solution of carbonate of ammonium to the mixture, and boU it in the manner described in § 36. If there be no precipitate of the oxalates from Class IV, the filtrate from Class V will, of course, be treated directly with carbonate of ammonium, care being taken to add only a drop or two of the reagent, at first, to ascertain whether any of the members of Class VI are really con- tained in the solution. The solution to which the general reagent carbonate of ammonium is added, must contain chloride of ammonium, to prevent the precipitation of magnesium as a carbonate, and also ammonia-water, to hinder the decomposition of the carbonates of barium, strontium and calcium, by the boUing chloride of ammonium. But since the excess of ammonia-water and the chloride of ammonium, added to the solution before the separation of Class IV, are stiU 66 SEPARATION OF CLASS VI. § 39 contained in it, no new quantity of either of tliem need here be added. It is to be remembered, in this connection, that the carbonates of barium, strontium and calcium, are all shghtly soluble in a solution of chloride of ammonium, and that no precipitate whatever is produced when car- bonate of ammonium is added to a weak solution of either of the members of Class VI, in case a large quantity of chloride of ammonium has been previously mixed with it. In a solution containing traces of barium or strontium these elements might fail to be detected, in case the chlor- hydric acid employed in the process of separating Classes I and n was contaminated with sulphuric acid, or in case the original Uquid contained nitric acid to oxidize a por- tion of the sulphur of the sulphuretted hydrogen employed to precipitate Class II, or even if the nitric acid, employed to oxidize iron in the filtrate from Classes 11 and IH, were added before the sulphuretted hydrogen had been expelled. All danger could be avoided, however, by usintr j)ure chlorhydric acid to precipitate Class I, and expelling the nitric acid from the filtrate by evaiiorating the latter to dryness upon a water-bath, covering the residue with pure concentrated chlorhydric acid, again evaporating until the mixture became dry, and finally dissolving ia acidulated water. §§ 40, 41 CLASS VTI. CHAPTEE YIII. CLASS VII.— mCLUDES THE REMAINING COMMON ELE- MENTS NOT COMPRISED IN THE PRECEDING CLAS- SES, NAMELY : MAGNESIUM, SODIUM AND POTASSIUM. 40. The detection of the Several Members of Class VII depends : — 1st, Upon the insolubility of a double phos- phate of magnesium and ammonium, and the solubility of the phosphates of potassium and of sodium; and 2d, Upon the facts that compounds of sodium and potassium impart peculiar colorations to non-luminous flames, like those of alcohol and of a mixture of coal-gas and air. Prepare a mixture of ten or twelve drops of strong solutions of almost any one of the salts of magnesium, sodium and potassium, and add to the mixture an equal bulk of chloride of ammonium. Pour a quarter of the mixture into a test-tube and the remainder into a small porcelain dish. Add to the contents of the test-tube two or three drops of a solution of diphosphate of sodium (§ 121), and as much ammonia-water, and shake the cold mixture at frequent intervals during one or two hours. A crystaUine, white precipitate of phosphate of j^^ magnesium and ammonium wiU appear after a for longer or shorter interval, according as the ori- "*s- giaal solution was more or less dilute. 41, Evaporate the contents of the porcelain dish to dryness, ignite the residue untU the chloride of ammonium has been completely expelled — a point which wiU be in- dicated by the cessation of fuming — allow the dish to cool, and pour into it three or four drops of water. 68 TESTS FOE SODIDM AND POTASSIUM. § 41 Carefully clean the loop on a piece of platinum wire by washing it repeatedly with water, and finally holding it in the lamp flame until the last traces of sodium compounds are burned ofif, and it ceases to color the flame. "Without touching the loop with the fingers, dip it into the aqueous solution in the dish, and again hold it in the flame. A ,jggj bright yellow color will be imparted to the flame for by the sodium contained in the mixture ; but the '*"• color peculiar to potassium compoirnds will be in- visible, since the yellow color of the sodium overpowers and conceals it. Dip the loop a second time in the solu- tion, and again hold it ta the lamp flame ; but this time look at the flame through a piece of deep-blue cobalt glass. This cobalt glass is the ordinary blue glass used for stained glass windows ; it is essential that the glass should be of moderate thickness, and colored blue j,gj throughout, not simply "flashed" with blue. The for characteristic violet color imparted to flame by "*' potassium compounds will now be visible, for the blue glass shuts off completely the yellow sodium light, whUe it permits the free passage of the violet rays. Since traces of compounds of sodiiun and potassium are to be found almost everj-nhere, it is sometimes diffi- cvilt to determine by the foregoing tests whether the substance under examination contains one or other of these elements as an essential ingTedient, or merely as an accidental impurity. It is always possible, however, to separate the sodium or the potassium from the other members of the class, and to decide, by actual inspection of the isolated compounds, whether one or both of those substances is contained in really appreeiable quimtity in the stibstiince subjected to analysis. If onlj- potassium is sought for, filter th<> aqueous solution, last mentioned, through a very smaU filter, add to the filtrate a di-op or § 41 REMOVAL OF MAGNESIUM. 69 two of chlorhydric acid and several drops of a solution of bichloride of platinum (§ 146). A yellow crystalline pre- cipitate of chloroplatinate of potassium will separate after some time. Since chloride of ammonium would produce a similar precipitate, it is, of course, essential that the am- moniacal salt should be expelled by ignition before potas- sium can be tested for. In case sodium, or both sodium and potassium, be sought for, the magnesium must first be got rid of. To this end, moisten the dry residue, which contains the chlorides of magnesium, of potassium and of sodium, with a drop or two of water, mix it thoroughly with an equal bulk of red oxide of mercury, and ignite the mix- ture until fuming ceases. The chloride of magnesium win be changed to oxide, while the easily volatile chloride of mercury escapes : — MgCl,+HgO=MgO+HgCl,. The ignition should be effected beneath a chimney, or in a draught of air powerful enough to carry away the poisonous fumes of the corrosive sublimate. Boil the ignited residue with a small quantity of water ; separate the insoluble oxide of magnesium, together with the excess of oxide of mercury, by filtration ; evaporate the filtrate to a small bulk ; throw down the potassium as chloroplatinate, collect the latter upon a filter, and from the filtrate remove the excess of chloride of platinum by means of sulphuretted hydrogen. Filter off the sulphide of platinum, and evaporate the filtrate to dryness to ob- tain the chloride of sodium. Or, instead of employing sulphuretted hydrogen, evaporate the filtrate from chlo- roplatinate of potassium in a watch glass, at a gentle heat, until the liquid begins to become dry at its edges, and 70 ISOLATION or CLASS VII. §§ 42, 43 then examine it with a magnifying glass. Characteristic crystals of chloroplatinate of sodium will be seen in the form of long, slender prisms or needles of yellow color. 42. The Isolation nf Class Til, by the removal of the preceding classes, has been described in § 12. Care must always be taken to concentrate the whole of the filtrate from Class VI by evaporation, before testing a portion of it for magnesium ; and time enough must be allowed for the magnesium precipitate to crystallize. The remainder of the filtrate from Class VI must be evaporated to dryness and ignited, before testing for sodium and potas- sium, in order that the flame reactions of these elements may not be concealed or obscured by the vapors of am- monium-salts, or the combustion of particles of organic matter derived from the various reagents which have been added in the coui'se of the analysis. 43. An outline of the methods employed for separa- ting the several classes is presented in tabular form on the opjDOsite page. The method of separating Class IH from Class 11 must be shghtly modified when mercui-y is present in the form of a mercuric salt. Sulphydiate of ammonium should in that case be substituted for sul- phydrate of sodium ; because the sulphide of mercury is rather soluble in sulphydrate of sodium. The presence of mercury will generally be made known during the preliminary examination (§ 70, III, c). Sulphide of cojjper also is somewhat soluble in the sulphydratos of sodium and ammonium, in presence of the sulphides of Class III ; but enough of this sulphide will always remain undissohed to insure the detection of copper in Class II. Since sulphydrate of ammonium often fails to dissolve §§43 SEPARATION INTO CLASSES. 71 ?5 O o H ^2; OS O o P4 w m O Eh S ^S °M d -S §1 ii'seiu'e or absence in a given § 44 METAL PIEST SOUGHT FOE. 73 solution. Tlie sodium in the three different salts, sul- phate, sulphite and hyposulphite of sodium, for example, is detected in one and the same method ; but, when the other elements of these salts are sought for, three differ- ent reactions will occur, according to the varying nature of the ingredients other than sodium. A sulphate in solution gives one set of reactions, a sulphite another, and a hyposulphite a third. It is important to do more than determine the mere presence of sulphur and oxygen. We want to know whether the sodium salt be a sulphate, sulphite, or hyposulphite. Analogous questions arise with regard to other non-metaUic elements ; there is chlorine both in chlorides and chlorates, and carbon both in carbonates and oxalates. Arsenic, too, may be present in the form of arsenite or arseniate, and these two different kinds of salts exhibit many quite dissimilar reactions. •The examination into the nature of the other ingre- dients of any compound is invariably subsequent to the determination of the metallic element or elements by the method detailed in the preceding chapters. In the lan- guage of the dualistic theory, when the base has been found, the acid is sought for. By whatever words the object of the analyst be described, the process itself is in general as follows : — The analyst tries to identify each class of salts by precipitating, or otherwise making mani- fest, some familiar member of that class. Thus he iden- tifies sulphates by precipitating sulphate of barium, chlo- rides by precipitating chloride of silver, carbonates by throwing down carbonate of calcium, and so forth. The practically important inquiry is, how to find means of identifying each of the principal classes or kinds of salts. The word " class " or " kind " of salts is used in this con- nection as a collective name for all the salts from which 74 GENERAL EEACTIONS. § 44 the same acid may be derived, or which, in dualistic lan- guage, "contain" the same acid: thus all sulphates con- stitute one class or kind, all carbonates another, and so forth. The following common classes of salts are those for which more or less perfect means of recognition will be given in this chapter: — Sulphates, sulphites, hyposul- phites, sulphides, arseniates, arsenites, phosphates, car- bonates, oxalates, tartrates, borates, silicates, chromates, fluorides, chlorides, bromides, iodides, cyanides, nitrates, chlorates, acetates. No system of successive testing and elimination, analo- gous to that already described for the metallic elements, has been devised for the non-metallic constituents of salts. There are, indeed, certain so called general reagents for ax;ids ; but these reagents are chiefly useful to show the simultaneous presence or absence of members of several classes of salts, and hardly help towards the iden- tification of any individual class, except in cases of the simplest sort in which only a single class of salts is repre- sented. The knowledge of the metallic element or elements present, previously gained, is usually a great help in the determination of the other constituents. A single exam- ple will illustrate sufficiently for our present piu-pose this important principle, which is of very wide application in qualitative analysis. Suppose calcium to have been found in an aqueous solution of various salts ; it is dii-ectly to be inferred with groat confidence, though not with entire cer- tainty, for example, that there is no sulphate, phosphate, silicate, carbonate, oxalate, or taatrate in the original liquid, since these calcium salts are insoluble in water ; that, in short, the j^reater number of the classes of salts aboY(! enumerated are absent. The Ust of salts excluded by the demonstrated presence of calcium would be very § 45 THE BAHIUM TEST. 75 long. So it is in greater or less degree -with many other metallic elements. It is, indeed, no easy matter to make a solution containing even one representative of the seven classes into which the metallic elements have been divided, because each of these elements, except sodium and potassium, present in solution excludes one or more whole classes of salts. By attending to the just infer- ences to be drawn from the quality of the metallic ele- ments, much time will be saved, and the want of a systematic procedure in searching for the non-metaUic elements will be little felt. The presence of the arsenites and arseniates, of chromates, sulphides, sulphites, and hyposulphites will ordinarily be revealed in the course of the search for the metallic element. Before giving the special tests by which the above- mentioned classes of salts are identified, we proceed to describe certain general tests which are of value, particu- larly when they give negative results. 45. The Barium Test. When a solution of chloride (or nitrate) of barium is added in suitable quantity to a neutral or slightly alkaUne solution containing represent- atives of any or all of the following classes of salts, pre- cipitation usually occurs, for all these salts of barium are insoluble in water and alkaline liquids, if no ammonium- Baits be present : Sulphates, Arseniates, Tartrates, Sulphites, Arsenites, Borates, Hyposulphites, Carbonates, Silicates, Phosphates, Oxalates, Chromates, Fluorides. If the chloride (or nitrate) of barium fail to produce a precipitate under the prescribed conditions, the complete 76 THE BARIUM TEST. § 4:6 absence of all the above tbirteen classes of salts is at once demonstrated, provided that no ammonium-salts be con- tained in the original solution. 48. Illustration of the Barium Test. Prepare in a test- tube a solution containing at once sulphate, phosphate, and carbonate of sodium ; a very small bit of each salt will be sufficient. The solution -will be found to be alkahne to litmus paper. Add to it chloride of barium (§ 135), little by little, until a fresh addition of the re- agent no longer produces an additional precipitate. The white precipitate consists of sulphate, phosphate and car- bonate of barium. AH the thirteen barium salts which are liable to precipitation under these circumstances are white, with the single exception of chromate of barium. The yeUow color of the chromate of bariimi (§ 36) distin- guishes this one precipitate from aU the rest. If this color is well marked, the presence of a chromate in the original solution (which must also have been yellow) may be inferred with certainty. In all other cases, however, the precipitate is white, as in the present experiment. The next question is, can anything further be learned from this white precipitate ? Add to the contents of the test-tube dilute chlorhydric acid, until the Hquid has a decidedly acid reaction to litmus paper. An (.ffervcseence indicates the escape of carbonic acid, displaced by tlie less vobitile chlorhydric acid. The bulky precipitate which the chloride of barium produced will in part disappear, but a portion of it remains undissolved, riltcv the contents of the tube. The pai-tick'K of prcciintatod sulphate of barium are so very fine that tlioy oftiMi pass throui^h the pores of the paper, necessitating repeated filtration through the same filter. To the filtrate add ammonia-water imtil the liquid § 46 THE BARIUM TEST. 77 has an alkaline reaction. A precipitate will reappear. Of all the barium salts which may be precipitated under these circumstances, only one, the sulphate of barium, is insoluble in chlorhydric and other strong acids. A separation of sulphur from a hyposulphite wiU not be mistaken for a barium precipitate (§ 22, p. 37). The fact that any of the original precipitate remains undis- solved by the chlorhydric acid demonstrates the presence of a sulphate. The portion of the original precipitate which dissolved in the acid, and was reprecipitated by ammonia, consisted in this particular experiment of phos- phate of barium; but in an actual analysis the possible salts represented would be so numerous as to make the indication of but Httle value. If ammonia-water should cause no reprecipitation in the acid liquid which was filtered from the original pre- cipitate, it must not be inferred that the acid of course dissolved nothing. The borate, oxalate, arseniate, arsen- ite, tartrate and fluoride of barium, are all moderately soluble in solutions of ammoniacal salts, and may not be precipitated on the addition of ammonia. Of course, if the original solution contained ammonium-salts, these six barium salts, if present in small quantity only, might fail to be precipitated. In fact, all the thirteen above- mentioned barium salts, except the sulphate, are more or less soluble in solutions of ammonium-salts, so that when- ever these ammonium-salts are known to be present, there is really but one perfectly satisfactory indication with chloride of barium. The presence of a sulphate is revealed by it with certainty, but the results of the other tests must be received with some distrust. If the original solution be acid, it is necessary to neutralize it with am- monia-water before the chloride of barium is added. Sometimes a precipitate is produced by the ammonia- 78 THE CALCIUM TEST. § 4:7 water so added; in that ease it is necessary to filter and proceed with the filtrate, although the ammonia-water may have thrown down salts of several of the classes above named, such as phosphates, oxalates, and fluorides. Even if the ammonia-water produce no precipitate, the testing is then performed under the disadvantage of the presence of ammonium-salts. If the original solution contained silver or lead salts, or mercurous salts, it would be impossible to use chloride of barium and chlorhydric acid as reagents ; they would throw down the chlorides of those metals. Nitrate of barium (§ 136) and dilute nitric acid must then be used. The acids added to the precipitate formed by the barium salt must be always dilute acids. Chloride and nitrate of barium are themselves iasoluble in concentrated chlorhv- di'ic and nitric acids, and if a strong acid were used as a solvent, the reagent salt might itself separate from the liquid. 47. The Calcium Test. Chloride (or nitrate) of calcium precij)itates the same classes of salts as chloride (or nitrate) of barium, with the single exception of the chro- mates. When sulphali'^ and all ammoniacal salts are absent, or present only in minute quantities, something may be learned by testing a neutral or slightly aikaliue solution supposed to contain rcjiresentatives of some of the other classes of salts enumerated in § -45, with chloride or nitrate of calcium. The calcium salts liable to precipita- tion under these circumstances are aU soluble in acetic acid, except the oxalate and the fiuorido. The precipitate produced by tlie cak'ium reagent is, therefore, treated with acetic acid ; if it cDiupletcly redissolves, oxalales and fluorides are most probably absent. The presence of not- able quantities of ammonium-salts renders this test of §§ 48, 49 THE SILVER TEST. 79 uncertain value ; because the fluoride and many other salts of calcium are soluble in solutions of ammonium- salts. Since sulphate of calcium is sparingly soluble ia water and acetic acid, the presence of a sulphate, causing precipitation of sulphate of calcium, obscures the reac- tion for oxalates and fluorides. Nitrate of calcium must be used instead of the chloride whenever silver or lead salts, or mercurous salts, are present in the solution under examination. 48. Illustration of the Calcium Test. Prepare in a test-tube an aqueous solution of phosphate, oxalate and tartrate of sodium. A very small quantity of each salt win be enough. The solution will be neutral or faintly alkaline. Add to this solution a solution of chlo- ride of calcium (§ 134) until the precipitation is com- plete. Collect the white preciisitate upon a filter, and, when drained, transfer it to a test-tube and treat it with acetic acid. The phosphate and tartrate of calcium will redissolve, but the oxalate remains untouched. To verify this result, and identify each one of the sodium salts pre- sent in the original solution, special tests, to be hereafter described, must be resorted to. 49. The Silver Test. Nitrate of silver produces a pre- cipitate in neutral or acid solutions with all chlorides, bromides, iodides and cyanides, and in neutral solutions with most of the classes of salts enumerated in § 45. In order to obtain the most comprehensive negative conclu- sion in the case that nitrate of silver produces no precipi- tate, it is necessary to operate upon a neutral solution. If the original solution be neutral, the nitrate of sUver may be immediately added to a portion of it. If no pre- cipitate appear after the lapse of several minutes, neither 80 THE SILVEE TEST. § 49 chlorides, bromides, iodides, cyanides, sulphides, phos- phates, arseniates, arsenites, chromates, silicates, oxalates, nor tartrates can be present. If the original solution contained any considerable quantity of a borate, the borate of silver would be precipitated under these condi- tions ; but a small proportion of some borate might es- cape precipitation. If the original solution be acid to test paper, add nitrate of silver to a portion of it in a test- tube, and then pour in upon the liquid some dilute am- monia-water, so gently that the two liquids do not mix at once. At some layer near the junction of the two dis- similar liquids, the fluid must be neutral. If at that layer no precipitate or cloud appear, the twelve kinds of salts above enumerated are absent. If the original solution is alkaline, dilute nitric acid is to be added in precisely the same manner as the ammonia-water in the opposite case. The neutral layer between the two liquids is attentively observed, and the absence of any film or cloud therein justifies the same sweeping conclusion as that above given- If any precipitate is produced by nitrate of silver, its color is to be observed, for some conclusions may often be di-awn from this color. Chloride, bromide; cyanide, oxalate, tartrate, silicate, and borate of silver are white ; iodide, phosphate, carbonate and arsenite of silver are yellow ; arseniate of sUver is brownish-red ; chromate of silver is purplish-red ; sulphide of silver is black. When the silver precipitate is white, black, or of some obsciu-e, indecisive color, the operations in the wet way at this stage should be directed to proving or disproving the presence of chlorides, bromides, iodides, cyanides and sulphides. To this end the portion of the original solu- tion which has been already tested with nitrate of silver, should be made decidedly acid with dilute niti-ic acid. Of all tlio silver salts which can be precipitated on the addi- § 50 THE SILVER TEST. 81 tion of nitrate of silver, only the chloride, bromide, iodide, cj'anide and sulphide can resist dilute nitric acid. If the precipitate once formed redissolves completely in nitric acid, no chloride, bromide, iodide, cyanide, or sul- phide was present in the original solution. If, on the contrary, a residue remain, one or more of these kinds of salts must have been represented in the original solution. If the residue be black or blackish, the presence of a sul- phide is to be iaferred ; if it be white or whitish, the ab- sence of sulphides and the presence of a chloride, bro- mide, or cyanide is to be inferred ; if it be distinctly yel- lowish, an iodide is probably present. An experiment win best illustrate the most appropriate treatment of a silver precipitate insoluble in nitric acid. 50. Illustration of the Silver Test. Prepare in a test- tube a weak solution of chloride of sodium, iodide of potassium, cyanide of potassium, and phosphate of so- dium. Add nitrate of silver (§ 131) to this slightly alka- line solution, untn the precipitation is complete. The dense precipitate is yellovrish-white. Pour dilute nitric acid into the mixture, until the solution is strongly acid ; shake up the contents of the tube thoroughly, and after the lapse of several minutes collect the insoluble precipi- tate on a filter, and receive the filtered Uqiiid in a test- tube. If the filtrate be neutralized again with ammonia, a yeUow precipitate of phosphate of silver will reappear. The precipitate on the filter is then thoroughly washed to free it from the superfl.uous nitrate of sUver. Wash the precipitate into a clean test-tube, decant the water from above it, pour over it ammonia- water, and gently heat the mixture. The sUver precipitate will visibly diminish in bulk, but a yellowish portion remains undissolved. Filter again, and neutralize the filtrate with nitric acid ; a white 82 NITEATES, CHLORATES, ACETATES. § 51 precipitate will faU. This experiment proves that a por- tion, but not all, of the mixed silver salts which are in- soluble in nitric acid, are soluble in ammonia-water. The fact is that the chloride, cyanide and bromide of silver dis- solve in ammonia-water, the latter with difficulty, while the iodide is insoluble in that reagent. Special tests, hereafter to be described, are appUed in order to confirm the presence of iodine, and to detect each and all of the three substances which are liable to be confounded in the white precipitate just mentioned. Cyanide of mercury does not give a precipitate with nitrate of silver. When mercury has been detected in the substance under examination, cyanogen must be sought for in other ways (§ 55) than this. When the hquid under examination contains a ferrous salt, protochloride of tin, or any other active reducing agent, metallic silver is liable to be precipitated as a dark, heavy powder. The examination for the metallic element will generally have revealed the presence of any such agent. 51. Nitrafcft, Ghlnratex, and Acetates. It is quite clear that no method of precipitation whatever wiU apply to nitrates, chlorates, and acetates, since these kinds of stilts are all soluble in water. No insoluble nitrate, chlorate, or acetate is known. Special tests must be resorted to for these three classes of salts. §§ 52, 53 SPECIAL TESTS. 83 CHAPTEE X. SPECIAL TESTS FOB THE NON-METALLIC ELEMENTS. 52. We now proceed to indicate the most available special tests for tlie non-metallic elements and tlieir com- monest compounds. It is noteworthy that the non- metallic elements enter into composition under various forms, which produce with one and the same metallic element various salts. Thus within the narrow range of this treatise, sulphur is to be sought in sulphides, sul- phates, sulphites and hyposulphites ; carbon in cyanides, acetates, carbonates, oxalates and tartrates, and arsenic in arsenites and arseniates. The various classes of salts will be taken up successively. It should be premised that these special tests are sometimes applied to the original solution, before the precipitation with chloride of barium and nitrate of silver, and sometimes during or after these more general testings. In the first case the student is seeking guidance in the appUcation of the more compre- hensive tests ; in the latter case he is trying to confirm results already almost sure. 53. Effervescence. When a solution containing a car- bonate, cyanide, sulphide, sulphite, or hyposulphite, or a mixture of representatives of some or all of these kinds of salts, is treated with chlorhydric acid and then warmed, an evolution of gas occurs with more or less eifervescence. The gases evolved are aU colorless ; but they aU have very characteristic odors except carbonic acid, the gas which 84 CARBONATES. § ^^ escapes from a carbonate. A cyanide gives off the l^ungent odor of cyanhydric acid. A sulphide yields sul- phuretted hydrogen of familiar presence. Sulphurous acid escapes from sulphites and hyposulphites alike ; but in the latter case a deposition of sulphur makes the liquid turbid. If only one of these gases were present, the eifer- vescence and the smell would identify it ; but when mix- tures are to be dealt with, further means of identification are necessary. 54. Carbonates. To prove the presence of carbonic acid gas, when effervescence has occurred, add chlor- hydric acid, little by little, to the effervescing solution, until the acid is decidedly in excess ; meanwhile keep the mouth of the test-tube loosely closed with the thumb to promote the accumulation of the gas evolved, ^^^^en the tube is supposed to be full, carefuUy decant the gas into a second test-tube containing a teaspoonful of Hme-water (§ 133), taking care not to allow any of the liquid to pass over with the gas. INIix the lime-water and the gas in the second test-tube by thorough shaking. A white precipitate of carbonate of calciiim will be produced, if the gas tested is, or contains, carbonic acid. If the effervescence is sUght, and the quantity of gns evolved seems too small to be decanted in this way, dip the end of a dark-colored glass rod into hme-water, and thrust the moistened end into the test-tube, bringing it close to the surface of the fluid. If the gas bo carbonic acid, the lime-water adhering to the rod wUl become visibly turbid. The student who dosivcs to see the working of this test before having occasion to apply it in an actual analysis, can operate upon a morsel of carbonate of sodium dis- solved in a little water. §§ 55, 56 CYANIDES SULPHIDES. 85 55. Cyanides. When the smell of the gas which escapes from the solution under examination (§ 53), or the qualities of the precipitate with nitrate of silver (§§ 49, 50), give occasion to suspect the presence of a cyanide, the following confirmatory test may be resorted to : — Add to the solution supposed to contain free cyan- hydric acid, or an alkaline cyanide, a few drops of a solu- tion containing both a ferrous and a ferric salt (a solution of ferrous sulphate which has been exposed to the air, for example), and a small quantity of caustic soda solution. If cyanogen is present, a bluish green precipitate forms, which consists of a mixture of Prussian-blue and the hydrates of iron. "Warm the liquid, and add to it an excess of chlorhydric acid. The hydrates of iron dissolve, but the Prussian-blue remains undissolved. If only a very small quantity of cyanogen be present, the liquid simply appears green after the addition of chlorhydric acid, and it is only after long standing that a trifling blue precipitate separates from it. This test may be well illustrated by means of a small particle of cyanide of potassi^^m dissolved in a teaspoon- ful of water. To detect cyanogen in cyanide of mercury, it is neces- sary to precipitate the mercury as sulphide, by means of sulphuretted hydrogen, and to identify the free cyan- hydric acid in the filtered or decanted fluid. 56. Sulphides. Many sulphides give off sulphuretted hydrogen when heated with chlorhydric acid. If the quantity of gas is so small that its odor is imperceptible, the lead-paper test (§31) should be applied. T\Tien sulphides are dissolved in nitric acid or aqua- regia, their sulphur is partly separated in a free state and partly converted into sulphuric acid. The free sulphur- is 5 86 SULPHITES HYPOSULPHITES. §§ 57-59 identified by its color and texture, and by its behavior when burnt. The sulphuric acid in the liquid is detected in the usual manner (§§ 45, 46). 57. Sulphites. All the sulphites evolve sulphurous acid, without any deposition of sulphur, when treated vnth chlorhydric acid. The very sharp odor of this gas is enough to identify it. As has been before stated, nitrate of silver produces in solutions of sulphites a white precipitate ; but this preci- pitate blackens when the liquid is boiled, on account of the reduction of silver. AYhen the sulphites are heated with strong nitric acid, or other powerful oxidizing agent, they are converted into sulphates without precipitation of sulphur. The sul- phates so produced may be identified in the usual way (§§ 45, 46). 58. Hijposulphites. The hyposulphites disengage sul- phurous acid and deposit sulphur when warmed with chlorhydric acid. This decomposition is not immediate if the solution be dilute. The precipitate produced in the solution of a hyposul- phite by nitrate of silver, dissolves again readily in an excess of the hyposulxahite. On standing, the precipitate of hyposulphite of silver turns black spontaneously, being decomposed into sulphide of silver and sulphiuic acid. Heating produces this effect almost immediately. Hyposulphite of sodium is a good sivlt from which to get the above reactions of hyposulphites. 59. Diu'ing tlie examination for tho metallic elements, chromium and arsenic are deteetetl, and the aiiidj-st geu- craUy obtains pretty certain evidence concerning the §§ 60, 61 CHEOMATES AKSENITE3 AND AESENIATES. 87 actual condition in ■which these elements enter into the substance under examiaation, whether as chromate or salt of chromium, as arsenite or arseniate ; for a chro- mate is reduced with change of color (§ 22), and sulphide of arsenic is thrown down immediately from an arsenite, but only after long contact with sulphuretted hydrogen from an arseniate. To confirm the indications then ob- tained, the following tests are used. 60. Chromaies. When acetate of lead (§ 137) is added to a neutral solution of a chromate, yellow chromate of lead separates, insoluble in acetic acid, but soluble in caustic soda. As has been before stated, the purplish-red color of chromate of silver (§ 49), and the yellow color of chro- mate of barium (§ 46), are valuable indications of the presence of a chromate. A solution of normal chromate of potassium is the best substance from which to obtain for the first time the re- actions of chromates. 61. Arsenites and Arseniafes. Though sure of the pres- ence of arsenic, the analyst is often left in doubt which of these two classes of arsenic compounds he has to deal with. Discriminating tests are necessary. A neutral solution of an arsenite yields with nitrate of silver a yellow precipitate of arsenite of sUver. A neutral solution of an arseniate gives with the same reagent a brownish-red precipitate of arseniate of silver. Both these precipitates are readily soluble in dilute nitric acid and in ammonia, and they are by no means insoluble in nitrate of ammonium. If solutions containing free arse- nious or arsenic acid are to be tested, they must first be cautiously neutralized with the least possible quantity of ammonia-water. 88 SULPHATES PHOSPHATES. §§ 62, G3 The above tests are generally sufficient, but circum- stances may arise in which they would be inapplicable. The following tests afford further means of discrimina- tion : — If to a solution of arsenious acid or an arsenite, caustic soda be first added in excess, and then five or six drops of a dilute solution of sulphate of copper, a clear bluish liquid is obtained, which, upon boiling, deposits a red precipitate of dinoxide of copper (Cu^O), while soluble arseniate of sodium is simultaneously produced, and re- mains in the solution. This test is good as a means of distinguishing between arsenites and arseniates when no organic matters are contained in the solution under ex- amination. The quahfication is necessary, because grape- sugar and many other organic substances exercise a like rediicing action on copper salts. If a solution of arsenic acid, or of an arseniate soluble in watec, be added to a clear mixture of sulphate of mag- nesium, chloride of ammonium and ammonia-water (§ 139), a crystalline precipitate of arseniate of magnesium and ammonium ^vill separate, after an interval which is short in proportion to the concentration of the arsenic solution. 62. Sii}phalr-i. The chloride of barium test (§§ 4:.'>, 46) is all-sufficient for the detection of sulphates. The operator should make sure that the chlorhydric acid itself contains no sulphuric acid, that an excess of acid is really present, and that the solution is tolerably dilute. Concentrated acids and strong solutions of many salts impair the delicacy of the reaction. 63. Phosjiha/r^. When the previous steps of the analysis have proved that the iihospliates present in the § 63 PHOSPHATES. 89 solution under examination are soluble in ammoniacal liquids, and that no arsenic acid or arseniates are present, the following test wQl satisfactorily identify a phosphate or free phosphoric acid : — Add to the solution to be tested a clear mixture of sul- phate of magnesium, chloride of ammonium and ammo- nia-water (§ 139). '\Mien a phosphate or free phosphoric acid is present, a white, crystaUine precipitate of phos- phate of magnesium and ammonium is formed, even in very dilute solutions. Stirring and shaking promote its separation. The precipitate dissolves readily in acids. When arsenic acid or arseniates are present in the original mixture, this test for phosphates can stiU be ap- plied, if all the arsenic be previously removed by precipi- tation as sulphide (§ 23). The magnesium mixture can be used in the filtrate from the sulphide of arsenic. The preceding test can only be applied when the phos- phate present is soluble in ammoniacal solutions. The fol- lovnng test is of much more general application ; it can be used in presence of arsenic acid, and is applicable to either neutral or acid solutions of phosphates ; it is also extremely delicate. "WTien two or three drops of a neutral or acid solution of a phosphate (even of iron, aluminum, barium, stron- tium, calcium or magnesium [compare § 27]), are poured into a test-tube containing four or five teaspoonfuls of a solution of molybdate of ammonium in nitric acid (§ 115), there is formed in the cold a pale-yellow precipitate which is apt to gather upon the sides and bottom of the tube. If the precipitate does not appear in a few minutes, a few drops more of the solution to be tested may be added. This precipitate is soluble in an excess of phosphoric and other acids ; and certain organic substances also prevent its formation. A yellow coloration of the liquid merely 90 OXALATES TAETBATES. §§ 64, 65 is not enough to prove beyond question the presence of a phosphate ; a precipitate must be waited for. The yellow precipitate can be easUy recognized, even in dark-colored hquids, when it has settled. The solution to be tested must not be heated, nor must it be more than blood- warm. Phosphate of sodium is the best substance on which to try the test for phosphates. 64. Oxalates. The precipitation of white, finely divid- ed oxalate of calcium, by all soluble calcium salts, from solutions of oxalates or oxaUc acid, has been already de- scribed (§ 48). Even the solution of sulphate of calcium gives this reaction with oxalates. If oxalic acid, or an oxalate in the dry state, be heated in a test-tube with an excess of concentrated sulxihuric acid, a mixture of carbonic oxide and carbonic acid is set free with effervescence ; the carbonic acid may be identi- fied by the lime-water test ; and if the quantity operated upon is considerable, the carbonic oxide may be inilanied at the mouth of the tube. 65. Tartrates. Tartaric acid and the tartrates, when heated in the dry state char, and emit a very character- istic odor which somewhat resembles that of burnt sugar. This is the only class of salts, among all those within the scope of this treatise, which exhibit this carbonization by heat. Strong sulphuric acid blackens tartaric acid and the tartrates. To confirm the iiroscnce of tartaric acid, or a tartrate, in any li(iuid supposed to contain it, a concentrated solu- tion of acetate of potassium is added to the liquid, and the mixture violently shaken. The procipitato, when one forms, is a difficultly soluble acid tarti-ate of potassium. § 66 BOEATES. 91 The addition of an equal volume of alcohol increases the delicacy of the reaction. The more concentrated the solution to be tested, the better. To prepare the required solution of acetate of potassium at the moment of use, rub together ia a dish half a teaspoonful of car- bonate of potassium and as many drops of acetic acid as will dissolve three-quarters of the carbonate ; throw the mixture on a small moistened filter and use the filtrate. Tartaric acid is a good substance from which to get these reactions. 66. Borates. To confirm the presence of a borate, strong sulphuric acid is mixed with the dry substance under examination ia quantity sufficient to make a thin paste, and an equal bulk of alcohol is added to the mixture. The alcohol is then kiadled. Boracic acid imparts to the alcohol flame a yellowish-green color. The test is made more delicate by stirring the mixture, and by repeatedly extinguishing and rekindling the flame. Copper salts impart a somewhat similar color to the flame ; but this metal, if present, may be got rid of by sulphuretted hydrogen before testing for boracic acid. If a solution of boracic acid, or of a colorless borate, is mixed with chlorhydric acid to slight but distiact acid reaction, and a slip of turmeric paper (§ 149) is dipped half way into the liquid and then dried at 100° C, the dipped half shows a peculiar red tint. This test is deli- cate, but there are a few other solutions which impart, not the same, but somewhat similar tints to turmeric paper. The reactions of borates may be obtained with a frag- ment of borax. 92 SILICATES FLDOKIDES. §§ 67, G8 67. Silioakx. The silicates of sodium and potassium are the only sUicates which are soluble in water. The solutions of these aUcaline silicates are decomposed by all acids. If chlorhydric acid is added gradually to a strong solution of an alkaline siUcate, tlie greater part of the silicic acid separates as a gelatinous hydrate. As a rule, the more dilute the fluid, the more silicic acid remains in solution. If the solution of an alkaline silicate, mixed with chlorhydric or nitric acid in excess, be evaporated to dryness, sUicic acid separates ; if the dry mass be ignited and then treated with dilute chlorhydric or nitric acid, the whole of the silicic acid remains insoluble in the free state, as a gritty, whitish powder, while the other sub- stances dissolv.e. A solution of chloride of ammonium produces a gelati- nous precipitate in strong and moderately dilute solu- tions of the alkaline silicates. This precipitate is hydi-a- ted sihcic acid containing alkali. A solution of waterglass is the best substance in which to study the reactions of the silicates of the alkali-metals. 68. Fluorides:. If a finely pulverized fluoride is heat- ed in a small leaden capsule or platinum criicible with concentrated sulphuric acid, fluorhydric acid is dis- engaged. Coat with wax the convex face of a watch-glass large oiu>ii;^h to cover the capside, by heating the glass cau- tiously, and spreading a small bit of wax evenly over it while the glass is hot. Trai^'c some lines or letters through the wax with a pointed instrument of wood or horn. Fill the hoUow of the glass with cold Avator, and coAcr with it the capsule which contains the fluoride mix- ture. Heat the capsule gently for half an hour or an § 69 CHLORIDES. 93 hour. Then remove the watch-glass, dry it, heat it cau- tiously to melt the wax, and wipe it with a bit of paper. The lines or letters traced through the wax will be found etched into the glass. A barely perceptible etching is made more visible by breathing upon the glass. If much silicic acid is present, this reaction fails. When a fluoride, naturally combined or artificially mixed with sibca, is heated vsdth strong sulphuric acid, fluoride of silicon is evolved. This reaction is available as a test for fluorine. A mixture of the supposed fluoride and fine dry sand is heated in a short, dry test-tube, with concentrated sul- phuric acid. A drop of water, caught in the loop of a clean platiaum wire, is held in the mouth of the test-tube. This drop of water becomes merely dim, quite opaque, or almost solid with silicic acid, according to the quantity of fluoride of sUicon evolved from the mixture. The gaseous fluoride of sUicon shows white fumes when it comes in contact with moist air. If a considerable quantity of fluoride of siUcon be evolved from the mixture tested, it can be decanted into another tesi-tube, and there shaken up with water. If the substance to be tested for fluorine is known to contain sihca, it is, of course, unnecessary to add sand to it. This method applies to all fluorides de- composable by hot sulphuric acid. It is evident that this test reversed can be applied to the detection of sUica. Fluoride of calcium (fluor-spar) is a good material from which to obtain these two tests for fluorine. 69. Chlorides. The following confirmatory test is ap- plied to chlorides in the dry state : — "When a chloride, in powder, is heated in a test-tube with black oxide of manganese and strong siilphuric acid, chlorine gas is evolved ; this gas is recognized by 94 BEOMIDES. § 70 its odor, greenish-yellow color, and reaction -witli iodo- starch paper. The gas evolved by a chloride gives no colored reaction with starch alone ; but when a moistened slip of paper, on which a mixture of starch paste and iodide of potassium (§ 130) has been spread, is held in an atmosphere or current of chlorine, the paper is colored blue in consequence of the liberation of iodine which the chlorine effects. The yellow color of the gas is best seen by looking lengthwise through the tube. 70. Bromides. The confirmatory tests for bromides depend upon the setting free of bromine itself. Hot nitric acid liberates the bromine from all bromides except those of silver and mercury. In solutions, the free bromine produces a yellow coloration ; when set free from solid bromides, the brownish-yeUow vapors of bro- mine condense into a Uquid upon the cold walls of the tube. When bromides, in powder, are heated in a test-tube with black oxide of manganese and strong sulphuric acid, brownish-red vapors of bromine are evolved. If chlo- rides are also present, the bromine will be mixed with chlorine. To identify bromine and disting^ush it from chlorine, moistened starch is brought into contact with the fi-ee bromine. A yeUow or orange-yellow coloration of the starch marks the presence of bromine. To apply this test, thrust a rod smeared with starch-paste into the tube which contains the bromine vapors ; or, when greater deUcacy is requisite, perform the oxporimont which is exjoected to liljorate bromine in a very small bealcor, and cover this boaker with a watch-<^lass to whose under-side is attached a bit of paper moistened with staixh-paste and sprinkled with dry stareh. §§ 71, 72 IODIDES ^NITRATES. 95 Bromide of potassium is a good substance with wMch to study the tests for bromine. 71. Iodides. When an iodide, in the solid form or in solution, is heated with strong nitric acid, iodine is libe- rated and sublimes in violet vapors. Free iodine in vapor is recognized by the deep blue color which it imparts to starch-paste. Vapors may be tested by bringing into contact with them a glass rod Bmeared with thin starch-paste, or a shp of white paper on which the paste has been spread. The best method of detecting iodine in a solution is to add a few drops of thin, clear starch-paste to the liquid, and then set free the iodine by means of nitrite of potassium (§ 129), as follows : — The cold fluid to be tested is acidulated with dilute chlorhydric or sulphuric acid, after the addition of the starch-paste, and a drop or two of a concentrated solution of nitrite of potassium is then added. A dark blue color will be instantly pro- duced. It is essential that the liquid should be kept cool, for the blue coloration is destroyed by heat. Like chlorine and bromine, iodine is Hberated by heat- ing an iodide with black oxide of manganese and sulphu- ric acid. The iodine so liberated is readily distinguished by the above tests. The student can try all these tests for iodine with a small crystal of iodide of potassium. 72. Nitraies. To confirm the presence of a nitrate, one or both of the two following tests may be used : — If the solution of a nitrate is mixed with an equal volume of strong sulphuric acid, the mixture cooled in cold water, and a concentrated solution of ferrous sul- phate then cautiously added to it in such a way that the 96 CHLORATES. § 73 two fluids do not mix, the etratum of contact shows a purple or reddish color, which changes to a brown. If the fluids are then mixed, a clear, brownish-purple liquid is obtained. The color fades on heating. Another way of performing the same test is to drop a crystal of cop- peras into the cold mixture of nitrate and sulphuric acid. There forms around the crystal a dark halo, which dis- appears with a kind of effervescence on the application of heat. It is, of course, essential that the sulphuric acid employed for this test should be so free from nitric and hyponitric acids, as not itself to give this reaction with ferrous sulphate. Boil some chlorhydric acid in a test-tube, add to it one or two drops of a dilute solution of sulphindigotic acid (§ 147), and continue the boiling a moment. If the chlorhydric acid is sufliciently free from chlorine, the re- sulting liquor will be of a faint blue color. If a nitrate, either solid or in solution, be added to this Hquid, and the mixture be again boiled, the hquid will be decolor- ized. This reaction is dehcate ; but there are some other substances, especially free chlorine, which have a like bleaching effect. Nitrate of potassium is a suitable material on which to illustrate the tests for nitrates. 73. ChJorates. The preliminary examination gives warning of the presence of chlorates. "When a few particles of a chlorate in the solid form arc cuvoved with two or three times as much strong sul- j)huric acid, and the mixtm-e is gently warmed, the Liquid becomes intensely yellow, and a groeuish-vellow irritating gas of ])ci'u1iar odor (hY]iochloric acid, CIO.-) is evolved, which explodes with violeneo at a moderate heat. After this decomposition, the gas e\olved has tlie ehiu-acterislic § 74 ACETATES. 97 odor of chlorme. The quantity of chlorate operated upon should be very small. The solution of a chlorate decolorizes indigo-solution precisely Hke the solution of a nitrate, under Hke con- ditions (§72). A chlorate is converted by ignition into chloride, from a solution of which nitrate of silver precipitates the chlorine. Chlorate of potassium illustrates very weU the reac- tions of chlorates. 74. Acetates. When acetates are moderately heated with strong sulphuric acid, hydrated acetic acid distils from the mixture, and may be recognized by its pungent odor. "When an acetate is heated ■ndth alcohol and sulphuric acid in equal volumes, acetic ether is formed. The agree- able odor of this ether is highly characteristic. Hot concentrated sulphuric acid produces no blacken- ing with an acetate. When a few drops of a solution of ferric chloride (§ 140) are added to a solution of a neutral acetate, or to a solution of an acetate previously neutralized with ammonia, the liquid acquires a dark red color, because of the formation of ferric acetate. If the liquid contain an excess of the acetate, a basic acetate of iron is precipi- tated in yeUow flocks upon boiling, and the fluid finally becomes colorless. PART SECOND. PRELIMINAEY TEEATMENT. THE ORDER OF PROCEDURE. 75. The substance to be examined may be either solid or liquid. We shall consider first the preliminary treat- ment of a soHd ; afterwards that of a liquid. The soHd may be a metallic substance, that is, a pure metal or an alloy, or it may be a salt, mineral, or other non-metaUic body. The method of procedure differs in the two cases. "We shaU describe first the treatment of a salt, mineral, or other non-metallic substance. The two following observations, however, apply to aU cases. The student should, iu the first place, learn as much as possible from the external properties of the substance to be analyzed, from its color, consistency, and odor, if it is a Hquid ; from its color, texture, odor, lustre, hardness, gravity, and crystalline or amorphous structure, it it is a soHd. By attentively observing the characteristics or individual peculiarities of every siibstance which passes through his hands, the student wUl soon learn to recognize many sub- stances at sight, — by far the quickest and easiest way of identifying them. Secondly, since the original substance must be several times reverted to in order to complete an 100 CLOSED-TUBE TEST. § 76 analysis, the student should husband liis stock of the substance to be analyzed, never employing the whole of it for any single course of experiment. It is well also to reserve a portion for unforeseen contingencies. CHAPTEE XI. TREATMENT OF A SALT, MINERAL, OB OTHER NON- METALLIC SOLID. A. PEELIMINAEY EXAMINATION IN THE DEY WAY. 76. Closed-tube Test. Prepare a hard glass tube Xo. 4 (§ 171), about 3 inches long, and closed at one end. Let fall into this tube a minute fragment of the sohd, or a little of its powder. If the substance be used in powder, wipe out the tube with a tuft of cotton on a wire, in order that the interior walls of the tube may be clean to receive a sublimate. Heat the substance at the end of the tube, at first gently in the lamp, but finally intensely in the blow-pipe flame. The following are the most noteworthy reactions with the inferences to be di'awn from them ; it not unfrequently happens that a single substance gives several of these reactions : — I. The substance blach'ns, and gases or vapors arc evolved. These vapors often have a disagreeable smell, sometimes like that of burnt sugai", papei", or feathers. Sometimes they condense in tarry droplets ; water also condenses on the cold part of the tube. These appear- ances indicate the jiresenee of organic substances. Now, the piesenco of fixed organic matter interferes § 76 CLOSED-TUBE TEi3T. 101 with the detection of many substances, and it must be destroyed before the analysis can be proceeded with. A portion of the original substance, suiScient for the regular course of examination for the metallic elements, is ignited in a porcelain crucible, with free access of air, or on pla- tinum foil, if the presence of no metal be suspected, until all the carbon is burnt out of it. This ignition is best performed on successive small portions rather than on a large mass at once. It is obvious that some inorganic volatile matters may be lost during this igfnition. Furthermore, some sub- stances, especially alumina and chromic and ferric oxides, are made very insoluble by ignition. Exceptionally, therefore, the following process, which is not liable to these objections, is employed: — The substance in powder, paste, or concentrated solution, is heated in an evapora- ting-dish, with strong nitric acid, to a temperature just below boiling. To this hot mixture chlorate of potassium, in small bits, is added gradually, until the organic matter is all destroyed. The solution is then evaporated to dry- ness on a water-bath ; the dry residue is moistened with strong chlorhydric acid, the mixture diluted with water, warmed and filtered, if there be any residue. The filtrate is fit for the regular course of analysis, except that potas- sium, having been added, must not be tested for in this liquid. The residue, if any, must be examined for the insoluble chlorides of Class I. This process is simply a combustion at a low temperature. Simple blackening is not proof of the presence of or- ganic bodies. Some salts of copper and cobalt, for ex- ample, blacken through the formation of a black oxide. When organic matter is shown to be present, the student should look particularly for acetic (§ 74) and tar- taric (§65) acids ; but he wiH not forget that there are 102 CLOSED-TUBE TEST. § 76 hundreds of organic acids which are not comprehended in the plan of this treatise. II. The substance does not carbonize, but vapors or gases escape from it. The most important are : — a. Aqueous vapor, which condenses in the upper part of the tube. Test this water with litmus paper ; if it is alkaline, ammonia may be suspected ; if acid, some Tola- tile acid (HjSO^, HCl, HBr, HI, HFl, HNO3, &c). b. Oxygen, recognized by its relighting a glowing match. This gas indicates nitrates, chlorates, and perox- ides. If the heated substance fuses, and a smaU frag- ment of charcoal thrown in is energetically consumed, the presence of a nitrate or chlorate may be assumed. c. Eyponitric acid, recognized by the brownish-red color of the fumes. It results from the decomposition of nitrates. d. Sulphurous acid, recogmze^hj lis od.or. It not un- frequently results from the decomposition of sulphates, sulphites, and sulphides. e. Carbonic acid, derived from decomposable carbon- ates, and to be recognized by lime-water (§ 54). f. Cyanogen, derived from decomposable cyanides, and to be recognized by its odor, and the blue flame with which it burns when there is enough of it to be lighted. g. SnJphydric acid gas, derived from moist sulphides and to be known by its smeU. h. Ammonia, resulting sometimes fi-om the decompo- sition of ammoniacol salts. § 76 CLOSED-TUBE TEST. 103 III. A sublimate forms beyond the heated portion of the tube. The whole of the substance may volatihze. The following are the commonest sublimates : — ■ a. Sulphur, which sublimes in reddish drops. The sublimate becomes solid and yellow, or yellowish-brown, on cooHng. 6. Am/monium-salts give white sublimates. Test a separate small portion of the original substance for the salts of ammonium, by mixing it in a small test-tube with an equal bulk of slaked lime and a few drops of water, and heating the mixture. Ammonia, when evolved, may be recognized by its smell, and by the white fume pro- duced when a rod, moistened with a mixture of equal parts of strong chlorhydric acid and water, is held above the mouth of the tube. Unless the original solid is ob- viously inalterable by heat, it should be invariably tested in this way for ammonium-salts. c. Metallic mercury and some of its compounds. The metal sublimes in metallic droplets. The two chlorides of mercury give subUmates which are white when cold. The red iodide of mercury gives a yellow subUmate. The sulphide of mercury gives a dull black sublimate. d. Arsenic and some of its compoudns. MetalUc arsenic gives a black sublimate of metallic lustre. Arsenious acid gives a white sublimate, which looks crystalline under a magnifying lens. The sulphides of arsenic give sublimates which are brownish-red while hot, but reddish- yellow to red when cold. These sublimates look not un- Jike that of pure sulphur. e. Teroxide of antimony first fuses to a yellow liquid, and then gives a white sublimate, composed of needle- like crystals. 104 REDUCTION TEST. § 77 /. 0:raJi(- acid gives a white, crystalline sublimate, -ivith dense fumes in the tube. The inferences to be drawn from this simple preHminary experiment are of very unequal value. Thus the detec- tion of organic matter is of the first importance, because, as has been seen, such matters must be got rid of before the analysis can be proceeded with. Again, nitrates and chlorates should be detected with a good degree of cer- tainty by their reactions in the closed tube. Thirdly, the presence, or entire absence, of ammonium-salts should be put beyond doubt at this first stage of the examination. Fourthly, the presence of mercurj-, or of mercru-ous salts, determines the choice of the acid solvent in favor of nitric acid, in case water will not dissolve the substance under examination (§ 81), and the presence of mercuric salts renders necessary the substitution of sulphydrate of ammonium for sulpliydr.ito of sodium as the solvent for the sulphides of Class III (§ iS). Accordingly, it is useful to get information of the presence of merciuy or its com- pounds at this early stage of the examination. As to the other appearances, they give information which may be convenient, but is never essential for the safe conduct of the regular course of analysis. They have been described because they may occur* with or instead of the really im- portant reactions. 77. BediwHon TeM. IMix a little of the powder of the substance under examination (the bulk of a hemp-seed) with an equal quantity of carbonate of sodium, and make the mixture into a pasty ball with a small drop of water. Srk'ct a piece of dry, well-burnod, soft-wood charcoal, and cut out of it a rcctantjular block about 6 inches long, 1\ in. wide, and \ to | in. thick, having its § 77 METALLIC GLOBULES. 105 flat, smooth surface (6 in. by 1| in.) at right angles to the rings of growth in the tree. It is this surface which is always to be used. A good piece of charcoal may be made to serve for many assays, by filing off the used sur- face and exposing a new one. At a quarter to half an inch from the end of such a piece of charcoal, scoop out with a penknife a little cavity of the size of half a pea. Place the prepared pellet in. this cavity, and expose it for several consecutive minutes to the reducing flame of the blow-pipe (§ 167). Under these conditions, vapors of characteristic odor or appearance may be evolved ; some of them will be mentioned below. The two objects, however, to which attention is specially to be directed are the residue in the cavity and the incrustation on the charcoal outside of the cavity. The following metals may be found as fused metalUc globules in the cavity ; lead, silver, and gold are reduced with ease, even by an inexperienced operator ; tia and copper with some difficulty : — a. Gold — a yellow, malleable globule, produced with- out incrustation. b. Copper — a red, malleable globule, produced without incrustation. c. Tin — a bright, white, malleable globule. An in- crustation is simultaneously produced, which is faint yellow when hot, and white when cold ; it immediately surrounds the globule. d. Lead — a very fusible and very malleable globule. A yellow incrustation is simultaneously pro- duced. e. Silver — a brilliant, white, malleable globule, pro- duced without incrustation. 106 METALLIC GLOBULES. § 77 Two other common metals, bismuth and antimony, m:iy be reduced to gray metallic globules ; but these globules are brittle, and are not liable to be confounded with the malleable globules just described. Bismuth gives a yellow incrustation which resembles that of lead. Common charcoal is itself very apt to show a grajash incrustation of ash round about the heated assay ; this incrustation remains unaltered or increases, when directly exposed to the flame. The student should test each piece of charcoal before the blow-pipe flame, in order that he may not imagine a deposit of ash to be an incrustation derived from the substance under examination. If a distinct globule has been obtained, it must be picked out with a pair of jewellers' tweezers, and pounded on some smooth and hard body to test its malleability. If it is malleable, replace it upon the charcoal at an vm- usod spot, and heat it strongly with the oxidizing flame. Gold and silver globules iuae, but maintain their brUliancy and give no incrustation ; this proof distinguishes a genuine gold globule from a yellow globule composed of an alloy of copper and some white metal. A yellow globule composed of oxidizable metals tarnishes instantly in the oxidizing flame. A tin globule fuses, biit its bright surface is instantly tarnished, and a white incrustation of binoxide of tin is produced which cannut be driven off by either flame. A lead globule is rapidly converted into litharge, a yellow incrustation being produced, which volatilizes with a bluish color when toxiched -with the reducing flame. A copper globule is blackened by the formation of oxide of copper, and the blow-pipe flame is tinged with green. (V^rtain other phenomena miiy manifo.'^t themselves during the experiiuont for the reduction of malleable metallic globules. Sulphur, ammonium-salts in general. § 77 METALLIC GLOBULES. 107 the chlorides, bromides, iodides, and sulphides of sodium and potassium, the chlorides of lead, bismuth, tin and copper, metallic mercury, arsenic, antimony and zinc, and many compounds of these four elements, are liable to pass off in vapors, which are often in part deposited upon the coal at a greater or less distance from the hot assay according to their volatility. "With the exception of sul- phur, these sublimates are white, but when deposited in a thin film upon the black coal they have a gray or blue appearance. During the production of the arsenic sublimate a peculiar odor is evolved ; this sublimate being very volatile is only deposited at a considerable distance from the assay. The incrustation produced by zinc is distinctly yeUow while hot, but turns white on cooling ; it settles near the assay and is driven away again with difficulty. These phenomena are aU of secondary importance ; the main object of the experiment is the reduction of the five malleable metals above enumerated. "We may thus obtain knowledge of the presence of gold (for a confirmatory . test, see § 92, b), a metal not included in our scheme of analysis in the wet way. Tin generally gives warning of its presence during this experiment ; and this warning is of use, because it is inconvenient to apply nitric acid as a solvent to a substance containing tin, since this reagent converts tin into the very insoluble binoxide of tin. The detection of copper at this stage is of little ad- vantage. The most important fact deducible from the reduction-test is the presence of either silver or lead. In dissolving an unknown substance which proves to be insoluble in water, it is customary to try, as the second solvent, chlorhydric acid. The chlorides of silver and lead being insoluble, or difficultly soluble, this 108 DISSOLVING IN WATER. §§ 78, 79 acid should not be used as a solvent when either of these two metals is present. Nitric acid must be used instead. B. DISSOLVING A SALT, MINERAL, OR OTHER NON-METALLIC SOLID, FREE FROM ORGANIC MATTER. 78. Before a solid substance can be submitted to the systematic course of analysis, it must be brought into so- lution. There is no universal solvent. Different sub- stances require different solvents. The four solvents employed in qualitative analysis for salts, minerals, and other non-metallic solids, are water, chlorhydric acid, nitric acid, and aqua-regia ; and these four liquids are invariably to be tried in the precise order in which they here stand. Water is always to be tried first ; to what- ever resists water, strong chlorhydric acid is appKed ; if chlorhj^dric acid fails to dissolve the solid completely, or is unsuitable, for reasons disclosed in the preliminary examination as just explained, nitric acid is tried, and after nitric ^cid, aqua-regia as the last resort. A solid substance should invariably be reduced to a very fine powder, before being submitted to the action of solvents (§ 180). 79. Dissolving n? vain: About half a thimbleful of the powdered substance is boiled with ten times as much water in a test-tube. If an effervescence occurs, as is possible with mixtures containing an acid salt (yoast- powdiTs, for example), the gas evolved should be carofully tested (§§ 5:! -58). If the substance dissolves completely, the solution is ready tor analysis. When undissolved powder remains in tlio tube after protraeted boiling, filter a low drops of the liquid, and evaporate a drop or two of § 80 AN AQUEODS SOLUTION. 109 the filtrate to dryness on clean platinum foil, at as low a heat as possible. If there be no residue on the foil, or if the residue be scarcely appreciable, the substance is prac- tically insoluble in water, and acids must be tried as solvents. But if, on the contrary, a tolerable residue re- mains on the foil, decant the liquid in the tube into the filter, and boil the powder again with water. Persevere with this treatment until it is evident that a part of the powder is insoluble in water. The insoluble residue in the test-tube is thrown upon the filter ; the clear Uquids which have passed through the filter, collected together and concentrated by evaporation if of unreasonable bulk, are ready for the regular course of analysis. In tliis case, and in the still more favorable case in which all the substance has dissolved in water, it is a simple aqueous solution which is submitted to analysis. 80. An aqueous solution. If the student is assured that the unknovsm substance is a simple salt, he may draw some trustworthy inferences from the fact that the sub- stance dissolves in water. Of the salts which fall within the scope of this manual, the following are practically soluble in water : — 1. All salts of sodium, and aU of potassium and am- monium, except their double platinum-chlor- ides. 2. AU nitrates, chlorates, aaid acetates. 3. Chlorides, bromides, and iodides, except those of silver and mercury. (Mercuric chloride is solubla The lead salts are difficultly soluble. ) 4. Sulphates, except those of barium, strontium, and lead. a 110 TESTING AN AQIJE'JUS SOLUTION. § 80 5. Many liyposulphites. 6. The sulphides of sodium, potassium, ammouium, magnesium, barium, strontium, and calcium. 7. A few cyanides, oxalates, tartrates, and chromates, besides those of the alkali-metals ah-eady men- tioned. It is obvious that any element of the thirty-six con- sidered in this treatise, may be present in an aqueous solution ; but it is also evident from the above list, that a great number of salts are absolutely excluded because of their insolubility in water. If, on the contrary, there is no certainty that the sub- stance under examination is not a comities artificial mix- ture, no safe conclusions can be drawn fi'om the fact that a part of it, or the whole of it, dissolves in water. Test the solution vdth litmus paper. The solution is either neutral, acid, or alkaline. Nrulral. The normal salts of most of the metals have an acid reaction. Sodium, potassium, barium, strontium, calcium, magnesium, manganese, and silver are the only metallic elements which form salts whose solutions are neutral. Add to two or three di'ops of the solution a ili'op or two of carbonate of sodium. If a precipitate forms, any of the above-meiitic)ned elements may be present ; but if no precipitation ensues, only sodium and potassium can be present. Acid. The acidity may be caused by a normal salt having an acid rcaeliun, or by an acid salt. Xeither car- bonates nor sulphides can be present in an aqueous solu- tion with an arid reaelion. Alhiliiif. The alknlluity may be due to the hydrates, sulpludos, I'yauides, or carbonates, of the metals belong- § 80 TESTING AN AQUEOUS SOLUTION. Ill ing to Classes VI and VII ; to the presence of a borate, silicate, phosphate, arseniato, or aluminate of sodium or potassium ; to free ammonia, or carbonate of ammonium. If the alkalinity proceed from an alkaUne sul^^hide, the metals whose sulphides are insoluble in water, and alkahne sulphides, must be absent. If it is due to the presence of the hydrates or carbonates of the metals of Classes VI and VII, a very large number of substances are ex- cluded. If it proceed from ammonia or carbonate of ammonium, aU substances precipitable by these reagents are absent. An alkahne solution may obviously contain some sub- stance, soluble in an alkahne solvent like caustic soda or sulphydrate of ammonium, but liable to immediate pre- cipitation when tljfcsolvent is destroyed by the addition of chlorhydric aoOTm the first step of the analysis. Thus any sulphide of C1|bs HI dissolved in caustic soda, or an alkaline sulphide, or compounds of alkaline hydrates with the hydrates of alutninum, zinc or chromium, would be precipitated when the alkaline solvent was neutralized. Chloride of silver dissolved in ammonia- water would be thrown down by any acid added in excess. Again, the alkaUne solution of a sihcate of sodium or potassium, when neutralized with acid, yields a very gelatinous, whitish precipitate of hydrated sUicic acid. Prom a very concentrated solution of a borate, boracic acid separates in colorless, shining, flat crystals, when the solution is acidified with chlorhydric acid ; but the boracic acid thus separated dissolves when the solution is diluted. In view of these possibilities, an alkaline aqueous solu- tion should be carefully neutralized with nitric acid, as a preliminary measure, before chlorhydric acid is added to it. Eiforvescence should be watched for, and if it occurs, studied as directed in §§ 53-58. Several different cases 112 DISSOLVING IN ACIDS. § 81 of precipitation may be distinguished, requiring some- what different treatment. a. If the characteristic gelatinous precipitate of silicic acid ajDpears, the acidulated solution must be evaporated to dryness and ignited. The sihcic acid is thus icndi-red insoluble. The ignited residue is digested with dilute nitric acid and filtered. The filtrate is ready for the usual course of analysis. The insoluble residue is silicic acid. 6. If the glistening, colorless plates of boracic acid aj)pear, dilution vsrith warm water will cause them to re dissolve. c. If a precipitate appear on neutralization, whose color or texture proves that it is neither silicic nor boracic acid, but some substance insoluble in \\ater and dilute acids, thrown down in consequence of the destruction of its aLkaUne solvent, the liquid is made slightly acid, and then filtered. The filtrate is ready for the usual course of analysis. The precipitate, rinsed with a Uttle water, is reserved for further treatment ; it is not properly a sub- stance soluble in water, and it must be brought into solution by other methods, hereafter to bo described. Sometimes a precipitate forms on exact neutralization of an alkaline fluid, which reilissolves when the acid is added in excess. 81. Dissolving in acith. The substance wliich water has failed to dissolve, cither in whole or in part, is next boiled in a small dish with three or four times its bulk of cinicciitruttHl clilorliydric acid, itnlvss the tube-test (§ 7()) or the rccluctimi-test (§ 77) has proved the presence ol' silver, load, or mercury ; in whicli case nitric acid is the § 81 DISSOLVING IN ACIDS. 113 first acid to be tried. (Seethe next paragrapli. ) If an effervescence occur, the escaping gas is to be tested, as described in §§ 53-58. After boiling the powdered sub- stance with the strong acid, dilute the fluid with twice its bulk of water, and repeat the boUing if any residue remain undissolved. The acid is diluted because, though the substance to be dissolved is best attacked in the first instance by strong acid, the salts formed by the action of the concentrated acid are more likely to dissolve readily in a dUute than ia a strong acid. Not a few salts which scarcely dissolve in strong acids, are readily soluble ia the same acids when dUuted. If the whole of the substance finally dissolves, the solution stiU farther diluted is ready for the transmission of sulphuretted hydrogen (§ 22), for it is of course unnecessary to ex- amine it for members of Class I. If, on the contrary, an undissolved residue remaiu in the tube, ascertain if any- thing has dissolved, by carefully evaporating two or three drops of the fluid to dryness on platinum foil. Should an appreciable residue, in excess of that given by two or three drops of the acid employed, remain upon the foil, separate the liquid in the tube from the undissolved substance by decantation or filtration. Eeserve the solu- tion, labeUing it " HCl Sol." Einse the undissolved powder with water, and then boil it in an evaporating dish with three or four times its bulk of strong nitric acid. If the original substance contained silver, lead, or a mercurous salt, chlorhydric acid will not have been used, and it will be the residue from the aqueous solution, which is now to be bcwled with nitric acid. In this case, effervescence is to be watched for. If the substance dissolves completely in the strong acid, or dissolves, vsdth the exception of a light yellow mass of sulphur, which often separates from a sulphide, 114 AN ACID SOLUTION. § 82 evaporate the liquid to a very small bulk to drive off tlie free acid, dilute the evaporated solution with several times its bulk of v^ater, separate the sulphur, if necessary, by filtration, and reserve the solution, labelling it " HXO3 Sol." If the substance does not completely dissolve in the strong acid, dilute the fluid with twice its bulk of water, and repeat the boihng. If the dilute nitric acid effects complete solution, reserve the solution, labelling it as before, " HNO3 Sol." If neither the strong nor the diluted nitric acid effects the complete solution of the substance, ascertain if anything has dissolved in the dilute acid by the usual test on platinum foil If an appreciable residue remain on the foil, separate the un- dissolved sohd hx the dish from the Uquid by decantation or filtration, and reserve the solution. Bod the powder, which has resisted both acids taken singly, with aqua-regia. If it dissolves completely, evap- orate the solution to a very small bulk, dilute the evap- orated solution largely with water, and reserve it for analysis, labelling it " Aq. reg. Sol." It is useless to look for members of Class I in such a solution. If, on the contrarj', it does not completely dissolve after protracted boding, test the liquor to see if anything has dissolved. If an appreciable residue remains on the foil, dilute the acid fluid, filter it, reserve the solution labelled as before, and wash the undissolved residue thoroxiglily with water, to prepare it for fui'ther treatment (§ 83). 82. Jn acid solution. Of the three kinds of acid solutions hero described, any one, any two, or all three, may be obtained from a single mixture of ditt'orentsoUds. There is an advantage in kno^\■ing that a part of a com- i:ilex mixture is snhiblo in water, a part in chlorhydi'ic acid, a part in uiti'ic acid, and a pai-t only in aqua-regia ; § 82 ^ TESTING ACID SOLUTIONS. 115 because this knowledge may enable the student, when he has found out all the elements of the mixture, to make a more probable guess at the manner of their combination in the original mixture than he would otherwise be able to. But it is quite unnecessary to keep the three kinds of acid solution apart, when all three have been obtained, and to analyze them separately. On the contrary, all three should be mixed together, and analyzed in one course of testing. It must only be borne in mind that when lead, silver, or mercurous salts are present, the nitric acid solution of the residue from the aqueous solu- tion will give a precipitate of the insoluble chlorides of Class I, on being mixed with a chlorhydric acid or aqua- regia solution. The student must be careful to use no more acid than is absolutely essential. Nitric acid, particularly, is very objectionable ; because, when free, it reacts upon sulphur- etted hydrogen with mutual decomposition, sulphur being set free. Sometimes a strongly acid solution becomes turbid when merely diluted with water. This phenomenon points to the presence of bismuth or antimony. The turbidity will disappear again on the addition of chlor- hydric acid. Certain silicates, when boiled with concentrated acids, are decomposed, and gelatinous silicic acid is separated. This happens but rarely, however, in the rapid processes of quaUtative analysis ; and if it should happen, it is not likely to lead the student into error. A residue insoluble in all acids will remain ; this residue is, or contains, free silicic acid. It must not be supposed that it is common to try all four solvents on one and the same substance. Water and chlorhydric acid are the common solvents ; nitric acid IIG SUBSTANCES INSOLUBLE lU ACIDS. § 83 and aqua-regia are, actually, but seldom re-sorted to as solvents, cxcejit for metals (§ 92). It would require some ingenuity to devise an artificial mixture ■which would put to the test all the capaljilities of the above- described method of brinf;ing solids into solution in water and acids. Such mixtures are not met with in ordinary experience. It is the object of any method of analysis to meet real problems, not artificial comphcations which may be imagined, but which do not occur in fact. C. TREATMENT OF INSOLUBLE SUBSTANCES. 83. The substances of common occurrence which are practically insoluble in water and acids are : — The sulphates of barium, strontium, and lead. Chloride of silver. The anhydrous sesquioxides of aluminum, chromium, and iron, either native or the result of an intense igni- tion. Chrome-iron-ore, a native mineral. Some aluminates. Binoxide of tin, native, or the result of ignition. Silica and many silicates. Fluoride of calcium (fluor-spar). Besides the substances included in this list, sulphur and carbon, or graphite, should, perhaps, be mentioned, because thoy are insoluble ; but they will have been de- tected during the preliminary bL >w-pipe examination, and tlieu- prcs(MU'o allowed for. Bromide, iodide and cyanide of silver, are decomposed by l>oiling with aqua-regia, and converted into the clilorido, so that those substances never appear in their proper form in the fimU insoluble residue. §84 SUBSTANCES INSOLUBLE IN ACIDS. 117 84. Substances which resist solution in liquids are generally liquified by the action of fluxes at a high tem- perature ; they are fused in contact with some powerful decomposing agent, like the carbonate or acid sulphate of an alkaU-metal, or the hydrate or carbonate of an alkaHne-earth metal. Certain preliminary experiments should precede the fusion. The insoluble powder is first examined carefully (with the help of a lens, if convenient), to ascertain if it is a homogeneous substance of the same color throughout, or a mixture composed of dissimilar, variously-colored par- ticles. The following blow-pipe experiments sometimes give decisive indications, particularly with homogeneous substances : — a. The reduction-test (§ 77) is repeated with great care, looking especially for silver, lead, and tin, and apply- ing to the globule, if any is obtained, the test for distin- guishing between these three white metals. This test has already been applied to the original substance ; but if this substance was a complex mixture containiag soluble ingredients, it is quite possible that the test should give a more satisfactory result, now that all substances soluble in water and acids have been removed, than it yielded before. If any reducible metal is detected, it is neces- sary to use a porcelain crucible for the fusion which it maybe desirable to make (§ 85), in order to convert the insoluble substance into a more manageable form. A platinum crucible, which is employed for most fusions, cannot be used with safety when the substance to be fused contains any reducible metal ; for many of the alloys of platinum are readily fusible. Sometimes, when the substance under examination con- tains but a small proportion of metal, some metal may 6* 118 SUBSTANCES INSOLUBLE IS ACIDS. § 84 be reduced during the blow-pipe experiment on charcoal, but tlie detached particles maj' not run together into a single conspicnoiiH globule. Since a uiistuke as to the presence of a reducible metal may involve the destnic- tion of a platinum crucible, it is best, in doulitful cases, to operate in a more delicate fashion. To ascertain, be- yond question, whether any reduced metal has been sepa- rated in this experiment, moisten the cavity in the char- coal with water after the fusion has been finished, cut the charcoal out for a little distance, both around and below the cavity, and transfer the contents of the canity and the scraps of charcoal to an agate or porcelain mortar. Pulverize the whole mass,, and then carefully wash away the powdered charcoal, and all the lighter portion of the mixture. Any malleable metal that may have been re- duced remains in the mortar in little flattened grains or spauLjies, in which the peculiar color and lustre of the metal or alloy are generally visible. Sometimes metaUic streaks are produced on the mortar or pestle by Uttle jiarticlcs of metal ground between them. The student must not mistake gUsteuing particles of wet charcoal sticking to the mortar or pestle for metallic spangles. b. Prepare another pellet of a mixture of equal parts of the insoluble powder and carbonate oi sodium, adding a little charcoal jDowder to the paste. Fuse this mixtiu-e upon charcoal in the reducing tlaiiie of the blow-pii)o. >S(SOop out the fused mass and the surrounding charcoal with a ]U'nl;iiife, place the dry mass upon a bright siu'face of silver (coin or foil), and wet it with a drop of water. If a l)i-(iwn stain bo produced on the silver, it is e\idruco of the ])V('Sonce of sulphide of sodium in the fused mass. I'liis sulphide results from the reduction of a sulphate, and is cxidenco of the presence of a sulphate in the sub- § 8-1 SUBSTANCES INSOLUBLE IN ACIDS. 119 stance tested. The odor of sulphuretted hydrogen is often perceptible when the fused mass is moistened. The silver coin or foil may be replaced by a piece of lead- paper, if care be taken not to mistake the mere dirtying of the paper for a stain of sulphide. It is obvious that the carbonate of sodium used in this test must be so free from sulphate of sodium as not itself to give this reaction on silver, after fusion on charcoal. Since coal-gas in- variably contains traces of sulphur compounds, this test cannot be performed with a gas-flame. c. Make the loop on the end of the bit of plattaum wire (§ 168) white-hot in the blow-pipe flame, and thrust it white-hot into some powdered borax ; a quantity of bor^x will adhere to the hot wire ; reheat the loop in the oxidizing flame ; the borax will puff up at first, and then fuse to a transparent glass. If enough borax to form a soUd, transparent bead within the loop does not adhere to the hot wire the first time, the hot loop may be dipped a second time into the powdered borax. "When a transparent glass has been formed withia the loop of the platinum wire, touch the bead of glass whUe it is hot and soft to a few particles of the insoluble powder, and reheat the bead with the adhering powder in the oxidizing flame. If the substance dissolves slowly in the borax, and the bead has a fine yehovTish-green color when cold, chromium is probably present. Reheat the bead in the reducing flame. If it presents a bright green color both when hot and cold, there is no doubt of the presence of chromium. It sometimes happens, when too much of the substance to be tested has been added, that the borax bead becomes so dark-colored as to be practically opaque. It may then be flattened, while soft, by sudden pressure betjveen any 120 SUBSTANCES INSOLUBLE IN ACIDS. § 84 smooth metallic surfaces, like the flat parts of jewellers' tweezers. If the flattening makes the color of the borax- glass visible, nothing more is necessary ; but if the glass is stiU too dark, all the glass outside the loop of platinum may be broken off by gentle hammering, and the re- maining glass may be reheated and largely diluted by the addition of more borax. It is convenient to be informed of the presence of chromium, because chromic oxide and chrome-iron-ore are substances which it is particularly difficult to decom- pose effectually by fusion. In presence of chromium, no other bead reaction which can be anticipated under the circumstances will give a decisive result ; but in the ab- sence of chromium, the presence of iron may be deter- mined. A suitable quantity of oxide of iron causes the borax-bead, heated in the oxidizing flame, to look red when hot and yellow when cold. In the reducing flame the u'on bead becomes gi-eenish, or Ught brownish-green. d. The test for fluorine (§ 68) should be applied to the original substance, if it has not akeady been done. ^Vhen all the above-mentioned tests {a-d) give negative results, the simplification of the problem is very con- spicuous ; the substances which may be present ai-e re- duced to alumina and some alumiuatcs, sUica and silicates. Again, when some of the proUminary tests j^ive afiirma- tive results, the evidence may be almost conclusive, if the substance under examination be evidently honiogonoous. Thus c]dorid(^ of silver, sulphate of lead, clu'omio or fer- ric oxide, binoxidc of tin, or fluoride of caleium, may be satisfacirorily identilied. There! aw two methods of ch;uiging insoluble sub- stances into more man;i;;-eahle forms by tlio application of §§ 85, 86 FUSIONS. 121 heat, with sufficient exactness for the purposes of the qualitative analyst, — the method by fusion, and the method by deflagration. 85. Fusions. Mis the fine powder of the insoluble substance with about four parts by weight of dry carbon- ate of sodium in powder. Both powders must be as fine as they can be made, and they must be intimately mixed. Keep the mixture at a bright red heat, in a platiaum crucible (a porcelain crucible if a reducible metal has been found in the substance, and fusion is for any reason preferred to deflagration), until the mass has been brought to a state of quiet fusion (§ 164). Place the hot platinum crucible, when withdrawn from the lamp or fire, on a cold block, or thick plate of iron, and let it cool. When the crucible has been cooled in this way, the fused mass can generally be removed from the crucible in an unbroken lump. Soak the lump in boiling water until everything is dissolved which is soluble in water. If the mass cannot be detached from the crucible, the crucible and its contents must be soaked in boiling water. When the green borax bead, and the dark color of the insoluble powder, point to the presence of chrome-iron- ore, a mixture of two parts, by weight, of carbonate of sodium with two parts, by weight, of nitre, may be sub- stituted for the four parts of carbonate of sodium alone. 86. Treatment of the fused mass. The aqueous solu- tion of the fused mass is filtered from the residue in- soluble in water. Small portions of it are to be tested separately at this stage of the process, for sulphate, chro- mate, chloride and fluoride of sodium, either of which salts (besides others not regarded for the moment) may result from the decomposition of the insoluble substance. 122 TESTING AFTER FUSION. § 86 and be found in the aqueous solution. A chromate colors the solution' yellow. a. Acidify a small portion with chlorhydric acid, and test for sulphates with chloride of barium (§ G2). The student must learn by trial how much sulphate, if any, his carbonate of sodium contains. h. Acidify another small portion with acetic acid, and apply the acetate of lead test for chi'omates (§ 60). In presence of sulphuric acid this test will be obscured, but not rendered whoUy useless (§ 2 '.J, p. 49). c. Acidify a third portion with nitric acid, and apply the nitrate of silver test for chlorine (§ 69). The stu- dent must first prove that his carbonate of sodium con- tains no chlorine. d. A fourth portion, having lieen concentrated by evaporation in a porcelain dish, and again cooled, is acidi- fied with chlorhydric acid, and then left at rest until the carbonic acid has escaped. It is then snpersatnvatfd with ammonia, heated, and filtered while hot. The fil- trate is collected in a bottle ; chloride of calcium is im- mediately added to it ; the bottle is closed and allowed to stand at rest. If the original substance contained a fluoride, the fluorine will have combined with sodium during the fusion, and fluoride of sodium will be con- tained in the aqueous solution. The carbonic aoid hav- ing been expelled, and all substaneos procipitable by ammonia having been removed, the eldorido of calcium will throw down the fluoride of calcium. If a in-ocipitate separates from the Liquid in the bottle aftiu be proceeded with. A volatile (U'ganic solvent can, of coiu'ye, be got rid of by a simple evaporation to dryness. §§ 94^96 TEST FOR AMMONIA. 131 94. Testing with Litmus. The next step is to test the solution with Htmus-paper. a. If it is neutral, and the solvent is water, consult §80. h. If it is acid, the acidity may be due to a normal salt having an acid reaction, or to an acid salt, or to free acid. No general inferences can be drawn from the acid reaction, except that carbonates and sulphides are absent. If dUutiou of the acid fluid produces turbidity, the presence of antimony or bismuth may be inferred. c. If it is alkaline, consult § 80 {Alkaline). 95. By evaporating a portion of the original solution to dryness, the dissolved solid is obtained. This solid may be subjected to the whole of the preliminary treat- ment prescribed for a salt, mineral, or other non-metallic soUd (§§ 76, 77); but inasmuch as the main object of all preliminary treatment of a solid is to learn how to get it into solution with the least difficulty, it is seldom worth while for the analyst to make a solid out of a solution, and thus forego the advantage of having the solution, al- ready made to his hand. 96. Testing for Ammonia. A small portion of the original solution must always be tested for ammonium salts, by heating it in a test-tube with an equal bulk of slaked lime. The gas is recognized by its smell and its reaction with chlorhydrio acid (§ 76). 132 TECHNICAL DETAILS. The means of identifying and isolating the rare ele- ments, the methods by which minute traces of one substance may be detected when hidden in projsortion- ally large quantities of other substances, as when the impurities of chemicals and drugs are exhibited, and the processes to be employed in special cases of peculiar diffi- culty, such as the analysis of complex insoluble minerals, or the detection of mineral poisons in masses of organic matter, must be studied in complete treatises upon chemi- cal analysis, or in works specially devoted to these technical matters. Such details, however valuable to the professional analyst, or expert, would not be in harmony with the plan of this manual. PART THIRD. CHAPTEE XIV. REAGENTS. [** Those reagents in tlie following list which are marked with the double asterisk are rarely employed ; a single small bottle of each of them in the laboratory will be enough for many students.] 97. Ghlorhydric Acid ( Concentrated). The strong com- mon acid prepared by chemical mannfacturers, though usually far from pure, will answer for most of the pur- poses of this manual. It must, however, be continually borne in mind that the commercial acid is usually con- taminated with sulphuric acid, and very often with traces of arsenic and iron. These impurities may be present in sufficient quantity to render the acid unfit for use when these very substances are to be tested for in the mixture to be analyzed. The yellow color of the commercial acid, though often attributed to iron, is reaUy due for the most part to the presence of a peculiar organic compound which is soluble -'n the strong acid. Pure acid may be prepared by disti llin g a mixture of fused chloride of sodium and sulphuric acid, and coUect- 7 X34 EEAGENTS. §§ 98-102 ing the gas in water (see the authors' Manual of Inor- ganic Chemistry, Exp. 49). If in any experiment doubts arise concerning the char- acter of a reagent, a quantity of it, somewhat larger than that which has been mixeil with the substance under ex- amination, should be tested by itself, and the reaction compared with that exhibited in the doubtful case. If the result of this trial is unsatisfactory, the experiment must be repeated with reagents which are known to be pure. 98. Ghlorhydric Acid {Dilute). Mix 1 volume of the common concentrated acid, or — where special purity is required — of the pure strong acid, with 4 volumes of water. 99. Nitric Acid (Concentrated). Use the colorless commercial acid of 1.38 or 1.40 specific gravity. Strong nitric acid of tolerable purity can usually be obtained from the dealers in coarse chemicals. An acid, which when diluted with five parts of water gives no decided cloudiness with either nitrate of silver or nitrate of ba- rium, is good enough for most uses in qualitative analysis. 100. Nitric Acid (Dilute). Mis 1 volume of the strong acid with 5 volumes of water. 101. Aqita-rcgia should be prepared only in small quantities, at the moment of use, by mixing in a test-tube one volume of Mrong nitric acid, with three or four times as much strong chlorhydric acid. 102. Stdphuric Jrld {Ciincrntrated). The oil of vitriol of commoroo will usually be foiuid pure enough for the purposes of this manual. §§ 103-108 EEAGENTS. 135 103. Sulphuric Acid (Dilute) is prepared by gradually adding 1 part of the concentrated acid to 4 parts of water contained in a beaker or porcelain dish ; the mix- ture must be constantly stirred with a glass rod. "When the mixing is finished, the liquid is left at rest until all the sulphate of lead which has separated from the strong acid has settled to the bottom ; the clear liquid is then decanted into bottles. 104. Oxalic Acid. Dissolve 1 part, by weight, of the commercial crystals in 20 parts of water. 105. Acetic Acid. The ordinary commercial acid. - 106. Tartaric Acid should be kept in the state of pow- der, since solutions of it slowly decompose. For use, dis- solve a small portion of the powder in two or three times its volume of hot water. 107. Sulphuretted Hydrogen Gas {Sulphydric Acid) is prepared, as needed, by acting upon fragments of sul- phide of iron vnth dilute sulphuric acid in the apparatus described in §§ 178, 179. The apparatus should always be placed either in the open air, or in a strong draught beneath a chimney. 108. Sulphuretted Hydrogen Water. Pass sulphuretted hydrogen gas into a bottle of water until the water can absorb no more. To determine when the absorption is complete, close the mouth of the bottle tightly with the thumb, and shake the liquid. If the water is saturated, a small portion of the gas will be set free by the agitation^ and a slight outward pressure agaiast the thumb wiU be felt. If the water is not fully saturated, the agitation 13G EEAGENTS. §§ 109, 110 will enable it to absorb the gas -which lay in the upper part of the bottle, and a partial vacuum will be created, so that an inward pressure will be felt. Since sulphuretted hydrogen water soon decomposes when exposed to the air, it should always be kept in tightly closed bottles ; and no very large quantity of it should be prepared at once. A good way of keeping the solution is, to fill a number of small phials with the fresh Uquid, cork them tightly, and invert them in water, so that their necks shall always be immersed and protected from the atmosphere. At the moment of using this reagent, its quality should always be proved by smelling of it, or by adding a drop or two of the Hquid to a drop of acetate of lead. 109. Ammonia- Water. Commercial aqua-ammonisB may usually be obtained pure enough for the purposes of this manual. Dilute 1 volume of the strong hquor with 3 volumes of water. Ammonia-water should be free from carbonic acid ; when diluted, as above, it ought not to yield any precipitate when tested with lime-water. 110. Sulphydrate of Ammonium. Pass sulphuretted hydrogen gas through ammonia-water, diluted as de- scribed ia § 109, until a portion of the liquid yields no pre- cipitate when tested with a drop of a solution of stdphate of magnesium. Since sulphydrate of ammonium decomposes after a while, when exposed to the air, it is not advisable to pre- pare it in large quantities. In case any doubt arises as to the quality of the reaj::font, add some of it to a di-op of acetate of load. Unless a denso, Mack precipitate of sulphide of lead is immediately thrown down, the sulphy- drate is worthless. §§ 111-llG EnSAGENTS. 137 111. Carbonate of Ammonium. Dissolve 1 part, by- weight, of the commercial salt in 4 parts of -water, and add to the mixture 1 part of strong ammonia--water. 112. Chloride of Ammonium. Dissolve 1 part, by- weight, of the crystallized commercial salt in 10 parts of water. 113. Oxalate of Ammonium. Dissolve 1 part, by weight, of the salt in 24 parts of water. 114. Nitrate of Ammonium. The commercial salt, kept as dry as possible, in the form of small crystals. 115. ** Molyhdate of Ammonium. Digest 1 part, by weight, of molybdic acid for some hours in 4 or 5 parts of fitrong ammonia- water, and mix the clear solution -with 12 or 15 parts of strong nitric acid ; or dissolve 1 part of molybdate of ammonium in 3 or 4 parts of weak am- monia-water, and mix the liquid with 12 or 15 parts of nitric acid, as before. 116. Caustic Soda. Place 1 part, by weight, of the best commercial caustic soda in a large stoppered bottle ; pour upon it 8 or 9 parts of water, and shake the bottle at intervals, until the whole of the soda has dissolved. Leave the bottle at rest until the liquid has become clear, and finally transfer the solution, with a siphon, to the small bottles in which it is to be kept for use. The solu- tion thus prepared, though pure enough for the uses pre- scribed in this manual, is really far from j)ure. It would be unfit for use in a delicate research, because it is usually contaminated -with chloride, sulphate and carbonate of sodium, and is liable to contain traces of aluminate. 138 KEAGENTS. §§ 117, 118 phosphate, and silicate of sodium. Since some nitrate of sodium is added to it in the process of manufacture, the soda is liable to be contaminated with this salt and the products of its decomposition, including ammonia. This last impurity is Uable to be given off when the solution is boiled. Caustic potash, as prepared for surgeons' use, may be substituted for caustic soda whenever it can be more readily obtained. The potash should be dissolved in about 10 parts of water. Since solutions of the caustic alkaUes act upon glass rather easUy, especially when its outer surface or " fire- glaze " has once been removed, it often happens, when the soda solution is kept in glass-stoppered bottles, that the stoppers become immovably cemented to the glass by the silicate of sodium which forms in their necks. This diffi- culty may be avoided by wiping the necks of the bottles dry after any of the solution has been poured from them ; but it will usually be found more convenient to replace the glass stoppers with plugs of vulcanized caoutchouc, or, better stUl, with small glass stoppers, over the bodies of which short pieces of caoutchouc tubing have been stretched. 117. Sulphydrate of Sodium. Dissolve 1 part, by weight, of commercial sulphide of sodium in 8 parts of water. Sulphide of potassium is not an available substi- tute for sulphide of sodium. 118. Carbonate of Sodium. The anhydrous snlt of com- merce ■will answer for most uses. It should not contain uuich sulphate of sodium. For those oases iu which the use of carbonate of sodium, freo from any contamination of sulphate, is proscribed, the salt may bo propai'od by §§ 119-124 EEACJBNTS. 139 •washing a pound or two of bicarbonate of sodium re- peatedly upon a filter, with small quantities of ice-cold water, until the original quantity is reduced to a fifth or a sixth of its bulk. 119. Bihorate of Sodium. Common borax, powdered. 120. Nitrate of Sodium. Select a white, clean sample of the commercial salt, and dissolye 1 part, by weight, in 3 parts of water. 121. Diphosphate of Sodium. Dissolve 1 part, by weight, of " common phosphate of soda " in 10 parts of water. 122. ** Acid Sulphate of Sodium. Heat a mixture of 16 parts, by weight, of Glauber's saft, and 5 parts of con- centrated sulphuric acid, in a platinum vessel, until a portion of the melted mass becomes distinctly solid when taken up on a glass rod. Then allow the mixture to be- come cold; remove the cold lump from the platinum vessel, and break it into fragments. Keep the coarse powder in a tight, glass-stoppered bottje. 123. Sulphate of Potassium. Dissolve one part, by weight, of the crystallized salt in 200 parts of water. A solution of this strength contains the same proportional quantity of sulphuric acid as is contained in a saturated aqueous solution of sulphate of calcium. Hence it can- not precipitate the latter when added to solutions of the soluble calcium salts. 124. Ghromate of Potassium. (The normal or " neu- tral " yellow chromate. ) Dissolve 1 part, by weight, of the salt in 8 parts of water. 140 EEAQENTS. §§ 125-129 125. Ferrocyanide of Potaj made either of brass or platinum. The tip should be drilled out of a sohd piece of metal, and should not be fastened upon the brass-tube with a screw. A trumpet-shaped mouth-piece of horn or box- wood is a convenient, though by no means essential addi- tion to this blow-pipe. The blow-pipe may be used with a candle, with gas, or with any hand-lamp proper for burning oil, petroleum, or any of the so-called burning fluids, provided that the form of the lamp below the wick-holder is such as to per- mit the close approach of the object to be heated to the side of the wick. When a lamp is used, a wick about 1.2 c. m. long and 0.5 c. m. broad is more convenient than a round or narrow wick ; a wick of this sort, though hardly so wide, is used in some of the open burning-fluid (naph- tha) lamps now in common use. The wick-holder should be filed off on its longer dimension a little obliquely, and 1G4 BLOW-PIPE. §1G7 the wick cut parallel to tlie holder, in order that the blow- pipe flame may be directed downwards when necessary (rig. 16). A gas flame suitable for the blow-pipe is readily obtained by slipping a narrow brass-tube, open at both ends, into the tube/ of Bunsen's burner. (See Fig. 7. ) This blow-pipe-tube must be long enough to close the air apertures in the tube /, and should be pinched together and filed off obliquely on top, as shown iu Fig. 16 ; it may usually be obtained with the burner from dealers in chemical ware. To use the mouth blow-pipe, place the open end of the tin tube between the lips, or, if the pipe is provided with a mouth-piece, press the trumpet-shaped mouth-piece against the lips ; iill the mouth with air tiU the cheeks are widely distended, and insert the tip in the flame of a lamp or candle ; close the communication between the lungs and the mouth, and force a current of air through the tube by squeezing the air in the mouth with the muscles of the cheeks, breathing, in the meantime, regu- larly and quietly through the nostrils. The knack of blowing a steady stream for several minutes at a time is readily acquired by a little practice. It wUl be at once observed that the appearance of the flame varies consider- ably, according to the strength of the blast and the posi- tion of the jet with reference to the wick. "\^"lien the jet of the blow-pipe is inserted into the middle of a candle-flame, or is placed in the lamp- Hame in the position shown in Fig. 16, and a stror.i;- blast is forced thiouirh the tube, a Fig. 16. §167 OXIDIZING AND REDUCING FLAME. 165 long, blue cone of flame, a b, is produced, beyond and outside of whicli stretches a more or less colored outer cone towards c. The point of greatest heat in this flame is at the point of the inner blue cone, because the combustible gases are there supplied with just the quantity of oxygen necessary to consume them, but between this point and the extremity of the flame the combustion is concentrated and intense. The greater part of the flame thus produced is oxidizing in its effect, and this flame is technically called the oxid- izing Jlame. From the point a of the inner blue cone, the heat of the flame diminishes in both directions, towards 6 on the one hand, and towards c on the other ; most sub- stances require the temperature to be found between a and c. Oxidation takes place most rapidly at, or just be- yond, the point c of the flame, provided that the tempera- ture at this point is high enough for the special substance to be heated. A flame of precisely the opposite chemical effect may be produced with the blow-pipe. To obtain a good reducing flame, it is necessary to place the tip of the blow-pipe, not within, but just outside of the flame, and to blow rather over than through the middle of the flame (Pig. 17). In this manner the flame is less altered in its general char- acter than in the former case, the chief part con- ^'S- 17. sisting of a large, lu- -~^C!I^ minous cone, contain- ing a quantity of free carbon in a state of intense ignition, and just in the condition for taking up oxygen. This flame is, therefore, re- 16G PLATINUM FOIL AND 'WIIIE. § 168 ducing in its effect, and is technically called the reducing flame. The substance which is to be reduced by expo- sure to this flame, should be completely covered up by the luminous cone, so that contact with the air may be entirely avoided. It is to be observed that, whereas to produce an effective oxidizing flame a strong blast of air is desirable, to get a good reducing flame the operator should blow gently, with only enough force to divert the lamp-flame. Substances to be heated in the blow-pipe flame are supported, sometimes on charcoal, and sometimes on platinum foil or wire, or in platinum spoons or forceps. Charcoal is especially suitable for a support in experi- ments of reduction. 163. Plaliaum foU and wire. Pincers. A piece of platinum foil about IJ inches long and 1 inch wide will be sufficient. The foil should be at least so thick that it does not crinkle when wiped ; and it is more economical to get foil which is too thick than too thin, for it requires frequent cleaning. To keep foil in good order it should be frequently scoured with fine moist sand, and in case the foil becomes wrinkled it may be burnished by placing it upon the bottom of an inverted agate or porcelain mortar and rubbing it strongly with the pestle. A bit of platinum wire, not stouter than the wire of a small pin and about 3 inches long, wUl last a long time with careful usage. It may be cleaned by long-continued boiling in water. A small loop about as lai-ge as this O, should be bent at each end of the wu-o. 'W'luni platinum foil is to be heated it may be held at one end with a pair of ihe small stoel pincers known as joweller.s' tweezers. A pii-cc of platinum wire, as long as the one above described, can be held in the fingers with- §§ 169, 170 PLATDTOM OBirCIBLES WASH-BOTTLE. 167 out inconvenience, for platinum is, comparatively speak- ing, a bad conductor of heat. Pieces of wire too short to be held may be made serviceable by thrusting one end of the wire into the end of a glass rod or closed tube which has been softened in the blow-pipe flame. 169. Platinum, Crucibles. For several of the opera- tions of quantitative analysis as now practised, platinum crucibles are indispensable, and though not absolutely necessary for the profitable study of qualitative analysis, one of these vessels will often be found convenient by the student of the elements of analysis. It will be well, therefore, for the student who proposes to continue his chemical studies beyond qualitative analysis, to procure a platinum crucible once for all. A crucible of the ca- pacity of about 20 cubic centimetres will be large enough for most uses ; it should be cylindrical rather than flaring, and should be provided with a loose cover in the form of a shallow dish. No other metal, and no mixture of substances from which a metal can be reduced, must ever be heated in a platinum crucible, or upon platinum foil or wire, for platinum forms alloys with other metals which are much more fusible than itself. If once alloyed with a baser metal, the platinum ceases to be applicable to its peculiar uses. Platinum may be cleaned by boiling it in either nitric or chlorhydric acid, by fusing acid sulphate of sodium upon it, or by scouring it with fine sand. Aqua-regia and chlorine- water dissolve platinum; the sulphides, cyanides, and hydrates of sodium and potassium, when fused in platinum vessels, slowly attack the metal. 170. Wash-loUle. A wash-bottle is a flask with a uniformly thin bottom, closed with a sound cork or caout- 1G8 GLASS TUBING. § 171 chouc stopper through which pass two glass tubes, as shown in Fig. 18. The outer end of the longer tube is drawn Fig- 18. to a moderately fine point. A short bend near the bottom of this longer tube, in the same plane and dii-ection as the upper bend, is of some use, because it enables the operator to empty the flask more completely by in- clining it. By blowing into the short tube, a stream of water will be driven out of the long tube with considerable force. This force with which the stream is projected adapts the apparatus to removing precipi- tates from the sides of vessels as well as to washing them on filters. For use in analytical opera- tions, it is often convenient to attach a caoutchouc tube 12 or 15 c. m. long to the tube through which the air is blown ; this flexiljle tube should be provided with a glass mouth-piece, consisting of a bit of glass tubing about 3 c. m. long. As the wash-bottle is often filled with hot or oven boiling water, it may be improved by binding about its neck a ring of cork, or winding the neck closely with saiooth cord. It may then be handled without inconve- nience when hot. The method of making a wash-bottle is described in the following paragraphs. ni. (7/rt>R Tuhivg. Two qualities of glass tubing are used in chemical experiments : tliat wliich softens readily in the flame of a gas or spirit-lamp, and that which fuses with extreme difliculty in the flame of the blast-lamp. These two qualities are distin^-uished by the terms »i]fl r.nd liard glass. Soft glass is to bo preferred for all uses except the intense heating, or ignition, of dry substances. §§ 172, 173 CUTTING AND CEACKINa GLASS. 169 Pig. 19 represents the common sizes of glass tubing, both hard and soft, and shows also the proper thickness of the glass walls for each size. The numbers ranging from 4 to 8 are best suited for use in qualitative analysis. 172. Stirring Rods. Cut a short stick of glass rod, No. 8 or 7, into pieces four or five inches long (see the next paragraph), and round the sharp ends by fusion in the blow-pipe-flame. 173. Gulling and cracJdng glass. Glass tubing and glass rod must generally be cut to the length required for any particular apparatus. A sharp triangular file is used for this purpose. The stick of tubing, or rod, to be cut is laid upon a table, and a deep scratch is made with the file at the place where the fracture is to be made. The stick is then grasped with the two hands, one on each side of the mark, while the thumbs are brought to- gether just at the scratch. By pushing with the thumbs and pulling in the opposite direction with the fingers, the stick is broken squarely at the scratch, just as a stick of candy or dry twig may be broken. The sharp edges of the fracture should invariably be made smooth, either with a wet file, or by softening the end of the tube or rod in the lamp (§ 174). Tubes or rods of sizes four to eight inclusive may readily be cut in this manner ; the larger sizes are divided with more difficulty, and it is 170 CUTTING AND CBACKING GLASS. § 173 often necessary to make the file-mark both long and deep. An even fracture is not always '^'S-^"; to be obtained with large tubes. The lower ends of glass funnels, and those ends of gas delivery-tubes which enter the bottle or flask in which the gas is generated, should be filed off or ground off on a grindstone, obliquely (Fig. 20), to facilitate the dropping of liquids from such extremi- ties. In order to cut glass plates, the" glazier's diamond must be resorted to. For the cutting of exceedingly thin glass tubes, and of other glass ware, Hke flasks, retorts, and bottles, still other means are resorted to, based upon the sudden and unequal appHoation of heat. The process divides itself into two parts, — the producing of a crack in the required place, and the subsequent guiding of this crack in the desired direction. To produce a crack, a scratch must be made with the file, and to this scratch a pointed bit of red-hot charcoal, or the jet of flame pro- duced by the mouth blow-pipe, or a very fine gas-flame, or a red-hot glass-rod, or iron wire, may be applied. If the heat does not produce a crack, a wet stick or file may be touched upon the hot spot. Upon any part of a glass surface escej)t the edge, it is not pos- sible to control perfectly the direction and extent of this first crack ; at an edge a small crack may be started with tolerable certainty by carrying the file mark entirely onr the cdi;o. To guide the crack thus started, a pointed bit of charcoal or slow-match may bo used. The hot point must bo kept on the glass from 1 c. m. to 0.5 c. m. in advance of the point of the crack. The crack will follow the hot point, and may therefore bo carried in any dcsirod direction. By tiu-n- § 174 BENDING AND CLOSING GLASS TUBKS. 171 ing and blowing upon the coal or slow-match, the point may be kept sufficiently hot. Whenever the place of experiment is suppUed with common illuminating gas, a very small jet of burning gas may be advantageously substituted for the hot coal or slow-match. To obtain such a sharp jet, a piece of hard glass tube, No. 5, 10 c. m. long, and drawn to a very fine point (§ 174), should be placed in the caoutchouc tube, which ordinarily de- livers the gas to the gas-lamp, and the gas should be lighted at the fine extremity. The burning jet should have a fine point, and should not exceed 1.5 c. m. in length. By a judicious use of these simple tools, broken tubes, beakers, flasks, retorts, and bottles may often be made to yield very useful articles of apparatus. No sharp edges should be allowed to remain upon glass apparatus. The durabihty of the apparatus itseK, and of the corks and caoutchouc stoppers and tubing used with it, vriU be much greater, if all sharp edges are removed with the file, or still better, rounded in the lamp. 174. Bending and closing glass tubes. Tubing of sizes four to eight inclusive, can generally be worked in the common gas or spirit-lamp ; for larger tubes the blast- lamp is necessary (§ 164). Glass tubing must not be introduced suddenly into the hottest part of the flame, lest it crack. Neither should a hot tube be taken from the flame and laid at once upon a cold surface. Gradual heating and gradual cooling are alike necessary, and are the more essential the thicker the glass ; very thin glass wiU sometimes bear the most sudden changes of temper- ature, but thick glass and glass of uneven thickness absolutely require slow heating and anneahng. "When the end of a tube is to be heated, as in rounding sharp edges, more care is required in consequence of the great 172 BENDING AND CLOSING GLASS TUBES. § 174 facility with which cracks start at an edge. A tube should, therefore, always be brought first into the current of hot air beyond the actual flame of the gas or spuit- lamp, and there thoroughly warmed, before it is intro- duced into the flame itself. If a blast-lamp is employed, the tube may be warmed in the smoky flame, before the blast is turned on, and may subsequently be annealed in the same manner ; the deposited soot will be burnt off in the first instance, and in the last, may be wiped off when the tube is cold. In heating a tube, whether for bending, drawing, or closing, the tube must be constantly tiu'ned between the fingers, and also moved a little to the right and left, in order that it may be uniformly heated aU round, and that the temperature of the neighboring parts may be duly raised. If a tube, or rod, is to be heated at any part but an end, it should be held between the thumb and first two fingers of each hand in such a manner that the hands shall be below the tube or rod, with the pahns upward, while the lamp-flame is between the hands. When the end of a tube or rod is to be heated, it is best to begin by warming the tube or rod about 2 c. m. from the end, and from thence to proceed slowly to the end. The best glass wiU not be blackened or discolored during heating. Blackening occiu's in glass which, like ordinary flint glass, contains oxide of lead as an ingre- dient. Glass containing much of this oxide is not well adapted for chemical uses. The blackening may some- times be removed by putting the glass in tlao upper or outer part of the flame, whcve the reducing gases are consumed, and the air has the best access to the o-lass. 'i'ho blackening may be altogctlior avoided by always kecjiing the glass in the oxidizhig part of the llaiue. (ilaw.s begins to sol'lcn and bend bolow a visible red § 174 BENDING AND CLOSING GLASS TUBES. 173 heat. The condition of the glass is judged of as much by the fingers as the eye ; the hands feel the yielding of the glass, either to bending, pushing, or puUing, better than the eye can see the change of color or form. It may be bent as soon as it is hot enough to yield in the hands, but can be dra-mi out only when much hotter than this. Glass tubing, howeyer, should not be bent at too low a temperature ; the curves made at too low a heat are apt to be flattened, of unequal thickness on the convex and concave sides, and brittle. In bending tubing to make gas-deUvery tubes and the Uke, attention should be paid to the following points : 1st, the glass should be equally hot on all sides ; 2d, it should not be twisted, pulled out, or pushed together dm-ing the heating ; 3d, the bore of the tube at the bend should be kept round, and not altered in size ; 4th, if two or more bends be made in the same piece of tubing (Fig. 21, a), they should all be in the same plane, so that the finished tube will he flat upon the level table. When a tube or rod is to be bent '^' ■ or drawn close to its extremity, a temporary handle may be attached to it by softening the end of the tube or rod, and pressing against the soft glass a fragment of glass tube, which will adhere strongly to the softened end. The handle may subsequently be removed by a slight blow, or by the aid of a file. If a considerable bend is to be made, so that the angle between the arms will be very small or nothing, as in a siphon, for example, the curvature cannot be weU produced at one place in the tube, but should be made by heating, progressively, several centimetres of the tube, and bending continu- ously from one end of the heated portion to the other b 174 BEHDINa AND CLOSING GLASS TUBES. § 174 (Fig. 21, 6). Small and thick tube may be bent more sharply than large or thin tube. In order to draw a glass tube down to a finer bore, it is simply necessary to thoroughly soften on all sides one or two centimetres' length of the tube, and then taking the glass from the flame, pull the parts asunder by a cautious movement of the hands. The larger the heated portion of glass, the longer will be the tube thus formed. Its length and fineness also increase with the rapidity of mo- tion of the hands. If it is desirable that the finer tube should have thicker walls in proportion to its bore than the original tube, it is only necessary to keep the heated portion soft for two or three minutes before drawing out the tube, pressing the parts shghtly together the while. By this process the glass will be thickened at the hot ring. To obtain a tube closed at one end, it is best to take a piece of tubing, open at both ends, and long enough to make two closed tubes. lu the middle of the tube a ring of glass, narrow as possible, must be made thoroughly soft. The hands are then separated a little, to cause a contraction in diameter at the hot and soft part. The point of the flame must now be dii-ected, not upon the narrowest part of the tube, ))ut upon what is to be the bottom of > ^s CT' the closed tube. This point is indi- ated by the line a in Fig. i'l. By withdrawing the right hand, the narrow part of the tube is attenuated, and finally molted off, leaving both halves of the original tube closed at one end, but not of the same form ; the right- hand half is drawn out into a long point, the other is nior(! roundly closed. It is not possible to close hand- somely the two pieces at once. The tube is seldom per- § 175 BiiOwnia bulbs. 175 fectly finislied by the operation ; a superfluous knob of glass generally remains upon the end. If small, it may be got rid of by heating the whole end of the tube, and blowing moderately with the mouth into the open end. The knob, being hotter, and therefore softer than any other part, yields to the pressure from within, spreads out and disappears. If the knob is large, it may bo cut off with scissors while red hot, or drawn off by sticking to it a fragment of tube, and then softening the glass above the junction. The same process may be applied to the too pointed end of the right-hand half of the original tube, or to any misshapen result of an unsuccess- ful attempt to close a tube, or to any bit of tube which is too short to make two closed tubes. When the closed end of a tube is too thin, it may be strengthened by keeping the whole end at a red heat for two or three minutes, turning the tube constantly between the fingers. It may be said in general of all the preceding operations before the lamp, that success depends on keeping the tube to be heated in constant rotation, in order to secure a uniform temperature on all sides of the tube. 175. Blowing Bulbs. Bulb-tubes, like the one repre- sented in Fig. 23, are employed for reducing substances capable of forming sublimates upon the cold walls of the tube. They are readily made Fig- 23. from bits of tubing, in the flame of Bunsen's burner, or in the common blow-pipe flame. If the bulb desired is large in proportion to the size of the tube on which it is to be made, the walls of the tube must be thickened by rotation in the flame before the 17G BLOWIN« BULBS. § 175 bulb can be blown. The thickened portion of the glass is then to be heated to a chorry-red, suddenly withdrawn from the flame, and expanded while hot by steadily blowing, or rather pressing, air into the tube with the . mouth ; the tube must be constantly turned on its axis, not only while in the flame, but also while the bulb is being blown. If too strong or too sudden a pressure be exerted with the mouth, the bulb will be extremely thin, and quite useless. By watching the expanding glass, the proper moment for arresting the pressure may usually be determined. If the bulb obtained be not large enough, it may be reheated and enlarged by blowing into it again, provided that a sufficient thickness of glass remain. If a bulb is to be blown in the middle of a piece of tubing, the thickening is effected by gently pressing the ends of the tube together while the glass is red-hot in the place where the bulb is to be ; if a lai-ge bulb is to be placed at the end of a tube, this end is first closed, and then suitably thickened by pressing the hot glass up with a piece of metal until enough has been accumulated at the end. It is sometimes necessary to make a hole in the side of a tube or other thin glass apparatus. This may be done by directing a pointed flame from the blast-lamp iipon the place where the hole is to be, uutU a small spot is rod-hot, and then blowing forcibly into one end of the tube while the other end is closed by the finger ; at the hot spot the glass is blown ovit into a tliiu bubble, which bursts or may be easily broken ofl', lea\iug an aperture in the side of the tube. It is hoped that those few directions will enable the altentivo stxulent to perform, sufficiently well, all the iiianipuLiiidiiM witli glass tubes which the cx]icriments (li'scribed in this muuual require. Much praetieo ^^■ill § 176 CAOUTCHOUC. 177 alone give a perfect mastery of the details of glass- blowing. 178. Caoutchouc. Vulcanized caoutchouc is a most useful substance in the laboratory, on account of its elas- ticity, and because it resists so well most of the corrosive substances with which the chemist deals. It is used in three forms : (1) in tubing of various diameters com- parable with the sizes of glass tubing ; (2) in stoppers of various sizes, to replace corks ; (3) in sheets. Caout- chouc tubing may be used to conduct all gases and liquids which do not corrode its substance, provided that the pressure under which the gas or liquid flows be not greater, or theu- temperature higher, than the texture of the tubing can endure. The flexibility of the tubing is a very obvious advantage in a great variety of cases. Short pieces of such tubing, a few centimetres in length, are much used, under the name of connectors, to make flexible joints in apparatus of which glass tubing forms part ; flexible joints add greatly to the durabihty of such apparatus, because long glass tubes bent at several angles and connected with heavy objects, like globes, bottles or flasks fuU of liquid, are almost certain to break, even with the most careful usage ; gas-delivery tubes, and all con- siderable lengths of glass tubing, should invariably be divided at one or more places, and the pieces joined again with caoutchouc connectors. The ends of glass tubing to be thus connected should be squarely cut, and then rounded in the lamp, in order that no sharp edges may cut the caoutchouc ; the internal diameter of the caout- chouc tube must be a httle smaller than the external di- ameter of the glass tubes ; the slipping on of the con- nector is facilitated by wetting the glass. In some cases 178 CAOUTCHOUC. § 176 of delicate quantitative manipulations, in which the tight- est possible joints must be secured, the caoutchouc con- nector is bound on to the glass tube with a silk or smooth linen string ; the string is passed as tightly as possible twice round the connector, and tied with a square knot ; the string should bo moistened in order to prevent it from slipping while the knot is tying. Caoutchouc stoppers of good quaUty are much more durable than corks, and are in every respect to be pre- ferred. The Grerman stoppers are of excellent shape and quality ; the American, being chiefly intended for wine bottles, are apt to be too conical. Caoutchouc stoppers can be bored like corks (see the next section) Ijv means of suitable cutters, and glass tubes can be fitted into the holes thus made with a tightness unattainable with corks. German stoppers may be bought ah'eady provided with one, two, and three holes. It is not well to lay in a large stock of caoutchouc stoppers ; for, though they last a long time when in constant use, they not infrequently deteri- orate when kept in store, becoming hard and somewhat brittle with ago. These stoppers must not be confounded with the very inferior caxjs which were in use a few years ago. Pieces of thin sheet caoutchovic are very conveniently used for making tight joints between large tubes of two different sizes, or between the neck of a flask, or bottle, and a large tube which enters it, or between the neck of a retort and the receiver into which it enters. A suflS- c-iently brciad and long piece of slicct caoutchouc is con- Kiilrriil)ly stretched, wr;ipiiod tightly over the glass parts a Ijoining the aperture to bo closod, and secured in place liy a string wound closely about it and tied with a squai-e knot. § 177 CORKS. 179 177. Corks. It is often very difficult to obtain sound, clastic corks, of fine grain and of size suitable for large flasks and wide-mouthed bottles. On this account, bottles with mouths not too large to be closed with a cork cut across the grain should be chosen for chemical uses in preference to bottles which require large corks or bungs cut with the grain, and therefore offering continuous channels for the passage of gases, or even liquids. The kinds sold as champagne corks and as satin corks for phials, are suitable for chemical use. The best corks gen- erally need to be softened before using ; this softening may be effected by rolling the cork under a board upon the table, or under the foot upon the clean floor, or by gently squeezing it on aU sides with the well-known tool expressly adapted for this purpose, and thence called a cork-squeezer ; steaming also softens the hardest corks. Corks must often be cut with cleanness and precision ; a sharp, thin knife, such as shoemakers use, is desirable for this purpose. When a cork has been pared down to reduce its diameter, a flat file may be employed in finish- ing ; the file must be fine enough to leave a smooth surface upon the cork ; in filing a cork, a cylindrical, rather than a conical, form should be aimed at. In boring holes through corks to receive glass tubes, a hollow cylinder of sheet brass sharpened at one end is a very convenient tool. Fig. 24 represents a set of such little cylinders of graduated sizes, slipping one within the other into a very compact form ; a stout wire, of the same length as the cylinders, accompanies the set, and serves a double purpose — ^passed transversely through two holes in the cap which terminates each cylinder, it gives the hand a better grasp of the tool while penetra- ting the cork ; and when the hole is made, the wire thrust through an opening in the top of the cap expels the little 180 PUTTING TUBES THEOUGH COKKS. §177 cylinder of cork wliicli else would remain in the cutting cylinder of brass. That cutter, -whose diameter is' next below that of the glass tube to be inserted in the cork, is always to be selected, and if the hole it makes is too small, a round file must be used to enlarge the aperture ; the round file, also, often comes in play to smooth the rough sides of a hole made by a dull cork-borer. A pair of small calipers is a very conve- nient, though by no means essential, tool in determining which size of cutter to employ. A flask which pre- sents sharp or rough edges at the mouth can seldom be tightly corked, for the cork cannot be introduced in- to the neck without being cut or roughened ; such sharp edges must be rounded in the lamp. In thrusting glass tubes through bored corks, the following directions are to be observed: (1.) The end of the tube must not present a sharp edge capable of cutting the cork. (2.) The tube should be grasped very close to the cork, in order to escajie cutting the hand which holds the cork, should the tube break ; by observing this pre- caution, the chief cause of breakage, viz., irregular lateral pressure, will be at the same time avoided. (3.) A funnel-tube must never be held by the funnel in di'iving it through a cork, nor a bent tube grasped at the bend, unless the bend comes immcdiatoly above the cork. (4.) If the tube goes very hard through the cork, the applica- tion of a little soap and water will facilitate its passixge; but if so.ip is usi-d, the tube can seldom be withdrawn from tlio cork after the lattiT has become dry. {~^.) The tube must not bo pushed straight into the cork, but §178 GAS-BOTTLE. 181 screwed in, as it were, with a slow rotary as well as on- ward motion. Joints made with corks should always be tested before the apparatus is used, by blowing into the apparatus, and at the same time stopping up all legitimate outlets. Any leakage is revealed by the disappearance of the pressure created. To the same end, air may be sucked out of an apparatus and its tightness proved by the permanence of the partial vacuum. To attempt to use a leaky cork is generally to waste time and labor, and to insure the failiu'e of the experiment. Fig. as. 178. Gas-bottle. Fig. 25 represents a gas-bottle fitted for evolving sulphuretted hydrogen, carbonic acid, and other gases which can be prepared without heat. A straight glass tube of convenient length is shpped into the caoutchouc connector at the right to carry the gas into the solution to be tested. The neck of the bottle should be rather narrow, since it is difficult to obtain tight stoppers for bottles with wide mouths, but must nevertheless be wide enough to admit a cork, or better a caoutchouc stop- per, capable of carrying both the de- livery and the thistle tubes. To prepare, for example, sulphuretted hydrogen gas, put a tablespoonful of fragments of sulphide of iron in the bottom of the bottle, replace the cork vri.th its tubes, and press, or rather twist, it tightly into the neck of the bottle ; pour in enough water through the thistle-tube to seal the lower end of that tube, and finally as much con- centrated sulphuric acid as would be equal to a tenth or a twelfth of the volume of the water. 9 182 SELF-EEGULATINO GEXEEATOE. § l'''^ At the start it is well thus to mix strong acid with the water in the bottle, for the heat generated by the union of the two liquids serves to warm the apparatris, and to facilitate the decomposition of the sulphide of iron ; but it must be remembered that strong sulphuric acid is by itself unfit for generating sulphuretted hydrogen, and that the evolution of gas would be checked if much of it were added. When the flow of gas ceases, jxyur a small portion of dilute sulphuric acid into the thistle-tube, and rejDeat this operation as often as may be necessary to maintain a constant stream of gas. Dilute acid fit for this purpose may be prepared by mixing 1 volume of strong sulphuric acid with 14 volumes of water; the water should be weU stirred and the acid poured into it in a fine stream. In precipitating the members of Classes II and lU with sulphm-etted hydrogen, the gas delivery-tube should not dij) do('iier than about an inch beneath the surface of the Uquid in the beaker. A rapid current of gas is usf- less and wasteful. The best method of operating is to pom- dilute sulphuric acid into the thistle-tube in such quantity that the bubbles of gas may follow one another slowly enough to be coiuited without effort. 179. Self-regulating Gaf-ffrnerator. An apparatus whicli is always ready to deliver a constant stream of sulphuretted hydrogen, and yet dins not generate the gas except wlien it is immediately wnuti'd for use, is a gri'at convenience in an active laboratory. The same re- mark api)lies to the two gases, hydrogen and carbonic acid, which are likewise used in considerable quantities in quantitative analysis, and -whicli can be conveniently gencrati'd in precisely tlic same form of apparatus which is advantageous for sulpluu-etted hydrogen. .Such a §179 SELF-EEGTOATING GENE1JA.T0R. 183 Fig. 20. generator may bo made of divers dimeBsions. The fol- lowing directions, with the accom- panying figure (Fig. 26), will enable the student to construct an apparatus of convenient size. Procure a glass cyUuder, 20 or 25 c. m. in diameter, and 30 or 35 c. m. high ; ribbed candy jars are sometimes to be had of about this size ; procure also a stout tubulated beU-glass, 10 or 12 c. m. wide, and 5 or 7 c. m. shorter than the cylinder. Get a basket of sheet-lead, 7.5 c. m. deep, and 2.5 c. m. narrower than the beU- glass, and bore a number of small holes in the sides and bottom of this basket. Cast a circular plate of lead, 7 m. m. thick, and of a diameter 4b c. m. larger than that of the glass cylinder ; on what is intended for its under side, solder three equidistant leaden strips, or a continuous ring of lead, to keep the plate in proper position as a cover for the cylinder. Fit tightly to each end of a good brass gas-cock a piece of brass tube 8 c. m. long, 1.5 to 2 c. m. wide, and stout in metal. Perforate the centre of the leaden plate, so that one of these tubes wUl snugly pass through the orifice, and secure it by solder, leaving 5 c. m. of the tiibe pro- jecting below the plate. Attach to the lower end of this tube a stout hook on which to hang the leaden basket. By means of a sound cork and common sealing-was, or a cement made of oil mixed with red and Avhite lead, fasten this tube into the tubulature of the bell-glass air-tight, and so firmly that the joint wiU bear a weight of several pounds. Hang the basket by means of copper wire 184 MOETARS. § 180 within the bell, 5 c. m. above the bottom of the latter. To the tube which extends above the stop-cock attach by a good cork the neck of a tubulated receiver, of 100 or 150 c. c. capacity, the interior of which has been loosely stuffed with cotton. Into the second tubulature of the receiver fit tightly the delivery-tube carrying a caoutchouc connector ; into this connector can be fitted a tube adapted to convey the gas in any desired direction. When many persons use the same generator, each person must bring his own tube. To charge the apparatus, fill the cylinder with dilute acid to within 10 or 12 c. m. of the top ; fill the basket with fi-agments of sulphide of iron ; hang the basket in the bell, and put the bell-glass full of air into its place, with the stop-cock closed. On opening the cock, the weight of the acid expels the air fi-om the bell, the acid comes in contact with the solid in the basket, and a steady supply of gas is generated until either the acid is satu- rated or the solid dissolved ; if the cock be closed, the gas accumulates in the bell, and pushes the acid below the basket, so that all action ceases. In cold weather, the ajjparatus must be kept in a warm place. For gen- cirating svdphuretted hydrogen, sulphuric acid, dilutetl with fourteen parts of water, is used ; for hydrogen, zinc and sulphuric acid, diluted with foiu- or five jxu-ts of water ; while for carbonic acid, chalk and mmiatic acid, diluted with two or tlnoo parts of watei-, sliould be taken. 180. Jlfdiiara. "\Mienevcr the substance to be ana- lyzed occurs in tlio form of largo piccts or coarse powder, it should, as a general rule, be pulverized by mechanical means before sul>j(>ctiug it to the action of solvents. Mortars of iron, steel, agate, or iiorcelaiu are used for § 180 MOBTAES. 185 this purpose, according to the character of the substance to be powdered. An iron mortar is useful for coarse work, and for effect- ing the first rough breaking up of substances which are subsequently powdered in the agate or porcelain mortar. If there be any risk of fragments being thrown out of the mortar, it should be covered with a cloth or piece of stiff paper, having a hole in the middle through which the pestle may be passed. Instead of the common iron mortar, a small steel mortar, of the kind called diamond mortars by dealers in chemical waj'e, may be used for crushing minerals. Pieces of stone, minerals, and lumps of brittle metals may be safely broken into fragments suitable for the mortar by wrapping them in strong paper, laying them so enclosed upon an anvil, and striking them with a heavy hammer. The paper envelope retains the broken particles, which might otherwise fly about in a dangerous manner, and be lost. The best porcelain mortars are those known by the name of Wedgewood-ware, but there are many cheaper substi- tutes. Porcelain mortars will not bear sharp and heavy blows ; they are intended rather for grinding or tritura- ting saline substances than for hammering ; the pestle may either be formed of one piece of porcelain, or a piece of porcelain cemented to a wooden handle ; the latter is the less desirable form of pestle. Unglazed porcelain mortars are to be preferred. In selecting mortars, the following points should be attended to : 1st, the mortar should not be porous ; it ought not to absorb strong acids or any colored fluid, even if such liquids be allowed to stand for hours in the mortar ; 2d, it should be very hard, and its pestle should be of the same hardness ; 3d, it should be sound]; 4th, *it should have a lip, for the con- venience of pouring out liquids and fine powders. As a 186 Sl'ATULiE. § 181 rule, porcelain mortars will not endure sudden changes of temperature. They may be cleaned by rubbing in them a little sand soaked in nitric or sulphuric acid, or, if acids are not appropriate, in caustic soda. Agate mortars are only intended for trituration ; a blow would break them. They are exceedingly hard and im- permeable. The material is so precious and so hard to work, that agate mortars are always small. The pestles are generally inconveniently short, a difficulty which may be remedied by fitting the agate pestle into a wooden handle. In all grinding operations in mortars, whether of por- celain or agate, it is expedient to put only a small qiian- tity of the substance to be powdered into the mortar at once. The operation of powdering will be facilitated by sifting the matter as fast as it is powdered, retui'ning to the mortar the particles which are too large to pass through the sieve. 181. Spntnhr. For transferring substances in powder, (u- in small grains or crystals, from one vessel to another, spatulai and scoops, made of horn or bone, are convenient tools. \ coarse lione paper-knife makes a good spatula for laboratory use. Cards, free from glaze and enamel, are excellent substitutes for spatulte. INDEX. Acetate of Lead, as reagent, 142. Acetates, tests for, 97. Acid solutions, 110, 114. Alkaline solutions, 110. AluiTiinates, precipitated with Class IV, 46. Aluminum, confirmatory test for, 50. a member of Class IV, 20, 45. precipitated as hj'drate, 20, 50. presence of indicated, 53. Ammonia-water, as reagent, 136. Ammonium salts, testing for, 103, 131. Antimony, confirmatory test for, 42. converted into an insolu- ble oxide by HNO', 128. Bee sulphide of. globule, brittle, 106. a member of Class III, 19, 39. oxide of, dissolved by tartaric acid, 42. precipitated as sulphide, 19, 38, 42. presence of indicated, 41, 45. teroxide of, as a subli- mate, 103. Aqua-rcgia, how prepared, 134. its use as a solvent, 114. Arseniates, test for, 87. Arsenic, confirmaton^ tests for, 40, 43. a member of Class III, 19, 39. presence of indicated, 36, 45. Bee sulphide of. separation as sulphide,19, 38. as a sublimate, 103. Arsenic acid, tests for, 87. Arsenious acid, how distinguished from arsenic acid, 88. as a sublimate, 103, testa for, 87. Arsenites, tests for, 87, Ash of charcoal, 106. Bakiom, a member of Class VI, 22,61. precipitated as carbonate, 22, 61. precipitated as chromate, 62. salts soluble in ammoniacal solutions, 77. Barium-test for certain classes of salts, 75. Beakers, 150. Biborate of sodium, as reagent, 139. Bichloride of platinum, as reagent, how prepared, 143. Bismuth, confirmatory test for, 32. globule, brittle, 106. a member of Class II, 19, 29. precipitated as hydrate, 32. " " sulphide, 19. 30. presence of indicated, 37. Blast-lamps, 156. Blowers, 156. Blowing bulbs, 171. Blowpipe, 163. how to use, 164. lamp, 163. Boracic acid, precipitated from an alkaline solution, 111. tests for, 91. Borates, tests for, 91. Borax-bead, how to dilute, 120. " make, 119. Bottles, how to handle, 147. Bromides, tests for, 79, 94. Bromine, tests for, 94. Bunsen's burner, 165. 188 Cadmium, a mcziibcr of Class II, 19, 29. precipitated as sulphide, 19, presence of indicated, 3G. Cadmium, separatiun of, 33. Calcium, ainuiiilH-r uf (Jlasw VI, 22, 61. precipitated as carbonate, 22, Gl. precipitated as oxalate, 63. Calcium -test, for certain classes of salts, 7H. CaouU'lmiir stn]i]i('rM, 178, tui.irif,', 177. Carbonate of ammonium, as reagent, 137. Carbonate of sodium, as reagent, how purified, 13h. Carbonates, lest for, 84, C-irbonic nu'id, tests for, 84. Caustic soda solution, how prepared and kejit, 137. Cbiircoal for bluw-iiipe use, 104. ( lihinites, tests for, Uil. Chloride of ammonium, as reagent, 137. URC^ of, 21, 53, 65. Chloride of l.arium asreau;iMU, 112. -Chloride of calcium, as reagent, how preparoil, 1 11. ( 'hloriae of lead, j-tibibility of, 27. ( 'Iiloride of mercur\', as readout, 143. Cldoride of silver soluble in ammonia- -vvater, 2M. riiloriilrs tests for, 71), 93. ChlMili\ilric acid, us reagent, 133. its ap|ilicalion as a solvent, l(w. pure, when needed, 66. Clilorino, tests for, 79, 93. (.'hromatc of leail, a test for chro- mium, 19. ( 'bromatc of poia^siuni, as reagent, C«>rk-cuttors, iso. 139. Chromium gives a green borax-bead» 119. precipitated as hvdrate, 20, 45. presence of indicated, 53. Class, term defined, 14, Cla^s I, delined, 15. how to precipitate, 2G. Class II, defined, 19. how to precipitate, 29, Class III, defined, 19, how to disptilve the sulphides in Nall.S, 3H. Clacs III, procipifariou of^ 38. Class IV, fK'linea, 2i>. how to precipitate, 46, o2, r,3. salts precipitated with, 4o. treatment of with oxalic acid, 47. Class Y, dciinod, 21. how to precipitate, 54, 60. Class YI. defined, 22. ]v<\\- to precipitate. 61, 64. Class VII, defined, 22. how isulatt^d, 22, 70. Clay cbiniiiev for Bunsen's bnmer, 100. Closed-tube test. li'^^'K Cobalt, a nicmtier of Cla^s V, 21, 55. blowpipe te.st for, 57. coiiiirmaton" test for, 5?. prccii>itated a^^ sulphide, 21, 55. presence of indicatotl, ii'\ C-'ppcr, a mcmhcr of Cla.-is II. IH, 20. confinnatorv te.--t for. 3i- pi\es hlue ^'dution-<, :'>.'. globule described, lu.i. 106. precipitated as sulphide, 19, 2:i. pre.-once of indlc.ited. 37. ('Iiromates, barium test for. Corks l"i'- to force tubo^ Llir-niiih, IniI reduction of I'v U-'S, 37, 87. Cyanide of mercun-, to detect cvano- tests fnr, 87. I * gen in. ^.^ (lirome-iidn ore, Irani to decomjinse. Cyanide of potassium, as rMizont. 120, J 21, 126. '140. ( 'liiomic-oxiile, hard to docompo.«o, (^-aniilos, tests for, 80, S?. S5. ^20. Cvanogen, te^t? tor. b2. ."^o. ChromiteM, preelpilated with I'lass IV, HI. 1 DfKT At;KATTON. 125. Chromium, a member of Class IV, Itipho^pbale of s«.Hlium, as reairont, 2(t, l.'». ' 139. lii'leetnl us chroma te of I>i-^M-I\ing in acids, 112. Niliiini, -IS. in ^^;^te^. los. INDEX. 189 Effervescence, what it indicates, 83. Elements, identified by compounds, 10. Elements, 34 treated of, 9. Etching glass, a test for fluorine, 92. Evaporatmg test, applied to a liquid, 130. Ferki- and Ferro-cyanides of po- tassium, as reagents, 140. Filtering, 150. Filter-stand, 162. Flaslts, 149. Fluoride of silicon, a test for fluorine and silicon, 93. Fluorides, tests for, 92. Fluorine, " '* 92. Fluorine, to be sought in an insoluble mineral, 120. Folding filters, 151. Funnels, 150. Fused minerals, how treated, 121. Fusion with acid sulphate of sodium, 123 with CaCOs and NH,C1. 124. ■with carbonate of sodium, 121. . Fusions in platinum crucibles, 159. Gas-bottle, 181. Gas-generator, self-regulating, 182. General reagent, defined, 15. General reagents for acids, 74. General reagents, to be used in a cer- tain order, 24. Glass, bending and closing tubes, 171. cutting and cracking it, 169. tubing, 168, 169. Gold globule, described, 105, 106. insoluble in HNO', 128. a member of Class III, 19, 43. presence of indicated, 44. purple of Cassius test for, 128. Hydrogen, its presence inferred, 72. Hyponitric acid, 102. Hyposulphites, tests for, 86. Tndigo solution, how prepared, 144. Insoluble substances, 116. iodides, tests for, 95, Iodine, tests for, 95. lodo-starch paper, 141. Iron, discrimination between ferrous and ferric salts, 52, Iron, to be converted into ferric salt, 52. Iron, u member of Class IV, 20, 45. precipitated as hydrate, 20, 43. presence of indicated, 53. rrussian-blue tost for, 48. reaction in borax bead, 120, Iron stand, 161. Labelling, importance of, 17. Lamps, 155. Lead, belongs to two classes, 19. see chloride of. globule described, 105, 106. Lead a member of Class I, 15, 27. " " " II, 19, 29. paper, how prepared, 142. precipitated as sulphide, 19, 29. precipitation of as chloride, 26. precipitation of as sulphate, 27, 32. presence of indicated, 36. the sulphate changed to chro- mate, 32. Lime-water, as reagent, 141. Liquids to be tested with litmus, 131. Litmus paper, how prepared, 144. Magmesidm, as member of Class VII, 23, 67. Magnesium, precipitated as phosphate of Mg and (NHi), 23, 67. separation as oxide, 69. Manganate of sodium, 49. Manganese, confirmatory test for, 56. green manganate test for, 49. precipitated with Class IV, 46. precipitation of, as hydrate, 56. presence of indicated, 60. Mercurous chloride, reaction with am- monia-water, 28. MercuTj^, belongs to two classes, 19. compounds as sublimates, 103. a member of Class I, 1 5, 28. " " " " II, 19, 29. precipitation as subchloride, 26. presence of indicated, 35. reduction of the metial in a closed tube, 28. 190 Morcurj', reduction of the metal on copper, 31. ecparation as sulphide, 19, 29. as a sublimate, 103. Metallic elements, 7 classes of, 25, 71. f^luljulcs descril)(_'(l, 105. glnliulea tested in oxidizing flame, KHi. Metals, action of HNOnon, 127. used in the arts, 12it. Molybdalc of ammonium, a test for phosphates, 89. Molybdatc of ammonium, as reagent, how prepared, 1^7. Mortarf, 184. Nkutrat^ SoT.r-noNs, 110. Nickel, blowpipe tL■^t for, 57. a member of Class V,21, 51. precipitated as cyanide, 5h. " sulphide, 21, 5J. Nickel, presence of indicated, (10. Nitrite of ammonium, as reagent, 137. Nitrate of barium, as reagent, 11'^. when used, 78. Nitrate of ohnU, as reagent, 113, Nilrate of potassium, as reagent, 140. Nitrate of silvi-r, as reagent, 141, Nifrates, tests for, 95. Nitric aciii, aciinn on metals, 127. dilute, as reajj;ont, 134. Iiow expellid, G(!. strong, as rt'a;:;(_'nt, 134, tests for, 95. ■when to bo used as a sol- vent, 113. Nitrite of potas.^imn, as reagent, how prepared, 140. Ken-metallic elements, how detected, Orgaxic Matter, detection of, 100. how destroyt'd, 101. Organic subsljinces hiiitUT the pro- (.ipit.ition of riasa IV, 54. Oxalali' nf ammonium, as reagent, 137. Ox;tlatt's converted into carbonates, (15. tpsta f(.r, 90. C)xalic acid as a sublimato, 101. as rrai^rnt, l;i5. tests fur, 90. C).\i(li' uf iiH'r(iir\, as rr.'igcnt, 113. Oxiiil/.ing liliiu]iijM' llnnu', llIl.lfM. (l.\yt,';i'n, how rccn^rni/ed, 1(L'. its presL'Moo inferred, 72. PlNCKRS, 106. riatinum, a member of Class III, 19, 43. crucibles, 1G7, foil, i(;f;. insoluble in HNO^ 123. pr».-sence of indicated, 44. test for, 129. "wire, 166, Phosphate of calcium, presence of in- dicated, 53. Phosphates, preiipitated with Class IV, 4(i. Phosphates, tL"-t3 for, J^h, Phosphoric acid, tc'-ts for, 88. Porcelain crucibles, 153. dishes, 153 Potassium, precipitated as chloropla- tinate, 69. flame-test for, Hs. a member of Class A'll, 22, 67. Precipitate^ compacted by boiling und shaking'. 33, 55. Preliminarv examiuation of a liquid, 130. Preliminary treatment, 99. of a pure .metal or all"v, 126. Protochloride of tin, how to make, 143. Prussian blue, a test for iron, 48. Pulverizing, 185. QtAUiTATivE Analysis defined, 9. ItrAi.ENT P"TTLE«, 146. lieagents, 13;M 15. Reducing blowjiiio flame, 165. KediK-tion test, 104. how to perfonii with deli- cacy. US. Koduction tc-"t, to bo applied to in- si'lublo substaiioos, 117, Salts, kinds of conoid. 'retl. 74. solublo in ^^ater, 109. ,Sand-baf insolu- ble suli^t.moo?, 124. 191 Silicic acid, precipitated from an al- kaline solution, 112. Silver, a metaber of Class I, 15, 20. globule described, 105, 106. precipitated by reducing agents, 82. precipitation as cliloride, 2G. salts, insoluble in dilute ni- tric acid, 80. salts, sundry colors of, 80. see chloride of. Silver-test, for certain classes of salts, 79. Slaked lime, as reagent, 141. Sodium, crystallization of chloropla- tiuate, 69. Sodium, flame-test for, 68. a member of Class VII, 22,67. Solvents, the order of use, 108. Spatulas, 186. Special tests for non-metallic ele- ments, 83. Starch paste, how prepared, Hi. Starch-test for bromine, 94. iodine, 95. Stirring-rods, 169. Stoppers, stuck, how to loosen, 147. Strontium, a member of Class VI, 22, 61. precipitated as carbonate, 22, 61. as sulphate, 63. Sublimates on charcoal while reducing metals, 106. Sulphate of copper, as reagent, 143. Sulphate of magnesium, as reagent, how mixed, 142. Sulphate of magnesium, a test for phosphates and arseniates, 88, 89. Sulphate of sodium, acid, how pre- pared, 139. Sulphates, barium test for, 77. how to detect, 88. insoluble, reduced to sul- phides, 118. Sulphate of potassium, as reagent, how prepared, 139. Sulphide of antimony, oxidation of by nitrate of sodium, 11. Sulphide of arsenic, soluble in car- bonate of ammonium, 39. Sulphide of tin, oxidation of, by ni- trate of sodium, 41. Sulphides, tests for, 85. Sulphides of arsenic, as sublimates, 103. Sulphites, tests for, 86. Sulphur, as a sublimate, 103. Sulphm-etted hydrogen, decomposed by oxidizing agents, 36. how prepared, 135, 181, 1«2. how to employ it, 29, 35. necessity of expelling, 51, G6. Sulphuretted hydrogen water, how prepared and kept, 135. Sulphuric acid, as reagent, 134, 135. Sulphuric acid, tests for, 88. Sulphurous acid, 102. Sulphur, precipitation of, 36, 37. Sulphj'drate of ammonium, as rea- gent, 136. Sulphydrate of sodium, as reagent, 138. Table for Qass I, 29. II, 35. III, 42. IV, 51. V, 60. VI, 64. the separation of the 7 classes of metallic elements, 71. 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Physical and Celestial Mechanics, by Benjamin Pierce, Perkins Professor of Astronomy and Mathematics in Harvard University, and Consulting Astronomer of the American Ephemeris and Nautical Almanac. Developed in four systems of Analytical Mechanics, Celestial Me- chanics, Potential Physics, and Analytic Morphology. 1 vol. 4to, cloth $10.00 "I have re-examined the memoirs of the great geometers, and have striven to consoli- date their latest researches and their most ox^lted forms of thought into a consistent and aniform tEeatise. 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OO " We find In this work tables of the tensile strength of timber, metals, stones, wire, rope, hempen cable, strength of thin cylinders of cast iron; modulus of eliistieity, strength of thick cylinders, as cannon, &c., effects of reheating, etc. , resistance of timber, metals, and stone to crushing; experiments on brick-work; strength of pillars, collapse of tube; experiments on punching and shearing; the transverse strength of materials; beams of uniform streng.h; table of coefficients of timber, stone, and fron; relative strength of weight in cast-iron, transverse strength of alloys; experiments on wrought and cast-iron beams; lattice girders, trussed cast-iron girders; deflection of beams; torsional strength and torsional elasticity." — American Artisan, WHITNEY (J. P.) Colorado, in the United States of America. Schedule of Ores contributed by sundry persons to the Paris Universal Exposition of 1867, with some Information about the Region and its Resources. By J. P. 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