methods of ascertaining whether a particular substance be simple or complex, and, if complex, of determining its constituents. See Vol. V. As general chemistry is divided into inorganic and organic, so analytical chemistry is divided p. 397 Am. into inorganic analysis and organic analysis; ed. (p. 489 and both of these are again divided into Edin. ed.). qualitative and quantitative analysis. The first of these latter branches ascertains the elemental chemical composition of any substance or mixture, and the second the relative proportion in which these constituents are present. Of course the successful application of the second method of analysis presupposes an acquaintance with the results of the first in any particular case. Quantitative chemical analysis is classified, moreover, under the headings of gravimetric analysis, in which the material to be analyzed is weighed, and its component parts are likewise determined by weight; volumetric analysis, in which the composition of a substance is determined by measuring the volumes of solutions of known strength which are used in the reactions incident to the analysis; and eudiometric, or volumetric, gas analysis, which determines both the qualitative and the quantitative composition of gaseous mixtures. Organic quantitative analysis, lastly, is divided into proximate and ultimate analysis, according as the complex vegetable or animal compound is resolved into simpler compounds only, or at once into the few chemical elements which in organic compounds unite in so many different forms of molecular combination. The methods of ultimate analysis dealing with some three or four elements only are quite simple, while proximate analysis involves the use of many reagents and methods, as the various organic principles contained in plant and animal tissues have very different physical and chemical properties. The space at our disposal will allow of only a cursory view of the most important of these several branches of chemical analysis. The methods of inorganic qualitative analysis will first be passed in review; of the two branches of inorganic quantitative analysis, gravimetric and volumetric, as the methods of the former correspond in principle almost uniformly with those of qualitative analysis, they will not be noted here, and for a description of the latter the reader is referred to manuals on the subject; eudiometric, or gas, analysis will then be noted, especially in its application to industrial gases. The subject of ORGANIC ANALYSIS will be treated under that title. INORGANIC QUALITATIVE ANALYSIS.-In qualitative analysis the student attempts to determine the composition of the different forms of matter by applying to them reagents-bodies of known properties which when applied properly give him information in the form of reactions. The reactions yield new products, with accompanying changes in appearance and properties. When the reaction takes place between two liquids, a not infrequent result is the formation of an insoluble compound, a precipitate. Or the result of the reaction may be the escape of a gas with what is called effervescence. According to the action of reagents we can divide the metals or basic elements into six groups, the members of which are in many respects similarly affected by reagents. These six groups are: Before treating of the differences of the several groups, certain preliminary analytical operations which are in constant use will be mentioned. 1. Solution. Some solids, when brought in contact with water or other liquid, gradually pass into the liquid state, or dissolve; such are said to be "soluble." The liquid which effects the solution is "the solvent," and the liquid obtained is termed the "solution." If the substance can be recovered without material alteration, the solution is said to be "simple;" but if a chemical change has taken place, the product is a chemical solution." 2. Evaporation is the driving off of the solvent by boiling. 3. Precipitation occurs when, on mixing two perfectly clear liquids, turbidity ensues, an insoluble substance called a "precipitate" being formed. Precipitates differ greatly in appearance and properties, being described as flocculent, crystalline, gelatinous, etc. 4. Filtration consists in separating a precipitate from the liquid in which it is produced. This is accomplished by the use of filtering paper, a soft bibulous varie y analogous to but looser in texture than blotting-pad paper; which paper is fitted inside of a glass funnel. In the filtration of strong acids, etc. asbestos fibre or spun-glass is substituted for paper. 5. Decantation is resorted to in some cases where the insoluble compound is rather heavy and separates rapidly. The liquid is removed by pouring it off with the aid of a glass rod held against the edge of the vessel, or by the use of a syphon. Precipitates are usually washed upon the filter upon which they are collected by directing a jet of distilled water upon them and continuing until the water running through the funnel is found to leave no residue on evaporation. If washed by decantation, the process is continued until the water poured off answers the same test. When it is desired to dry a precipitate, the funnel with filter can be placed on a support over a sand-bath or hot iron plate, or in a drying-oven. If it is to be ignited, it can be placed in a crucible and heated over a lamp, at first slowly, and finally to a red heat. The ash of the filter must be allowed for, of course, if the ignited precipitate is to be weighed. The First Group.-We have no group reagent for the alkali metals, but special tests enable us to recognize them without difficulty. Any salts of ammonium, when heated in a dry test-tube, will volatilize, condensing again, in most cases, upon the cooler portion of the tube. When, in concentrated solution, in the presence of a little free hydrochloric acid, platinic chloride is added, a yellow crystalline precipitate is formed of the composition (NH),PtCl. This double chloride is insoluble in alcohol; it resembles that of potassium and platinum, but can be distinguished by the fact that upon ignition it leaves only spongy platinum. On warming ammonium salts with potassium hydrate or lime-water, ammonia gas is liberated, and is at once recognized by its pungent odor. The most delicate test for ammonium salts is their action with Nessler's solution (a potassium hydrate solution of potassio-mercuric iodide). This reagent produces in dilute solutions a yellowish coloration, and in concentrated solutions a reddish-brown precipitate. Potassium salts require an intense heat for volatilization. Their concentrated solutions, in the presence of a little free acid, yield with platinic chloride a double salt, K,PtCl,, analogous to that of ammonium and resembling it. This salt is somewhat soluble in water, but insoluble in alcohol. ignition it leaves metallic platinum and potassium chloride. A ready test for potassium compounds is to dip a clean platinum wire into the solution, and then to hold it in the flame of a Bunsen burner, when we have a violet-colored flame. Sodium salts obscure the violet of the potassium; but if a piece of blue glass or a prism filled with an indigo solution be held between the eye and the flame, the yellow of the sodium flame is absorbed, and the violet color due to potassium becomes visible. The intense yellow color imparted to flame by sodium compounds is the best means of identifying sodium. When to a solution of sodium chloride On platinic chloride is added and the solution allowed to evaporate, a double chloride, Na,PtCl, results, which separates in aurora-red needles. This color and its solubility in water and alcohol distinguish it from the corresponding potassium and ammonium salts. Potassium pyroantimoniate (K,H,Sb,O,), in concentrated neutral solutions of sodium salts, throws down a crystalline white precipitate of Na,H,Sb,O,. The double chloride of platinum and lithium, like that of sodium, is soluble. In concentrated lithium solutions sodium carbonate produces, after some time, a white granular precipitate of lithium carbonate. With hydro-sodium phosphate, HNA,PO, no precipitate is obtained in the cold; but when the liquid is boiled, there separates a white crystalline compound, lithium phosphate, soluble in hydrochloric acid, but not reprecipitated from a cold solution on the addition of ammonium hydrate. Lithium salts give to the colorless gas or alcoholic flame a rich carmine color. sulphide. The fixed alkalies, as KOH, precipitate from manganese solutions white manganous hydrate, Mn(OH)2, rapidly turning brown, owing to oxidation. With zinc the hydrate is white in color and readily soluble in an excess of the reagent; with nickel the hydrate is apple-green; with cobalt is formed a blue basic hydrate which changes on boiling to a pink. Both nickel and cobalt hydrates are insoluble in excess of the reagent. The fixed alkaline carbonates precipitate the entire group; ammonium hydrate and carbonate only precipitate manganese completely. With the group reagent, ammonium sulphide, manganese yields a fleshcolored sulphide soluble in acetic and the mineral acids; while nickel and cobalt furnish black sulphides insoluble in the dilute mineral acids, but soluble in concentrated nitric acid or aqua regia. Of these four sulphides, nickel is the only one appreciably soluble in the group reagent. Its solubility is shown by the dark color of the supernatant liquid. Concentrating the solution and adding acetic acid will cause it to separate out. With a bead or globule of fused borax three of the four elements in this group give characteristic color-manganese, an amethyst color; nickel, a reddish-brown; and cobalt, a deep blue. Manganese compounds, also, when heated on platinum foil with sodium carbonate and nitrate. yield a bright-green mass of manganate of soda. The different effect of potassium cyanide upon nickel and cobalt solutions gives us a means of separating these elements. Potassium cyanide precipitates from nickel a dirty-green cyanide of nickel, which dissolves in excess of cyanide of potassium. From this solution the nickel may be precipitated as cyanide by careful neutralization with hydrochloric acid or as hydrated sesquioxide on addition of a hypochlorite. Boiling does not alter the double nickel salt. From cobalt solutions potassium cyanide precipitates a chocolate-colored cyanide also soluble in excess. But by boiling the solution the potassio-cobaltous cyanide is oxidized to potassio-cobaltic cyanide, which is no longer precipitable. From cobalt solutions nitrite of potash precipitates, in the presence of acetic acid, a yellow crystalline precipitate of double nitrite of cobalt and potash, while nickel gives no such result. If the four elements of this group be precipitated together as sulphides, this mixture, after washing, is to be treated with warm dilute HCl, which will dissolve MnS and ZnS, but leave CoS and NiS. On adding excess of sodium hydrate to the solution containing manganese and zinc the former only is precipitated, the latter remaining in solution. The mixture of insoluble NiS and CoS is dissolved in concentrated HNO3 evaporated to dryness and the two elements separated by the nitrite-of-potash method given The Second Group is known as the group of the alkaline earths; its reagent is ammonium carbonate. Magnesium may be considered as a separate section of this group, being distinguished from the other members by the insolubility of its hydrate, the ready solubility of its sulphate, and the non-precipitation of its carbonate, in the presence of ammoniacal salts. Again, the alkaline hydrates have no effect upon barium, strontium, or calcium salts, but precipitate magnesium hydrate from the solutions of that metal. Sulphuric acid or soluble sulphates precipitate barium readily, strontium more slowly, and calcium only in concentrated solutions or upon addition of alcohol. The three sulphates are all white in color, and differ chiefly in relative solubility. The best precipitant for calcium is ammonium oxalate. Both bichromate and neutral chromate of potassium precipitate barium chromate, insoluble in acetic acid, but do not precipitate strontium chromate from either acid or neutral solutions. All the carbonates are white and soluble in dilute acids; the sulphates of strontium and calcium are soluble in dilute acids, but that of barium is not. Barium salts impart a yellowish-green color to flame, calcium salts an orangered, and strontium salts a crimson color. Magnesium solutions, in the presence of ammoniacal salts, are precipitated on the addition of hydro-sodium phosphate, yielding a white crystalline precipitate of MgNH,PO, When this is ignited, it loses water and ammonia and leaves Mg,P,O,, pyrophosphate of magnesia. From solutions of magnesium free from ammoniacal salts a concentrated solution of ammonium carbonate will, after standing some time, precipitate a double carbonate, (NH)2CO3. MgCO3. This furnishes a means of separating magnesium from the alkalies. Or if the mag-above. nesium solution be free from ammonium salts, it can The Fourth Group includes aluminium, chromium, be boiled with barium hydrate, and magnesium hydrate and iron, and has for its reagent ammonium hydrate, will be precipitated. The excess of barium hydrate can NH.OH. This reagent precipitates them as hydrates, then be removed by adding dilute sulphuric acid, and that of aluminium being white and gelatinous, only the filtrate from the barium sulphate which separates slightly soluble in excess of precipitate; that of chrowill contain only the alkalies. The following method mium, bluish-green, soluble in excess of ammonium is used in separating the members of this group when hydrate. With iron in the ferric condition is gotten a together in solution: First add some NHCl, and then reddish-brown precipitate insoluble in excess of the amthe group reagent, (NH),CO,. A precipitate forms, monium hydrate. Ferrous solutions, if pure, yield a which is filtered, and to the filtrate add HNa,PO,, when, white precipitate of ferrous hydrate, but this very if magnesium be present, a precipitate of MgNH,PO, speedily oxidizes and becomes dirty-green or brown in is obtained. Dissolve the original carbonate precipi- color. The fixed alkalies precipitate the entire group, tate in dilute HCl, evaporate the solution to dryness, the hydrates of aluminium and chromium dissolving in and treat the dry residue with alcohol. If insoluble in excess of the reagent, Boiling will, however, cause the alcohol, dissolve in water, adding H,SO,, when, if reprecipitation of the chromium hydrate. The alkabarium be present, insoluble BaSO, will be found; but line carbonates behave like their hydrates except in the if soluble, boil off the alcohol, add ammonium carbon-case of ferrous salts, where white ferrous carbonate is ate, filter, and dissolve the precipitate in HNO3. Evaporate to dryness, and treat the dry residue with alcohol. If soluble, expel the alcohol, add ammonium oxalate, and calcium oxalate will be precipitated; but if insoluble, test in the Bunsen flame, when the intense red color will prove the presence of strontium. The Third Group includes manganese, zinc, nickel, and cobalt, and has as a group reagent ammonium precipitated. The group reagent of the preceding group, (NH)2S, precipitates aluminium and chromium as hydrates, and iron as black ferrous sulphide, FeS. The blow-pipe tests are among the most characteristic_with the metals of this group. Aluminium compounds heated upon charcoal, and then moistened with cobaltous nitrate and reheated, show a blue color. Chromium compounds impart a beautiful emerald-green color to way be distinguished from the deposit of metallic ar- the borax glass, and, fused with sodium carbonate and It should be said that ammonium hydrate, in addition to the hydrates of this group, precipitates the phosphates of this group and the phosphates, oxalates, borates, and fluorides of the alkaline earths. The Fifth Group, consisting of tin, arsenic, antimony, gold, and platinum, yield insoluble sulphides when treated with hydrogen sulphide in acid solution. It is true that the succeeding, or sixth, group show the same behavior, but from the latter the fifth group is distinguished by the solubility of its sulphides in ammonium or potassium sulphides or the fixed alkaline hydrates. Tin, the first element of the group, may exist in either the stannous or the stannic state. Stannous salts form purple of Cassius with chloride of gold, reduce mercuric salts to mercurous, and ultimately separate fine gray metallic mercury, form a brownish-black sulphide, not very soluble in alkaline hydrates, but easily in alkaline sulphides, with which it forms double sulphides. From this solution, however, dilute acids precipitate yellow stannic sulphide. Any tin compound heated on charcoal together with sodium carbonate and some potassium cyanide is reduced to the metallic condition. Antimony is characterized by the following tests: On adding water to the acid solution of its chloride, a white precipitate of oxychloride forms, soluble in tartaric acid. The group reagent precipitates orangeyellow antimony trisulphide. Antimony compounds, placed in an apparatus in which hydrogen is being generated, yield stibine, H,Sb. If this gas be conducted through a glass tube, narrowed at intervals, and heat be applied to the tube near the narrowed portions, mirror-like deposits of metallic antimony will be formed; the escaping gas, when ignited, burns, and on holding a cold object in the flame a black spot of metallic antimony deposits. This metallic deposit is not soluble in sodium hypochlorite (chlorinated soda), and can in this Platinum is recognized by the yellow precipitate gotten in hydrochloric acid solution with potassium or ammonium chlorides. The precipitate in the latter case, when ignited, leaves spongy platinum as the only residue. Gold salts in solution are precipitated on the addition of ferrous sulphate. Stannous chloride containing some stannic salt produces a purple precipitate (purple of Cassius) even in dilute gold solutions. The group precipitate, consisting usually of stannic filtrate from the antimoniate is boiled, to expel alcohol. The Sixth Group includes mercury, silver, lead, cop- Silver with NaOH precipitates brown oxide; with ammonium hydrate, the same precipitate, soluble in excess of the reagent. Hydrogen sulphide forms black silver sulphide insoluble in dilute acids; hydrochloric acid or chlorides form a white curdy precipitate (AgCl) soluble in ammonium hydrate. Silver compounds heated with sodium carbonate on charcoal before the blowpipe are reduced to metal yielding a white ductile globule. Lead salts with NaOH yield a white hydrate soluble in excess of reagent. Sodium carbonate precipitates a basic carbonate. Hydrochloric acid and chlorides throw down a white curdy precipitate of lead chloride soluble in large quantity of water when heated. HS precipitates black-lead sulphide soluble in warm nitric acid. Sulphuric acid produces a white precipitate of lead sulphate readily soluble in a solution of ammonium acetate. Lead compounds heated on charcoal with sodium carbonate yield soft malleable globules of metal, the charcoal at the same time receiving a slight yellow incrustation of lead oxide. The salts of mercury must be distinguished as mer curous or mercuric. Mercurous salts with sodium hydrate yield black mercurous oxide, while with ammonium hydrate a black mercur-ammonium compound is produced. With H&S a black sulphide is at once produced, insoluble in nitric acid; with potassium iodide a green iodide is formed; with hydrochloric acid a white curdy precipitate of mercurous chloride (calomel) is formed. Mercuric salts with sodium hydrate yield a reddish-brown precipitate, which becomes yellow if the reagent is added in excess; with ammonium hydrate a white mercur-ammonium compound (white precipitate) is formed. HS produces a precipitate turning from white to yellowish, brownish, and with excess of the reagent to black, color. Stannous chloride reduces the mercuric to mercurous salt and then precipitates calomel, an excess of the reagent reducing the latter to metallic mercury. Potassium iodide added to mercuric solutions produces a precipitate of scarlet mercuric iodide. Mercury compounds in general, when heated with sodium carbonate in a narrow glass tube, give a sublimate of metallic mercury. A piece of clean copper immersed in a mercury-salt solution becomes coated with gray mercury, which, rubbed, yields a bright amalgam surface. Bismuth solutions yield with alkaline hydrates a white hydrate insoluble in excess, and with sodium carbonate a basic carbonate. A characteristic reaction for bismuth is the decomposition of its salts by water; this is most sensitive with the chloride, which, poured into water, yields a white precipitate of oxychloride of bismuth. This oxychloride, unlike that of antimony, is not soluble in tartaric acid. Hydrogen sulphide precipitates black sulphide of bismuth. Before the blowpipe bismuth compounds mixed with sodium carbonate yield brittle reddish-white globules of metal. The incrustation of oxide is orange while hot and yellow when cold. Copper salts yield a bluish hydrate with potassium hydrate, turning black on boiling; ammonium hydrate gives a greenish-blue precipitate soluble in excess of the reagent with azure-blue color. Hydrogen sulphide gives a brownish black precipitate of sulphide soluble in warm nitric acid. A piece of bright metallic iron immersed in copper solutions is rapidly coated with red copper. Copper compounds heated on charcoal with sodium carbonate yield a button of metallic copper. Borax glass is colored by copper compounds, when heated in the oxidizing flame, green while hot, blue when cold. Cadmium salts are precipitated white by sodium or ammonium hydrates; the precipitate in the first case is not soluble, but in the second case is soluble in excess. Hydrogen sulphide precipitates a yellow sulphide soluble in warm nitric acid and in boiling HCl and H,SO,, thus distinguishing it from copper. When cadmium compounds are heated with sodium carbonate on charcoal, the latter becomes covered with reddish-brown cadmium oxide. Acids do not admit of the same exact classification as bases, as there are no general group-reagents which serve to distinguish them with much accuracy. For individual tests the reader must consult the manuals of analysis. GAS ANALYSIS.-In the analysis of gaseous mixtures volumes only can be determined, as the weights of the gases concerned are relatively small, and the experimental difficulties connected with the weighing would be so great as almost certainly to vitiate the results. In measuring the volumes, on the other hand, after allowing for the change in volume due to the varying conditions of temperature and pressure, the measurements can be made with reasonable accuracy. No uniform course of procedure can be laid down for all cases of gas analysis, as the mixtures that arise in practice are of very different character, and the procedure must be based largely upon the physical and chemical properties of the gases concerned. Thus we have to deal with quite a complex mixture in illuminating gas, where hydrogen, carbonous oxide, numerous hydrocarbons, and free nitrogen are all to be determined; with a much simpler mixture of some of these constituents in the Vol. II.--D either by absorption, with the aid of some reagent introduced into the tube containing the gaseous mixture, or by what is termed "combustion," which may be a slow chemical combination of the combustible gas with oxygen or air, or an instantaneous one brought about by the aid of an electric spark caused to flash through the tube containing the gas. We shall mention briefly the methods most generally practised, and show how they are applied to the case of the most commonlyoccurring mixtures. The first carefully-elaborated method, and one still in many respects the most perfect, is that of Bunsen, in which the gases are measured in closed tubes over mercury, the absorption reagents are as far as possible used in the solid form, and the combination of the combustible gas with oxygen effected by the passage of the electric spark between platinum wires fused in the upper end of the tubes. Observations of the thermometer and barometer are made with each reading of gaseous volume, in order to apply to the reading of volume the corrections for varying temperature and pressure. These reading are all made through a telescope, called a cathetometer," placed on the opposite side of the room, so that the heat of the body may not affect the confined gas or gases, as it would if the observer came sufficiently close to make the reading with the unaided eye. Fig. 1 shows the arrangement of the apparatus 50 spectively, and allowing for the tension of aqueous in the case of an analysis by Bunsen's method; m is The method of analysis of a gaseous mixture may now ents is complete so far as reagents can effect it, and the |