(63.) LIQUID OR DISSOLVED SUBSTANCES.

A few drops of the liquid are evaporated on a glass slip, and the residue, if any, examined microscopically. Should there be an appreciable solid residue, a further quantity of liquid may be evaporated down in a capsule, the vapour examined for its odour and reaction, and the residue submitted to ignition, &c., as described in pars. 25 and 26.

The reaction of the liquid to test-paper is next ascertained. Among volatile liquids, water, alcohol, and ether are neutral; ammonia, alkaline; and the sulphuric, nitric, hydrochloric, and acetic acids, strongly acid. These several liquids are readily distinguishable from one another by a few simple tests.

Solutions which leave a saline residue on evaporation, and are perfectly neutral, will most probably prove to contain some salt of an alkali- or alkaline earth- metal; salts of the heavy metals, with a few exceptions only, exhibiting a more or less marked acidity.

Solutions which have an alkaline reaction, known by their turning rose paper green, turmeric paper brown, or reddened litmus paper blue, may contain the hydrate or sulphydrate of an alkaline earth-metal; or the hydrate, sulphydrate, carbonate, phosphate, borate, or silicate of an alkali metal, or some heavy metal dissolved in excess of alkaline hydrate or carbonate (vide par. 64).

Solutions which have an acid reaction, known by their reddening blue litmus paper, may contain a free acid, an acid salt, or the normal salt of a heavy metal, in which last case the addition of even a drop of potash will most probably cause a precipitate.

After the above preliminary examination, the solution may be tested according to the directions of Tables I., II., III., and V. ; or, in some cases, the evaporated residue may be dissolved in water or acid, and the solution so formed be employed by preference. The original solvent, if suspected to be other than water, may be distilled off, condensed in a receiver, and separately examined.

(64.) ALKALINE SOLUTIONS OF HEAVY METALS.

The hydrates of barium, strontium, and calcium, like those of the alkali metals, are soluble in water. The hydrates of all other metals are insoluble, and consequently, precipitable by caustic alkalies. The hydrates of lead, chromium, aluminum, and zinc, are readily soluble in excess of potash or soda; those of silver, copper, cadmium, nickel, cobalt, manganese, zinc, and magnesium readily, and those of chromium and iron (ferrous salts) sparingly soluble in excess of ammonia, especially in presence of neutral ammoniacal salts; while those of bismuth, mercury, and iron (ferric salts), are insoluble in excess of either reagent. On boiling alkaline solutions of chromium, the whole of the chromic hydrate is reprecipitated.

The hydrates of the metals tin, antimony, and arsenic, whose sulphides are soluble in sulphide of ammonium, have no practical interest in analysis. The teroxide of arsenic is slightly soluble in water, and freely soluble in ail alkaline liquids. The hydrate of antimony and both hydrates of tin are soluble in excess of potash, while stannic hydrate is soluble also in excess of ammonia. The potash solution of stannous hydrate is decomposed on boiling into metallic tin, which is deposited as a black powder, and stannate of potassium which remains dissolved.

The precipitates produced by carbonate of ammonium in solutions of silver, copper, nickel, cobalt, zinc, and magnesium, are - readily soluble in excess of the reagent, especially when chloride of ammonium is also present, while those of iron (ferrous salts) and chrome are sparingly soluble. The precipitates produced in solutions of cadmium and manganese are insoluble in excess, as are also all those produced in solutions of metals whose hydrates are insoluble in ammonia. The precipitates produced by fixed alkaline carbonates are all insoluble in excess, except that produced in stannic salts, which dissolves in excess of the precipitant, and is again thrown down on ebullition.

:.

§ VIII.-INDIVIDUAL BASES OF GROUP I.

The reactions of the individual bases of this group may be conveniently realised by operating with the following substances:

TIN . . The crystallised proto-chloride and precipitated peroxide.
ARSENIC The white oxide.

ANTIMONY. The native tersulphide and tartar-emetic.

BISMUTH. The crystallised nitrate and precipitated oxide.

MERCURY. Corrosive sublimate, the red mercuric oxide, and the crystallised mercurous nitrate.

LEAD. The oxide, carbonate, nitrate, and acetate.

SILVER. The nitrate and oxide.

COPPER The sulphate and oxide.

CADMIUM. The sulphate and carbonate.

(65.) TIN.

Tin salts are of two kinds, stannous or protosalts, represented by protochloride of tin SnCl,, and stannic or persalts, represented by perchloride of tin SnCl.

a. When compounds of tin are heated upon charcoal with a mixture of carbonate of sodium and cyanide of potassium, a globule of white malleable metal is produced with very slight, if any, incrustation. If this globule be hammered out, and dissolved in hydrochloric acid, the tests for stannous salts can be applied to the solution so formed.

STANNOUS SALTS.

a. Sulphydric acid produces a brown precipitate of protosulphide of tin SnS, which dissolves in yellow sulphide of ammonium with conversion into persulphide of tin SnS2, so that on adding an acid to the solution, a yellow and not a brown precipitate is separated. The protosulphide of tin first thrown down is converted by boiling nitric acid into a white insoluble powder consisting of stannic anhydride SnO.

B. Solution of corrosive sublimate, added carefully to stannous solutions, produces a white precipitate of calomel HgCl, which speedily becomes grey, and finally black, from its reduction to the state of metallic mercury.

STANNIC SALTS.

a. Sulphydric acid produces a yellow precipitate of disulphide of tin SnS2, which is insoluble in the carbonate, but soluble in the hydrate and sulphide of ammonium, and reprecipitable therefrom on the addition of an acid. It is likewise soluble in boiling hydrochloric acid, more readily on the addition of a little nitric acid also, and is converted by concentrated nitric acid into a white insoluble powder of stannic anhydride SnO2.

(66.) ARSENIC.

Arsenious acid is convertible into arsenic acid by boiling it with concentrated nitric acid, to which a little hydrochloric acid may be added with advantage. But in order to apply the various tests successfully, the acid liquid must be evaporated to dryness, and the residue dissolved in water. Arsenic acid is readily convertible into arsenious acid by the passage of sulphurous acid gas through its solution, or by heating it with sulphite of sodium and dilute hydrochloric acid.

a. Sulphydric acid produces, in acidulated solutions of arsenious acid, or of arsenic acid after the addition of sulphurous acid, a yellow precipitate of trisulphide of arsenic As2S, which is soluble in carbonate, hydrate, and sulphide of ammonium, and reprecipitated on the addition of an acid. It is insoluble in boiling hydrochloric acid, but is readily dissolved by hot nitric or nitro-hydrochloric acid.

B. Nitrate of silver produces in neutral or slightly ammoniacal solutions of arsenious acid a yellow precipitate of arsenite of silver Ag ̧AsO, and from similar solutions of arsenic acid a brick-dust red precipitate of arseniate of silver Ag,AsO,. Both precipitates are soluble in excess of either ammonia or nitric acid.

y. Sulphate of copper produces, in neutral or very faintly ammoniacal solutions of arsenious acid a grass-green precipitate of arsenite of copper HCu"AsO,, and in similar solutions of arsenic acid a pale blue precipitate of arseniate of copper Cu"3(AsO4)2• Both precipitates are soluble in excess of either ammonia or nitric or hydrochloric acid.

. When a compound of arsenic is mixed with soda-flux, and heated in a subliming tube, a steel-grey ring of reduced metal condenses in the upper or cool part of the tube.

(67.) ANTIMONY.

a. Sulphydric acid produces an orange-coloured precipitate of trisulphide of antimony Sb,S,, which is insoluble in carbonate, but soluble in hydrate and sulphide of ammonium, and reprecipitable on the addition of an acid. It is also dissolved by hydrochloric acid with the aid of heat, and is converted almost entirely by strong nitric acid into a white insoluble powder, consisting of tetroxide of antimony Sb204.

B. Water, added to certain antimony solutions (not to all), produces a white precipitate of a basic salt of antimony, soluble in excess of tartaric, hydrochloric, or nitric acid.

7. Antimony compounds, when fused with carbonate of sodium on charcoal in the reducing flame, yield a bead of brittle metal with an abundant bluish-white incrustation. If the heat be prolonged, the metal volatilises entirely with the production of white fumes of teroxide of antimony Sb,O,.

(68.) BISMUTH.

a. Sulphydric acid produces a brownish-black precipitate of trisulphide of bismuth Bi,S,, which is insoluble in sulphide of ammonium. It dissolves readily in hot nitro-muriatic, nitric, or hydrochloric acid.

B. Caustic alkalies give a white precipitate of hydrate of