α.

(71.) SILVER.

Sulphydric acid gives a black precipitate of sulphide of silver Ag2S, insoluble in sulphide of ammonium, soluble in warm nitric acid, and converted by ebullition with hydrochloric acid into a white deposit of chloride of silver AgCl.

B. Caustic alkalies give a brown precipitate of hydrate of silver Ag2O.H,O, which is insoluble in excess of potash, but soluble in ammonia, forming a colorless solution.

7. Hydrochloric acid gives in solutions of silver salts a white precipitate of chloride of silver AgCl, which is insoluble even in boiling nitric acid, but readily soluble in ammonia. The color of the precipitate changes to a slate-purple by exposure to light.

8. Silver compounds, when fused with carbonate of sodium upon a charcoal support in the reducing blowpipe flame, yield a button of hard white malleable metal, without any incrustation being formed on the charcoal.

α.

(72.) COPPER.

Sulphydric acid produces a dark-brown precipitate of sulphide of copper CuS, which is insoluble in sulphide of potassium, and but sparingly soluble in sulphide of ammonium. It dissolves readily in nitric but not in hydrochloric acid, save by an application of heat.

B. Potash gives a pale blue precipitate of hydrate of copper CuO.H2O, which is insoluble in excess, and converted by ebullition into black oxide of copper CuO. Ammonia gives a similar blue precipitate of hydrate of copper, which is soluble in excess of the reagent, forming a deep blue solution, the transparency of which is not affected by the addition of a moderate quantity of potash. The pale blue precipitate pro

duced by carbonate of ammonium is also readily soluble in excess of the reagent, with production of a deep blue liquid.

7. Ferrocyanide of potassium gives a chocolate-colored precipitate of ferrocyanide of copper Cu,FeСy, which is decomposed by caustic potash, and is then freely soluble in ammonia, forming a deep blue liquid.

s. A piece of clean iron or steel dipped into an acidulated copper solution becomes coated with metallic copper, which may be dissolved off by the conjoint action of ammonia and air into a deep blue liquid.

. The borax bead heated with a particle of any copper-compound becomes blue or green in the oxidizing, and nearly colorless or reddish-gray in the reducing, flame.

(73.) CADMIUM.

a. The precipitate of sulphide of cadmium CdS, produced by sulphydric acid, is of a bright yellow color, and insoluble in sulphide of ammonium. It disappears readily on the addition of nitric or hydrochloric acid, and does not form in very acid solutions.

B. Caustic alkalies give a white precipitate of hydrate of cadmium CdO.H,O, soluble in excess of ammonia, but not in that of potash. The precipitate produced by carbonate of ammonium does not disappear in excess of the reagent.

2. Cadmium compounds, fused with carbonate of sodium in the reducing blowpipe flame, give a reddish-brown incrustation of oxide of cadmium CdO, but no bead of metal.

? IX.-INDIVIDUAL BASES OF GROUP II.

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

NICKEL
COBALT

MANGANESE.
IRON.

ZINC

The oxide and sulphate.

The oxide.

The sulphate, chloride, and carbonate.

The red and black oxides, the sulphate and sulphide.
The oxide and sulphate.

CHROMIUM The precipitated oxide and chrome alum.
ALUMINUM The hydrate and sulphate.

(74.) NICKEL.

Solutions of nickel are generally of a green color.

a. Sulphide of ammonium gives with nickel salts a black precipitate of sulphide of nickel NiS, not soluble in hydrochloric acid until after the addition of a drop or two of nitric acid.

ß. Ammonia gives a slight greenish precipitate of hydrate of nickel NiO.H,O, soluble in excess of the reagent, forming a violet-blue liquid, from which potash reprecipitates the green hydrate. Moreover, potash throws down this hydrate readily from all ordinary nickel solutions.

7. In the reducing flame, nickel renders the borax bead purplish-gray and turbid, and in the oxidizing flame of a dark sherry color with a tinge of violet. If a fragment of nitre be added, and the bead again heated in the oxidizing flame, a well-marked purple color is produced.

(75.) COBALT.

Cobalt solutions are pink when dilute, blue when concentrated.

a. Sulphide of ammonium gives with cobalt salts a black precipitate of sulphide of cobalt CoS, not soluble in hydrochloric acid until after the addition of a few drops of nitric acid.

B. Potash gives a blue precipitate of prothydrate of cobalt CO.H,O, insoluble in excess of the precipitant. Excess of ammonia, especially in presence of chloride of ammonium, produces a brownish-pink solution,

becoming brown and opaque on exposure to air, from the deposition of the insoluble sesquihydrate.

7. Cobalt compounds impart to the borax bead, when heated in either flame of the blowpipe, a deep sapphire-blue color.

(76.) MANGANESE.

Manganese solutions are of a faint pink tinge, or altogether colorless.

a.

Sulphide of ammonium gives a buff-colored precipitate of sulphide of manganese MnS, soluble even in acetic acid.

B. Potash gives a white precipitate of prothydrate of manganese MnO.H2O, speedily becoming brown on exposure, from its conversion into the sesquihydrate Mn,O,.H2O. If to the solution of a manganous salt containing chloride of ammonium, an excess of ammonia be added at once, a clear colorless solution will be produced, quicky becoming brown and opaque when exposed to the air, from a conversion of the soluble proto- into the insoluble sesqui-compound.

The borax bead with manganese is amethyst-red in the oxidizing, and nearly colorless in the reducing, flame. Its appearance is much interfered with by the presence of a trace of iron.

8. Compounds of manganese, fused upon platinum foil with carbonate of sodium in the oxidizing flame of the blowpipe, either with or without the addition of a little nitre, yield a bluish-green fusible mass of manganate of sodium Na,MnO, For this experiment but a very small quantity of the manganese compound should be employed.

(77.) IRON.

There are two classes of iron salts, namely, ferrous or protosalts, represented by green vitriol FeSO and ferric or persalts, represented by sesquichloride

of iron FeCl, or Fe,Cl. The protosalts are rarely ever free from some admixture with persalts.

a. Sulphide of ammonium gives a black precipitate of protosulphide of iron FeS, readily soluble in hydrochloric acid. The precipitate, when thrown down from ferric salts, is accompanied by free sulphur.

B. Iron compounds dissolve in the borax bead, forming a glass which is of a bottle-green color in the reducing, and of a yellowish-brown color in the oxidizing, flame. Ferrous compounds give the green, and ferric compounds the yellow, color most readily.

FERROUS SALTS.

Ferrous solutions are generally colorless, or of a pale green tint.

a.

Caustic alkalies give a dingy green precipitate of ferrous hydrate FeO.H,O, which becomes red on exposure to air. The pure, nearly white prothydrate is sparingly soluble in excess of ammonia and chloride of ammonium.

B. Ferrocyanide of potassium gives a pale blue precipitate of double ferrocyanide of iron and potassium K,Fe,Cy, which becomes dark blue on exposure

to air.

7. Ferrideyanide of potassium gives a dark-blue precipitate of ferrideyanide of iron Fe,Cy12, or Fe", Fe,""Cy, insoluble in dilute acids and decomposable by caustic alkalies.

FERRIC SALTS.

Ferric solutions are generally of a yellow, brown, or red color.

a. Caustic and carbonated alkalies alike give a brickdust red precipitate of ferric hydrate Fe,O,.H2O, accompanied in the case of the carbonates by an evolu