creasing admixture of black sulphide causes the precipitate to pass through the several gradations of color above mentioned. Sulphide of mercury is not dissolved by sulphide of ammonium, nor by potassa or cyanide of potassium; it is altogether insoluble in hydrochloric acid and in nitric acid, even upon boiling. It dissolves completely in sulphide of potassium, and is readily decomposed and dissolved by nitrohydrochloric acid.

4. Potassa, added in small quantity, produces in neutral or slightly acid solutions of oxide of mercury a reddish-brown precipitate, which acquires a yellow tint if the reagent is added in excess. The reddishbrown precipitate is a BASIC SALT; the yellow precipitate consists of OXIDE OF MERCURY. An excess of the precipitant does not redissolve these precipitates. In very acid solutions this reaction does not take place at all, or at least the precipitation is very incomplete. In presence of salts of ammonia, potassa produces in solutions of salts of oxide of mercury, instead of reddish-brown or yellow, white precipitates. The precipitate thrown down by potassa from a solution of chloride of mercury containing an excess of chloride of ammonium is of analogous composition to the precipitate produced by ammonia (see 5).

5. Ammonia produces in solutions of salts of oxide of mercury white precipitates quite analogous to those produced by potassa in presence of chloride of ammonium; thus, for instance, ammonia precipitates from solutions of chloride of mercury a double compound of chloride of mercury and amide of mercury (Hg Cl + Hg N H2).

6. Protochloride of tin, added in small quantity to salts of oxide of mercury, reduces the oxide to suboxide, thus giving rise to the formation of a white precipitate of SUBCHLORIDE OF MERCURY (Hg, Cl); but if added in excess, this reagent deprives the mercury completely of the oxygen and acid, or of the salt-radical, and throws it down in the metallic state, the same as in the case of the suboxide of mercury. cipitate, which was white at first, acquires therefore now a gray tint, and may be readily united into globules of metallic mercury by boiling with hydrochloric acid.

The pre

7. The salts of oxide of mercury present the same deportment as the salts of the suboxide, both with metallic copper and when heated together with carbonate of soda in a glass tube before the blowpipe.

§ 119.

b. OXIDE OF COPPER (Cu O).

1. Metallic copper has a peculiar red color, and a strong lustre; it is moderately hard, malleable, ductile, rather difficultly fusible; in contact with water and air it becomes covered, with a green crust of basic carbonate of oxide of copper; upon ignition in the air it becomes coated over with black oxide. In hydrochloric acid and dilute sulphuric acid it is insoluble or nearly so, even upon boiling. Nitric acid dissolves the metal readily. Concentrated sulphuric acid converts it into sulphate of oxide of copper, with evolution of sulphurous acid.

2. Suboxide of copper is red, its hydrate yellow; both change to oxide upon ignition in the air. On treating the suboxide with dilute sulphuric acid, metallic copper separates, whilst sulphate of oxide of copper dissolves; on treating suboxide of copper with hydrochloric acid,

white subchloride of copper is formed, which dissolves in an excess of the acid, but is reprecipitated from this solution by water.

3. Oxide of copper is a black, fixed powder; its hydrate (Cu O, HO) is of a light blue color. Both the oxide of copper and its hydrate dissolve readily in hydrochloric, sulphuric, and nitric acids.

4. Most of the neutral salts of oxide of copper are soluble in water; the soluble salts redden litmus, and suffer decomposition when heated to gentle redness, with the exception of the sulphate, which can bear a somewhat higher temperature. They are usually white in the anhydrous state; the hydrated salts are usually of a blue, or green color, which their solutions continue to exhibit even when much diluted.

5. Hydrosulphuric acid and sulphide of ammonium produce in alkaline, neutral, and acid solutions of salts of oxide of copper, brownishblack precipitates of SULPHIDE OF COPPER (Cu S). This sulphide is insoluble in dilute acids and caustic alkalies. Hot solutions of sulphide of potassium and sulphide of sodium fail also to dissolve it or dissolve it only to a very trifling extent; but it is a little more soluble in sulphide of ammonium. The latter reagent is therefore not adapted to effect the perfect separation of sulphide of copper from other metallic sulphides. Sulphide of copper is readily decomposed and dissolved by boiling concentrated nitric acid; it dissolves completely in solution of cyanide of potassium. In solutions of salts of copper which contain an excess of a concentrated mineral acid, hydrosulphuric acid produces a precipitate only after the addition of water.

6. Potassa or soda produces in solutions of salts of oxide of copper a light blue, bulky precipitate of HYDRATE OF OXIDE OF COPPER (Cu O, HO). If the solution is highly concentrated, and the potassa added in excess, the precipitate turns black after the lapse of some time, and loses its bulkiness, even in the cold; but the change takes place immediately if the precipitate is boiled with the fluid in which it is suspended (and which must, if necessary, be diluted for the purpose). In this process the (Cu O, H 0) hydrated oxide is converted into the (3 Cu O, H 0) hydrated oxide.

7. Carbonate of soda produces in solutions of salts of oxide of copper a greenish-blue precipitate of HYDRATED BASIC CARBONATE OF COPPER (Cu O, CO, + CuO, HO), which upon boiling changes to brownish-black oxide of copper, and dissolves in ammonia to an azure-blue, and in cyanide of potassium to a brownish fluid.

COPPER.

8. Ammonia added in small quantity to solutions of salts of oxide of copper produces a greenish-blue precipitate, consisting of a BASIC SALT OF This precipitate redissolves readily upon further addition of ammonia, giving a perfectly clear solution of a magnificent azure-blue, which owes its color to the formation of a BASIC DOUBLE SALT OF AMMONIOOXIDE OF COPPER. Thus, for instance, in a solution of sulphate of oxide of copper, ammonia produces a precipitate of N H,, Cu O+ N H, O, S 03. The blue color ceases to be perceptible only in very dilute solutions. Potassa produces in such blue solutions in the cold, after the lapse of some time, a precipitate of blue hydrate of oxide of copper; but upon boiling the fluid this reagent precipitates the whole of the copper as black oxide. Carbonate of ammonia presents the same deportment with salts of copper as pure ammonia.

4

9. Ferrocyanide of potassium produces even in moderately dilute solutions a reddish-brown precipitate of FERROCYANIDE OF COPPER (Cu,, Cfy)

which is insoluble in dilute acids, but suffers decomposition when acted upon by potassa. In very highly dilute solutions the reagent produces only a reddish coloration of the fluid.

10. Metallic iron when brought into contact with concentrated solutions of salts of copper is almost immediately covered with a COPPERY-RED COATING OF METALLIC COPPER; very dilute solutions produce this coating only after some time. Presence of a little free acid accelerates the reaction.

If a fluid containing copper and a little free hydrochloric acid is poured into a small platinum dish (the lid of a platinum crucible), and a small piece of zinc is introduced, the bright platinum surface speedily becomes covered with a COATING OF COPPER; even with very dilute solutions this coating is clearly discernible.

11. If a mixture of a compound of copper with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, METALLIC COPPER is obtained, without simultaneous incrustation of the charcoal. The best method of freeing this copper from the particles of charcoal, is to triturate the fused mass in a small mortar with water, and to wash off the charcoal powder; when the coppery-red metallic particles I will be left behind.

12. Copper, its alloys, and other compounds, when exposed to the inner blowpipe flame, impart an EMERALD GREEN tint to the outer flame. Addition of chloride of silver considerably heightens the delicacy of the reaction.

13. Borax and phosphate of soda and ammonia readily dissolve oxide of copper in the outer blowpipe flame. The beads are green while hot, blue when cold. In the inner flame the bead produced with borax appears colorless, that produced with phosphate of soda and ammonia turns dark green; both acquire a brownish-red tint upon cooling.

$120.

c. TEROXIDE OF BISMUTH (Bi 01).

1. Bismuth has a reddish tin-white color and moderate metallic lustre; it is of medium hardness, brittle, readily fusible; when fused upon a charcoal support, it forms a coating of yellow teroxide on the surface of the charcoal. It dissolves readily in nitric acid, but is nearly insoluble in hydrochloric acid, and altogether so in dilute sulphuric acid. Concentrated sulphuric acid converts it into sulphate of teroxide of bismuth, with evolution of sulphurous acid.

2. The teroxide of bismuth is a yellow powder; when heated, it transiently acquires a deeper tint; it fuses at a red heat. Hydrate of teroxide of bismuth is white. Both the teroxide and its hydrate dissolve readily in hydrochloric, sulphuric, and nitric acids.

3. The salts of bismuth are non-volatile, with the exception of a few (terchloride of bismuth). Most of them are decomposed at a red heat. They are colorless; some of them are soluble in water, whilst others are insoluble in this menstruum. The soluble salts, in the neutral state, redden litmus paper, and are decomposed into soluble acid and insoluble basic salts when treated with a large amount of water.

4. Hydrosulphuric acid and sulphide of ammonium produce in neutral and acid solutions of salts of bismuth black precipitates of TERSULPHIDE OF BISMUTH (Bi S ̧), which are insoluble in dilute acids, alkalies, alkaline

sulphides, and cyanide of potassium, but are readily decomposed and dissolved by boiling concentrated nitric acid. In solutions of salts of bismuth which contain a considerable excess of hydrochloric or nitric acid, hydrosulphuric acid produces a precipitate only after the addition of water.

5. Potassa and ammonia throw down from solutions of salts of bismuth HYDRATE OF TEROXIDE OF BISMUTH as a white precipitate, which is insoluble in an excess of the precipitant.

6. Carbonate of soda throws down from solutions of salts of bismuth BASIC CARBONATE OF BISMUTH (Bi O, CO2) as a white bulky precipitate, which is insoluble in an excess of the precipitant, and equally so in cyanide of potassium.

7. Chromate of potassa precipitates from solutions of salts of bismuth CHROMATE OF BISMUTH as a yellow powder. This substance differs from chromate of lead in being soluble in dilute nitric acid and insoluble in potassa.

8. The reaction which characterizes the teroxide of bismuth more particularly, is the decomposition of its neutral salts by water into soluble acid and insoluble basic salts. The addition of a large amount of water to solutions of salts of bismuth causes the immediate formation of a dazzling white precipitate, provided there be not too much free acid present. This reaction is the most sensitive with terchloride of bismuth, as the basic chloride of bismuth (Bi Cl,, 2 Bi 01) is nearly insoluble in water. If water fails to produce a precipitate in nitric acid solutions of bismuth, owing to the presence of too much free acid, the excess of the acid must be removed by evaporation, before the water is added. From the basic salts of antimony which are formed under analogous circumstances, the precipitated basic salts of bismuth may be readily distinguished by their insolubility in tartaric acid.

9. If a mixture of a compound of bismuth with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, brittle GLOBULES OF BISMUTH are obtained, which fly into pieces under the stroke of a hammer. The charcoal becomes covered at the same time with a slight yellow incrustation of TEROXIDE OF BISMUTH.

$121.

d. OXIDE OF CADMIUM (Cd O).

1. Metallic cadmium has a tin-white colour; it is lustrous, not very hard, malleable, ductile; it fuses at a temperature below red heat, and volatilizes at a temperature somewhat above the boiling point of mercury. Heated on charcoal before the blowpipe, it takes fire and burns, emitting brown fumes of oxide of cadmium, which form a coating on the charcoal. Hydrochloric acid and dilute sulphuric acid dissolve it, with evolution of hydrogen; but nitric acid dissolves it most readily.

2. Oxide of cadmium is a yellowish-brown, fixed powder; its hydrate is white. Both the oxide and its hydrate dissolve readily in hydrochloric, nitric, and sulphuric acids.

3. The salts of oxide of cadmium are colorless or white; some of them are soluble in water. The soluble salts, in the neutral state, redden litmus paper, and are decomposed at a red heat.

4. Hydrosulphuric acid and sulphide of ammonium produce in alkaline, neutral, and acid solutions of salts of cadmium, bright yellow precipitates

of SULPHIDE OF CADMIUM (Cd S), which are insoluble in dilute acids, alkalies, alkaline sulphides, and cyanide of potassium. They are readily decomposed and dissolved by boiling concentrated nitric acid. In solutions of salts of cadmium which contain a considerable excess of acid, hydrosulphuric acid produces a precipitate only after dilution with

water.

5. Potassa produces in solutions of salts of cadmium a white precipitate of HYDRATE OF OXIDE OF CADMIUM (Cd O, H O), which is insoluble in an excess of the precipitant.

6. Ammonia likewise precipitates from solutions of salts of cadmium white HYDRATE OF OXIDE OF CADMIUM, which, however, redissolves readily to a colorless fluid in an excess of the precipitant.

7. Carbonate of potassa and carbonate of ammonia produce white precipitates of CARBONATE OF CADMIUM (Cd O, C O,), which are insoluble in an excess of the precipitants. The presence of salts of ammonia does not prevent the formation of these precipitates. The precipitated carbonate of cadmium dissolves readily in solution of cyanide of potassium. From dilute solutions the precipitate separates only after some time.

8. If a mixture of a compound of cadmium with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, the charcoal becomes covered with a reddish-brown coating of OXIDE OF CADMIUM, owing to the volatilization of the reduced metal and its subsequent re-oxidation in passing through the oxidizing flame. The coating is seen most distinctly after cooling.

§ 122.

Recapitulation and remarks.-The perfect separation of the metallic oxides of the second division of the fifth group from suboxide of mercury and oxide of silver may, as already stated, be effected by means of hydrochloric acid; but this agent fails to separate them completely from oxide of lead. The oxide of mercury is distinguished from the other oxides of this division by the insolubility of the corresponding sulphide in boiling nitric acid. This property affords a convenient means for its separation. Moreover, the reactions with protochloride of tin or with metallic copper, as well as those in the dry way, will, after the previous removal of the suboxide, always readily indicate the presence of oxide of mercury.

From the still remaining oxides the oxide of lead is separated by addition of a sufficient quantity of dilute sulphuric acid; the separation is the most complete if the fluid, after the addition of the sulphuric acid, is evaporated on the water-bath, and the residue diluted with water. Teroxide of bismuth may be separated from oxide of copper and oxide of cadmium by addition of ammonia in excess, as the latter two oxides are soluble in an excess of this agent. If the filtered precipitate is dissolved in one or two drops of hydrochloric acid on a watchglass, and water added, the appearance of a milky turbidity is a confirmation of the presence of teroxide of bismuth.-The presence of a notable quantity of oxide of copper is revealed by the blue color of the ammoniacal solution; smaller quantities are detected by evaporating the ammoniacal solution nearly to dryness, adding a little acetic acid, and then ferrocyanide of potassium. The separation of oxide of copper from oxide of cadmium may be effected by means of carbonate of ammonia; however, by that method minute quantities of cadmium might readily escape detection.