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 S1), 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. Ŏxide 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, CO2), 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.

The separation by means of cyanide of potassium is safer.-The process is very simple, being as follows: precipitate the solution with hydrosulphuric acid, let the precipitate settle, wash it slightly by decantation, and treat it with some cyanide of potassium, when the sulphide of copper will dissolve, the yellow sulphide of cadmium remaining undissolved.

Palladium greatly resembles platinum; its color is somewhat darker. It fuses with great difficulty; when heated in the air to dull redness, it becomes covered with a blue coating; but, upon more intense ignition, it recovers its light color and metallic lustre. It is difficultly soluble in pure nitric acid, but dissolves somewhat more readily in nitric acid, containing nitrous acid; it dissolves very sparingly in boiling concentrated sulphuric acid, but readily in nitro-hydrochloric acid. It combines with 1 and 2 eq. of oxygen to form protoxide and binoxide. The latter, when heated with dilute hydrochloric acid, evolves chlorine, and gives solution of protochloride of palladium. Protoxide of palladium is black, its hydrate dark brown; both are, upon intense ignition, resolved into oxygen and metallic palladium. The salts of protoxide of palladium are mostly soluble in water; they are brown, or reddish-brown; their solutions, when concentrated, are reddish-brown; when dilute, yellow. Water precipitates from a solution of nitrate of protoxide of palladium containing a slight excess of acid, a brown-colored basic salt. The oxygen salts, as well as the protochloride, are decomposed upon ignition, leaving metallic palladium behind. Hydrosulphuric acid and sulphide of ammonium throw down from acid or neutral solutions of salts of protoxide of palladium, black protosulphide of palladium, which dissolves neither in sulphide of ammonium nor in boiling hydrochloric acid, and with difficulty in boiling nitric acid, but readily in nitro-hydrochloric acid. From the solution of the protochloride potassa precipitates a brown basic salt, soluble in an excess of the precipitant, ammonia, flesh-colored ammonio-protochloride of palladium (Pd Cl, N H ̧), cyanide of mercury, yellowish-white gelatinous protocyanide of palladium, soluble in hydrochloric acid, and in ammonia. Protochloride of tin produces, in absence of free hydrochloric acid, a brownish-black precipitate; in presence of free hydrochloric acid, a red-colored solution, which speedily turns brown, and ultimately green, and, upon addition of water, brownish-red. Sulphate of protoxide of iron produces a deposit of palladium on the sides of the glass. Iodide of potassium precipitates black protiodide of palladium. Chloride of potassium precipitates from highly concentrated solutions of protoxide of palladium, potassio-protochloride of palladium (K Cl, Pd Cl), in form of golden-yellow needles, which dissolve readily in water giving a dark red fluid, but are insoluble in absolute alcohol.

$124.

SIXTH GROUP.

TEROXIDE OF GOLD, BINOXIDE OF PLATINUM, TEROXIDE OF ANTIMONY, BINOXIDE OF TIN, PROTOXIDE OF TIN, ARSENIOUS ACID AND ARSENIC ACID.*

Properties of the group. The sulphides corresponding to the oxides of the sixth group are insoluble in dilute acids. These combine with alkaline sulphides forming soluble sulphur salts, in which they perform the part of the acid. Hydrosulphuric acid precipitates these oxides therefore, like those of the fifth group, completely from acidified solutions. The precipitated sulphides differ, however, from those of the fifth group in this, that they dissolve in sulphide of ammonium, sulphide of potassium, &c., and are reprecipitated from these solutions on the addition of acids.

IN

We divide the oxides of this group into two classes, and distinguish, 1. OXIDES WHOSE CORRESPONDING SULPHIDES ARE INSOLUBLE HYDROCHLORIC ACID AND IN NITRIC ACID, and are reduced to the metallic state upon fusion in conjunction with nitrate and carbonate of soda: viz., teroxide of gold and binoxide of platinum.

2. OXIDES WHOSE CORRESPONDING SULPHIDES ARE SOLUBLE IN BOILING HYDROCHLORIC ACID OR NITRIC ACID, and are upon fusion with nitrate and carbonate of soda converted into oxides or acids, which combine with the soda: viz., Teroxide of antimony, protoxide and binoxide of tin, arsenious and arsenic acids.

FIRST DIVISION.

Special Reactions.

§ 125.

a. TEROXIDE OF GOLD (Au 0 ̧).

1. Metallic gold has a reddish yellow color, and a high metallic lustre : it is rather soft, exceedingly malleable, ductile, difficultly fusible; it does not oxidize upon ignition in the air, and is insoluble in hydrochloric, nitric, and sulphuric acids; but it dissolves in fluids containing or evolving chlorine, e. g. in nitro-hydrochloric acid. The solution contains terchloride of gold.

2. Teroxide of gold is a blackish-brown, its hydrate a chesnut-brown powder. Both are reduced by light and heat, and dissolve readily in hydrochloric acid, but not in dilute oxygen acids. Concentrated nitric and sulphuric acids dissolve a little teroxide of gold; water reprecipitates it from these solutions.

3. Salts of gold with oxygen acids are nearly unknown. The haloid salts of gold are yellow, and their solutions continue to exhibit this color up to a high degree of dilution. The whole of them are readily decom

* I have placed the two acids of arsenic with the metallic oxides, since the deportment of the sulphides of arsenic might readily lead to their being confounded with some of the oxides of the sixth group, and because in the systematic course of analysis the sulphide of arsenic is invariably obtained in the same precipitate with the sulphide of antimony, the sulphide of tin, &c.