(Hg, Cl), as a fine powder of dazzling whiteness. Cold hydrochloric acid and cold nitric acid fail to dissolve this precipitate; it dissolves, however, although very difficultly and slowly, upon long protracted boiling with these acids, being resolved by hydrochloric acid into chloride of mercury and metallic mercury, which separates; and converted by nitric acid into chloride of mercury and nitrate of oxide of mercury. Nitrohydrochloric acid and chlorine water dissolve the subchloride of mercury readily, converting it into chloride. Ammonia and potassa decompose the subchloride of mercury, and separate black suboxide from it.

7. If a drop of a neutral or slightly acid solution of suboxide of mercury is put on a clean and smooth surface of copper, and washed off after some time, the spot will afterwards, on being gently rubbed with cloth, paper, &c., appear WHITE and LUSTROUS like silver. The application of a gentle heat to the copper causes the metallic mercury precipitated on its surface to volatilize, and thus removes the silvering.

8. Protochloride of tin produces in solutions of suboxide of mercury a gray precipitate of METALLIC MERCURY, which may be united into globules by boiling the metallic deposit, after decanting the fluid, with hydrochloric acid.

9. If an intimate mixture of an anhydrous compound of mercury with anhydrous carbonate of soda is introduced into a drawn-out glass tube, and covered with a layer of carbonate of soda, and the tube is then heated before the blowpipe, the mercurial compound invariably undergoes decomposition, and metallic mercury separates, forming a coat of gray sublimate above the heated part of the tube. The minute particles of mercury may be united into larger globules by rubbing this coating with a glass rod.

§ 116.

c. OXIDE OF LEAD (Pb O).

1. Metallic lead is bluish-gray; its surface recently cut exhibits a metallic lustre ; it is soft, malleable, readily fusible. Fused upon charcoal before the blowpipe, it forms a coating of yellow oxide on the charcoal. Hydrochloric acid and moderately concentrated sulphuric acid act upon it but little, even with the aid of heat; but dilute nitric acid dissolves it readily, more particularly on heating.

2. Oxide of lead is a yellow or reddish-yellow powder,* which upon exposure to a red heat fuses to a vitreous mass. Hydrated oxide of lead is white. Both the oxide and its hydrate dissolve readily in nitric and acetic acids.

3. The salts of oxide of lead are non-volatile; most of them are colorless; the neutral soluble salts redden litmus paper, and are decomposed at a red heat.

4. Hydrosulphuric acid and sulphide of ammonium produce in solutions of salts of lead black precipitates of SULPHIDE OF LEAD (Pb S), which are insoluble in cold dilute acids, in alkalies, alkaline sulphides, and cyanide of potassium. Sulphide of lead is decomposed by boiling concentrated nitric acid; the whole of the lead is first converted into nitrate of lead, and the greater part of the sulphur separates, whilst another portion is converted into sulphuric acid. The sulphuric acid thus

* While hot, the oxide of lead appears red.

formed decomposes a portion of the nitrate of lead, and forms with the liberated oxide sulphate of lead, which precipitates as a white powder; the deposit in the solution consists therefore of a mixture of sulphate of lead and sulphur. In solutions of salts of lead containing an excess of a concentrated mineral acid, hydrosulphuric acid produces a precipitate only after the addition of water or after neutralization of the free acid by an alkali. If a solution of lead is precipitated by hydrosulphuric acid, in presence of a large quantity of free hydrochloric acid, a red precipitate is formed, consisting of chloride and sulphide of lead, which, however, is converted by an excess of hydrosulphuric acid into black sulphide of lead.

5. Potassa and ammonia throw down BASIC SALTS OF LEAD in the form of white precipitates, which are insoluble in ammonia, and difficultly soluble in potassa. In solutions of acetate of lead ammonia does not immediately produce a precipitate, owing to the formation of a soluble triacetate of lead.

6. Carbonate of soda throws down from solutions of salts of lead a white precipitate of BASIC CARBONATE OF LEAD [e. g. 5 (Pb O, CO2) + Pb O, HO], which is insoluble in an excess of the precipitant and also in cyanide of potassium.

7. Hydrochloric acid and soluble chlorides produce in concentrated solutions of salts of lead heavy, white precipitates of CHLORIDE OF LEAD (Pb Cl), which are soluble in a large amount of water, especially upon application of heat. This chloride of lead is converted by ammonia into basic chloride of lead (Pb Cl, 3 Pb O + H O), which is also a white powder, but almost absolutely insoluble in water. In dilute nitric and hydrochloric acids, chloride of lead is more difficultly soluble than in water.

8. Sulphuric acid and sulphates produce in solutions of salts of lead white precipitates of SULPHATE OF LEAD (Pb O, SO1), which are nearly insoluble in water and dilute acids. From dilute solutions, especially from such as contain much free acid, the sulphate of lead precipitates only after some, frequently after a long time. It is advisable under all circumstances to add a considerable excess of dilute sulphuric acid, since sulphate of lead is more insoluble in this menstruum than in water. The separation of small quantities of sulphate of lead is best effected by evaporating, after the addition of the sulphuric acid, as far as practicable on the water-bath, and then treating the residue with water. Sulphate of lead is slightly soluble in concentrated nitric acid; it dissolves with difficulty in boiling concentrated hydrochloric acid, but more readily in solution of potassa. It dissolves also pretty readily in the solutions of some of the salts of ammonia, particularly in solution of acetate of ammonia; dilute sulphuric acid precipitates it again from these solutions.

9. Chromate of potassa produces in solutions of salt of lead a yellow precipitate of CHROMATE OF LEAD (Pb O, Cr O,), which is readily soluble in potassa, but difficultly so in dilute nitric acid.

10. If a mixture of a compound of lead with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, soft, malleable METALLIC GLOBULES OF LEAD are readily produced, the charcoal becoming covered at the same time with a slight yellow incrustation of

OXIDE OF LEAD.

$117.

Recapitulation and remarks.—The metallic oxides of the first division of the fifth group are most distinctly characterized in their corresponding chlorides; since the different respective deportment of these chlorides with water and ammonia affords us a simple means both of detecting them and effecting their separation from one another. For if the precipitate containing the three metallic chlorides is boiled with a somewhat large quantity of water, or boiling water is repeatedly poured over it on the filter, the chloride of lead dissolves, whilst the chloride of silver and the subchloride of mercury remain undissolved. If these two chlorides are then treated with ammonia, the subchloride of mercury is converted into a black basic salt, insoluble in an excess of the ammonia; whilst the chloride of silver dissolves readily in that agent, and precipitates from this solution again upon addition of nitric acid. When operating upon small quantities, it is advisable first to expel the greater part of the ammonia by heat. In the aqueous solution of chloride of lead the metal may be readily detected by sulphuric acid.

SECOND DIVISION OF THE FIFTH GROUP: OXIDES WHICH ARE NOT PRECIPITATED BY HYDROCHLORIC ACID.

Special Reactions.
$118.

a. OXIDE OF MERCURY (Hg O).

1. Oxide of mercury is generally crystalline, and has a bright red color, which upon reduction to powder changes to a pale yellowish-red; the oxide precipitated from solutions of the nitrate of the oxide, or from solutions of the chloride, forms a yellow powder. Upon exposure to heat it transiently acquires a deeper tint; at a dull red heat it is resolved into metallic mercury and oxygen. Both the crystalline and non-crystalline oxide dissolve readily in hydrochloric and nitric acids.

2. The salts of oxide of mercury volatilize upon ignition; they suffer decomposition in this process; chloride, bromide, and iodide of mercury volatilize unaltered. Most of the salts of oxide of mercury are colorless. The soluble neutral salts redden litmus paper. The nitrate and sulphate of oxide of mercury are decomposed by water added in large quantity, into soluble acid and insoluble basic salts.

3. Addition of a very small quantity of hydrosulphuric acid or sulphide of ammonium produces in solutions of oxide of mercury, after shaking, a perfectly white precipitate. Addition of a somewhat larger quantity of these reagents causes the precipitate to acquire a yellow, orange, or brownish-red color, according to the less or greater proportion added; an excess of the precipitant produces a purely black precipitate of SULPHIDE OF MERCURY (Hg S). This progressive variation of color from white to black, which depends on the proportion of the hydrosulphuric acid or sulphide of ammonium added, distinguishes the oxide of mercury from all other bodies. The white precipitate which forms at first consists of a double compound of sulphide of mercury with the still undecomposed portion of the salt of oxide of mercury (in a solution of chloride of mercury, for instance, Hg Cl + 2 Hg S); the gradually in

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. 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).

The

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. The precipitate, 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.

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, H 0) 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 O) 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, C 0, + Cu O, HO), which upon boiling changes to brownish-black oxide of copper, and dissolves in animonia 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 0 ̧. 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)