Class I.

to a solution of nitrate of cadmium a white precipitate falls, at first very bulky, but in a few hours it contracts much in size. This precipitate is a white powder, insoluble in water. It has not been analyzed, but if it be neutral, its constituents must be 1 atom arsenic acid

7:25

7. Borate of cadmium. This salt is a white powder scarcely soluble in water, and after having been exposed to a red heat its constituents, according to Stromeyer, are

8. Chromate of cadmium.

This salt may be obtained by mixing solutions of sulphate of cadmium and chromate of potash. It falls in the state of a beautiful yellow powder. which has little or no taste and yet is not absolutely insoluble

in water.

Its constituents are

1 atom chromic acid

1 atom oxide of cadmium

5 atoms water

6.5

8

5.625

20.125

9. Molybdate of cadmium. When molybdate of ammonia is mixed with sulphate of cadmium a grayish white powder falls, which becomes brown when gently ignited.

*

10. Oxalate of cadmium. Obtained by mixing solutions of oxalate of potash and nitrate of cadmium. A white tasteless powder insoluble in water. Its constituents are

11. Acetate of cadmium. When a very concentrated solu- Sect. XXIII tion of this salt is exposed for about ten days to the air it is gradually converted into a crystalline mass, while a thick liquid remains floating above it. The crystals are prisms very soluble in water, and not altered by exposure to the air. They are composed of

1 atom acetic acid

1 atom oxide of cadmium

2 atoms water

6.25

8.00

2.25

16.5

12. Formate of cadmium. Obtained by digesting carbonate of cadmium in formic acid. Crystals, cubes, and rhomboidal dodecahedrons, of a sweetish, astringent, and metallic taste. It loses its water with difficulty when heated, but is at last decomposed, leaving oxide of cadmium. Its constituents, according to the analysis of Göbel, to whom we are indebted for the examination of this salt, are as follows:

13. Tartrate of cadmium. If tartrate of potash in slight excess be added to a solution of nitrate of cadmium there instantly falls a pretty bulky precipitate. The liquid separated from this precipitate deposites at the end of 24 hours a small quantity of transparent granular crystals. The supernatant liquor gives a slight precipitate with carbonate of soda. Hence tartrate of cadmium is slightly soluble in water. These crystals are tasteless and composed of

14. Succinate of cadmium. Cadmium is very little soluble in succinic acid, but carbonate of cadmium dissolves very readily. By evaporation transparent prisms are obtained, which dissolve readily in water, and which, when treated with alcohol, are decomposed into a bisalt soluble in alcohol, while a neutral salt remains undissolved.*

Class I.

15. Citrate of cadmium. Citrate of ammonia produces a remarkably bulky gelatinous precipitate in nitrate of cadmium, which is white and scarcely soluble in water. Its constituents

Characters.

SECTION XXIV.-SALTS OF PROTOXIDE OF LEAD.

The salts of lead were formerly distinguished by the name of saturn, the title by which lead was known among the alchymists. The protoxide only of this metal seems capable of combining with acids so as to form salts. These bodies may be distinguished by the following properties:

1. A considerable number of them are scarcely soluble in water without an excess of acid. These before the blow-pipe on charcoal yield very readily a button of lead.

2. The solution of the soluble salts of lead in water is generally colourless and transparent.

3. They have almost all less or more of a sweet taste, accompanied with a certain degree of astringency.

4. Prussiate of potash occasions a white precipitate when poured into solutions containing salts of lead.

5. Hydrosulphuret of potash occasions a black precipitate. The same precipitate is produced by sulphuretted hydrogen. 6. Gallic acid and the infusion of nut-galls occasion a white precipitate.

7. A plate of zine kept in a solution of lead occasions either a white precipitate, or the lead appears in its metallic state.

8. When potash is dropt into a solution of a salt of lead a white powder falls, which is redissolved by adding an excess of the potash.

9. When chromate of potash is dropt into a solution of lead a beautiful orange precipitate falls.

1. Sulphate of lead. Sulphuric acid does not attack lead while cold; but at a boiling heat it communicates a portion of its oxygen, sulphurous acid gas is emitted, and the whole is converted into a thick white mass, which is sulphate of lead. may be obtained readily by pouring sulphuric acid into acetate of lead, or by mixing this last salt with any of the alkaline sulphates. The sulphate of lead precipitates in the state

It

of a white powder. This salt is tasteless. It is insoluble in Sect, XXIV. alcohol and in nitric acid. According to Kirwan, it requires 1200 parts of water to dissolve it; but when it contains an excess of acid, it is more soluble, and yields by evaporation small white crystals, which, according to Sage, have the form of tetrahedral prisms. It dissolves in strong muriatic acid when the action of the solvent is promoted by heat; the solution, on cooling, deposites many crystals of muriate of lead.†

This salt occurs native in transparent colourless crystals having the diamond lustre and a specific gravity of 6.3. The primary form of the crystal is a right rhombic prism, whose contiguous faces are inclined at angles of 103° 42'. But it frequently occurs in octahedrons and other shapes easily deducible from the primary crystal. It is anhydrous; though it usually contains a little hygrometrical water. Its constituents

2. Disulphate of lead. According to Vauquelin when the preceding salt is digested in ammonia it loses half its acid and is converted into disulphate.

3. Sulphite of lead. Sulphurous acid has no action whatever on lead. It absorbs oxygen from the red oxide of that metal, and is converted into sulphuric acid. But it combines with the protoxide of lead, and forms with it a sulphite, which is in the state of a white powder, insoluble in water, and tasteless. Before the blow-pipe on charcoal it melts, becomes yellow, and the lead is at last reduced. When exposed to a red heat, it loses 5 per cent. of its weight; sulphurous acid exhales; and there remains a blackish mass composed of sulphate of lead and sulphuret. When treated with nitric acid, the sulphuret is decomposed, and crystals of nitrate obtained. Its consti

4. Hyposulphite of lead. This salt is obtained by pouring nitrate of lead into the solution of any hyposulphite. A white

• Mineralogy, ii. 211.

Descotils, Nicholson's Jour. xii. 221.

Fourcroy and Vauquelin, Connoissances Chimiques, vi. 86.

precipitate falls which is at first redissolved; but upon adding the requisite quantity of nitrate it becomes permanent. This byssalt hite is a white mealy powder, which leaves an im

ssion of sweetness when held long in the mouth. At a cat under 212; it turns black, and when the heat is raised it takes fire. becoming red hot, and burns with a weak flame. If it be now removed from the fire, the ignition and combustion may be maintained for any length of time by cautiously ating small quantities of the substance. When heated in a retort it loses 20 per cent. of its weight, which is pure sulphurous acid gas. When fully ignited, the loss is 20-6 per cent. the residuum. which is a black powder, is, according to Mr. Herschell, a sulphuretted oxide of lead. The consti tuents of hyposulphite of lead, according to the analysis of Mr. Herschell, are as follows:

5. Hyposulphate of lead. This salt may be obtained by dissolving carbonate of lead in hyposulphuric acid, and leaving the solution to spontaneous evaporation. Large transparent crystals are obtained, the form of which is not easily described, but they have been figured and measured by Heeren, who considers the primary form to be a bipyramidal dodecahedron.* The taste of the salt is very sweet and astringent, and it is very soluble in water. Its constituents, according to the analysis of Heeren, are

1 atom hyposulphuric acid

1 atom oxide of lead

4 atoms water

9

14

4.5

27.5

6. Dihyposulphate of lead. This salt may be obtained by mixing the solution of the preceding with a quantity of ammonia not sufficient to decompose it completely. Soft white needles fall which react as an alkali. When digested in nitric

* Poggendorf's Annalen, vii. 183.