The carbonate appears as a white, scaly, brittle matter, on the surface of the lead, and is separated "by spreading the coils upon a perforated wooden floor covered with water, and drawing them to and fro by rakes, which detaches the carbonate, and causes it to sink through the water and the holes of the floor to the bottom of a vessel placed below,"8 In some places, this operation is performed by merely scraping off the carbonate with a knife. It is afterwards ground in mills fitted for the purpose. It was formerly ground dry, and the workmen suffered very severely; but it is now ground in water, and the carbonate is afterwards dried in earthen pans placed in stoves, heated by means of flues. The beauty of the carbonate depends on the purity of the lead.

Dioscoridis.

2 The various appellations given to this substance by the different colleges, arise from the indeterminate ideas which prevail of its composition.

3 Aihin's Dictionary.

It is now more generally formed by passing a stream of carbonic acid through a solution of the acetate; and when the settling takes place it is dried in stoves, in glazed earthen pots. It is sometimes adulterated with whiting, and sometimes with sulphate of baryta.

Qualities.-Carbonate of lead is inodorous, and nearly insipid; in the form of a very heavy white powder, insoluble in water, but soluble in pure potassa. When exposed upon charcoal to the action of the blowpipe, a button of metallic lead is produced. Its constituents, according to Berzelius, are yellow oxide of lead 83.5, and carbonic acid 16.5, in 100 parts'; or 1 prop. of protoxide of lead = 111.6 +1 of carbonic acid = 22.12, making the equivalent 133.72. Its adulteration with chalk may be discovered by pouring distilled vinegar on the suspected carbonate, and then adding oxalic acid, or oxalate of ammonia, to the solution. The formation of a precipitate proves the presence of chalk.

Medical properties and uses.-This preparation of lead is a very powerful astringent. It is used externally only, being sprinkled on inflamed and excoriated parts. Some writers, however, regard even its external employment dangerous: but we have ordered it a thousand times, without witnessing any bad effects to follow. It enters into the composition of some ointments.

It is from this preparation that most of the cases of poisoning from the internal use of the lead occur. Its effects as a poison were known to Galen. This often happens to painters, and to those employed in grinding white lead, from the want of cleanliness in not washing their hands before eating, by which some of the white lead is introduced into the stomach with their food: and it is this carbonate which is the poison, whether white lead or sugar of lead be put into acid wines for the purpose of sweetening them, and into hollands to deprive the spirit of the colour which it acquires when long kept in the wood. The symptoms which preparations of lead produce are obstinate costiveness, pain in the stomach, and vomiting: the pulse becomes small and hard; the respiration laborious; and tremors, ending in paralysis of the extremities, or death, ensue, when its operation is not counteracted by medicine. The exhibition of cathartics, particularly castor oil, and sulphate of soda or of magnesia, combined with opium or henbane, plentiful dilution with mucilaginous liquids, the warm bath, and injecting mutton broth per anum, are the best antidotes: and if paralysis follow, recourse must be had to acetate of strychnia, administered in gradually augmented doses, commencing with half a grain, until tetanic twitches display themselves.

Galvanism will also be found useful.

1 Annates de Chin. lxxvii. p. 83.

When the presence of any salt of lead is suspected in a dry substance, it may be discovered by reducing it to a metallic state with the blowpipe upon charcoal; if in a liquid, by pouring into the suspected solution a solution, of sul-phureted hydrogen gas1, when the lead is made obvious by a dark brown precipitate, which is insoluble in tartaric acid, the salt of lead being formed into an insoluble sulphuret. This sulphuret should be next washed and digested in nitric acid, diluted with twice its weight of water. This nitrate being brought to dryness by heat, to expel any nitric acid, should be dissolved, and hydriodate of potassa dropped into the solution; if it be lead, a yellow iodide will be formed.

Officinal preparations.-Plumbi Acetas, L. E. D. Unguentum Cerussae D.

2. Semi-vitrified Oxide of Lead. Officinal. Plumbi Oxydum, Lond. Edin. Dub. Litharge.

Syn. Litharge (F.), Bleiglatte (G.), Loot glans (Dutch), Silwer-glitt (Swed.), Piombo, semi-vitreo (I.), Almastago (S.), Marudar Singhie (Tarn.), Moordar singh (Pers. Duk. Hind.).

This oxide is prepared by the simple action of heat and air upon lead. It is generally obtained during the calcination of lead, when separating the silver with which this metal is often combined. The lead is placed in a wind furnace, on a large cupel, or hollow dish made of ashes, and kept at a red heat with the blast of a large pair of bellows directed upon its surface; a scaly, yellowish white, glistening oxide is soon produced, and successively formed by raking it off and exposing new surfaces till the whole of the lead is thus converted into litharge.2 The varying of the circumstances of the process varies the colour of the oxide: some kinds of it, from having a silvery gloss, are denominated litharge of silver; and others, from the colour being a reddish yellow, litharge of gold.

1 To prepare this solution, put into a phial a paste made of iron filings and sulphur; then after some time add to it a small portion of sulphuric acid, and receive the gas which is produced, through a bent tube connected with the phial, into a flask tilled with distilled water, and inverted in a basin or pneumatic trough full of water.

2 The Harz miner, yield annually 70 tons of litharge.