Qualities.-Litharge is inodorous and insipid: it is in flakes with a vitreous lustre; dissolves in many of the acids:

and is a protoxide, containing 103.6 parts of lead and 8 of oxygen, or 1 proportion of each = 111.6. For an account of the action of this oxide on fixed oil, see Plasters.

Medical properties and uses.-Litharge, like the other preparations of lead, is a powerful astringent. The ancients were acquainted with it.1 It is never given internally; and is used only for pharmaceutical purposes. Litharge is sometimes added to wines which are sour. It may be detected either by passing sulphureted hydrogen gas through the suspected wine; or evaporating this to the consistence of syrup, and then reducing the lead with charcoal, in a crucible. In all cases of poisoning by salts or oxides of lead the best antidote is a solution of magnesiae sulphas, with the addition of some sulphuric acid; which, uniting with the deleterious salt of lead, forms an inert sulphate of lead, which is carried out of the bowels by the sulphate of magnesia.

Officinal preparation.-Emplastrum Plumbi, L. E. D.

3. Sesquioxide of Lead.2 - Officinal. Oxydum Plumbi Rubrum, Edin. Red Oxide of Lead.

Syn. Minium (F.), Monnige, Mennig (G.), Minio (I.), Vermilion (S.), Isrenj (Arab.), Sindur (H), Segapoo Sindoorum ( Tarn.), Sindura (San.), Te-mamera (Malay).

This preparation is lead in the highest state of oxidizement. It is prepared in a reverberatory furnace, vaulted like a baker's oven, and having two internal walls rising from the floor, but not reaching to the roof. The coals are placed between these internal walls and the wall of the furnace, by which means the flame is drawn over the top, and reflected from the roof down upon the surface of a quantity of lead placed on the floor. The metal soon melts, and is altogether converted into a yellow oxide, or massicot, by successively raking off the pellicles which form on its surface: this is then ground in a mill, and washed, to separate any metallic lead, by which it becomes of a uniform yellow colour, and, after being replaced in the furnace, is exposed to the flame while it is constantly stirred for about forty-eight hours, when it is converted into red oxide of lead.3 By this process, 20 cwts, of lead produce on an average 22 cwts. of red lead, notwithstanding a portion is necessarily volatilized.

To save the previous calcination, litharge is sometimes employed.

1 It was known to Dioscorides, Aetius, and others, but we have no records of its employment as a medicine until 1541, when it was prescribed by Paracelsus.

Dioscoridis. Watson's Chymical Essays, iii, 338. Atkins Dictionary.

Qualities. - Red oxide of lead, the minium of commerce, is inodorous and insipid; in the form of a very heavy, scaly powder, its specific gravity being 8.940l; and of an intense red or scarlet colour, verging into orange. When heated to redness, it gives out oxygen gas, and runs into a dark-brown, hard glass. It is a sesquioxide, containing 310.8 parts or 3 equivalents of lead + 32, or 4 of oxygen=342.8.

Medical properties and uses.-Red lead may be applied to the same uses as litharge, but is now rarely or never used. Its chief use is in the arts, as a pigment.