Synonym. Plumbi Oxidum. Lond. Dub.

Prep. It is usually made during the cupellation of lead ores containing silver, when the oxide becomes fused or semi-vitrified.

Prop. & Comp. Red or orange-red scales; almost entirely soluble in nitric or acetic acid, either solution when neutral giving a copious yellow precipitate with iodide of potassium. It dissolves without effervescence in nitric acid diluted with 6 volumes of water, and the solution when supersaturated with ammonia and then cleared by filtration does not exhibit a blue colour, indicating the absence of a carbonate or copper. The solution is precipitated black by sulphuretted hydrogen, white by caustic potash, and re-dissolved by it in excess. Composition (Pb O).

Off. Prep. Emplastrum Lithargyri. Litharge Plaster. [Em-plastrum Plumbi. Plaster of Lead. U. S.]

Synonym. Emplastrum Plumbi. Lond.

(Oxide of lead, reduced to very fine powder, four pounds; olive oil, a gallon; water, seventy fluid ounces. Boil them together over a slow fire for four or five hours, constantly stirring, until the oil and oxide of lead unite into the consistence of a plaster; a little boiling water may be added, if that which was used at the first has evaporated before the end of the boiling.)

Therapeutics. Litharge is never given internally. The plaster, in which the lead exists in combination with margaric and oleic acids, is used as a mechanical support; it is less irritating than many other plasters, and perhaps slightly astringent.