Litharge is prepared by exposing melted lead, at a high temperature, to a current of air from a pair of blast-bellows, which blows off the oxide formed on the surface of the metal into a recipient, where it solidifies in minute scales. It is a protoxide of lead, containing one equivalent of lead and one of oxygen.

Sensible and Chemical Properties. This oxide is in small, shining scales, of a yellowish colour usually tinged with red, inodorous and tasteless, fusible and at a high temperature volatilizable, and reducible by heat with charcoal to the metallic state. For practical purposes it may be considered insoluble, though it is said that one part is dissolved by 7000 parts of water. It is wholly dissolved by dilute nitric acid, and is blackened by hydrosulphuric acid. On exposure to the air, it slowly absorbs carbonic acid, and therefore usually contains a little carbonate of lead.

Effects on the System

Litharge is capable of producing the peculiar effects of lead upon the system, whether taken into the stomach, or inhaled, in the state of vapour or of powder, into the lungs. But it is never used internally. Locally it has the ordinary sedative properties of the metal.

Medical Uses

It has sometimes been used, sprinkled, in fine powder, on the surface of ulcers; but its almost exclusive employment at present is as an ingredient in various officinal preparations, for which it is very important. I shall notice here those which are considered under no other head.