Caustic

Caustic (Gr., 'burning'), a term for substances that exert a corroding action on the skin and flesh. Lunar caustic (so called because silver was called luna, 'the moon,' in the alchemists' mystical jargon) is nitrate of silver, and common caustic is potash. When used as a caustic in medicine, the substance is fused and cast into moulds, which yield the caustic in small sticks the thickness of an ordinary lead pencil, or rather less.—Caustic is also used in chemistry in an adjective sense—thus caustic lime, or pure lime, CaO, as distinguished from mild lime, or the carbonate of lime, CaCO₃, caustic magnesia, MgO, and mild magnesia, MgCO₃, caustic potash, caustic soda (for these, see POTASH, SODA, &c.). See CAUTERY.