Cadmium

Cadmium (sym. Cd, atomic weight 112) is a metal which occurs in zinc ores. In the preparation of zinc, when heat is applied, the cadmium, being more volatile than that metal, rises in vapour, and distils over with the first portions of the metal (see ZINC). Cadmium is a white metal, somewhat resembling tin, than which it is rather denser, its specific gravity being 8.6. It is very soft, and is malleable and ductile, crackling like tin when a rod of it is bent. It fuses at 442° (227.8° C.), and volatilises a little below the boiling-point of mercury. It is rarely prepared pure, and is not employed in the arts as a metal, though several of its salts have been serviceable in medicine, and the iodide and bromide have been useful in photography. There are alloys of cadmium with various other metals. The sulphide of cadmium, CdS, occurs naturally as the mineral Greenockite, and when prepared artificially, is of a bright yellow colour. It is known as Cadmium Yellow, and is of great value to the artist. A great variety of tints are produced by mixing it with white-lead. Much of what is sold as Naples Yellow is thus prepared, but the genuine Naples Yellow, prepared by heating antimonic anhydride with plumbic oxide, has a greenish tint. See YELLOW.