Cadmium
a diatomic metallic element, discovered in 1818; symbol, Cd; at. wt., 112; sp. gr., 8.6; melting point, 320°, boils at 778°. It is a white. ductile, malleable metal; scarcely tarnishes in the air; burns when heated in the air, forming a brown oxide, CdO. It dissolves readily in nitric acid, and decomposes water at red heat. Cadmium is found in some zinc ores; when these are distilled it rises in vapor before the zinc does so. It also occurs in the form of sulphide in greenockite. Cadmium is easily separated from zinc by passing HS. into their solution in HCl; the cadmium is precipitated as yellow sulphide, CdS. Cadmium can be separated from copper in analysis by dissolving their sulphides in nitric acid and adding ammonia in excess, filtering off oxides of other metals; then potassium cyanide is added till the precipitate first formed redissolves, then H₂S gas is passed through the liquid, from which it throws down the cadmium as sulphide.