COBALT, a metal of a reddish-gray colour, rather brittle, and very infusible. It is never found in a pure state, but occurs usually as an oxide, or in combination with arsenic or its acid, with nickel, sulphur, iron, &c. The oxide yields a rich blue colour, on which account it is extensively employed in the arts. The impure oxide is called zaffre; but by fusion with two or three parts of fine silicious sand and an alkaline flux it is converted into a blue glass, which, when reduced to powder, is called smalt. This is largely employed to colour glass, porcelain, and stoneware, and also to give a blue tint to writing-paper. The word cobalt is derived from kobold, a goblin—the name applied to it by the German miners, who regarded its occurrence as unfavourable to the presence of more valuable metals. See CHEMISTRY; MINERALOGY; SMALT.