Cobalt

Cobalt (symbol Co., at. wt. 58.6), is a reddish-white malleable metal of specific gravity 8.9, which is found naturally, in combination with arsenic and sulphur, as smaltine (CoAs₂), and cobalt glance (CoAsS). The metal is slightly magnetic, and dissolves slowly in acids. It forms two oxides, the cobaltous (CoO) and cobaltic (Co₂O₃), which form corresponding series of salts. Of these the cobaltous chloride is sometimes used for sympathetic inks, as writing in this compound, though invisible when cold, becomes blue on warming. Cobalt compounds are also used for imparting a blue colour to glass and porcelain, and for the manufacture of pigments, as smalt, by fusing cobalt ores with quartz and potashes; Thenard's blue, by heating the oxide with alumina; Rinman's green, in which oxide of zinc takes the place of alumina; and others.