Cobalt

Cobalt (sym. Co, eq. 59, from Cobalus, 'a malicious sprite' or 'gnoine') is a metal the ores of which are sparingly distributed. In the metallic state it is found in meteoric stones or aerolites to the extent of one per cent., but it generally occurs combined with arsenic as Speiss-cobalt, $\backslash text\{CoAs\}\_2$, or as cobalt-glance, the arsenide and sulphide of the metal, $\backslash text\{CoSAs\}$. To obtain the metal itself from its ores is a matter of some difficulty, and although it is more tenacious than iron, yet it has not been applied to any practical use. It is of a gray colour with a reddish tinge, brittle, hard, and very magnetic. Many of its compounds are valued on account of the brilliance and permanence of their colours. The Protoxide of Cobalt, $\backslash text\{CoO\}$, is employed as a blue pigment in porcelain-painting. Zaffre is the impure oxide obtained by partially roasting cobalt ore previously mixed with two or three times its weight of fine sand. Smalt is the term applied to a deep-blue glass, which owes its colour to the presence of oxide of cobalt, and which, when reduced to very fine powder, is employed occasionally by laundresses to correct the yellow colour of newly-washed linen, and by paper-makers as a blue pigment for staining writing-paper. Smalt is also used in the production of the blue colours in porcelain, pottery glass, encaustic tiles, fresco-painting, &c., and forms the principal ingredient in Old Sevres Blue, Thenard's Blue, Turquoise Blue, &c. (see BLUE). A compound containing the oxides of cobalt and zinc is of a beautiful green colour, and is known as Rinman's Green. The chloride of cobalt dissolved in much water, may be employed as a sympathetic ink. In dilute solutions, it is of a faint pink colour, which is not observable when it is used for writing upon paper; but when heated before the fire, it loses water, and becomes blue, and the writing is then capable of being read. On allowing the paper thereafter to lie in a damp place, or exposing it to the vapour of steam from a kettle, water is again absorbed, and the writing returns to its invisible state. The addition of a little perchloride of iron to the ink makes the writing appear green; a solution of zinc imparts a red tint; and a salt of copper, a yellow shade.