COBALT (from Cobalus, a malicious sprite or gnome) is a metal of no use in the arts and manufactures, but which forms compounds of commercial importance. C. (symbol Co) is found naturally in combination with arsenic (As), as speiss C. (Co As); in combina tion with arsenic and sulphur, as C. glance, the arsenide and sulphide of C. (CoS,,CoAs), in ores of nickel (q.v.); and in the metallic state, it is found in meteoric stones or acre lites (q.v.). The metal has been obtained in laboratory experiments, and presents a gray color with a reddish tinge, is highly magnetic, and is as hard and infusible as iron. It is a brittle metal, and forms no alloys of commercial use. The protoxide of C. (CoO) is employed in painting on porcelain, for producing a rich blue color. Zaffre is the impure oxide obtained by partially mixing C. ore with two or three times its weight of fine sand. Basalt is the term applied to a deep blue glass, which owes its color to the pres ence of oxide of C., and which, when reduced to very fine powder, is employed occa sionally by laundresses to correct the yellow color 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 colors in porcelain, pottery glass, encaustic tiles, fresco painting, etc., and forms the principal ingredient in old Sevres blue, l Itenard'a blue, turquoise blue, and variegated blue. See &um A compound containing the oxides of C. and zinc is of a beautiful green color, and is known as Rininan's green. The chloride of C., dissolved in much water, may be employed as a sympathetic ink. In dilute solutions, it is of a faint pink color, 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 tht writing is then capable of being read. On allowing the paper thereafter to lie in a damp place, or exposing it to the vapor 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 cop-_ per, a yellow shade,