COBALT, a metal which occurs combined with arsenic, nickel and other metals; also as a sulphide and as an arsenate. After the ore has been calcined, oxide of cobalt remains, but impure from the presence of other metallic oxides. When this oxide has been purified and reduced to the metallic state the cobalt is ob tained of a white color inclining to gray, and, if tarnished, to red, with a moderate lustre. Its fracture is compact; it is hard, brittle and of a specific gravity of 8.5 to 8.9. Like nickel, it is strongly magnetic. It undergoes little change in the air, but absorbs oxygen when heated in open vessels. It is attacked, though slowly, by sulphuric or hydrochloric acid, and is readily oxidized by means of nitric acid. Two basic oxides of cobalt are known, and some inter mediate oxides. The protoxide is of an ash gray color and is the basis of the salts of cobalt, most of which are of a pink hue. When heated to redness in an open vessel it absorbs oxygen and is converted into a higher oxide. It may be prepared by decomposing the carbonate of co balt by heat in a vessel from which atmospheric air is excluded. It is easily known by its giving a blue tint to borax when melted with it. It is employed in the arts, in the form of smalt, for communicating a similar color to glass, earthen ware and porcelain. Smolt, or powder blue, is made by melting three parts of fine white sand, or of calcined flints, with two of purified pearl ash and one of cobalt ore previously calcined, and ladling it out of the pots into a vessel of cold water; after which the dark-blue glass, or zaffer, is ground, washed and distributed into different shades of color, which shades are occasioned by the different qualities of the ore and the coarser or finer grinding of the Smolt, besides being used to stain glass and pottery, is often substituted, in painting, for ultramarine blue, and is likewise employed to give to paper and linen a bluish tinge. The chloride of cobalt is well known as a sympa thetic ink. When diluted with water so as to
form a pale pink solution, and then employed as ink, the letters, which are invisible in the cold, become blue if gently heated. It is pre pared by dissolving precipitated oxide of co balt in hydrochloric acid with the aid of heat, and diluting with water. The nitrate of cobalt is obtained by dissolving cobalt or its oxide in nitric acid and crystallizing the solution. It is a deliquescent red salt, which dissolves in water with a pink color. The peroxide of co balt is black, and is formed by adding a solu tion of bleaching-powder to a cobaltous salt, or by passing a current of chlorine gas through water holding cobaltous hydrate in suspension. It does not unite with acids; and when digested in hydrochloric acid the cobaltous chloride is generated with the disengagement of chlorine. When heated it is converted into one of the intermediate oxides.
Ores of *Bright white cobalt ore' is the popular name for the mineral cobaltite (q.v.), a sulph-arsenide of cobalt. "Gray co balt ore,* also sometimes called "tin-white cobalt,* is the mineral smaltite (q.v.). It is the chief ore of cobalt and is essentially cobalt diarsenide, though it always contains nickel and iron. "Red cobalt,* also known as "cobalt bloom,* is the mineral erythrite (q.v.), a hy drous cobalt arsenate. "Earthy cobalt,* or "black cobalt,* is the mineral asbolite, a variety of wad containing up to 32 per cent oxide of cobalt. "Cobalt pyrites" is the mineral linnaite, a sulphide of cobalt, often containing much nickel. The principal supply of cobalt was for merly derived from the smaltite of Germany and the cobaltite of Norway and Sweden. The discovery, about 1904, of rich cobalt and silver ores in northern Ontario has made the town of Cobalt the centre of production. In the cobalt district smaltite and cobaltite occur in veins with native silver and other metallic minerals in rocks of Pre-Cambrian Age.