4249. Cobalt

4249.     Cobalt. A metal found in ores associated with arsenic and other metals; also present in meteoric iron. It is white, brittle, and does not change in the air; has a high melting point, and is strongly magnetic. Specific gravity 8.5. (Cooley.)

4250. Nitrate of Cobalt

4250.    Nitrate of Cobalt. This may be obtained by dissolving metallic cobalt in nitric acid, and collecting the crystals. These crystals are ready soluble in water; of a red color; deliquescent, and melt below 212° Fahr. At a higher heat, nitrous fumes are given off, and peroxide of cobalt remains.

4251. Chloride of Cobalt

4251.     Chloride of Cobalt. Dissolve carbonate of cobalt in muriatic acid ; the solution deposits rose-colored crystals on standing, which contain water. By evaporating the solution, anhydrous blue crystals of the chloride are obtained. (Cooley.)

4252. Carbonate of Cobalt

4252.    Carbonate of Cobalt. This is precipitated from a solution of nitrate of cobalt, by carbonate of potassa, producing a pale peach-colored powder, soluble in acids. ( Cooley.)

4253. Acetate of Cobalt

4253.    Acetate of Cobalt.' The acetate is obtained by dissolving carbonate of cobalt in acetic acid. Acetate of cobalt forms a sympathetic ink. (See No. 2540 (Sympathetic Inks Developed by Heat).)

4254. Manganese

4254.     Manganese. A hard, brittle, greyish-white metal, very easily oxidized, fuses with difficulty, unaffected by cold water, but dissolving freely in dilute sulphuric acid, evolving hydrogen gas. It has a specific gravity of 8.013. It is obtained by calcination in a crucible, at a strong heat, of 10 parts by weight of an oxide of manganese, made into a paste with oil, and combined with 1 part calcined borax.

4255. Peroxide of Manganese

4255.    Peroxide of Manganese. The Hack oxide is the only oxide of manganese that is directly employed in the arts. It is a plentiful mineral production in a crude state ; and is purified by grinding the native mineral or pyrolusite in mills, and removing the earthy matter by washing. The blackest samples are esteemed the best.

4256. Alum

4256.    Alum. The alum of commerce is a sulphate of alumina and potassa, obtained by lixiviation (see No. 23 (Lixiviation)) from crude alum ore, or schist. It is obtained in large crystals, slightly efflorescent. It is applied in the arts to a great variety of purposes. When deprived of its water of crystallization by heat, it becomes burnt or dried alum. Pure red or roche alum was originally imported from Italy, where it is found in a native state. This has a reddish tinge, which extends more or less through the crystals.

4257. Hydrate of Alumina

4257.    Hydrate of Alumina. Dissolve alum in 6 times its weight of boiling water, add a solution of carbonate of potassa, in slight excess, agitate the mixture for a few minutes, and then allow it to repose. After a time, pour the clear supernatant liquor from the precipitate or sediment, and wash the latter three or four times with tepid distilled or soft water. Next collect the precipitate on a fine calico filter, and again wash it with tepid water. "When it has drained, press it between bibulous paper, and, lastly, dry it either without heat, or at a temperature not higher than 120° to 130° Fahr. The product is a soft white powder. (Cooley.) '