CO′BALT

Co. Syn. Reg′ulus of cobalt ; Cobalt′tum , L. A metal discovered by Brandt, in 1733. It generally occurs in the same ore as nickel, and the separation of the two metals is a task requiring great patience and expertne . Spei cobalt and cobalt glance are the ores from which the metal is commonly extracted. Prep. 1. Di olve oxide of cobalt in hydrochloric acid, and pa sulphuretted hydrogen gas through the solution, until all the arsenic is thrown down; filter, and boil with a little nitric acid, then add carbonate of pota ium, in exce , and digest the precipitate in a solution of oxalic acid, to remove any oxide of iron; wash and dry the residuum (oxalate of cobalt), and expose it to great heat, in a covered crucible lined with charcoal; the product is pure metallic cobalt. 2. Mix equal parts of oxide of cobalt or roasted Cornish cobalt ore, and soft soap, and expose them to a violent heat in a covered crucible. 3. Pa hydrogen gas over oxide of cobalt strongly heated in a porcelain tube. Prop., Use, . Cobalt is a white, brittle metal; unchanged in the air; feebly acted on by dilute hydrochloric and sulphuric acids; has a high melting-point, and is strongly magnetic; sp. gr. 8·5. It is seldom employed in the metallic state, from the great difficulty of reducing its ores, but its oxide (black oxide) is largely employed in the arts. It forms salts with the acids, which are interesting from the remarkable changes of colour which they exhibit. See Ink , Smalts , Zaffre , and below . Char., Tests. Solutions of the salts of cobalt are known as follows:—1. Ammonia gives a blue precipitate, slightly soluble in exce , giving a brownish-red colour.—2. Pota a gives a blue precipitate, turning to violet and red when the solution is heated.—3. Carbonate of ammonium and carbonate of sodium give pink precipitates; that from the former is soluble in exce .—4. Cyanide of pota ium gives a yellowish-brown precipitate, soluble in exce ; and the clear solution, after being boiled, is unaffected when mixed with hydrochloric acid.—5. Sulphuretted hydrogen produces no change in acid solutions.—6. Sulphydrate of ammonium gives a black precipitate in neutral solutions.—7. Melted with borax, before the blowpipe, it gives a bead of a magnificent blue colour, almost verging on black, if much is present. Phosphate of sodium and ammonium give a similar bead; but the colour is le intense.