This metal occurs sparsely in some arsenical ores, usually accompanied by nickel; its chief sources are cobalt speiss ([CoNiFe] As,), cobalt glance ([CoFe] [AsS],2 ) and cobalt bloom ( [Co2(As04)2 + 8H20] ). These ores are roasted or calcined in the air, yielding an impure cobalt arsenate, termed " zaffre." The iron is got rid of by a smelting process resembling that used in copper extraction; the roasted ore being fused with a flux of sand or lime carbonate, by which the iron slag rises to the surface, leaving the cobalt below as a heavy speiss. This latter is dissolved in strong hydrochloric acid, and any iron arsenate present is precipitated by careful addition of solution of lime chloride and a little milk of lime. The clear supernatant solution is drawn off and treated with sulphuretted hydrogen to throw down the copper and bismuth; cobalt oxide is then precipitated from the clarified solution by means of lime chloride, and is washed and ignited ready for the market. Metallic cobalt is obtained as a grey powder by igniting the oxide or chloride in a current of dry hydrogen, or the metal can be procured in a compact state by strongly heating the oxalate under a layer of powdered glass; and fused to a regulus by heating in a graphite, lime, or magnesia crucible.
Cobalt melts at a lower temperature than iron, but is harder, malleable, very tough, and magnetic. It dissolves easily in nitric, hydrochloric, and dilute sulphuric acids; its colour resembles that of polished iron, and its sp. gr. is 8.5 to 8.7. In the coherent form, it suffers no change in the air at ordinary temperatures, but slowly oxidizes on heating, and at a very high temperature burns with a red flame.