COBALT. 567 



SECTION III. 



COBALT. 

 Eq. 369, or 29.57; Co. 



Cobalt occurs in the mineral kingdom chiefly in combination 

 with arsenic, as arsenical cobalt, Co As ; or with sulphur and 

 arsenic, as grey cobalt ore, Co As 4- Co S 2 , but contaminated 

 with iron, nickel, and other metals. Its name is that of the 

 Kobolds or evil spirits of mines, and was applied to it by the 

 superstitious miners of the middle ages, who were often de- 

 ceived by the favourable appearance of its ores. These remained 

 without value, till the middle of the sixteenth century, when 

 they were first applied to colour glass blue. They are now 

 consumed in great quantity for the blue colours of porcelain and 

 stoneware. Cobalt is likewise found in almost all meteoric 

 stones. 



To obtain metallic cobalt, the native arseniuret is repeatedly 

 roasted, by which the greater part of the arsenic is converted 

 into arsenious acid, and carried off in vapour, while the impure 

 oxide of cobalt, known as zaffre, remains. This is dissolved 

 in hydrochloric acid, arid the remaining arsenic precipitated as 

 sulphuret, by passing a stream of sulphuretted hydrogen through 

 the solution. To get rid of the iron present, the last solution, 

 after filtration, is boiled with a little nitric acid, to peroxidise 

 that metal; carbonate of potash is added in excess, which 

 throws down carbonate of cobalt and peroxide of iron. The 

 precipitate is treated with oxalic acid, which forms an insoluble 

 oxalate of cobalt and the soluble peroxalate of iron. The 

 oxalate of cobalt is dried and decomposed by ignition in a 

 covered crucible, when the oxide is reduced by the carbon of 

 the acid, which goes off as carbonic acid, while the metallic 

 cobalt remains as a black powder. To separate cobalt from 

 nickel, with which it is almost always associated, the mixed 

 oxalates of cobalt and nickel, obtained by the preceding process, 

 are dissolved in ammonia, after which the liquid is diluted and 

 exposed to the air in a shallow bason for several days. The 

 ammonia evaporates, and the salt of nickel precipitates as a 

 green powder, while the salt of cobalt remains in solution. The 



