J 2 Methods of purifying Col alt and Nickel 



with charcoal powder until no more arsenic (or at least very 

 little, for it is impossible to tree it wholly from arsenic and 

 sulphur,) or sulphur is volatilized. Upon the ore thus partly 

 desulphurated, &x., pour 2-3ds of its weight concentrated 

 sulphuric acid previously diluted with double its quantity 

 of water: heat the mixture in earthen pans placed on a sand- 

 bath nearly to the boiling point, and add to it gradually 

 nitrate of potash till no further action takes place, or till 

 no more red vapours are disengaged. This being done., eva- 

 porate the whole to dryness, and heat the dry mass strongly; 

 a new disengagement of red vapours again takes place ; keep 

 up the heat till no more red fumes are evolved. The heated 

 mass must then be thrown into water, and its soluble part 

 washed out by the repeated affusion of this fluid. The in- 

 soluble residue is to be treated in a similar way till the re- 

 sidue consists of nothing else but part of the matrix of the 

 ore. 



The before- obtained solution, after having been suffered 

 to subside, must be decanted or filtered, and mingled with 

 a solution of carbonate of potash. By this means the bis- 

 muth and a considerable quantity of iron (frequently also 

 arseniate of iron) become separated ; sometimes also copper 

 and nickel, in combination with arsenic acid. The colour 

 of the precipitate cannot be determined, for it differs ac- 

 cording to the nature of the ore. 



The fluid may now be examined for copper. If a polished 

 cylinder of iron, after having been immersed in the solution, 

 acquires the slightest reddish hue, copper may be suspected. 

 It is, however, not advisable to separate the copper by iron ; 

 for part of the cobalt would also be precipitated in combina- 

 tion with the copper, and a loss would thus be occasioned. 

 It is therefore, more profitable to decompose the. whole solu- 

 tion at once by carbonate of potash. The precipitate ob- 

 tained must be washed, dried, and sublimed with muriate 

 of ammonia. 



If the cobalt is contaminated with a small quantity of 

 copper, that part of the sublimed muriate of ammonia which 

 escapes undecomposed elevates all the copper, and the sub- 

 limate has a blueish colour. If a larger quantity of copper 

 be present, the sublimation must be repeated successively 

 until the last sublimed muriate does not show any vestige 

 of copper by the usual tests. 



The cobalt thus purified from copper (if it contained any) 



may again be dissolved, and the solution decomposed by 



carbonate of potash ; taking care to add the alkali in 



excess. The precipitate obtained is to be digested in a soju- 



5 tiou 



