from Bismuth, Arsenic, Iron, and Copper. 53 



tion of carbonate of potash ; or this trouble may be saved 

 by adding to the precipitated solution a considerable quan- 

 tity of carbonate of potash, and then suffering the whole 

 mixture to boil for some time : we are now sure that the 

 difficultly soluble arseniates, if any were present, are de- 

 composed and got rid of. 



In order to know the nature of the precipitate, let a 

 portion of it be neutralized with sulphuric acid ; mingle 

 the solution with sulphate of ammonia, evaporate the fluid, 

 and suffer it to crystallize. From the colour of the crystal- 

 lized salt, the experienced operator may form already some 

 judgment of what his precipitate principally consists : if, 

 namely, the crystals have a greenish colour, he is sure they' 

 contain nickel. In that case, it is necessary to redissolve 

 and recrystallize them till they acquire a red colour. Should 

 it, however, happen that during the repeated solution and 

 recrystallization the salt acquires a more lively green colour, 

 and that the noncrystallized fluid or mother-liquor acquires a 

 more lively red colour ; in that case his principal object should ' 

 be directed towards the direct separation of the nickel from 

 the solution. For that purpose, let the whole remaining so- 

 lution be divided into four equal parts ; neutralize one part 

 by sulphuric acid, and note the quantity of acid which was 

 necessary for that purpose, in order to learn the quantity 

 required for the rest. 



To save, however, the expense of the direct application 

 of sulphuric acid, it is more ceconomical to convert the 

 quantity of sulphuric acid necessary for the saturation of 

 the precipitate into sulphate of ammonia, by making it act 

 on muriate of ammonia. The muriatic acid, though not 

 wanted in the process in view, and the sulphate of ammo- 

 nia which will thus be obtained, will amply repay the ex- 

 pense incurred. 



The sulphate of ammonia must be dissolved in water, and 

 the before-obtained precipitate digested in this solution. If 

 the whole precipitate should not become dissolved, sulphuric 

 acid may be added to effect a solution. This, however, will 

 be seldom found to be the case. Should the solution be tur- 

 bid, suffer it to stand undisturbed to subside ; for it may 

 happen that a minute quantity of arseniate or oxide of iron, 

 or both, becomes deposited, which is in proportion to the 

 care with which the operator has conducted his former pro- 

 cesses. 



The clear fluid must then be evaporated at a low heat till 

 a considerable pellicle appears, and then suffered to cool : 



D 3 green 



