On the Purification of Nickel. 31% 



reseirible it in some of its chemical habitudes. On account 

 of its matjnctic property, it has been supposed impossible to 

 divest it "of iron; and until the method lately adopted by 

 R. Chenevix, esq. no certain means appear to havebeenknown 

 for the separation of the arsenic. 



In order to purify this metal the following method may 

 be adopted, which includes that above alluded to for the se- 

 paration of the arsenic.- Let nickel be dissolved in dilute 

 nitric acid to complete saturation ; to the tillered solution 

 add nitrate of lead in sufficient quantity to precipitate the 

 arsenic acid. If more should be employed than is required, 

 the excess occasions no inconvenience. Having separated^ 

 the arseniate of lead by the filter, add a small quantity of 

 nitric acid to the solution, and immerse a bar of iron to 

 precipitate the copper. This being done, there remain in 

 solution the oxides of nickel, cobalt, iron, and lead, which 

 may be precipitated by carbonate of potash. The precipitate, 

 after sufficient washing, is to be put, while moist, into a so- 

 lution of ammonia, which, dissolving the oxides of nickel 

 and cobalt, leaves those of iron and lead to be separated by 

 filtration. 



All that is now necessary is to separate the oxides of co- 

 balt and nickel, in order to' complete the purification of the 

 latter: but before the experiments for this purpose are re- 

 lated, it may not be amiss to state the properties of the ammo- 

 niacal solutions of some of the metallic oxides, although the 

 habitudes of all of them are not mmiediately connected with 

 the present inquiry. These I prepared by precipitating the 

 oxides from their solutions in acid, and putting them, while 

 moist, into solution of ammonia. Notwithstanding this is 

 the most favourable state for the ammonia to act upoa 

 them, yet in every case, even after long digestion, the am- 

 iTionia is in excess, since a part of it may be evaporated with- 

 out causing any precipitation of the oxide. As these solu- 

 tions possess different properties when the ammonia is in 

 fcxcess and when it is not, in the following experiments I 

 shall call the former solution, and the latter craporated so- 

 lution. The evaporation was continued until moist tur- 

 nicrie paper, when held over the solutions, suffered no 

 change. 



■Sfdution of oxide of silver in ammonia. Colourless : i3 

 not decomposed by water. Evaporated solution — Speedily 

 decomposed by water : the precipitate blueish white, be- 

 coming gradually brown by exposure to liglit. 



'Solution of oxide of topper in ammoma. — Colour purple. 



