6^ 



precipitated by 



The solutiou 

 treated with 

 sulphuretted 

 hidrogen. 



Large quantity 

 of precipitate. 



Treated with 

 muriatic dcid. 



PURIFICATION OP NICKEL. 



order to dispose the arseuiates of iron and cobalt to separate 

 more fully ; and as these two salts require more acid, to 

 retain thern in solution, than the arseniate of nickel, I ac- 

 complished their separation pretty easily, by adding gra- 

 dually a solution of potash, but so as to leave an excess of 

 acid in the liquor. The precipitate, that was formed, ap- 

 peared to the eye to contain two substances: the lower stra- 

 tum was composed of granular rosecoloured particles, which 

 indicated arseniate of cobalt; the other, which was much 

 less in quantity, consisted of finer particles, more floccu- 

 lent, and of a dirty white. This I considered as arseniate 

 of iron, but I found in it also some arseniate of copper. 

 These two arseniates united and dried weighed ten ounces. 



The solution was treated with sulphuretted hidrogen, as" 

 directed by Mr. Proust, for the purpose of separating the 

 copper, oxide of arsenic, and arsenic acid.' In fact I ob- 

 tained so copious a precipitate, that at the end of some 

 days I was obliged to filter, because the tube, through 

 which the gas was introduced, though of considerable dia- 

 meter, was perpetually getting choked up. I continued to 

 keep up the stream of sulphuretted hidrogen gas, as long 

 as it occasioned any sediment in the solution. 



This operation, which continued near a month, and cou- 

 sumed 6 lbs. 8oz. of sulphuret of iron, yielded me on the 

 whole 1 lb. 14 oz. of precipitate, which I separated at three 

 different periods. The first was of a brown gray colour, 

 and when dried was intermixed with spots of white ; the se- 

 cond was more homogeneous, and deeper coloured ; and the 

 last was nearly black. 



The quantity of these different sulphurets T had obtained 

 appeared to me so exorbitant in respect to the speiss em- 

 ployed, that I was desirous of ascertaining their nature, in 

 order to know, whether I had really separated nothing but 

 copper and arsenic by this process. Accordingly I treated 

 a portion of the first with muriatic acid. The solution was 

 readily accomplished, and the sulphur separated. The 

 filtered liquor was of a fine green, but precipitated white 

 Ly prussiate of potash. Sulphuretted hidrogen did not 

 render it turbid till after the lapse of a few moments. Hav- 

 ing separated the arsenic by this means, I precipitated the. 



whole 



