Copper and Nickel in quantitative analysis. 133 



calcined sulphuret, equivalent, if reckoned as CuO, to 

 1408 gr. metallic copper, or 56*32 per cent. This 

 oxide dissolved in nitric acid, and determined in the 

 usual manner by precipitation by potash, with all pre- 

 cautions, gave 1410 gr. CuO = to 11*25 gr. me- 

 tallic copper, or 4504 per cent. ; so that in this case, 

 if the ignited sulphuret had been considered as oxide, 

 the quantity of copper present would have been over- 

 estimated by more than ten per cent. 

 The copper in all these cases was thrown down from its 

 solution in nitric or hydrochloric acid, by a stream of sul- 

 phuretted hydrogen, and worked with water impregnated 

 with that gas. 



Again, in repeating these experiments with nickel, equally 

 unsatisfactory results were obtained ; thus — 



4*98 gr. nickel, equivalent to 6*34 gr. NiO, afforded 6*96 

 gr. incinerated sulphuret ; or an excess of 062 gr., equal 

 to 9*79 per cent, too much. 



1035 gr. nickel, equal to 13 16 NiO, gave 13*27 ; equal 

 to 0*11 gr. too much, or 82 per cent. 



The nickel being in these cases precipitated from its solu- 

 tion by hydrosulphuret of ammonium. 



It will also be noticed, that neither in the case of nickel or 

 copper does the excess appear constant, but perfectly un- 

 certain in amount. With the hopes that the pure oxide 

 would remain, on treating the ignited sulphuret with nitric 

 acid, in the same porcelain crucible in which it had been in- 

 cinerated, evaporating to dryness, and again igniting, so as 

 to drive off the sulphuric acid formed, — this was tried, and 



11*72 gr. of an alloy, containing by calculation 49*49 

 per cent, copper was dissolved, the copper precipitated by 

 sulphuretted hydrogen, washed and treated as above, yielded 

 7 74 gr. impure oxide, equal, if considered as CuO, to 

 6*179 metallic copper, or 52*72 per cent. ; shewing an excess 

 of above three per cent., arising from undecomposed sulphate 

 of copper. 



Further trials in which ihe oxides thus obtained were very 

 strongly ignited, with a view to decompose thoroughly all 

 sulphate present, afforded much better, and nearly if not 



