66 Memoir on Nickel. 



the state of arseniate. This process to be practicable require* 

 only a rigorous analysis ol^ the aiacnic acid, and of an inso- 

 luble aiseniate, such for example as that of lead. I made 

 the first by burainc: 100 parts of arsenic by nitric acid. I 

 found that the arsenic acid contained in 100 parts, 64 of 

 arsenic and 3G of oxygen; so that it contains only )0"24 

 more of oxyoien than the arsenious acid, since 100 parts of 

 the latter retjuire only 16 of oxygen to become arsenic acid. 

 One thing singular is, that these 100 parts of arsenious acid 

 require at least triple the time as 100 parts of arsenic to be 

 completely acidified. I analysed the arseniate of lead by 

 saturating with ammonia 100 parts of very dry arsenic acid, 

 and precipitating it by acetite of lead. I obtained 380 parts 

 of arseniate of lead, which, dissolved in nitric acid and pre- 

 cipitated by sulphate of soda, gave me 236 parts of sulphate 

 of lead. The liquor remained uncoloured by the sulphu- 

 rated hydrogen ; it contained no more lead ; whence it fol- 

 lows, almost rigorously, that in arseniate of lead the ratio 

 of the arsenic acid to the oxide of lead is as 5 to Q. 



Ex per nil cut IV, 



The oxides of the last experiment, being precipitated by 

 the hydro-sulphurel of potash, were introduced into a ma- 

 trass with the nitric acid. The solution was rapid, and 

 accompanied with a grtat disengagement of nitrous acid, 

 which caused the matter to swell up considerably: it was 

 of a still more beautiful green colour, especially as in the 

 liqtiorof the first experiment there were remarked flakes of 

 sulphur which were separated by the filter, and it was then 

 decomposed by potash. The oxides, to the nun)ber of three, 

 nickel, cobalt, and iron, were precipitated. Being washed 

 in a large quantity of water, the principal object was to se- 

 parate them exactly. I knew by mv own experiments that 

 black oxide of cob lit was not sensibly soluble in ammonia j 

 but I did not know how to reduce the blue oxide to that 

 state of oxidation. I tried for this purpose several means. 

 Desiccation in the air, by the help of a gentle heat and a 

 renewal of the surfaces to favour the absorption of oxygen, 

 gave n»e a result not very satisfactory. I did not obtain the 

 whole of the black oxide, some part of it having dissolved 

 in the anmionia. The u*c of oxygenated muriatic acid 

 was not more success^ful : it made the oxide, indeed, pass 

 immediately *') tlie maximum of oxidation, but it retained 

 a part in solution. Knowing with what facility oxygenated 

 muriatic acid saturated with lime gives up its oxygen, I 

 conceived, iiu idea that it might succeed; and, indeed, 



scarcely 



