182 . Dr. E. J. Mills and J. J. Smith. [June 19, 



according to the most valuable evidence we possess,* appear to be 

 entirely the same. We, therefore, thought it very advisable to inquire 

 on what terms they might prove to be mutually equivalent : and the 

 particular equivalence we have examined has been equivalent pre- 

 cipitability of the sulphates, by sodic hydrate, from an aqueous 

 solution. 



I. Preparation of the Salts. 



The pure cobaltous salt was prepared by converting some excellent 

 commercial crystallized chloride into luteochloride, the process em- 

 ployed having been already described by one of us.f The luteo- 

 chloride was purified by precipitation with hydric chloride, and the 

 mixture of oxides it left behind on ignition was evaporated with re- 

 distilled hydric sulphate. 



The pure nickelous salt was prepared from a sample of nickelous 

 chloride which contained copper, lime, and iron, but no cobalt. The 

 copper present was precipitated with hydric sulphide, and the nickel 

 in the filtrate was precipitated by hydric oxalate, in an acid solution. 

 The nickelous oxalate was washed thoroughly with dilute hydric 

 nitrate, ignited, and the oxide so formed heated with pure hydric 

 sulphate, and so converted into sulphate. 



II. Method of separating Nickel from Cobalt. 



We had next to select a method for the quantitative separation of 

 nickel from cobalt. The first to which we had recourse was Liebig's,^ 

 which consists in adding hydric cyanide and potash to the mixed 

 saline solutions, therebv forming nickelopotassic cyanide and potassic 

 cobalticyanide : these new compounds are boiled with freshly pre- 

 cipitated mercuric oxide, which throws down the nickel as oxide and 

 cyanide. The cobalt in the filtrate is then precipitated as mercurous 

 cobalticyanide. On the ignition of these precipitates, nickelous oxide 

 and cobaltic oxide are respectively left behind. We converted the 

 oxides into sulphates and weighed them as such (Throughout the 

 whole of these experiments the nickel and cobalt were always weighed 

 as sulphates.) We found, however, that after the expulsion, by 

 ignition, of the mercury in the precipitates, the oxides were left in so 

 dense and compact a state, that it was only with the greatest difficulty 

 that they could be converted into sulphates. To remedy this, a 

 weighed quantity of pure baric sulphate was added to the liquid 

 before precipitation ; the precipitate, becoming mixed with the baric 

 sulphate, was thus spread over a large surface, so that the oxide was 

 obtained in a finely divided state, and easily converted into sulphate. 



* Russell, " Journal of the Chemical Society," (1869), p. 294. 

 f " Philosophical Magazine," (4), xxxv, p. 245. 

 " Ann. Ch. Pharm.," lxv, 244. 



