NICKEL AND COBALT. 303 



Considered with reference to tlie purpose of the investigation, this 

 mean and its probable error liave no real significance. But it is very- 

 close to the means of other experimenters, and a study of the variations 

 represented by the several fractions seems to indicate fortuity rather 

 than system. Remmler regards his results as indicating lack of homo- 

 geneity in his material ; but it seems more probable that such differences 

 as exist are due to experimental errors and to impurities acquired in the 

 long process of purification to which each fraction was submitted, rather 

 than to any uncertainty regarding the nature of cobalt itself. For either 

 interjiretation the data are inconclusive, and I therefore feel justified in 

 treating the mean like other means, and in combining it finally with 

 them. 



From the same point of view — that is, with reference to the supposed 

 heterogeneity of nickel — Kriiss and Schmidt * carried out a series of frac- 

 tionations of the metal by distillation in a stream of carbon monoxide. 

 Nickel oxide, free from obnoxious impurities, was first reduced to metal 

 by heating in hydrogen, after which the current of carbon monoxide was 

 allowed to flow. The latter, carrying its small charge of nickel tetra- 

 carbonyl was then passed through a Winkler's absorption apparatus con- 

 taining pure aqua regia, from which, b}' evaporation, nickel chloride was 

 obtained, and from that, by reduction in hydrogen, the nickel. Ten 

 such fractions were successively prepared and studied ; first, by prepa- 

 ration of NiO and its reduction in hydrogen ; and, secondly, in some 

 cases, by the reoxidation of the reduced metal, so as to give a synthetic 

 value for the ratio Ni : 0. The data obtained are as follows, the successive 

 fractions being numbered : 



Reduction of NiO. 



* Zeit. Aiiorg. Chera., 2, 235. 1892. 



