NICKEL AND COBALT. 171 



For cobalt Sommaruga used the purpureo cobalt chloride 

 of Gibbs and Genth. This salt, dried at 110°, is anhydrous 

 and stable. Heated hotter, CoCL remains. The latter, ig- 

 nited in hydrogen, yields metallic cobalt. In every experi- 

 ment the preliminary heating must be carried on cautiously 

 until ammoniacal fumes no longer appear : 



Further along this series will be combined with a similar 

 one by Lee. It may here be said that Sommaruga's paper 

 was quickly followed by a critical essay from Schneider,* 

 endorsing the former's work, and objecting to the results of 

 Russell. 



In 1867 still another new process for the estimation of 

 these atomic weights was put forward by Winkler,t who 

 determined the amount of gold which pure metallic nickel 

 and cobalt could precipitate from a neutral solution of sodio- 

 auric chloride. Experimentally, the method seems to be 

 quite accurate ; practically, it involves a knowledge of the 

 defectively ascertained atomic weight of gold. In order to 

 obtain pure cobalt Winkler prepared purpureo-cobalt chlo- 

 ride, wdiich, having been four or five times recrystallized, 

 was ignited in hydrogen. His nickel was repeatedly puri- 

 fied hv precipitation with sodium hypochlorite. From ma- 

 terial thus obtained pure nickel chloride was prepared, 

 which, after sublimation in dry chlorine, was also reduced 

 by hydrogen. 100 parts of gold are precipitated by the 

 quantities of nickel and cobalt given in the third columns 

 respectively. In the cobalt series I include one experiment 



* Poggend. AnnaL, 130, 310. 



t Zeit. Anal. Chem., 6, 18. 1867. 



