NICKEL AND COBALT. 293 



of nickel and cobalt, using various methods, but publishing few details, 

 as he did not consider the determinations final. The sulphates, taken 

 as anhydrous, were calcined to oxides. From the ratio NiS0 4 : NiO, he 

 found Ni = 58.4 to 59.0, and from five measurements of the ratio 

 CoS0 4 : Co, Co = 58.64 to 58.76. If oxygen is taken as 16, these give for 

 the percentages of oxide in sulphate : 



CoO in CoSOv NiO in 



48.267 48.187 



48.307 48.387 



Mean, 48.287, d= .0135 Mean, 48.287, .0675 



The chlorides were dried at 100, but found to retain water; and in 

 most cases were then either fused in a stream of chlorine or of dry, 

 gaseous hydrochloric acid, or else calcined gently with ammonium 

 chloride. The determinations were then made by titration with a 

 standard solution of silver in nitric acid. Three experiments with an- 

 hydrous CoCl, gave Co = 58.72 to 58.84. Three more with CoCl 2 dried 

 at 100 gave Co = 58.84 to 59.02. Three with anhydrous NiCl 2 gave 

 Ni = 58.80 to 59.00. If the calculations were made with Ag = 108 and 

 Cl = 35.5, then these data give as proportional to 100 parts of silver : 



60.093 

 60.185 



Mean, 60.139, .0310 

 , Mean, 60.118, .0192 



In one more experiment NiCl. 2 was precipitated with a known quan- 

 tity of silver. The filtrate was calcined, yielding NiO ; hence the ratio 

 ,Ag- 2 : NiO, giving Ni = 59.29. This experiment needs no farther atten- 

 tion. 



In short, according to Marignac, and contrary to Schneider's views, 

 the two atomic weights are approximately the same. Marignac criticises 

 Schneider's earlier paper, holding that the nickel oxalate may have con- 

 tained some free oxalic acid, and that the cobalt salt was possibly con- 

 taminated with carbonate or with basic compounds. In his later papers 

 Schneider rejects these suggestions as unfounded, and in turn criticises 

 Marignac. The purity of anhydrous NiS0 4 is not easy to guarantee, and, 

 according to Schneider, the anhydrous chlorides of cobalt and nickel are 

 liable to be contaminated with oxides. This is the case even when the 

 chlorides are heated in chlorine, unless the gas is carefully freed from 

 all traces of air and moisture. 



