RICHARDS AND CUSHMAN, — ATOMIC WEIGHT OF NICKEL, 343 



with pure oxide of mercury, thus doing away with the use of au alkaline 

 precipitant. This improvement also lessened the danger of Russell's other 

 chief error, and at the same time introduced yet another with au opposite 

 tendency, the inclusion of mercury ; hence it is not surprising that his 

 result should be somewhat the lower of the two. An unprejudiced 

 critic cannot but consider Zimmermann's work as the best among the 

 older researches, and it is pleasant to call attention to the fact that Zim- 

 mermann's result differs by only the fiftieth of one per cent from ours. 

 The reason why this method gives a result more satisfactory in the case 

 of nickel than in that of cobalt is probably because cobaltous oxide is so 

 much more readily raised to the higher stage of oxidation. Both Rus- 

 sell's and Zimmermann's work may have been slightly vitiated by the 

 presence of occluded hydrogen in their nickel ; but it is impossible now 

 to appraise the error involved, because the phenomenon is so irregular. 



It is convenient to class together five more investigations which ap- 

 peared between 1857 and 1871.* In the light of present knowledge 

 concerning the possibilities of accurate quantitative work these con- 

 tributions may be dismissed with few words. Marignac showed that 

 Schneider's oxalate contained occluded impurities, and Schneider showed 

 that Marignac's chloride could hardly have been both anhydrous and 

 free from oxide. Our own experience entirely confirms both of these 

 criticisms. Dumas's lack of ability to determine chlorine with accuracy 

 throws out his analyses of the chloride at once, even if one is credulous 

 enough to believe that the choride itself was pure. Sommaruga precipi- 

 tated sulphuric acid from nickelous potassic sulphate as baric sulphate, 

 a method now ostracised except for crude work. Lee's work was won- 

 derfully accurate, considering the small quantities of materials which 

 he used, but these quantities were so microscopic, and his compounds 

 were so complex, that one could not have been expected to improve 

 much upon his error of one per cent without a radical reformation of 

 method. 



Within this same period appeared another paper by Russell, elaborated 

 as carefully as his previous one, but depending upon a less satisfactory 

 process. The hydrogen evolved by the action of nickel upon hydro- 

 chloric acid was measured. Many uncertainties combine to make this 



* (1857) Schneider, Pogg. Annal., CI. 387, CVII. 61G, 58.07 



(1858) Marignac, Arch. Sci. Nat., (nouv. sen), I. 375, 58.90 



(1860) Dumas, Annalen (Llebig's), CXIII. 25, 59.02 



(1866) Sommaruga, Sitzber. Wien. Acad., LIV. [2], 50, 58.0-3 



(1871) Lee, Am J. Sci., [3], II. 4-1, 58.01 



