440 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



On examination of the silver it was found that traces of cobalt were 

 retained — less than 0.5 mg. in the first determination and less than 0.2 

 mg. in the second. Taking these amounts as corrections, the two experi- 

 ments give for the ratio 2Ag: Co:: 100: a; the subjoined values: 



27.706 

 27.G87 



These figures confirm those previously found, and as they fall within 

 the limits of the preceding series, they may fairly be included in it, when 

 all eight values give a mean of 27.705, ±.0050. Hence Co = 59.78. 



Still another method, radically dift'erent from all of the foregoing proc- 

 esses, was adopted by Winkler in 1894.' The metals were thrown down 

 electrolytically upon platinum, and so weighed. Then they were treated 

 with a known excess of a decinormal solution of iodine in potassium 

 iodide, which redissolved them as iodides. The excess of free iodine was 

 then determined by titration with sodium thiosulphate, and in that way 

 the direct ratio between metal and haloid was ascertained. The results 

 were as follows, with the metal proportional to 100 parts of iodine given 

 in the third column : 



Cobalt. 



Mean, 23.462, ± .0027 



Hence Co = 59.56. 



Nickel. 



' Zeitsch. anorg. Chem., 8, 1. 1894. 



