ATOMIC WEIGHTS 441 



In these experiments, as well as in some previous series, a possible 

 source of error is to be considered in the occlusion of hydrogen by the 

 metals. Accordingly, in a supplementary paper, Winkler' gave the 

 results of some check experiments made witli iron, which, however, was 

 not absolutely pure. The conclusion is that the error, if existent, must 

 be very small. 



In 1895 Hempel and Thiele's work on cobalt appeared.^ First, cobalt 

 oxide, prepared from carefully purified materials, was reduced in hydro- 

 gen. The weights of metal and oxygen are subjoined, with the per- 

 centage of cobalt in the oxide deduced from them : 



Mean, 78.666, ± .0074 



Hence Co = 58.998. 



In their next series of experiments, excluding a rejected series, Hempel 

 and Thiele weighed cobalt, converted it into anhydrous chloride, and 

 noted the gain in weight. In four of the experiments the chloride was 

 afterwards dissolved, precipitated with silver nitrate, and then the silver 

 chloride was weighed. The data are as follows : 



Co. CI taken up. AgCl. 



.7010 .8453 



.3138 .3793 



.2949 .3562 1.4340 



.4691 .5657 2.2812 



.5818 .7026 2.8303 



.5763 .6947 



.5096 .6142 2.4813 



From these weights we get two ratios, thus : 



2AgGl:Co::100:x. 

 20.565 

 20.564 

 20.556 

 20.538 



Mean, 20.556, ± .0043 



.0241 



Hence Co = 58.93. 



1895. See preceding section of this work, on iron, tor tlie 



