308 THE ATOMIC WEIGHTS. 



metals. Accordingly, in a supplementary paper, Winkler* gives the 

 results of some check experiments made with 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. f First, cobalt 

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

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

 age of cobalt in the oxide deduced from them : 



Co. O. Percentage. 



.90068 .24429 78.664 



.79159 .21445 78.686 



1.31558 .357i6 78.648 



Mean, 78.666, .0074 



This mean combines with former means as follows : 



Russell ........... . ..................... 78.592, d= .0023 



Zimmermann ............................ 78-635, .0002 



Retnmler ............................ .*. , 78.613, .0099 



Hempel and Thiele ...................... 78.666, .0074 



General mean 78.633, .0002 



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. Cl Taken Up. AgCl. 



.7010 - 8 453 



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 : 



* Zeitsch. Anorg. Chem., 8, 291. 1895. 

 fZeitsch. Aiiorg. Chem., n, 73. 



