ATOMIC WEIGHTS 157 



impurity, and corrected the results previously obtained. The results 

 were as follows, with a vacuum reduction : 



1.06253 grm. CuO gave .84831 grm. Cu. 79.802 per cent. 



1.91656 " 1.5298 " 79.820 



Mean, 79.811, ± .0061 



Correcting for the occluded gases in the oxide, the sum of the two 

 experiments gives 79.901 per cent, of copper, whence Cu = 63.605. Three 

 other indirect results, similarly corrected, gave 79.900 per cent. Cu in 

 CuO, or Cu = 63.603. If we assign all five experiments equal weight, 

 and judge their value by the tAvo detailed above, the mean percentage 

 becomes 79.900, ±.0038. 



The recent experiments on copper oxide, by Murmann,' are of very 

 doubtful utility. Copper was oxidized by heating in oxygen, and the 

 oxide was also reduced in hydrogen, giving values for Cu varying from 

 63.513 to 64.397. The five experiments, with all corrections, including 

 reduction to a vacuum, and eliminating the excessively high figure given 

 above, may be stated in the following form : 



Mean, 79.937, ± .0278 



Hence Cu = 63.749. Murmann himself selected values from his series 

 varying between 63.512 and 63.560. 



These figures, by Eichards and Murmann, need not be combined with 

 the data given by previous observers, so far as practical purposes are 

 concerned; but as this work is, in part, at least, a study of the com- 

 pensation of errors, it may not be wasted time to effect the combination, 

 as follows : 



Berzelius 79.823, ± .0020 



Erdmann and Marchand 79.8645, ± .0038 



Millon and Commaille 79.7787, it .0043 



Hampe 79.8347, ± .0013 



Richards 79.900, ± .0038 



Murmann 79.937, ± .0278 



General mean 79.836, ± .0010 



1 Monatsh. Chem., 27, 351. 1906. 

 11 



