ATOMIC WEIGHTS 



23 



In their second and final series Dittmar and Henderson dried their 

 hydrogen, after deoxidation by red-hot copper, over caustic potash and 

 subsequently phosphorus pentoxide. The copper oxide and copper of 

 the combustion tube were both weighed in vacuo. The results were as 

 follows, vacuum weights being given : 



Mean, 15.861, ± .0052 



The authors reject the three bracketed determinations, because of 

 irregularities in the course of the experiments. The mean of the ten 

 remaining determinations is 15. 855, ±.0044. Both means, however, have 

 to be corrected for the minute trace of hydrogen occluded by the reduced 

 copper. This correction, experimentally measured, amounts to +.006. 

 Hence the mean of all the experiments in the series becomes 15.867, 

 ±.0052, and of the ten accepted experiments, 15. 861, ±.0044. The 

 authors themselves select out seven experiments, giving a corrected mean 

 of 15.866, which they regard as the best value. Taking all their evi- 

 dence, their two series combine thus : 



First series 15.865, ± .0103 



Second series 15.867, ± .0052 



General mean 15.8667, ± .0046 



Leduc,^ who also effected the synthesis of water over copper oxide, 

 following Dumas' method with slight modifications, gives the results of 

 two experiments, as follows : 



^ Compt. Rend., 115, 41. 1832. See also the complete memoir in Ann. Chim. Phj^s. (7), 

 48. 1898. In the latter Leduc gave a preliminary determination which inad« O = 15.860. 



15, 



