RECALCULATION OF THE ATOMIC WEIGHTS. 



OXYGEN. 



The ratio between oxygen and hydrogen is the foundation 

 upon which the entire system of atomic weights depends. 

 Hence, the accuracy of its determination has, from the 

 beginning, been recognized as of extreme importance. A 

 trifling error here may become cumulative when repeated 

 through a moderate series of other ratios. 



Leaving out of account the earliest researches, which have 

 now only a historical value, we find that three methods 

 have been employed for fixing this important constant. 

 First, the synthesis of water, effected by passing hydrogen 

 gas over red hot oxide of copper. Secondly, the exact 

 determination of the relative density of the two gases. 

 Thirdly, by weighing the quantity of water formed upon 

 the direct union of a known volume of hydrogen with 

 oxygen. 



The first of these methods has been employed in three 

 leading investigations, namely, by Dulong and Berzelius,* 

 by Dumas, and by Erdmann and Marchand. The essential 

 features of the method are in all cases the same. Hydrogen 

 gas is passed over heated oxide of cop23er, and the water 

 thus formed is collected and weighed. From this weight 

 and the loss of weight which the oxide undergoes, the exact 

 composition of water is readily calculated. Dulong and 

 Berzelius made but three experiments, with the following 

 results for the percentages of oxygen and hydrogen in 



in water : 



O. H. 



88. 942 11.058 



88.809 1 1. 191 



88.954 11.046 



* Thomson's Annals of Philosophy, July, 1821, p. 50. 



