OUR METHOD OF DETERMINATION. 59 



In a few cases, as for copper and chlorine, the atomic 

 weight approaches the exact half unit. 



Moreover these atomic weights have always been exten- 

 sively used under the name of common atomic weights. 



The trite atomic weights of the elements are experimen- 

 tally known to differ by very small quantities, if at all, from 

 these common values. 



This is the plain, unquestionable result of all the chem- 

 ical work of the nineteenth century in atomic weight deter- 

 minations. 



Hence the real problem to be solved is the determination 

 of the exact, but small, departure of the true atomic weight 

 from these common values. 



Standard Atomic Weights. 



These common atomic weights of whole numbers (or in 

 a few cases exact half units) shall in our calculations be 

 taken as the absolutely fixed standards of comparison. 



We therefore shall call them the standard atomic weights. 



The following table gives these values, carefully revised 

 by myself, and in alphabetical order of the chemical symbol. 



Table of Standard Atomic Weights. 



The mathematical problem to be solved by means of a 

 thorough discussion of all the actual analyses made by the 

 chemists of the nineteenth century, is the determination of 

 the departure of the trne atomic weights from these fixed 

 standard values. 



