XVI.l ON EQUIVALENT VOLUMES. 437 



3 and 5 corresponds to propionic acid C 6 H 6 4 , of whose specific 

 gravity I find no recorded observation. The density of many 

 of these liquids is not accurately known, and the results of 

 different experimenters are not precisely accordant. The spe- 

 cific gravity at their boiling-points should probably be chosen 

 for the purpose of comparison, and these approximations lead 

 us to expect that future observations will establish a simple 

 relation between the densities of liquids and their vapors. 



In a succeeding paper [XVII. of the present volume] it is 

 proposed to apply the principles explained in the present essay 

 in an examination of the equivalents of a number of minerals 

 and other crystallized species. 



