404 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



non-metals may be cited. Potassium is chosen in this last case because 

 it is probably among the most compressible of metals. 



Comparison of Contraction with Heat of Formation involved in 

 the Synthesis of the Bromides. 



Comparison of Contraction with Heat of Formation involved in 

 the Synthesis of Potassic Halides. 



When the more obvious experimental errors have been considered, 

 two important questions at once suggest themselves : Does this propor- 

 tionality signify equality, or is some of the energy of compression stored 

 as potential energy and not manifested as heat? Again, if this equality 

 exists, is it always exact, or is it modified by subordinate secondary 

 effects ? 



* These values are calculated from very accurate determinations of specific 

 gravity made recently in this Laboratory. See These Proceedings, 31, 163 

 (1895). 



t Approximately corrected for heat of evaporation and expansion. 



