CHEMISTRY 243 



that active, diverse, and important inorganic 

 substances usually contain oxygen or hydro- 

 gen, and that it is the union of other elements 

 with these two which renders them available 

 and useful to the organism. 



Ill 



THERMOCHEMISTRY 



Every chemical change consists in simul- 

 taneous rearrangements of matter and energy. 

 The true nature of the chemical process is to 

 be sought neither in the one nor in the other 

 of these two phenomena, but in both together ; 

 and properly energy is as much the chemist's 

 concern as matter itself. 



Thus far in the present investigation, con- 

 siderations regarding energy have been avoided 

 except in the case of hydrolytic cleavages, and 

 these constitute a unique class of reactions* 

 No other large and important class is char- 

 acterized by inappreciable heat of reaction, 

 for it is as heat that chemical energy commonly 

 manifests itself when liberated. It is evident, 

 however, in accordance with the fundamental 

 postulates, that the organism must have 

 energy to actuate as well as matter to form 

 its mechanism. Therefore the nature of the 

 energy transformations, which make up one 



