316 PROCEEDINGS OF THE AMERICAN ACADEMY. 



produce a cooling effect. The latter form of reaction may be called 

 " pseudo-endothermic." 



Physical reactions involving change of state such as vaporization may 

 be interpreted in a similar fashion. The extension of the argument would 

 throw light upon Trouton's rule,* explaining the approximate regularity 

 and the causes of the deviations, and would give a further insight into 

 the relation between the liquid and the vapor states. For the present, 

 however, this discussion must be postponed. In the near future these 

 and many other aspects of the new kinetic conception will be considered 

 in another paper. 



III. Summary. 



The conclusions attained in the following paper are summarized 

 below. The first six are generalizations upon fact, the certainty of 

 which is limited only by the moderate number of cases accessible. But 

 one exception has been found, and the probable irreversibility of that 

 reaction annuls its verdict. The last headings contain hypothetical 

 inferences based upon the preceding considerations. It may be that the 

 conclusions recorded below represent merely further approximations, to 

 which exceptions may be found in the future ; but the essential agreement 

 of so many facts seems to indicate that at least they are steps in the right 

 direction. 



1. In a reaction from which concentration effects have been eliminated, 

 where the total heat capacity remains constant during the reaction, the 

 change of free energy and the heat evolved are equal. 



2. When the heat capacity of such a system diminishes during a 

 reaction, the heat evolved is greater than the change of free energy. 



3. When the heat capacity of such a system increases during a reac- 

 tion, the heat evolved is less than the change of free energy. 



4. If in addition to these tendencies there is unbalanced osmotic or 

 gas pressure, this pressure adds its share of work algebraically to the 

 change of free energy treated in the three preceding paragraphs, accord- 

 ing to the equations 



A = R Tin ^LL" + <& - p = R Tin ^^ + U-f(A K). 



C • • ■ i . . . 



5. Thus in a complex cell containing precipitates the change of free 

 energy, which represents the tendency of the reaction to take place, is by 

 no means a measure of the attractive energy concerned, but has super- 

 posed upon this attraction at least two other modifying circumstances. 



* Ostwald, Lehrbuch, I. 354 (1891). 



