./ W. Gibhs — Equilibrium of Heterogeneous 8ubstcm<:es. 201 



mined by its temperature and pressure and its ultimate composition (in 

 respect at least to the particular substances just mentioned). By the 

 absorption of the substances 8^, . . . S^ independently and without 

 passive resistances, it is meant that when the absorbing body is in 

 equilibrium with another containing these substances, it shall be 

 possible by infinitesimal changes in these bodies to produce the ex- 

 change of all these substances in either direction and independently. 

 An exception to the preceding statement may of course be made for 

 cases in which the result in question is prevented by the occurrence of 

 some other kinds of change ; in other words, it is assumed that the 

 two bodies can remain in contact preserving the properties which 

 have been mentioned. 



The term catalysis has been applied to such action as we are con- 

 sidering. When a body has the property of reducing another, with- 

 out limitation with respect to the proportion of the two bodies, to a 

 phase of dissipated energy, in regard to a certain kind of molecular 

 change, it may be called a perfect catalytic ar/ent with respect to the 

 second body and the kind of molecular change considered. 



It seems not improbable that in some cases in which molecular 

 changes take place slowly in homogeneous bodies, a mass of which 

 the temperature and pressure are maintained constant will be finally 

 brought to a state of equilibrium which is entirely determined by its 

 temperature and pressure and the quantities of its ultimate compo- 

 nents, while the various transitory states through which the mass 

 passes, (which are evidently not completely defined by the quantities 

 just mentioned,) may be completely defined by the quantities of cer- 

 tain proximate components with the temperature and pressure, and 

 the matter of the mass may be brought by processes approximately 

 reversible from permanent states to these varioiis transitory states. 

 In such cases, we may form a fundamental equation with reference to 

 all possible phases, whether transitory or permanent; and we may 

 also form a fundamental equation of different import and containing 

 a smaller number of independent variables, which has reference solely 

 to the final phases of equilibrium. The latter are the phases of dissi- 

 pated energy (with reference to molecular changes), and when the 

 more general form of the fundamental equation is known, it will be 

 easy to derive from it the fundamental equation for these permanent 

 phases alone. 



Now, as these relations, theoretically considered, are independent 

 of the rapidity of the molecular changes, the question naturally arises, 

 whether in cases in which we are not able to distinguish such trausi- 



Trans. Conn. Acad., Vol. III. 26 February, 1876. 



