EQUILIBRIUM OF HETEROGENEOUS SUBSTANCES. 141 



by the action of any small body, or by a single electric spark, or 

 by any cause which is not in some way proportioned to the effect 

 to be produced. But when the proportion of the proximate com- 

 ponents of a mass taken in connection with its temperature and 

 pressure is not such as to constitute a phase of dissipated energy, 

 it may be possible to cause great changes in the mass by the contact 

 of a very small body. Indeed it is possible that the changes produced 

 by such contact may only be limited by the attainment of a phase 

 of dissipated energy. Such a result will probably be produced in 

 a fluid mass by contact with another fluid which contains molecules 

 of all the kinds which occur in the first fluid (or at least all those 

 which contain the same kinds of matter which also occur in other 

 sorts of molecules), but which differs from the first fluid in that the 

 quantities of the various kinds of molecules are entirely determined 

 by the ultimate composition of the fluid and its temperature and 

 pressure. Or, to speak without reference to the molecular state of the 

 fluid, the result considered would doubtless be brought about by 

 contact with another fluid, which absorbs all the proximate com- 

 ponents of the first, S v ... S n (or all those between which there 

 exist relations of equivalence in respect to their ultimate analysis), 

 independently, and without passive resistances, but for which the 

 phase is completely determined 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 

 S v ... S n independently and without passive resistances, it is meant 

 that when the absorbing body is in equilibrium with another contain- 

 ing these substances, it shall be possible by infinitesimal changes 

 in these bodies to produce the exchange 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 

 considering. When a body has the property of reducing another, 

 without 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 agent 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 



