178 BUTLER ART. D 



XIV. Phases of Dissipated Energy. Catalysis* 



41. Dissipated Energy. In considering the conditions of 

 equihbrium of heterogeneous masses, changes which are "pre- 

 vented by passive forces or analogous resistances to change" 

 have been excluded. Thus it often happens that "the number 

 of proximate components which it is necessary to recognise as 

 independently variable in a body exceeds the number of com- 

 ponents which would be sufficient to express its composition." 

 Thus, at low temperatures the combination of hydrogen and 

 oxygen may be regarded as prevented by passive forces, and 

 in a system containing hydrogen, oxygen and water it is neces- 

 sary to recognize all three substances as independently variable 

 components. 



At higher temperatures, when the combination of hydrogen 

 and oxygen is not prevented by passive forces, the state of the 

 system is entirely determined by the temperature, pressure and 

 the total quantities of hydrogen and oxygen present. The 

 value of f can be expressed as a function of these four variables. 

 The fact that part of the matter present exists in the form of 

 water vapour does not affect the form of this function, but it is 

 one of the facts which determine the nature of the relation 

 between ^ and the above mentioned variables. 



In cases like those first mentioned^ of all the phases which 

 may be formed from the given matter, there are some for 

 which the energy is as small as that of any other state of the 

 same matter having the same entropy and volume, or for which 

 the value of ^ is as small as that of any other state of the same 

 matter at the same temperature and pressure. These are 

 called phases of dissipated energy. 



It is characteristic of such phases that the equilibrium can 

 only be slightly disturbed by the action of a small body, or by 

 the action of a single electric spark. The effect produced by 

 any such action is in some way proportionate to its cause. But 

 in a phase which is not a phase of dissipated energy, it may be 

 possible to cause very great changes by contact with a very 

 small body, or other action. Such changes may only be limited 

 by the attainment of a phase of dissipated energy. 



* Gibbs, I, 138-141. 



