﻿230 Mr. Bernard Cavanagh on 



in embryo o£ the larger and more complex problem o£ " atom- 

 binding/'' and that in his distinction between "bound " and 

 " unbound " electrons in the atom, we may have in its 

 simplest aspect the distinction between "chemical" and 

 " physical " forces. 



II. Molecular Thermodynamics. 



In general thermodynamics, which is based on, and applies 

 to experience, the independent variables, besides temperature 

 and pressure, are the masses of the "components/' and 

 these are reduced to the minimum necessary to define the 

 system under all circumstances not conventionally or prac- 

 tically excluded from consideration. 



To take a familiar example, hydrogen and oxygen will 

 suffice as the components of a system containing in addition 

 water, provided low temperatures are excluded from 

 consideration, or the presence of efficient catalysts is assumed. 

 In so far as we may suppose that the decomposition and 

 formation of water do proceed even at low temperatures in 

 the absence of catalysts, though at an immeasurably small 

 rate, it is clear that theoretically the two components would 

 always suffice for this system if sufficient time ivere allowed. 



And conversely they would never suffice if the rate of experi- 

 mentation were sufficiently increased. 



Striking examples of the practical reality of this entry of 

 the time factor into the question of the necessary number of 

 components, have been given in recent years by the work of 

 A. Smith and of A. Smits, who by increasing the rate of 

 experiment ation, have increased the number of components 

 necessary to describe certain systems, the latter author having 

 propounded an interesting theory of allotropy on the basis 

 of his experiments. 



Now we can conceive this carried far beyond the bounds of 

 purely practical limitations, and the question arises, " How 

 far ? * 



The atomic or elementary theory of matter is introduced 

 when we say that at one extreme, when unlimited time is 

 available, the elementary atomic species will be necessary as 

 well as sufficient as the components of any system. 



Starting from this extreme and increasing the rate of 

 experimentation we can imagine one complex after another 

 of these elementary atoms (as its rate of formation and 

 decomposition ceases to be great in comparison with the rate 

 of experimentation) taking its place in the list of " com- 

 ponents necessary to describe the system." Remembering, 





