VALIDITY OF THE PRINCIPLE OF LE CHATELIER. 



35 



It is clear therefore that lines of constant composition are steeper 

 than lines of equilibrium composition. 



It follows at once that if G be increased while the system is kept in 

 equilibrium, so that the representative point travels along QT, then 

 the change in x from Xato Xb is that which at constant G increases H, 

 or at constant H increases G. 



But this is the principle of Le Chatelier. This principle therefore 

 holds whenever the conditions (55) (56) are satisfied, and the system 



H 



G 



Figure 2. 



is stable towards He both when x = constant and when x = xi (i.e. 

 when X has its equilibrium value). 



Similarly, it can be shown that if the conditions (55), (56) are re- 

 placed by 



<p (x, G, H) = 



dGs . ^ 



—r- — according as H — H. — 

 dt > ^ < 



