A NEW CONCEPTION OF THERMAL PRESSURE AND 

 A THEORY OF SOLUTIONS. 



By Gilbert Newton Lewis. 



Presented by Theodore W. Richards. Received July 19, 1900. 



Introduction. 



For an understanding of all kinds of physico-chemical equilibrium a 

 further insight is necessary into the nature of the conditions which exist 

 in the interior of any homogeneous phase. It will be the aim of the 

 present paper to study this problem in the light of a new theory, which, 

 although opposed to some ideas which are now accepted as correct, yet 

 recommends itself by its simplicity and by its ability to explain sev- 

 eral important phenomena which have hitherto received no satisfactory 

 explanation. 



The theory suggested itself in the consideration of certain remarkable 

 general laws which treat of heterogeneous equilibrium in which the 

 several phases are subject to different pressures. These laws will be 

 discussed in the first section of this paper, and in the second section it 

 will be shown that they can all be explained by a single simple assump- 

 tion. In the third section it will be shown that the same assumption is 

 alone sufficient to explain all the laws of dilute solutions. In the last 

 section other consequences of the new theory will be discussed, especially 

 in their relation to the theory of van der Waals. 



I. 



The Effect of Pressure on the Tendency to Pass from 



Phase to Phase. 



It has been shown by several investigators* that, in a number of cases 

 of heterogeneous equilibrium, if the pressure upon one of the phases 

 alone is changed, a readjustment takes place that can be easily calculated. 



* Poynting, Phil. Mag. (5), XII. 32 (1881) : Schiller, Wied. Ann., LIII. 396, 

 (1894) ; Hall. Jour, of Phys Chem., III. 452 (1899.) 



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