LEWIS. — THE LAW OF PHYSICO-CHEMICAL CHANGE. 



57 



Q,^, = Q, + ETln^- Q,, or Q, - Q, = Q,,, -ETln ^^. 



We may therefore write equation (9) as 



9 In 



n. 



9T 



QU2 



1 ^' 



>p 



BT' T 



Since we are dealing with infinitely dilute solutions in the same solvent, 

 t/^i = p III and \p. = p Ha, therefore 



"^ r= — , and the above equation becomes 



4'2 ^2 



Pln^ 

 . 9 T 



Ql,2 



ET' 



in^ 

 7' 



(10) 



This is the desired equation connecting temperature and escaping 

 tendency. Its form can be simplified by a slight rearrangement. 



Considering the quantity Tin -^ we notice that 



9T\n'tl 9\J' 



^^^T-^ + ln'^,ov 



9\J-^ . 9Tln'tl In?^ 



^2 



9T ~ ' 9T ' ^"./.s'" dT 

 Combining this equation with (10) gives 



£ 

 ^ 



{J/o 



^2 



9 T 



T 



9T\J-^ 

 IA2 



, 9T 



Ql.2 



ET 



(11) 



Leaving in this form for the present the equation connecting tempera- 

 ture and fugacity at constant pressure, let us determine the influence of 

 pressure on the fugacity at constant temperature. I have already dis- 

 cussed this question in a previous paper,* but instead of using the 

 general equation there derived it has seemed preferable to base all 

 the reasoning of this paper directly upon the four laws stated in the 

 introduction. 



Let us consider any simple substance and a solvent, so arranged f 

 that the pressure upon the substance in question may be altered without 



* Loc. cit. 



t Several such arrangements are described in the paper just mentioned. 



