572 Dr. E. D. Kleeman on Molecular Attraction 



Whittaker * has shown that X-T -^ = E = KLT, where 



E is the potential energy per cm. 2 of liquid surface, and K 

 is a constant which depends only on the nature of the 



liquid. The writer has shown that K = M — =P — > where 



lc 



M = 5'57 x 10 -1 . We will now find the form of the arbitrary 

 function in the law of molecular attraction to which this 

 relation corresponds. From equation (4) we have 



/ <n 4 / 3 \ n 4/3 



4/3 



where A 1 and A 2 are each the same for corresponding states 

 being functions of <£ 2 , which in Aj is a function of n Y and n 3 , 

 and in A 2 a function of n 2 and n § , where p^n^c, p 2 — n 2 p C) 

 and T=w 3 T c . We have therefore 



By means of equation (3) we obtain 



dl \ \ nj \ T nj dn 3 



-Mir-?*) 2^(^-1 ^V^W-,* 



\ nj 3 Ui <fo, n a dnj] \ m ) (* ^^ij > 



where k'" is a function of <f> 2 , and this a function of n 3 and 

 (ni— n 2 ) t If the above two expressions for E be equated we 

 get an equation containing n l9 n 2 , and n s only, as should be 

 the case since <f> 2 is a function of these quantities. The form 

 of <£ 2 to which the above relation corresponds is therefore 

 that which reduces this equation to an identity. 



Internal Heat of Evaporation. 

 Suppose we substitute 



~ 4 «>(,!+ Tc + -^ + ... .) 



for <£ 2 in the general equation for the internal heat of 

 evaporation. We then obtain 



* Proc. Roy. Soc. A. vol. lxxxi. p. 21 (1908) ; Phil. Mag., July 19 09 



