108 Prof. W. C. McC. Lewis on the Relation of the 



has in general large dielectric capacity. The results point 

 to the existence of some relationship between tt and K of a 

 more complex nature than that embodied in Obach's or 

 Walden's generalization. A possible relation in this con- 

 nexion will now be considered. 



From the chemical standpoint the formation of molecular 

 compounds through the operation of "residual affinity/' 

 along with the applicability — at least approximately correct 

 — of the inverse fourth power law of attraction, as expressed 

 in the work of Sutherland and the equation of van der Waals, 

 have rendered it fairly certain that molecules possess some- 

 thing of the nature of polarity. There seems to be no reason 

 why one should not identify cohesion with residual affinity. 

 In other words, cohesion is electromagnetic in origin. The 

 chemical significance of cohesion is thus apparent. Further, 

 this view of cohesion is in good accord with Baly's theory* 

 of residual affinity. 



If we suppose that the force F between two molecules 

 is of electromagnetic origin, the molecules being regarded as 

 equivalent to small magnets, the attractive force may be 

 written 



F= — 

 pi*' 



where m is the magnetic pole strength, assumed the same 

 for all molecules, and jjl the permeability of the medium 

 itself. It follows, therefore, that the force of attraction (71-) 

 across unit area of the liquid may be set proportional to 



— g or proportional to — 2 , where v is the specific or mole- 

 cular volume of the liquid. Denoting the proportionality 

 factor by a, it follows that 



a 



7r= 2? 



/JLV 2 



which only differs formally from the van der "Waals expres- 

 sion by the introduction of the factor //,. Now if the liquid 

 possess a refractive index N (for very long waves) /a may be 



N 2 . . 



written ^ , 2 , where C is the velocity of light in vacuo and 



K is the dielectric constant. 

 Hence 



_ aKC 2 a K 



77 " tf 2 V 2 -N 2 V 2 * 



* Balj and Kralla, Journ. Cliem. Soc. ci. 1912. 



