Do Molecules Attract, Etc. 



535 



TABLE 5 HEXANE 



The intramolecular heat (I) absorbed is obviously con- 

 siderable. 1 At corresponding temperatures the amount of 

 intramolecular latent heat is for gram mol quantities, greater, 

 the larger the number of atoms in the molecule as may be seen 

 in Table 4. 



The conclusion is, therefore, that van der Waals' re- 

 lationship, i. e., I, -- E = a(i/V 1 -- i/V w ) is correct close to 

 the critical temperature, but should be changed to the form 

 I, - - E - - I = a(i/V 1 - - i/V w ), where I is the heat made 

 latent intramolecularly by expansion of the molecules, or 

 increasing rotation, in passing from the liquid to the vapor; 

 and that while Mills relationship: L - - E = //(i/V 1 / 3 - 

 i/V^ /3 ) is empirically true except, possibly, near the critical 

 temperature, yet since L - - E does not represent solely the 

 increase in potential energy due to the separation of the mole- 

 cules, the inference he has drawn from it, that molecules 

 attract inversely as the square of the distance, is not justified. 

 On the other hand, the correct expression for the increase of 

 molecular potential energy, a/(i/V, i/VJ, is obtained very 

 simply if the molecules attract inversely as the fourth power 

 of the distance, as Sutherland has shown. 



University of Chicago 



1 "a " should be larger and the figures in column 3 should be somewhat 

 smaller. See footnote p. 525. 



