Forces of Attraction betiveen Atoms and Molecules. 795 



Since the above equation can also be obtained in another 

 way, as already mentioned, and it has been found to agree 

 well with the facts, we conclude that the assumptions made 

 in deducing this relation with respect to the kinetic energy 

 and attractive force of a molecule are true. Further evidence 

 of the truth of this result will appear in a subsequent paper. 



In order to get a foothold in the determination of the 

 nature of the function 



WS'4 



let us assume that 



</>3 ( -79 ft ) = </>3 ( — > ft ) = A a constant, 

 so that 



m l\m/ \m/ ) 



We will next compare the values of A with the correspond- 

 ing values of {pi i/3 — P2 4/3 }- Table V. contains the values of 

 these quantities at different temperatures for four liquids, 

 and the values of L, p } , p 2 , used in their determination. 

 The values of L, pi, p 2 , were taken from a paper by Mills*, 

 who has calculated the values of L at different temperatures 

 for a number of liquids by the help of thermodynamical 

 formulae, using the density and pressure data of Ramsay and 

 Young. It will be seen that the variation of A with tempera- 

 ture is small in comparison with that of \p x A 3 — /°2 4,3 }- The 



former quantity corresponds to </> 2 1 — , ft) and the latter to — . 



We may therefore assume that $2(^5 &) is approximately a 



constant, which we will denote by K. The attraction between 



two molecules is then approximately given by 5 (%^/m y; 



i. e., it is proportional to the square of the sum of the square 

 roots of the atoms of a molecule and inversely proportional 

 to the fifth power of their distance of separation. 



The variation of K with temperature — it varies propor- 

 tionally with A — may be due to two possible causes: (1) the 

 force of attraction may diminish with rise oE temperature; 

 (2) the inverse fifth power law may not be exactly true. 

 Very likely the variations are due to both causes, the exact 



* Journal of Phys. Chem. vol. viii. p. 405 (1904). 



