Chemical Attraction between Atoms from Physical Data. 89 



We will now illustrate the result obtained in this paper 

 by some examples. Mills * has put forward the theory that 

 the molecular attraction which accounts for latent heat &c. 

 is independent of the temperature and varies inversely as the 

 square of the distance between the attracting molecules. 

 This gives for the latent heat the equation 



L=C(p\' a - P l n ), (1) 



where C is a constant, which was found to agree well with 

 the facts. According to what has gone before it should be 

 possible to discover any number of laws of attraction which 

 will give latent heat formulae agreeing with the facts. Thus if 

 we assume that the attraction varies inversely as the seventh 

 power of the distance of separation of the molecules we 

 obtain the equation L= W(joJ — /o 2 ) for the latent heat, where 

 W is a constant. This equation will at once be obtained by 



substituting — ~ for (£(r)(E\/mi) 2 in the general formula for 



the latent heat given by the writer f. This equation agrees J 

 with the facts as well as that of Mills, and we can therefore 

 with equal justice assume that the attraction varies inversely 

 as the seventh power of the distance of separation of the 

 molecules. 



It can be very simply shown that the law of Mills cannot 

 possibly account for the magnitude of the latent heat of 

 evaporation and cannot therefore be true. The attraction 



between two molecules according to the law of Mills is — 2 2 -' 



where K 2 is a constant which is the attraction between the 

 molecules at unit distance apart. Substituting this expression 

 for the attraction for <j)(z)(% v/ ??? 1 ) 2 in the general formula 

 for the latent heat quoted above we obtain 



L= §5(^-^)2-96, 



where L is the latent heat per unit mass in ergs and m is the 

 mass of a molecule. By means of this equation the value of 

 K 2 can be calculated. In the case of ether at 273° C. we have 



L =86-16 x 4-2 xlO 7 ergs, m = 74 x 1*61 x 10 -24 gm., 



^ = •7362, and p 2 =0 s H27, 

 which on substituting in the equation ^ives K 2 =8"9x JO"- 1 

 dyne. Since the gravitational attraction also varies in- 

 versely as the square of the distance of separation of the 



* Journal of Pbvs. Chemistry, vol. vi. p. 209 ; vol. viii. p. 383 and 

 p. 593 : vol. ix. p. 402 : vol. xi. p. 594 and p. 182. 



t Phil. Mag. May 1910. p. SOI. J Phil. Map. Oct. 1910, p. 678. 



