502 Transactions. — Chemistry and Physics 



law connecting the latent heats of fusion with the atomic 

 weights and other physical constants. Berthelot (1895), 

 after proving, that in the case of the latent heads of vapor- 

 ization MW/T' = constant (where M is the molecular weight, 

 W the latent heat of vaporization, and T" the hoiling-point 

 on the absolute scale), supposed a similar law to be true in 

 the case of the latent heats of fusion. 



Holland Crompton, in a paper entitled "Latent Heat of 

 Fusion,"* endeavoured to show that the equation AicjTv = a 

 constant for the elements, A being the atomic weight, w the 

 latent heat of fusion, and v the valency. The difficulty first 

 encountered in this relation is due to the fact that the 

 valency of an element varies with its mode of combination 

 and with different physical conditions. 



Shortly afterwards Deerrf concluded that the relationship 

 Atv/T is constant only for certain groups of "similar" 

 elements. 



In 1897 Crompton published another paper,! in which he 

 attempted to disprove the hypothesis of electrolytic dissocia- 

 tion. He arrives at the result dw/T = constant for mono- 

 molecular liquids, where d is the density of the liquid. In 

 the same paper the results are given for the elements, the 

 densities in many cases being taken in the solid state. As 

 shown below, the numbers are exceedingly divergent. 



De Forcrand§ showed that M(W+w)/T' is approximately 

 constant : M is the molecular w eight of the substance in the 

 state of a gas at its boiling-point T', and W and w are the 

 latent heats of vaporization and fusion respectively. But W 

 is generally about ten times as great as w ; and, as MW/T' = 

 a constant is true (Trouton's law), the value of w wiil make 

 little difference in the result. Further, if the equation 

 M(W+w)/T be divided by the constant MW/T', it follows 

 that W/w = a constant. Using Traube's numbers for the 

 latent heats of vaporization of the following elements, which 

 gave very satisfactory numbers for Trouton's constant, the 

 values of W/w are — Mercury, 26; zinc, 14; cadmium, 15; 

 bromine, 3 ; iodine, 32 ; bismuth, 17- Since these num- 

 bers should be equal if De Forcrand's relationship is a 

 physical law, his generalisation may be dismissed without 

 further consideration. 



Now, let it be assumed for the present that Xiv/T = 8-8 

 (this value is only empirical, but its magnitude will not affect 

 the following argument). On dividing the values of A thus 

 obtained by the real atomic weights, the result is a series 



* Journ. Cbem. Soc, 1895, 67 315. 



f Proc. C-»pm. Soc, 1895, n.nd Cbem. Newe, 1897. 



+ Journ. Cbem. Soc, 70, 925. 



§ "Compces Rendus," 1901, 132, 878. 



