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XLV . A Xote on Latent Heats of Fusion and their relation to 

 Molecular Composition. By Harbord George Wayling, 



M.Sc* 



OINCE Trouton in 1884 formulated a rule showing thai, 

 k? in the case of liquids which were not associated in the 

 state of vapour, the ratio oE the molecular heat of vaporiza- 

 tion and the temperature of the boiling-point on the absolute 

 scale is a constant, approximately 21, other investigators 

 have applied the rule to the Latent Heats of fusion of ele- 

 ments and compounds. Crompton (J. C. S. .1895) introduced 

 Valency as another factor ; Robertson (J. C. S. 1902) with 

 more success substituted the cube root of atomic or mole- 

 cular volume for valency ; Nernst (Zeit. f. Electrochemie, 

 1908) showed a relationship between specific cohesion and 

 latent heats of fusion, and more recently E. Baud (Compt. 

 Rend. 1911) studied variation in volume at the melting-point, 

 as a function of latent heats ; de Guzman (Anal. fis. quim. 

 1913) investigated the relationship between latent heats of 

 fusion and coefficient of viscosity ; while H. S. Allen (Proc. 

 J. Phys. Soc. 1916) identified this form of energy as being 

 necessary to counterbalance that of a certain number of 

 oscillators involved in the maintenance of crystalline struc- 

 ture. Honda (Sci. Pep. Imp. Univ. Tokio, 1918) put 

 forward a connexion between latent heats and electronic 

 frequency, the former being the energy of rotation gained 

 by the electrons during the process of fusion ; and Tsutsumi, 

 another contributor to the same journal, has studied the 

 specific resistance of several metals near their melting-point 

 and found an abrupt increase in this factor. 



If we go back to Trouton's rule and express it in this form 



Latent Heat of fusion x Molecular number 

 Melting-point on Abs. scale 



the molecular number being the sum of Moseley's atomic 

 numbers of the atoms in the molecule, we find that for 

 several compounds the ratio is equal to the number of atoms 

 in the molecule. Take the commonest of the compounds- 

 water — 



Latent heat of fusion 80 



Sum of molecular numbers ... 2 + 8 

 Melting-point (absolute) 273 



* Communicated by the Author. 



