1894.] Complexity and Dissociation of Molecules of Liquids. 171 



II. " The Complexity and the Dissociation of the Molecules of 

 Liquids." By Professor W. RAMSAY, Ph.D., F.R.S. Re- 

 ceived April 26, 1894. 



Since the publication of a research on the molecular complexity of 

 liquids by Ramsay and Shields ('Trans. Chem. Soc.,'vol. 63, p. 1191) 

 two questions have arisen : First : What other evidence is there as 

 to the existence of complex molecules in certain liquids ? 



Second : How can the amount of dissociation of associating liquids 

 be inferred from measurements of their surface-energy ? 



The first of these questions has been treated of by Professor 

 Philippe Gruye, in the ' Archives des Sciences Physiques et N^aturelles 

 de Geneve,' 31 ; and as that periodical is not easily accessible to 

 English readers, a short account of his article is given here. 



I. Evidence in favour of the Molecular Complexity of Certain 

 Liquids. 



a. Guye has shown (' Annales,' vol. 31, [6], p. 206) that the quotient 

 obtained by dividing the absolute critical temperature of a liquid by 

 the critical pressure measured in atmospheres is equal to the 

 molecular refraction of the liquid multiplied by a factor which is 

 approximately equal to 1'8. His reason for this statement is as 

 follows : Equations such as that of van der Waals, which express 

 approximately the constants for gases and liquids in terms of temper- 

 ature, pressure, and volume, assume as one of their data the " co- 

 volume " (6) of the substance ; i.e., a number proportional to the 

 actual volume of the molecules, supposing them to be spherical. The 

 dielectric constant of a body k, according to Clausius, depends on 

 the ratio u of the real volume to the apparent volume occupied by 

 the molecules, in such a manner that 



Maxwell has shown that according to the electro- magnetic theory of 

 light, the dielectric constant k should be equal to the square of 

 its index of refraction for a ray of light of infinite wave-length ; 

 henca 



(n 2 +2) * 



The name molecular refraction is given to this quantity referred to 

 the volume of 1 gram, and multiplied by the molecular weight, or 



where MR signifies molecular refraction. 



