﻿A Theory of Super saturation. 35 



Summary. 



The refractivities of several gases have been referred to 

 the ideal state by means of the characteristic equation of 

 D. Berthelot. The corrected values are called the " ideal 

 refractivities." 



A comparison has been instituted between the ideal 

 refractivities and the dielectric constants of the gases. 



The conclusion of Bruhl that refractivity is highly additive 

 in character has been confirmed in the case of the ideal 

 refractivities. 



IV. A Theory of Super saturation. By W. J. Jones, M.Sc, 

 and J. R. Partington, M.Sc, Assistant Lecturers in 

 Chemistry, Manchester University *. 



THE solubility s of a given solid substance in a given 

 solvent depends on the temperature, the pressure, and 

 the size of the solid particles in contact with the saturated 

 solution. If we consider spherical particles of radius r, we 

 have 



4=/<T,P,r), (1) 



where T is the temperature and P the pressure. 



The problem of the surface energy between a solid and 

 its saturated solution was first systematically treated by 

 J. W. Gibbs f , and from a different standpoint by J. J. 

 Thomson J. The more recent investigations of Ostwald, 

 Hulett, and Freundlich have been considered in two papers 

 by W. J. Jones §, in which the theory is applied to various 

 special cases. 



The importance of the theory of surface energy in the study 

 of supersaturation does not, however, appear to have been 

 realized. The results of the investigations referred to may 

 be summarized in the formula 



RT' s 2 _2a/l 1\ . 



M lo ?°7rT\rrr} ■•••« 



where R is the gas-constant, T the absolute temperature, 

 M the molecular weight of the dissolved substance, a the 

 energy per unit area of the surface of separation of the solid 

 and the solution, p the density of the solid, s x and s % the 



* Communicated by the Authors. 



+ ' Scientific Papers/ New York, i. p. olo. 



X ' Applications of Dynamics to Physics and Chemistry,' p. 251. 



§ Zeitschr. physik. Chem. lxxxii. p. 448(1912); Ann. Phys. (4) xli. 

 p. 441 (1913). 

 1 1)2 



