90 Messrs. Rinshelwood and Hartley on the Probability oj 



o.-Nitrophenol was found to behave in a similar manner, 

 both as to the form of the curves showing the relation 

 between number of crystallizations and time, and as to the 

 average life relationships. There was, however, a con- 

 siderable variability in the tendency to crystallize from 

 experiment to experiment and in the distribution of sizes, 

 such as to hinder accurate calculation. 



An experiment at 38°' 7, the first of the series carried out 

 (see Table IV.), gave the following approximate results :-- 



Discrepancy between 

 equilibrium size and size of particle present. 



0-10 p. c. 10-20 p. c, 20-30 p. c. 30-40 p. c. 

 Average life, in minutes ... 5 30 115 290 



Effect of Heating on the form of the crystallization-time curves 

 for a given set of tubes. 



The effect of heating in causing a general diminution in 

 the tendency to crystallize has already been dealt with. But 

 the effect of heating for a given period at a given temperature 

 does not necessarily influence the activity of all the tubes to 

 the same extent. For example, the most active tubes may 

 at first be sterilized most rapidly, so that the curves change 

 somewhat in form. This may be seen from one of the 

 experiments on p.-toluidine. 



if it were possible to bring all the tubes into exactly the 

 same state, the curve would become a unimolecular curve ; 

 and it was by applying a unimolecular formula as an 

 approximation to a portion of the salol curves that the 

 relative values for the tendency to crystallize (p. 81) were 

 calculated. 



Discussion. 



To estimate the actual size of the particles about which 

 crystallization takes place it is necessary to know the value 

 of the surface energy of the solid. Little information is 

 available about the numerical magnitude of this property, 

 but the experiments of Hulett on the dependence of the 

 solubility of certain sparingly soluble salts on the size of 

 particles indicates that it is the neighbourhood of 10 3 (cf 

 Partington and Jones, loc. cit.), and numbers of the same 

 order may be deduced from the experiments of Pavlov on 

 salol. 



In these series of experiments (p.-toluidine, diphenyl- 

 amine, and ortho-nitrophenol) the contents of half of the 

 tubes crystallized instantaneously at temperatures where 



the equilibrium radius was of the order 0*1 to 0*2 x 10~ 7 x — . 



P 



