82 Messrs. Hinslielwood and Hartley on tlie Probability of 



It seems dear, therefore, that the fine organic dust particles 

 which are always floating in the air (Tyndall) are effective 

 agents in provoking crystallization. Tins conclusion is 

 supported by the observation o£ JafTe * that repeated and 

 intensive filtration of a liquid reduces its power of crystal- 

 lization. Crystallization of an organic liquid seems, therefore, 

 to be analogous to the condensation of a supersaturated 

 vapour. 



Since these particles lose their activity as a result of 

 heating, and also, but less markedly, as the result of ageing, 

 they are probably colloidal in nature. The formation of a 

 nucleus thus appears to be due to heterogeneous catalysis, 

 the effect of heating and ageing being to change the degree 

 of dispersion of the colloidal system, and hence its activity. 



Similar behaviour after heating was also found with phenol 

 (Table II.), p.-toluidine (Table III.), and diphenylamine. 



The following results relating to the "temperature of 

 spontaneous crystallization ' ; illustrate the same point : — 



p.-Toluidine heated in a tube for some time at 100 G 

 crystallized when cooled at 18°"5 and 17 c, 5. After 

 opening and exposing to the air, re-sealing, and melting 

 at 50°, crystallization took place on cooling at 28°*5 

 and 28°'5. 



a-Naphthylamine in a tube heated to 100° crystallized on 

 cooling at U°-9, 13°- 6, 16°'0, and 13°"3. After 

 exposure to air, crystallization took place at 2S°, 3b°, 

 and 29°. 



The relation between Time and Xumber of Crystallizations. 



Suppose there are n tubes, and the number whose contents 

 have crystallized after a time t be n ; then the relation between 

 ?? and t can give some information about the nature of the 

 phenomenon of nucleus formation. If, for instance, a nucleus 

 were formed as a result of slow consecutive changes in the 



solution, then -- would have a maximum at a certain point. 

 at 



There is, however, no s"gn of such a maximum. 



If, on the other hand, the formation were the result of 

 random chances, and the chance of formation were the same 

 for each tube, then n and t would be connected by the same 

 exponential relation as is found for a unimolecular chemical 

 reaction n=n (l— <?"**), where % is a constant whose mag- 

 nitude measures the probability of crystallization. 



* Zeitschr. phys. Chem. xliii. p. 565 (1903). 



