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"VII. T lie Probability of Spontaneous Crystallization of Super- 

 cooled Liquids. By 0. S". Hinshelwool, Fellow of Trinity 

 College, Oxford, and Harold Hartley, Fellow of Balliol 

 College, Oxford *. 



IT is well known that a supercooled liquid, even in the 

 absence of a crystal nucleus, usually crystallizes 

 spontaneously if the temperature is lowered sufficiently. 

 Ostwald put forward the view that there exists a definite 

 line of demarcation between the " metastable " region of 

 temperature, in which crystallization cannot take place in 

 the absence of a crystal nucleus, and the "labile" region, 

 in which spontaneous crystallization is possible. Failure 

 to crystallize in the metastable region is attributed to the 

 non-survival of the minute crystals which may be formed 

 momentarily as the result of favourable molecular en- 

 counters. It can be shown thermodynamically, and has 

 been verified experimentally by Pavlov f, that the smaller 

 the dimensions of a solid particle the lower is its melting- 

 point. The first formed minute crystals, therefore, may 

 possess a melting-point below the temperature of the liquid, 

 even though this is some degrees supercooled with respect 

 to a large plane crystal face, and hence they have but a 

 transitory existence. If, however, the temperature of the 

 liquid is lower than their melting-point they continue to 

 grow, and crystallization spreads throughout the system. 

 The dividing line between the regions of non-survival and 

 of continued growth is the metastable limit. 



The experiments of Miers and Isaac J, Hartley §, and 

 others showed that various substances and solutions, when 

 cooled, crystallized at more or less definite temperatures — 

 often about 10 degrees below the melting-point or satu- 

 ration temperature. Miers (| considered that this supported 

 Ostwald's theory of a metastable limit, but de Coppetlf 

 •pointed out that the distinction between the metastable 

 and labile conditions was arbitrary, and that the probability 

 of a nucleus large enough to survive and grow varies con- 

 tinuously with the temperature. The metastable limit 



* Communicated bv the Authors. 



t Pavlov, J. Russ.'Phys. Chem. Soc. xl. p. 1022 (1908). 

 % Trans. Chem. Soc. Ixxxix. p. 413 (1906) : Proc. Roy. Soc. A. Ixxix. 

 ■p. 322 (1907). 



§ Trans. Chem. Soc. xciii. p. 825 (1908). 

 || Loc. cit. 

 ^ Ann. chim.phys. x. p. 457 (1907). 



