Spontaneous Crystallization of Supercooled Liquids. 81 



De Coppet's statement that salol shows less tendency 

 to crystallize the higher the temperature to which it has 

 heen heated is confirmed, and in addition a rough quan- 

 titative measure of: this influence is obtained. 



__ ■ , , Relative probability of ■ 



Maximum temt>erature ■„. f. , 0; 6.o ri 



. . , tL * n , crystallization at 3*4 '3 0. 



to which tlie salol ,„,.* ,i , , n , ,■ 



n , , , , ». (± he method of calculating 



has been heated alter Vk . 1 . , i • j 



n . .." -, this number is explained 



sealing ol tubes. • , , .- l x 



° m a later section.) 



circa 60° 1000 



circa G5° 570 



75° 240 



85° 12 



100° 2 



It must be emphasized that the diminution in the tendency 

 to crystallize is governed by the highest temperature to 

 which the salol has been previously heated, independently 

 of whether it has been allowed to crystallize or not in the 

 meantime. Thus, tor example,, alter the tendency to 

 crystallize had been decreased by heating at 80°, the 

 contents of the tubes were made to solidify ; they were 

 then melted at 50°," when they behaved almost exactly as 

 in the experiment immediately preceding, having regained 

 none of their power of crystallizing. This is important, 

 because it disposes of two possibilities: (1) that the 

 diminished probability of crystallization alter heating is 

 merely due to the more complete removal of residual crystal 

 nuclei, and (2) that it may be due to some change in the 

 molecular state of the liquid brought about by the heating. 



Although the most marked and rapid diminution in the 

 tendency to crystallize is produced by heating, a slow 

 '•ageing*' effect gradually becomes evident, even in a series 

 of experiments in which the me I ting-up process is effected 

 at a constant tempeiature. The tendency of some tubes to 

 crystallize diminishes progressively. 



Possible explanations of these facts are : (1) that gradual 

 solution of alkali from the glass lias a disturbing influence, 

 (2) that gradual decomposition takes place, or (3) that 

 some catalytic agency provoking crystallization gradually 

 loses its activity. 



That the last explanation is the correct one is shown con- 

 clusively by opening the tubes, exposing the salol to the air, 

 and re-scaling. After a few days' exposure to the air in a 

 cupboard the salol had regained its lost power of crystallizing, 

 when the tubes were treated exactly as before. 



Phil. Mag. Ser. G. Vol. 43. No. 253. Jan. 1922. G 



