197 



drops. He made suspensions of water in mixtures of 

 eliloroform or petroleum and sweet almond oil (mixtures 

 wliieli have the same specific gravity as water), and he 

 observed that the smallest drops stayed liquid at -20°. 



Bigelow and Ryckenboer (1917) attempted to determine 

 the degree of subcooling in capillary tubes in terms of the 

 diameter of the latter. They encountered difficulties with 

 water which presents such a narrow range of subcooling 

 temperatures and they decided to use other substances, in 

 particular, sulphur. In a previous determination the same 

 degree of subcooling was obtained in tubes 4 millimeters in 

 diameter and in larger ones. It was then decided to use 

 tubes of about four millimeters as standards of comparison 

 and tubes of smaller size. Definite differences in the 

 degree of subcooling were sometimes observed in tubes of 

 different diameter; for example, a tube of 4.1 mm. gave 

 an average subcooling point of 59.5° while a tube of 0.164 

 mm. gave 53.5°. But in other cases, the results were so 

 inconsistent, and sometimes two tubes of the same size fur- 

 nished such different average data that the authors ques- 

 tioned the significance of the experiment. The inconsis- 

 tency of the results, especially in systematic investigations 

 like those of Bigelow and Ryckenboer, renders doubtful 

 the commonly accepted assumption that the degree of sub- 

 cooling increases gradually with the decreasing size of the 

 capillary spaces. There is some evidence that capillary 

 forces exert an action in rendering congelation more diffi- 

 cult, but the data so far obtained are not sufficient to say 

 anything on that relation. 



The biologists have generally admitted without discus- 

 sion that capillarity increases the degree of subcooling and 

 they attributed to capillary forces in the intercellulars or 

 within the cells the fact that plant and animal tissues sub- 

 cool to a greater degree than water. 



According to Mliller-Thurgau (1886) living plant tissues 

 undercool more than the extruded cell sap. The hindrance 

 of molecular motion in living protoplasm is considered 

 responsible for the maintenance of the subcooled condi- 

 tion. 



