11)4 



of .'>0 to .').') (Ici-rccs below llic fi-ccziiii;' |)oiiit. Willi su])('r- 

 saliiraleil solutions of sodium sulfate, maiutaiut'd at about 

 S di'iii-('('s below their saturation temperature, he succeeded 

 ill 10 out of 101 cases, in causing- crystallization by a con- 

 tinued stirring of several minutes. In another series of 

 experiments, in which the temperalui'e was about 9 degrees 

 below the saturation ])<)iiit, he obtained one crystallization 

 out of o7 trials. When small scaled tubes containing the 

 supersaturated solutions were dropped on a Avooden table 

 from a height of 10 cm,, no congelation occurred. 



Bachmetjew (1907) was not able to cause the freezing 

 of a subcooled butterfly by hammering on the table on 

 which the insect was lying, or by tapping the wire of the 

 thermoneedle inserted in its body. 



On the other hand, according to AVi-ight and Harvey 

 (1921), undercooling of potatoes maintained at -4° could 

 be terminated at any time by a shock. 



Wright and Taylor (1921) studied the effect of jarring 

 resulting from rough handling or incidental to hauling, in 

 causing the undercooled potatoes to freeze. They found 

 that dropping them on a hard floor or even tapping them 

 with a pencil was generally elTective. 



Luyet and Hodapp (1938a) determined the proportion 

 of efficient mechanical shocks on the congelation of potato 

 tissue. A cylindrical shell of tissue was fastened around 

 the bulb of a thermometer, and a slight tap was given to 

 the upper end of the thermometer with a wooden lover, 

 when the tissue was subcooled to temperatures from - 1 ° 

 to -5°. In 63 experiments out of 122, crystallization 

 occurred on tapping. The percentage of successful taps 

 increased at lower temperatures, but to express numeri- 

 cally the efficacy of tapping, one must eliminate from this 

 percentage that of possible coincident s])oiitaneous crystal- 

 lizations, which also increases at lower temperatures. 

 Unfortunately, the latter percentage is unknown. Sum- 

 marizing their results, the authors conclude that no doubt 

 is left as to the efficacy of tapping in some experiments, 

 and as to its inefficacv in others. Thev remark that such 



