FREEZING INJURY TO POTATOES WHEN UNDERCOOLED. 



11 



A Triumph potato was suspended in a metal container 18 inches long- 

 by 4 inches in diameter, which was in turn immersed in a brine tank. 

 Thermoelectric couples were located at the center and near the surface 

 of the potato; also one was suspended in the air 1 inch from the 

 potato. Periodical readings were made from the time the temperature 

 of the potato was near 40° F. The temperature of the atmosphere 

 surrounding the potato gradually fell from 27.2° to 25.6° F. The 

 temperature of the potato at the beginning was 40.8° at the surface 



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Fig. 1. — Temperatures at the center and near the surface of a Triumph potato as it 

 undercooled to between 26° and 27° F. At this point it was inoculated by tapping it 

 sharply with a pencil. As the potato froze, the temperature rose. When all the heat 

 was liberated, the temperature of the potato reached 28.7° F. and remained several 

 minutes. The temperature of the air bath to which the potato was exposed is also 

 shown. Note the accompanying rise in the temperature of the surrounding air as 

 the potato froze and liberated heat. 



and 39.9° F. at the center. The difference in temperature at the 

 surface and center gradually diminished until at 240 minutes there 

 was a difference of only 0.4 of a degree. After this the difference 

 became somewhat greater. In 285 minutes the temperature fell from 

 40.8° and 39.9° F. at' the surface and center, respectively, to 26.7° and 

 26.2° F. At this point the potato was tapped sharply with a pencil, 

 and freezing commenced. The temperature at both points began to 

 rise as heat was liberated, due to crystallization of the water. In five 

 minutes the temperature at the center rose to 30.2° F., and at the 

 surface to 29.5° F. In 10 minutes the temperature at both points was 

 practically the same, 28.7° F. This represents the freezing point. 



























































































































































































































































































































































































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