THE FREEZING POINT OF POTATOES. 7 
in the case of potato sections before tapping would start them to 
freeze. When undercooled to the same degree at which a slight tap 
would inoculate a potato section, even stabbing with a piece of wire 
would not cause the berries to freeze, although the temperature was 
then below the subsequent freezing point. 
In figure 1 two typical lines show the degrees of undercooling and 
the freezing points of two potatoes. Readings were taken every 
minute. The potatoes were allowed to undercool undisturbed until 
self-inoculation took place. In one case, represented by the solid 
line, the ether surrounding the freezing tube was held at 15.8° F. 
In the other case, represented by the broken line, the ether was held 
at 8.7° F. In the first case the potato reached a temperature of 
20.2° F. in 12.5 minutes after 32° F. was passed. At this point 
freezing commenced, and in half a minute the temperature had in- 
creased to 28.95° F., while in another half minute the freezing point, 
29.15 F., was reached. Here, the temperature remained stationary 
for two minutes. With the other, undercooling proceeded at prac- 
tically the same rate for six minutes, when 23° F. was reached and 
freezing commenced. In half a minute the temperature was 28.5° F. 
and in another half minute it was 29.15° F., the freezing point. 
Here it held for only a minute, when it commenced to fall, owing to 
the extremely low temperature of the surrounding air. 
SUMMARY. 
A thermoelectric method was used to determine the freezing point 
of 18 standard varieties of potatoes grown under the same condi- 
tions. The following facts were determined: 
(1) The freezing point tends to rise as the season advances. 
(2) The freezing point seems to vary with the variety. 
(3) The freezing points of varieties of the same family group are 
often comparable. 
(4) Early and midseason varieties have a higher freezing point 
than late varieties. 
(5) Undercooling is terminated at any point by an outside in- 
fluence, such as tapping or jarring. 
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