COOLING HOT-BOTTLED PASTEURIZED MILK. 
19 
TEMPERATURE VARIATIONS IN QUART BOTTLES OF MILK AND WATER 
UNDER VARYING CONDITIONS. 
A differential thermocouple was placed in a quart bottle of milk, 
another in one of water, and the difference in temperature at the top 
and bottom of the bottles noted under varying air conditions and 
directions of flow. One of the junctions of the differential couple 
was placed about one-half inch above the bottom while the other was 
placed in the top just beneath the surface of the liquid when the latter 
was cooled, both being in the center line of the bottle. 
The curve in figure 14 shows graphically the difference in tempera- 
ture between the top and bottom of a quart bottle of milk when 
cooled by an air blast from the bottom of the stack. The average 
temperature of the cold-air supply was 39.4° F. (4.1° C), and the 
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Fig. 12. — Cooling by forcing air from top downward.— Difference in temperature of bottles at different 
positions in stack. 
velocity at which the air was blown up through the stack was 1,625 
feet a minute. When the fan was started there was a difference of 
about 8° F. (4.4° C.) in temperature between the top and bottom of the 
bottle; 22 minutes later the difference had increased to about 23° F. 
(12.8° C). Upon standing for a few minutes the bottom layers of 
milk will naturally be the colder, and with the same source of cold 
applied to the bottom of the bottle the difference in temperature will 
of course be increased, owing to tho absence of convection currents 
in the milk itself. The rapidity with which the cooling goes on tends 
