COOLING HOT-BOTTLED PASTEURIZED MILK. 
21 
except that the velocity of air in the latter case was considerably 
greater than in the former. 
This experiment was repeated several times under different condi- 
tions, but the same general form of curve was obtained each time. 
Just after the fan supplying the cold air was started the difference in 
temperature between the top and bottom layers of milk was increased 
by a degree or two, after which it gradually fell. This slight increase 
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Fig. 14.— Variation in top and bottom of same bottle.— Difference in temperature between top and bottom 
of quart bottle of milk when cooled by air blown upward through stack. 
just after starting was probably caused by a quick cooling of the 
bottom layer which remained at the bottom on account of its greater 
density, while the top layer gradually fell, its place being taken by a 
warm layer. These results show the advantage of cooling by blowing 
air downward through the crates. 
The curves in figure 16 show the results obtained when either milk 
or water was cooled by cold air blown downward through the stack, 
the average tentperature of the incoming air being 19.8° F. (—7.7° C.) 
and the velocity of air 1,707 feet a minute. It will be seen in the 
figure that curves 2 and 8 show the variation in temperature of the 
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Fig. 15.— Variation in top and bottom of same bottle.— Difference in temperature between top and bottom 
of quart bottle of milk when cooled by air blown downward through stack. 
incoming and outgoing air, while curves 5 and 6 show the drop in 
temperature of a quart bottle of milk and one of water, respectively. 
Curve 7 shows the difference in temperature between the top and 
bottom layers of milk, and curve 10 shows similar temperature differ- 
ences taken in a quart of water. The solid line marked " ? ' is intended 
to represent the point where there is no difference in temperature 
between the top and bottom layers and is drawn on the temperature 
scale at 39.1° F. (3.9° C), representing the maximum density of 
water. Readings below the zero line as a matter of convenience are 
considered as minus, and those above as plus. Curve 10, represent- 
ing the action of water, is not so difficult of interpretation, but on the 
