20 BULLETIN 744, U. S. DEPARTMENT OF AGRICULTURE. 
previous experiment was, respectively, 2 hours and 10 minutes, 1 
hour and 15 minutes, 43 minutes, and 20 minutes. In terms of ice 
melted the precooling resulted in a saving of 11, 16, 19, and 22 pounds 
of ice, respectively. 
An efficient way of cooling milk on a dairy farm is well illustrated 
in figure 15. Warm milk that was not precooled was placed in a tank 
containing water at 37° F. and was cooled to 50° F. in about an hour. 
The same quantity of milk precooled with water at 55° and then 
placed in a tank of ice water at 37° was cooled to 50° F. in 20 
minutes. This illustrates an easy and rapid method of cooling milk 
to 50° F. or below if ice is used. 
While, from a cooling standpoint, wooden tanks give good results, 
an insulated concrete tank similar to the one shown in figure 1 is 
more satisfactory for the dairy farm. A tank of that kind is not 
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Fig. 15.—Showing quick method of cooling milk with ice water. 
hard to construct, is very durable, and can’ be set partly in the 
ground, which is an advantage in that cans can be lifted in and out 
with less effort. 
THE USE OF ICE. 
For best results ice should be put into the cooling tank a sufficiently 
long time ahead of the cans of milk to insure that the tank water is 
at a low temperature when the cans of milk are set in. To insure 
that milk is cooled to and is held at a sufficiently low temperature, a 
cooling tank always should contain ice during hot weather. The 
quantity of ice necessary depends upon the outside temperature, 
the quantity of milk to be cooled, and the size, construction, and loca- 
tion of the cooling tank. The quantity necessary for any given set of 
conditions can be determined readily by putting a definite quantity 
