APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 57 
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importance, their tightness and ability to be operated quickly is 
vastly more so. A poor-fitting door that allows the outside air to 
leak into the room is a source of endless expense ; consequently great 
care should be exercised in fitting doors in place. Usually it is 
economy to buy a good design of commercial door, as it will fit better 
and not be so liable to warp as a door built by the local carpenter. 
With slow and heavily moving doors which bind and work badly 
there is a tendency on the part of the workmen to leave them open, 
allowing the warm outside 
air to rush in and replace 
the cold air. Equal care 
should be exercised in the 
construction of windows 
in the walls of cold-stor- 
age rooms. They should 
be constructed of three 
plates of glass with two 
half -inch air spaces. The 
glass plates should be care- 
fully set in felt and made 
perfectly air-tight. The 
drawings of typical con- 
structions of cold-storage 
insulations with their in- 
sulating values are shown 
in figs. 23, 24, 25, 26, and 
27; they are taken from 
tests made by different 
authorities. 
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Fig. 24.— B. T. U. transmitted per square foot per 24 hours 
per degree difference in temperature. 
ESTIMATING THE SIZE OF 
REFRIGERATING PLANTS. 
In determining the size 
of machinery for any class 
of work it is necessary 
to carefully consider the 
maximum or peak load that it will be called upon to carry. This 
often results in having to install a great deal larger machine than 
would be required if the load were uniform. In no class of machinery 
is this more apparent than in refrigerating apparatus when applied 
to the dairy industry. 
In figure 28 (p. 61) are curves showing the relation between the milk 
supply and the temperature of the air. These curves are plotted from 
data obtained from the most important dairying States. The milk- 
