APPLICATION" OF REFRIGERATION TO HANDLING OF MILK. 55 
To use the curves in figure 22, suppose it costs $1 per ton per 24 
hours to produce the refrigeration, and it is desired to know the 
amount of insulation that will give the maximum economy when 
the inside temperature of the room is at 30 °F. and the average out- 
side temperature is 70° F. Look on the left-hand side of the figure, 
under "Cost per ton of refrigeration/' and follow the horizontal line 
opposite $1 until it crosses the curve marked "Maximum economy, 
30° to 70° F.," then read at the bottom directly under the point 
where the curve cuts the horizontal line indicating $1 per ton, and 
it will be found to require 3f inches of insulation. If the inside tem- 
perature of the room had been 0° and the average outside tempera- 
ture 70° F., the thickness of insulation required to obtain the maxi- 
mum economy would have been 4f inches. Then the estimate cost 
of insulation per square foot is found by projecting a line vertically 
through the intersection of the curves and the horizontal line indi- 
cating a cost of $1 per ton of refrigeration, until it cuts the straight 
line marked "Cost of insulation per square foot," then reading on 
the left opposite this point and under "Cost of insulation per square 
foot, " the cost per square foot of insulation is found to be 37J and 47 i 
cents, respectively. It is assumed that the cost per square foot of insu- 
lation will be a constant in small cold-storage rooms of the size com- 
monly used in milk plants. In the economical operation of a refrig- 
erating plant the insulation is the most important point and great 
care should be exercised in its selection and installation. All exposed 
piping between the expansion valve and the suction side of the 
machine should be carefully insulated, as well as the walls of the 
refrigerator itself. 
In the building of cold-storage rooms or boxes there is often used 
a construction of boards in combination with air spaces, and while 
cheap in first cost, in a few months in extreme cases the walls will 
begin to deteriorate and show increased losses. In a short time the 
piping in the box or room is not sufficient to hold the temperatures, 
and finally the capacity of the machine is not enough to do the work; 
whereas, with a sanitary box properly constructed of nonabsorbent 
material, no deterioration will occur after long and continued use. 
Consequently, it is very important wherever possible to eliminate 
wood in the construction and substitute for the walls hollow tile 
or brick. 
When placing the insulation in the walls, floor, and ceiling of cold- 
storage rooms it is of the utmost importance that the workmanship 
be of the best. The insulation should be continuous. There should 
be no break in continuity where floor, walls, and ceiling meet. Each 
course of insulation should be well set up before the next course is 
put in place. In all cases the blocks of insulation should fit tightly 
