APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 61 
creameries, and dairies, it is unnecessary to employ a regular attend- 
ant, as some persons regularly employed in other work on the premises 
can find time to start and stop the machine and to keep it oiled. 
The curve marked " Total cost per ton of refrigeration" has been 
calculated from the estimated cost of the plant, repairs, depreciation, 
and miscellaneous items, such as oil, waste, packing, etc. The in- 
terest on the money invested is figured at 6 per cent and the repairs 
and depreciation at 10 per cent. 
While the above curves representing the cost of producing refrig- 
eration in the smaller-sized creameries are believed to represent 
a fair average, it is 
also believed that the 
cost can be materially 
lessened if more atten- 
tion is paid to the 
economic operation 
of the compressor. 
In a great many in- 
stances the engine 
drove long lines of 
shafting that were not 
in the best of condi- 
tion and a number of 
idle pulleys in addi- 
tion to the refrigera- 
ting machine. 
In many instances 
where electricity is 
available motors may 
be installed at an ad- 
vantage for operating 
the refrigerating ma- 
chine as well as other 
apparatus. Motors of 
comparatively slow- 
speed type can be 
/*7<3IVTHS 
Fig. 28.— Curves showing the relation between the milk supply and 
the temperature of the air, averaged from the most important 
dairying States, and the hours necessary to operate the com- 
'pressor based on the maximum amount of work being done in 
eight hours. 
readily connected by belt to the compressor. With the present price 
of electric power the cost of operating small units with electricity 
is slightly greater than when operated by steam power, provided 
the steam plant is run at or about normal load. But when the 
engine and boiler are operated at only a fraction of their capacity 
they become very inefficient and the cost of power is greatly increased. 
In view of the fact that with electricity the consumption of power 
starts and stops with the opening and closing of the switch it is often 
more economical to install electric motors for operating small refrig- 
