16 BULLETIIT 951, U. S. DEPARTMEI^^T OF AGEICULTURE. 
COST OF OPERATION. 
The cost of electric energy for operating the" heating equipment 
and the motor-driven circulation fan at 6 cents a kilowatt hour 
averages about 50 cents a day of 24 hours for each room. 
Prior to the installation of the present incubating rooms a large 
number of gas-heated incubators were used, the temperature being 
controlled by means of a bimetallic thermostat which regulated the 
Fig. 13. — Chart of temperature maintained in incubating room, Biochemic Division, 
April 7 to 14, 1919. The system of control used is not so sensitive as that used ia 
the Pathological Division. 
flow of gas. These incubators occupied a large floor space, the con- 
trol of temperatures was poor, and the fire hazard was great. With 
the present installation of incubating rooms the capacity has been 
about doubled and the space occupied has been reduced about one- 
half. Furthermore, the cultures have grown better than ever before, 
a result mainly of the very uniform temperature which has been 
maintained in the incubating rooms. 
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