16 BULLETIN 951, U. S. DEPARTMEISTT OF AGEICULTUEE. 



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 2i 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 maintai.-'^ in incubating room, Biochemic Division, 

 April 7 to 14, 1919. The system of control used is not so sensitive as that used in 

 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 iiave 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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