CONTROL OF INCUBATING TEMPERATURES IN LABORATORIES. 11 



eLeCTFTIC COi\/VCCT/0/V 



eLeCTfr/C CO/wrwECT/Off 



is maintained only a fcAV decrees above that of the surronndinfr air^ 

 only small-capacity resistance units are recjuired. 



The special thermostat used in the incubator room is shown in 

 figure 8. It is capable of making and breaking the electric circuit 

 on a variation in temperature of about 1/100 of a degree F. Tem- 

 perature adjustments are made by transferring mercury from the 

 small reservoir to the capillary tube, and vice versa. 



A general view of 

 the temperature- i^^^S^^^^T^ 



control boards made 

 up of commercial 

 apparatus is shown 

 in figure 9, and a 

 diagram of the elec- 

 tric connections in 

 figure 10. Six rooms 

 are equipped with (m 

 this apparatus. Ee- N 

 ferring to the dia- 

 gram (figure 10), 

 one side of the line is 

 connected directly to 

 the heating coil and 

 from the heating coil 

 to the line-magnet 

 coil. The current in 

 this coil is controlled 

 by the pilot coil, 

 which in turn is con- 

 trolled by the ther- 

 mostat. "When the 

 pilot circuit is closed 

 through the thermo- 

 stat the pilot coil is 

 energized and closes 

 the circuit through 

 the line coil, which acts to close the line circuit through the heating 

 coils. When the temperature in the incubation room rises to the. 

 upper limit the thermostat makes contact with the stop point, thus 

 breaking the pilot circuit and opening the line coil, and hence the 

 current in the heating coils. 



TEMPERATURE RECORDERS. 



Each incubation room is fitted with a continuous 7-day recording 

 thermometer. The recording elements are mounted on the wall out- 

 side the room and the capillary passes through the wall, the bulb 



-Mercury tiiermostat used in temporaturo-oontrol 

 system of Patliolouical Division. 



