88 



INCUBATING OVENS AND THERMO-REGULATORS. 



the pressure of gas, especially, interfere with the maintenance of a 

 constant temperature, and for this reason a pressure regulator will 

 be required when great precision is desired. That of Moitessier is 

 commonly used in bacteriological laboratories (Fig. 60). But for 

 most purposes variations of temperature of 1 to 2 C. are not of 

 great importance. For ordinary use a brood oven should be regu- 

 lated to about 35 to 37 C. It is best to have a little cylindrical 

 screen of mica around the gas jet beneath the incubating oven, for 

 the purpose of preventing the flame from being extinguished by cur- 

 rents of air (Fig. 61). 



Koch's ingenious automatic device for shutting off the gas if the 

 flame is accidentally extinguished is shown in Fig. 62. 



FIG. 59. 



FiO.60. 



Another form of thermo-regulator, which answers very well, is 

 that of Reichert (Fig. 63). In this the gas enters at a and escapes 

 at c. The mercury, which fills the bulb, shuts off the gas at the 

 point for which the instrument is regulated. By means of the 

 screw d the height of the mercury in the tube may be very accu- 

 rately adjusted for any desired temperature. 



The regulator of Bohr, shown in Fig. 64, is more sensitive than 

 that of Reichert, and rather simpler in construction than the usual 

 form shown in Fig. 59. The thermometer bulb a contains only air, 

 and the gas which passes through the tube / is shut off at the 

 proper temperature by the mercury in the U-shaped tube c. The 

 stopcock b is left open when the bulb a is immersed in the water 



