GAS-PEESSUEB REGULATOES. 



97 



approaching the boiling-point of water mercury is most 

 frequently used. 



The temperature of the incubator is to be regulated, 

 then, by the use of some such form of apparatus as that 

 just described. It should be of sufficient delicacy to 

 prevent a fluctuation of more than 0.2° C. in the tem- 

 perature of the air within the chamber of the apparatus. 



Fii. 19. 



Gas-peessuee Regulatoes. — A gas-pressure regu- 

 lator is not rarely intervened between the gas supply 

 and the thermo-regulator. This apparatus has for its 

 object the maintenance of a constant pressure of the gas 

 going to the thermo-regulator. There are several in- 

 struments of this form in use, but none of them accom- 

 plishes the object for which they are designed. 



