GAS-PRESSUME REGULATORS. 



117 



depend in the main upon the temperatures to which it 

 is to be applied. For low temperatures such fluids as 

 ether, alcohol, and calcium chloride solution, which ex- 

 pand and contract rapidly and regularly under slight 

 variations in temperature, are commonly employed ; 

 whereas for temperatures approaching the boiling-point 

 of water mercury is most frequently used. 



Fig. 29. 



Moitessier's gas-pressure regulator. 



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. 



Ga8-pressube Regulatoes. — A gas-pressure regu- 

 lator is not rarely intervened between the gas supply 

 and the thermo-regulator. This apparatus has for its 



6* 



