250 



BACTERIOLOGY. 



Gas-pressure regulator.— The apparatus shown in Fig. 38 

 was designed by Murrill > and is used in this laboratory. In 

 cheapness, simplicity and effectiveness it excels any of the 

 ordinary gas-pressure regulators. 



As indicated, the gas enters through a valve which is 

 connected with a gas cylinder or float. The gas passes 

 into the interior and raises this cylinder. 

 The greater the pressure of gas the 

 higher will the cylinder rise. As it does 

 so, it turns off the valve, more or less 

 completely. The cylinder then falls, and 

 hence gas is readmitted. The pressure at 

 which the gas is delivered can be regu- 

 lated at will by placing suitable weights 

 on the cylinder. In this laboratory, the 

 float is weighted till the gas is delivered 

 at a pressure of 40 mm., as observed in a 



fi^ A^- rOP OF /IVKSIf 



CPOSZ-SSCrioN. 



Fig. 38. Murrill's gas-pressure regulator. 



U tube containing water. The cylinder may be floated in 

 water, but, inasmuch as this is liable to evaporate, it is 

 better to use liquid paraffin. The apparatus is provided 

 with two outflow tubes, which are to be connected with 

 thermo-regulators. It is of convenient size, being only 6 



1 Journ. of Applied Microscopy 1, p. 92, 1898. Centralblatt f fir 

 Bakteriologie 23, p. 1056, 1898. 



