182 



TECHNOLOGY OF BACTERIA. 



cury below, and air above. When the air is ex- 

 panded by heat, the mercury rises through the 

 __e_ tube c, which passes 



through the perforated 

 cork d, and flows into the 

 space above this cork. 

 The tube e is connected 

 by a piece of rubber tub- 

 ing with a gas-jet, and 

 the gas continues to pass 

 through the tube f to the 

 Bunsen burner, unless 

 arrested by the rising of 

 the mercury, which acts 

 as a valve to close the 

 lower extremity of the 

 tube e. This tube is ad- 

 jus table through the cork 

 i, and it is evident that 

 the temperature at which 

 the gas supply is shut off 

 will depend upon the position of its lower extrem- 

 ity. A minute aperture in the side of the tube 

 e permits a small quantity of gas to flow to the 

 burner, so that the flame may not be entirely ex- 

 tinguished when the extremity of this tube is 

 closed by the rising of the mercury. There is dan- 

 ger, however, when but a small amount of gas is 

 admitted to a Bunsen burner that the flame may 

 be extinguished by currents of air. It will there- 

 fore be found best, in practice, to close this aper- 



