72 



BIOLOGY AND TECHNIQUE 



is the same. The apparatus usually consists of a gun-metal cylinder 

 supplied with a lid, which can be tightly closed by screws or nuts, 

 and supplied with a thermometer, a safety-valve, and a steam pressure 

 gauge. In the simpler autoclaves, water may be directly filled into 

 the lower part of the cylinder, and the objects to be sterilized supported 



upon a perforated diaphragm. In this 

 case the heat is directly applied by means 

 of a gas flame. In the more elaborate 

 stationary devices, steam may be let in 

 by piping it from the regular supply used, 

 for heating purposes. Exposure to steam 

 under fifteen pounds pressure (fifteen in 

 addition to the usual atmospheric press- 

 ure of fifteen pounds to the square inch) 

 for fifteen to twenty minutes, is sufficient 

 to kill all forms of bacterial life, including 

 spores. 



In applying autoclave sterilization 

 practically, attention must be paid to 

 certain technical details, neglect of which 

 would result in failure of sterilization. It 

 is necessary always to permit all air to 

 escape from the autoclave before closing 

 the vent. If this is not done, a poorly 

 conducting air-jacket may be left about 

 the objects to be sterilized, and these 

 may not be heated to the temperature 

 indicated by the pressure. It is also nec- 

 essary to allow the reduction of pressure, 

 after sterilization, to take place slowly. 

 Any sudden relief of pressure, such as 

 would be produced by opening the air- 

 vent while the pressure gauge is still above zero, will usually result in 

 a sudden ebullition of fluid and a removal of stoppers from flasks. 



The temperature attained by the application of various degrees of 

 pressure is expressed in the following table: 



^oo 



FIG. 11. AUTOCLAVE. 



Lbs. Pressure Temperature 



1 102.3 



2 104.2 



3 105.7 



4 . . 107.3 



Lbs. Pressure . Temperature 



5 10S.8 



6 110.3 



7 111.7 



8 . .11? 



