STERILIZATION. 



6l 



with a thermometer, a pressure gauge, a stop-cock, and a 

 safety-valve which is set to allow the steam to escape when 

 the desired pressure is attained and thus prevents it from 

 running too high. Heat is furnished by a gas-burner under- 

 neath. The lower part of the cylinder contains water. The 

 objects to be sterilized are supported above this water on a 

 perforated bottom or shelf. 



FIG. 15. Autoclave. 



[t is necessary to follow certain precautions in the use of 

 the autoclave. Allusion has already been made to the neces- 

 sity for having the steam saturated with moisture. This is ef- 

 fected by allowing the air to escape after the heat is applied, 

 and in order to be sure that all the air has really been expelled, 

 the stop -cock, with which all autoclaves are provided, is 

 left open until the steam escapes freely. The stop-cock is then 



