STERILIZATION ANTISEPSIS FOOD PRESERVATION 



6 9 



gram and i kilogram per square centimeter, respectively. The 

 autoclave consists of a metal cylinder with a movable top, which is 

 fastened down tightly during sterilization. It is furnished with 

 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 underneath . The lower 

 part of the cylinder contains water. 

 The objects to be sterilized are sup- 

 ported above this water on a perforated 

 bottom or shelf. 



% It is necessary to follow certain pre- 

 cautions in the use of the autoclave. 

 Allusion has already been made to the 

 necessity for having the steam saturated 

 with moisture. This is effected 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 

 closed, and the pressure begins to rise. 

 After leaving the articles to be steril- 

 ized in the autoclave for the length of 

 time desired, the apparatus must not be 



opened while the steam contained within it is still under pressure, 

 as there may be a sudden evolution of steam upon the removal 

 of the pressure which may blow the media out of their tubes and 

 flasks. After the pressure has fallen to zero it is well to open the 

 stop-cock only a little way so that air may not be drawn in 

 too rapidly to replace the condensing steam. The autoclave 

 may be opened as soon as the internal and external pressure 

 become equal. 



The length of exposure necessary to accomplish sterilization 



FIG. 32. Autoclave. 



