STERILIZATION 7 



wastes of the laboratory is also best accomplished in this 

 manner. 



4. Sterilization by Hot Air. Exposure to hot air is the 

 usual method of sterilizing all glassware, instruments with 

 metal handles, etc., but it is not suitable for organic sub- 

 stances, with the exception of wool, cotton and paper. 



To insure efficient sterilization, the prepared glassware, 



FIG. 2. Hot Air Sterilizer. 



etc., must be placed in a gas or electrically heated oven 

 (containing a thermometer registering over 200 C.) whose 

 temperature is maintained at approximately 150 C. for 

 one hour, or 180 C. for ten minutes. The oven must be 

 allowed to cool down to 60 C. before opening the door 

 to avoid the breaking of glassware by cold-air currents. 

 Cotton, wool, and paper are slightly scorched at this tem- 

 perature, 



