HOT-AIR STERILIZATION. 49 
In the case of the test-tubes, the plugs should be 
tight enough so that the tubes can be lifted by 
them. 
(c) Place in the hot-air sterilizer, close the door, 
and bring the temperature to 150° C.; keep it there 
Fic. 26.—Hot-air sterilizer. | 
for three-quarters of an hour, or until the cotton 
plugs begin to turn brown. 
(2) Allow the oven to cool before opening the 
door. Place the glassware in a clean place free 
from dust until used, 
4 
