PHYSICAL AGENTS 



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material (Figs. 78-90). The latter type is in common use 

 in canning factories, dairy plants, hospitals, public institu- 

 tions, municipal and governmental disinfecting stations. 

 Very frequently there is an apparatus attached for pro- 

 ducing a vacuum both to exhaust the air before sterilizing, 

 so that the steam penetrates much more quickly and thor- 

 oughly and for removing the vapor after sterilizing, thus 

 hastening the drying out of the material disinfected. 



Fig. 81. — A "process kettle" (steam-pressure sterilizer) used in canning. 

 Diameter, 40 inches; height, 72 inches. 



The smaller types of pressure sterilizers are called "auto- 

 claves" and have become indispensable in laboratory work. 

 Fifteen pounds' pressure maintained for fifteen minutes is 

 commonly sufficient for a few small objects. For larger 

 masses much longer time is needed. The author found that 

 in an autoclave of the type shown in Fig. 79 it required ten 

 minutes for 500 c!c. of water at 15 pounds' pressure to reach 



