STERILIZATION IN STEAM UNDER PRESSURE 9 



room, is condensed and returned to the boiler. A further advantage is 

 that the water is added from the outside.] 



2. Sterilization in steam under pressure. 



Water, syringes, india-rubber apparatus, niters, etc., are generally steri- 

 lized by heating in steam under pressure. This method is also in general 

 use for the sterilization of certain culture media, but is not particularly 

 suitable for steel cutting instruments, as it destroys the edge. 



FIG. 5. Hearson's steamer. 



FIG. 6. Chamberland's autoclave. 



Exposure to steam at a temperature of 115 C. for 20 minutes is in most 

 cases sufficient to ensure sterilization, but some media, potato for example, 

 require a temperature of 120 C. 



Some of the commoner forms of autoclave may be shortly described here. 



Autoclaves. 



1. Chamberland's autoclave (fig. 6). This autoclave consists of a cylindrical 

 copper boiler, the free edge of which is turned out flange wise. A flanged 

 bronze cover is secured to this edge by screw bolts, and the whole is made 

 air-tight by the insertion of an india-rubber washer between the two metal 

 flanges. 



The cover is provided with a safety valve, a steam tap, and a manometer 

 which records the pressure in atmospheres and the temperature in degrees 

 centigrade. The boiler contains a removeable copper- wire basket, which 

 rests on short feet (5-6 cm.) on the bottom of the boiler. The boiler 



