76 



BACTEBIOLOGY. 



(Fig. 12), having a double- walled door, which closes 

 tightly, and a heavy copper bottom. They are pro- 

 vided with openings for the escape of the contained air 

 and the entrance of the heated air. The flame, usually 

 from a rose-burner (Fig. 13), is applied directly to the 

 bottom. The heat circulates from the lower surface 

 around about the apparatus through the space between 

 its walls. 



Fig. 12, 



Fig. 13. 



Laboratory hot-air sterilizer. 



Kose-burner. 



The construction of the copper bottom of the appa- 

 ratus upon which the flame impinges is designed to pre- 

 vent the direct action of the flame upon the sheet-iron 

 bottom of the chamber. It consists of several copper 

 plates placed one above the other, but with a space of 

 about 4 to 5 mm. between the plates. These copper 

 bottoms after a time become burned out, and unless 



