CHAPTER XVII. 



Various Experiments in Sterilization by Steam and by Hot Aii". 



Place in one of the openings in the cover of the steam 

 sterilizer an accurate thermometer; when the steam has 

 been streaming for a minute or two the thermometer will 

 register 100° C. Wrap in a bundle of towels or rags or pack 

 tightly in cotton a maximum (self -registering) thermometer; 

 let this thermometer be in the centre of a bundle large 

 enough to quite fill the chamber of the sterilizer. At the end 

 of a few minutes' exposure to the streaming steam remove 

 it; it will be found to indicate a temperature of 100° C. 



Closer study of the penetration of steam has taught us, 

 however, that the temperature found at the centre of such 

 a mass may sometimes be that of the air in the meshes of 

 the material, and not that of steam, and for this reason the 

 sterilization at that point may not be complete, because hot 

 air at 100° C. has not the sterilizing value that steam has 

 at the same temperature. It is necessary, therefore, that 

 this air should be expelled from the meshes of the material 

 and its place taken by the steam before sterilization is com- 

 plete. This is insured by allowing the steam to stream 

 through the substances a few minutes before beginning to 

 calculate the time of exposure. There is as yet no absolutely 

 sure means of saying that the temperature at the centre of 

 the mass is that of hot air or of steam, so that the exact 

 length of time that is required for the expulsion of the air 

 from the meshes of the material cannot be given. 



(309) 



