68 



BACTERIOLOGY 



the sterilizing chamber is filled with hot steam; or, what is better, 

 when the thermometer registers 100 C., if the sterilizer be pro- 

 vided with a thermometer. With a large Arnold sterilizer a 

 temperature of 100 C. may not be reached intil it has been 

 heated with a rose-burner for twenty to thirty-five minutes. 

 When bulky articles or large amounts of material are to be ster- 

 ilized, allowance must be made for the time necessary to bring the 

 temperature in the middle of the mass to 100 C. 



FIG. 31. Steam sterilizer, Massachusetts Board of Health. 



Autoclave Sterilization. Sterilization in the presence of 

 moisture and at temperature above 100 C., requires a 

 pressure greater than that of the atmosphere and the apparatus 

 used for this purpose is known as the autoclave. All bacteria 

 and their spores are killed by heating at 110 C., in the presence 

 of water, for fifteen minutes, and in about five minutes at 120 C. 

 The steam pressures corresponding to these temperatures are 

 approximately 7 J pounds and 1 5 pounds per square inch or J kilo- 



