1 6 <vi;rrRK METHODS AND TECHNIQUE 



dry heat may be used, depending upon the nature of the medium 

 or object to be sterilized. Liquids or any solids which may melt, 

 evaporate, or dry out in a dry atmosphere require moist or steam 

 heat ; while all heat-resistant dry apparatus and glassware, and well- 

 dried solids, such as sand, glass wool, etc., usually require dry heat. 

 Sterilization at IOO C. When steam heat is used, sterilization 

 is often given at the boiling point of water. Sterilization may thus 



FIG. 3. ON THK RIGHT, ARNOLD STEAM STERILIZER; ON THE LEFT, LAUTEN- 

 SCHI.AGER HOT AIR STERILIZER; I;OTH UNDER HOOD 



IK- effected in an ordinary boiler, or over a water bath. Steam 

 sterilizers of various patterns are now made, which accomplish this 

 work most effectively, and they should be in use in all laboratories. 

 The two general types of sterilizers in common use are those 

 which bear the name of Koch and Arnold. The latter are simpler 

 in design and less expensive. Fig. 3 shows a good form of this 

 sterilizer. From the diagram, Fig. 4, it will be seen that the water 



