GLASSWARE FOR STERILIZATION 



17 



times. Have the instructor demonstrate the method of 

 rolling. 



For hot-air sterilization, test tubes plugged with cotton 

 may be tied in large bundles or placed in wire baskets 



FIG. 6. (a) Proper Plug: (6) Plug 

 too Shallow and too Loose, too 

 Much Projecting; (c) Plug too 

 Loose, too Little Projecting. 



FIG. 7. Copper Cyl- 

 inder for Sterilizing 

 Pipettes. 



(never in agate cups), cotton plugs up. A few test tubes 

 should not be placed in a large wire-basket or in a wire 

 test-tube rack, as it is necessary to economize space in the 

 hot-air sterilizer. 



Petri dishes are wrapped separately in paper and tied 

 together in sets of three, One sheet of newspaper makes 



