CHAPTER II 



CLEANING, PREPARING, AND STERILIZING 

 GLASSWARE 



EXERCISE I. CLEANING GLASSWARE 



Culture-tubes, flasks, fermentation-tubes, and Petri 

 dishes must be free from organic matter, acids, and 

 alkalis. They are best cleaned as follows: 



a) Completely immerse them in a vessel containing 

 soapsuds or soap-powder, boil for at least lo minutes, 

 then thoroughly brush them with the tube-brush; or, 

 immerse them for an hour or more in the chromic-acid 

 cleaning-mixture, consisting of — 



Potassium dichromate 60 parts 



Water 300 parts 



Concentrated sulphuric acid 460 parts 



The sulphuric acid is to be added slowly with constant 

 stirring. 



b) Rinse thoroughly in tap-water. 



c) Again use the tube-brush, and soap and water, if 

 necessary. 



d) Rinse very thoroughly, and get rid of every trace 

 of acid, soap, or alkali. 



e) Turn upside down in a basket, and heat for 20 

 minutes in the hot-air sterilizer until perfectly dry. 



EXERCISE II. PLUGGING OF CULTURE-TUBES 



Directions for plugging. — Take a small amount of 

 ordinary, non-absorbent cotton of good quality, fold it 

 once, and by means of a glass rod push it into the mouth 



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