LABORATORY BACTERIOLOGY 



EXERCISE I 



CLEANING GLASSWARE 



1. It is necessary that the glassware employed should be 

 thoroughly cleaned before it is used. Several special methods 

 have been suggested for this purpose, but the one frequently 

 employed by chemists seems to be the most easily handled and 

 quite as efficient for general use as the more elaborate, special- 

 ized processes. It consists in applying the chromic acid clean- 

 ing mixture after washing the tubes and flasks with water. It 

 is sometimes necessary to employ other methods for cover- 

 glasses which are to be used in staining bacteria where a mor- 

 dant is required. Only one of these special methods will be 

 given here. 



2. Work for this Exercise. — Clean all of the glassware, test 

 tubes, fermentation tubes, flasks, Petri dishes, and reagent 

 bottles assigned. 



Put the slides and cover glasses in the cleaning mixture ; 

 they can be rinsed and wiped later. 



3. Methods to be followed in cleaning the different appa- 

 ratus : — 



(a) Test tubes. Wash the tubes carefully with soap and water, 

 using the test tube brush. After washing, stand them in a glass 

 jar (aquarium) and fill them to within about 2 cm. of the top 

 with cleaning mixture ' (this will be kept in stock in the labora- 



1 Formula for chromic acid cleaning mixture. Dissolve 80 grams of 

 potassium dichromate (KzCraO?) in 300 c.c. of warm water; when all of 

 the KsCraO? is dissolved and the solution cooled, add it slowly, with con- 



