EXERCISE I. 



CLEANING GLASSWARE. 



i. Explanatory note. It is necessary that the glass- 

 ware 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, specialized processes. It 

 consists in applying the chromic acid cleaning 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 mordant is re- 

 quired. But one of these special methods will be given 

 here. 



2. General directions. 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. 



Careful notes should be taken on the work of each exer- 

 cise. These should be handed to the instructor for examina- 

 tion and correction as often as every two weeks. 



(a} Test tubes. Wash these 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 laboratory). After it has acted for from 5 to 10 

 minutes (it is better to stand longer) pour it out of the tubes 

 into the bottle originally containing it. Rinse the tubes 

 thoroughly in tap water until all color disappears and then 

 in hot water and drain them, using individual drainage 



