Grade 



Date 



(18) 



EXERCISE 3. 



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V 



i'. 



J 

 J 



Trowbridge plug and 

 method of using. 



Object. — To determine the accuracy of the cali- 

 bration of the glassware used for the Babcock 

 test by the Trowbridge plug method; also a 

 method for washing up glassware. 



Apparatus. — Set of bottles used for the test, set of 

 Trowbridge (or Nefus) plugs, sheet filter paper. 



Part 1. Trowbridge Method. — Fill the bottle to the 

 zero. With filter paper, dry the neck inside 

 above the zero mark. Insert the plug until 

 the water rises half way between the two sec- 

 tions. In a correct bottle the surface will be 

 at 5 per cent. Lower the plug until the upper 

 portion is 1/8 inch below the surface. The 

 water should be at the 10 per cent mark. 

 Record all data. 



Part 2. All glassware should be thoroughly washed 

 and be always left clean at the end of each 

 ■ laboratory period. Take a dish pan of warm 

 water and put in it about two tablespoonfuls 

 of some good washing powder. Put the bot- 

 tles in the suds thus formed and let the bottles 

 fill about half full of the hot solution. Then 

 take bottles in each hand and shake well. 

 After they have been washed as well as pos- 

 sible in this manner use a small bottle brush 

 to clean out the necks of the bottles. Take 

 them out of the water and rinse with clean warm water. Use this 

 same method for all other glassware. This method if carefully used 

 will always keep all glassware in the best possible condition. Care and 

 attention should be given to always have all apparatus in the 

 best possible shape. 



