52 MODERN METHODS OF TESTING MILK 



the neck of the bottle as far as the top line of grad- 

 uation a close-fitting cork or plug, cut off square at 

 the lower end. Turn the bottle upside down, caus- 

 ing the mercury to run into the neck. The mercury 

 just fills the space in the neck between the o and 10 

 mark, if the graduation is accurate. The 

 same mercury can be used in the same way in 

 testing one bottle after another 

 by transferring all the mercury 

 from one bottle to another, 

 which may be conveniently done 

 by slipping a piece of elastic, 

 rubber tubing over the ends of 

 the necks of the two bottles. 

 In using the same mercury for 

 testing one bottle after another, 

 no mercury must be lost in 

 transferring, and none must be 

 left in the bottle last tested. 

 FIG. 21 The inside walls of the test-bot- 



BURETTE AND SUPPORT ., 



order to prevent any mercury adhering. (See p. 278). 

 Testing accuracy of pipette. When many pipettes 

 are to be tested, one runs into one pipette from an 

 accurately graduated burette (Fig. 21), 17.6 cc. of 

 mercury, closing the lower end of the pipette. The 

 mercury should fill the pipette just to the 17.6 cc. 

 mark, if the mark is correct. The same mercury can 

 be transferred to other pipettes in succession. Care 

 must be taken to have the pipettes clean and dry in- 

 side and that all the mercury is transferred without 

 loss. 



