THE BABCOCK TEST 49 



tested, remembering that each per cent, on the scale 

 should contain just .2 cc. of liquid. 



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. 



When only one or a few pipettes need testing, wa- 

 ter can be used, running from a burette into each pi- 

 pette 17.6 cc. of water, which should just fill the 

 pipette to the mark, if accurate. 



Testing accuracy of acid measure. — Ordinarily the 

 acid measure does not need testing, since a little varia- 

 tion does not affect the results. When desired, it can 

 be tested by running in water or milk from a 17.6 cc. 

 pipette, known to be accurate. 



KEEPING GLASSWARE CLEAN 



It is very important that the test-bottles and the 

 pipettes used in the Babcock test should be kept as 

 clean as possible from fat adhering to the inside sur- 

 face. Unless a special effort is made, the bottles 

 quickly become covered inside with a film of fat, 

 which may be sufficient to increase appreciably the 

 results obtained w-hen the bottles are used in testing. 

 The bottles should be kept entirely free from any fat- 



