THE BABCOCK TEST 47 



(i) Testing with water. This is the most satisfac- 

 tory method when reasonable accuracy is required and 

 when it is desired to test any point of the graduated 

 scale. The only special piece of apparatus required 

 is a burette (Fig. 21) holding 50 cc., accurately grad- 

 uated to 0.05 or o.i cc. A finely-graduated pipette 

 holding 5 cc. or 10 cc. can be used but is less con- 

 venient. 



The water used is tinged with ink or any convenient 

 colored solution to make easier the reading of the 

 height of the column of water in the neck of the bot- 

 tle. Alcohol can be used but is less desirable for some 

 reasons. 



In this and other methods, the temperature should 

 be the same for the liquid and apparatus used in test- 

 ing, and for the glassware tested. This is easily man- 

 aged by having everything at the temperature of the 

 room in which the testing is done. 



In detail the method is carried out as follows : First, 

 fill up to the zero mark with the colored water the 

 bottle to be tested. With a strip or coil of blotting- 

 paper or filter-paper, remove any drops of water ad- 

 hering to the inside of the neck. Then, from the 

 burette run into the bottle any desired amount of the 

 colored water and read the point on the graduated 

 neck to which the water comes. It should read the 

 same as, or within o.i per cent, of, the amount of 

 water run out of the burette. For example, in testing 

 an ordinary milk-bottle, the addition of 0.2 cc. of 

 water should fill the neck to the i per cent, point; 

 of 0.4 cc. to the 2 per cent, point; of i cc. to the 5 

 per cent point, etc., up to 2 cc. for the 10 per cent. 



