118 Testing Milk and Its Products. 



pletely dissolved before the standard solution is used 

 and the solution must be made with clean water. 



139. Making the test. The cream to be tested is thor- 

 oughly mixed, and 17.6 cc. is measured into the cup. 

 The pipette is rinsed once with water, and the rinsings 

 added to the cream in the cup. A few cc. of the tablet 

 solution prepared as given above are now poured from 

 the cylinder into the cream and mixed thoroughly with 

 it by giving the cup a gentle rotary motion. The tablet 

 solution is added in small quantities until a permanent 

 pink color appears in the sample. The number of cc. of 

 tablet solution which have been used to color the cream 

 is now read off on the scale of the cylinder. 



In comparing the results of one test with another, the 

 same shade of color should always be adopted. The 

 most delicate point is the first change from pure white or 

 light yellow to a uniform pink color which the sample 

 shows when the acid contained therein has just been neu- 

 tralized. This shade of color is easily recognized with a 

 little practice. The pink color is not permanent unless 

 a large excess of the alkaline solution has been added, on 

 account of the influence of the carbonic acid of the air 

 (129), and the operator should not therefore be led to 

 believe by the reappearance of the white color after a 

 time, that the point of neutralization was not already 

 reached when the first uniform shade of pink was 

 observed. 



140. Acidity of cream. 17.6 cc. of sweet cream is gen- 

 erally neutralized by 15-20 cc. of this tablet solution, 

 representing from .15 to .20 per cent, of acid. A mildly 

 sour cream is colored by 35 cc. tablet solution, and a sour 



