Testing the Acidity of Milk and Cream. 129 



142. Making the test. The cream to be tested is 

 thoroughly mixed, and 17.6 cc. are 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 quanti- 

 ties until a permanent pink color appears in the sam- 

 ple. The number of cc. of tablet solution which has 

 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. 1 

 The most delicate point is the first change from pure 

 white or cream color to a uniform pink which the sam- 

 ple shows when the acid contained therein has beer 

 neutralized. 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 (132), 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. 



143. Acidity of cream. 17.6 cc. of sweet cream is 



1 A helpful suggestion has been made by the Danish State Dairy In- 

 structor, Dr. G. Ellbrecht, for obtaining a uniform color in acidity tests. 

 Small strips of pink paper are moistened and attached to the cup or 

 glass in which the titration is made, and alkali solution is added, 

 until the color of the milk or cream corresponds to that of the strips. 



9 



