Testing the Acidity of Milk and Cream. 127 



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 sample 

 shows when the acid contained therein has been neu- 

 tralized. This shade of color is easily recognized with 

 a little practice. The pink color is 'not permanent un- 

 less 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 

 generally neutralized by 15 to 20 cc. of this tablet solu- 

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

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

 a sour cream ready for churning by about 50 to 60 cc. 



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

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

 tests. Strips of pink paper are 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. 



