MILK SUGAR AND LACTIC ACID 47 



neutralize the acid in the milk. The amount of 

 alkali used 'will vary directly with the amount of 

 acid in the milk, milks of high acidity requiring a 

 large amount of alkali. The alkali is prepared by 

 dissolving 4 gm. of pure sodium hydrate or 5.6 

 gm. of pure potassium hydrate in a liter of distilled 

 water. This standard alkali should be prepared only 

 by a chemist. The alkali must be kept in glass- 

 stoppered bottles protected from the air, and when 

 used it should not be diluted. 



53. Calculating the Acidity of Milk. Each cubic 

 centimeter of alkali neutralizes .009 gm. of lactic 

 acid. In case 50 cc. of milk are used and 20 cc. of 

 alkali required to produce the pink color, the per 

 cent of lactic acid in the milk will be found as 

 follows : 



20 x 100 = .36 per cent. 



In case a different quantity than 50 cc. of milk is 

 used, then substitute the number of cubic centimeters 

 of the sample tested for the 50 in the formula. The 

 test can be satisfactorily made with either a 25 or a 

 20 cc. sample, and if desired a 17.6 cc. pipette can be 

 used. In case a 20 cc. pipette is used for measur- 

 ing the milk, then the number of cubic centimeters 

 of alkali can be multiplied by .045 and the per cent 

 of acid obtained directly. In making the test, the 

 operator should cease adding the alkali as soon as a 

 permanent pink color is obtained. When the alkali 



