TESTING ACIDITY OF MILK 



21 



Van Norman's Alkaline Test. 

 Marshall's Acid Test. 



Mann's Acid Test 



Fill a 50 c.c. burette to zero mark with tenth 

 normal solution of sodium hydroxide NaOH. Meas- 

 ure 50 c.c. of milk or cream to be tested into a 

 beaker. In the case of cream dilute with water, 

 the amount depending upon the thickness of the 

 cream. Add a few drops, two 

 to five, of indicator; phenolph- 

 thalein is generally used. Add 

 the alkali solution to the cream 

 very slowly, and stir constantly 

 until a permanent pinkish color 

 remains in the milk. The per 

 cent of acid is found by mul- 

 tiplying the number of c.c. of 

 alkali solution used by .009, 

 dividing by the number of c.c. 

 of milk or cream used and mul- 

 tiplying the result by 100. The 

 explanation of this formula is 

 that the alkali of the sodium 

 hydroxide neutralizes the acid FIG. 21. Acid Bottle 



r ,1 MI r , with Burette 



of the milk. 1 c.c. of tenth nor- 

 mal solution contains .004 of a gram of sodium hy- 

 droxide which neutralizes .009 of a gram of lactic 

 acid. This is obtained from the fact that a normal 

 solution of lactic acid contains 90 grams of acid in 

 each liter, or 1000 c.c. Example: 



