Testing the Acidity of MUk and Cream. 121 



e. c. alkaliX.009 v 



Per cent. acidity= rXlOO 



c. c. sample tested 



If 50 cc. of cream required 32 cc. of alkali solution to 

 produce a permanent pink color, the per cent, of acid in 



the cream would be 32 *; OQ9 -XlOO=.58 per cent A 



50 



part of this calculation may be saved by using a factor 

 for multiplying the number of cc. of alkali added in 

 each test. This factor is obtained by dividing .009 (the 

 number of grams of lactic acid neutralized by one cc. 

 of alkali solution) by the number of cc. of sample 

 tested, and multiplying the quotient by 100. If a 50 

 cc. pipette is used for measuring the sample to be tested, 

 the factor will be (.009-=-50)X 100=^.018; if a 25 cc. 

 pipette is used, the factor will be (.009-f-25)XlOO= 

 .036; and if a 20 cc. pipette is used, (.009-1-20) X 100= 

 .045 will be the factor to be applied in calculating the 

 per cent, of acidity, the number of cc. of alkali used 

 being in all cases multiplied by the particular factor 

 corresponding to the volume of the sample tested. 



133. If a Babcock milk test pipette is used for measr- 

 uring the milk or cream to be tested for acidity, the 

 factor will be (.009^-17.6) XlOO=.051. This is so nearly 

 .05 that sufficiently accurate results may be obtained by 

 simply dividing the number of cc. used by two ; the re- 

 sult will be the tenths of per cent, of acid in the sample 

 tested, e. g., if 17.6 cc. of cream required 12 cc. of one- 

 .tenth normal alkali to give a pink color, then the per 

 cent, of acid is 12-^2=.6 per cent. If one-fifth normal 

 alkali is used for testing, the per cent, of acidity is 

 shown directly by the number of cc. used (Vivian). 1 



1 Van Norman recommends the use of a 50th normal solution for 

 testing cream (see Purdue exp..sta., bull. 104). 37 cc. of a normal soda 



