124 Testing Milk and Its Products. 



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

 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 



134. Manns' testing outfit The apparatus (see fig. 41) 

 and chemicals necessary for testing the acidity of milk or cream 

 by the so-called Manns' test include one gallon of a one-tenth 

 normal alkali solution; four ounces of an alcoholic solution of 

 phenolphtalein, a 50 cc. glass burette provided with a pinch- 

 cock, a burette stand and a pipette for measuring the sample. 

 This outfit will make about 100 tests and is sold for $5.00. a 



135. The alkaline tablet test. Solid alkaline tab- 

 lets were proposed by Farrington in 1894, as a substi- 

 tute for the liquid used in Manns* test. 3 It was found 

 possible to mix a solid alkali carbonate and coloring 

 matter, and compress the mixture into a small tablet, 

 which would contain an exact amount of alkali. The 

 advantage of the tablets lies in the fact that they 



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

 testing cream (see Purdue exp. sta., bull 104). 37 cc. 01 a normal soda 

 solution is diluted to 1850 cc. in a two-quart bottle, such as is used for 

 mineral waters. Each cc. of this solution represents .01 cc. of acidity 

 when 17.6 cc. of cream is measured off. The titration is made in the 

 usual manner, using phenolphtalein as an indicator. See also Cornell 

 Univ. circ. No. 7. 



*Devaida'8 acidimeter (Milchzeitung 1896, p. 785) is based oil the 

 same principle as Manns' test; one-tenth soda solution is added to 100 

 cc. of milk in a glass-stoppered granulated flask, j cc. of a 4 per cent, 

 phenolphtalein solution being used as an indicator. The graduations 

 on the neck of the flask give the "degrees acidity" directly. 



8 Illinois experiment station, bulletin 32, April, 1894. 



