DAIRY HUSBANDRY 
45 
EXERCISE NO. 33 
Object: To lest several lots of milk for acidity , using the n /i C NaOH solution 
( Mann’s test ) and various sized pipettes. 
Procedure: An acidity test is useful when: 
(1) Grading milk or cream at the receiving room. 
(2) Ripening cream for butter making. 
(3) Making cheese. 
(4) Bottling milk or cream in a city milk plant. 
(5) Condensing milk. 
(6) Making cultured milks. 
(7) Manufacturing casein. 
A. With an 8.8 cc. pipette measure out 8.8 cc. of well mixed milk 
from lot Number 1, into a clean white cup. Add one drop of 
phenolphtalein indicator and from a burette graduated to 
tenths of a cc., and while stirring the milk continuously, add 
enough n / 10 NaOH solution to produce a permanent faint pink 
color. Each cc. of NaOH solution used indicates .1% acidity. 
B. Use a 17.6 cc. pipette for measuring out a sample of the same 
lot of milk used for A and proceed as above. Use two drops 
of phenolphtalein indicator. Record the number of cc. of n / 10 
NaOH solution used and calculate the per cent of acidity 
present by using the following formula: 
cc. n /i 0 NaOH X-009 XlOO 
-= % acidity. 
cc. sample 
C. Use a 25 cc. sample of the same milk and proceed as in above. 
D. Perform the above three operations on each of the lots of milk 
provided. 
