204 Milk and Its Products 
that whatever amount is desired should be uniform 
from day to day. By far the larger proportion of 
consumers prefer the flavors that are characteristic of 
ripening till: sufficient acid to slightly coagulate the 
casein is present. Consumers of delicate taste 
readily distinguish between the flavors due to a 
greater or less amount of acid, and it is highly de- 
sirable that some means of determining the amount 
of acid present be available. The butter-maker of 
trained senses has little difficulty in distinguishing by 
the somewhat thickened and glistening appearance of 
his cream, when stirred, the proper condition of the 
cream for churning. Besides this, there are, fortunately, 
more exact means for determining the acidity. 
Acid tests.—Dr. A. G. Manns first suggested the 
use of an alkali of known strength to determine the 
proper acidity of cream for churning, and devised 
what is known as Manns’ acid test. It simply con- 
sisted in neutralizing the acid in the cream with a 
standard alkali, the standard used being that known 
to chemists as decinormal, or =., and the acidity was 
reckoned in terms of cubic centimeters of alkali re- 
quired to neutralize the acid in a given quantity of 
cream. In the use of this test, an indicator which 
changes color according as the medium is acid or 
alkaline, is used. A convenient indicator is phenol- 
phthalein, which is colorless in acid solutions and 
pinkish in alkaline. Later, Professor Farrington* 
devised tablets containing a known amount of alkali 
*Bull, 32, Il. Agr. Exp. Sta. Bull. 52, Wis. Agr. Exp. Sta. 
