Determination of Lactic Acid, 129 
to chemists as decinormal, or so, and the acidity was 
reckoned in terms of cubic centimeters of alkali re- 
quired to neutralize the acid in a given quantity of 
eream. 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 
for the same purpose, known as Farrington’s alkaline 
tablets. Each tablet contains an amount of alkali 
equal to 3.8 eubic centimeters of decinormal alkali, 
and a sufficient amount of phenolphthalein indicator. 
The cream to be tested is measured, and to it is 
added a solution of the tablets (one tablet in ten 
eubie centimeters of water) until the cream retains a 
pinkish tinge. The tablet solution should always 
be fresh, not mure than ten hours old. The tab- 
lets themselves will keep indefinitely. The proper 
degree of acidity is indictated when 30-38) ¢ «. of 
Farrington tablet solution, or 11-13 ©. ¢. of devi- 
normal alkali, are required to neutralize the acid in 
20 cubic centimeters of cream. 
Determination of lactic acid in milk or crean,.—Far- 
rington’s alkaline tablets may also be conveniently 
used to determine the percentage of lactic acid in any 
given sample of milk or cream. In order to do this, 
it is only necessary to understand that equal volumes 
of normal or decinormal acids and alkalies neutral- 
* Bull. 32, Ill. Agr. Exp. Sta. Bull. 52, Wis. Agr. Exp. Sta. 
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