Determination of Lactic Acid 205 



for the same purpose, known as Farrington's alkaline 

 tablets. Each tablet contains an amount of alkali 

 equal to 3.8 cubic 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 

 cubic centimeters of water) until the cream retains a 

 pinkish tinge. The tablet solution should always 

 be fresh, not more than ten hours old. The tab- 

 lets themselves will keep indefinitely. TKe proper 

 degree of acidity is indictated when 30-35 c. c. of 

 Farrington tablet solution, or 11-13 c. c. of deci- 

 normal alkali, are required to neutralize the acid in 

 20 cubic centimeters of cream. 



Determination of lactic acid in milk or cream. Far- 

 rington 7 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- 

 ize each other; and further, that a normal solu- 

 tion of lactic acid contains 90 grams of acid in each 

 liter, or 1,000 c. c. A decinormal solution would 

 contain 1-10 as much, or 9 grams in each liter, 

 and a cubic centimeter would contain oVo as much 

 as a liter, or .009 grams of lactic acid. Each 

 tablet of the Farrington alkali is egual in strength 

 to 3.8 c. c. of decinormal alkali, and if the tablet 

 solution is made by dissolving 10 tablets in 100 c. c. 

 of water, each cubic centimeter of the solution will 

 be equal to .38 c. c. of decinormal alkali, and will 



