Page:The story of milk.djvu/45

 The acidemeter

Acidity Test. —The acidity, or sourness, of milk or cream, which depends upon the amount of lactic acid developed in it, may be tested by a liquid normal alkali or by the Farrington Alkaline Tablets, a solution of which added to sour milk neutralizes the acid. A few drops of an indicator, Phenolpthalein, added to the milk, turns it pink when all the acid has been neutralized, and the amount of alkali solution used shows the percentage of acid in the milk. This is quite important in preparing "starters" for ripening the cream in butter making or milk in cheese making, and in the manufacture of "Commercial Butter-*milk," etc.*