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THE ALKALINE SOLUTION : ITS PREPARATION AND USE. 

 By R. Harcourt B.S.A., Professor of Chemistry. 



Causes of Acidity in Milk. The development of acid is caused 

 by the breaking- down of milk sugar into lactic acid, throug-h the influence 

 of certain acid-forming- ferments in the milk. But even sweet milk, im- 

 mediately after it is drawn from the udder, will have an acid reaction with 

 certain indicators. This acidity is not due to lactic acid nor any free 

 acid in the milk, but to the acid nature of the ash constituents, possibly 

 also to the carbonic acid g-as it contains, and to the acid nature of the 

 casein. When phenolphthalein is used as an indicator, freshly drawn 

 milk will g-enerally show as much as .10 per cent, of acid and immediately 

 after exposure to the atmosphere, lactic acid germs commence breaking 

 down the milk sugar. At a temperature of 70 degrees to 90 degrees F., 

 these germs multiply at an enormous rate, consequently lactic acid will 

 develop very rapidly in milk during a warm or sultry day or night. Cool- 

 ing retards the action, but even at a temperaure of 40 degrees to 50 de- 

 grees F., they will multiply and considerable lactic acid will be formed. 

 Milk intended for cheese-making should not contain more than .20 per 

 cent, acid when delivered at the factory ; whereas it does not usually 

 smell or taste sour until it contains .30 to .35 per cent. A further de- 

 velopment of acid will cause the milk to curdle, or, iu other words, 

 will produce coagulation of the casein. There is, however, a limit to 

 the development of acid; for, after a certain point, the germs which 

 break down the milk sugar are destroyed by the acid they produce, and 

 there is no further increase in acidity. 



In many ways a knowledge of the acid contents of milk or its 

 products is of value. In most cases, a determination of the percentage 

 of acid in the milk when delivered at the factory will indicate the care 

 the milk has received previous to that time. The acid test may be of 

 value in selecting milk best adapted for pasteurization, or for retail 

 trade, or manufacture of high-grade products. At the present time, 

 however, the chief uses made of the alkaline solution in dairy work are 

 to determine the acid in cream intended for churning, and the acid in 

 milk and whey in the various steps in the process of the manufacture 

 of cheese. Both in ripening cream and in cheese-making, acid is de- 

 veloped, and the alkaline solution is now frequently used to measure the 

 amount of acid nrescnt and thus control the work. 



How TO Measure the Acidity. The measurement of the amount 

 of acid or alkali in a solution depends upon the fact that it always takes 

 a definite quantitv of alkali to neutralize a definite quantity of acid. Thus, 

 for instance, it always takes a definite quantity of caustic soda to neu- 

 tralize a definite quantity of lactic acid, sulphuric acid, or any other acid. 

 If, then, we know the strength of a given caustic soda solution and meas- 

 ure the amount of it used to render a definite amount of milk or cream 

 neither acid nor alkaline, but neutral, we can figure the cinount of acid 



