] 84 XEUTRAUZATION 



A definite qiuuitit}- of a given alkali will always neutralize a 

 definite quantity of a given acid. To take a concrete example : 

 If upon trial we find that it takes S c.c. of a certain alkali solution 

 to neutralize lo c.c. of a given acid solution, subsequent trials 

 will show that they always combine with or neutralize each other 

 in exactly the same proportions. In a test of this kind we use 

 an " indicator " to tell us when the solution tested changes from 

 an acid to an alkali. If phenolphthalein be used it remains 

 colorless so long as the medium is acid, but as soon as the acid is 

 all neutralized and the liquid becomes alkaline to the slightest 

 degree, this indicator turns red. Litmus shows blue when the 

 medium is alkaline and red when it is acid. 



The principle of neutralization has been applied in dairy 

 work for many years, in the form of the difl^erent alkali tests used 

 in cheese- and butter-making to determine the acidit}' of the milk 

 or cream. The reagent used is an alkali solution of known 

 strength, usually a caustic soda (NaOH) solution. 



Lloydj an English chemist, made use of it in connection with 

 his study of the principles and practice of Cheddar cheese- 

 making about thirty years ago, and ^lann introduced his test, 

 which is still in quite common use, in 1S90. The principle of 

 these different tests is the same. It is only in the details that 

 they differ. 



In these acidity tests the acidit}- of the milk or cream is 

 reduced to the neutral point, or the point where the substance 

 tested is neither acid nor alkaline. This is true and complete 

 neutralization. 



" NEUTRALIZATION " OF CREAM FOR BUTTER-MAKING 



We now come to the use of the words "neutralization" and 

 "neutralizer" in a new sense, in connection with cream. What 

 is, in i)opular language, termed the "neutralization" of cream is, 

 in reality, merely a lowering or reduction of its acidity to a point 

 at which the cream can be efficiently pasteurized, without causing 

 an excessive loss of fat in the buttermilk. The substances most 

 commonly used for the purpose of reducing the acidity are milk 



