CHAPTER IX. 
ACID TESTS FOR MILK AND CREAM. 
Milk dealers and buttermakers who have had years of 
experience do not find it safe to rely upon their noses 
in determining the acidity of milk or the ripeness of cream 
for churning. They use in daily practice tests by which 
it is possible to determine the actual amount of acid pres- 
ent. The method of using these tests is based upon the 
simplest form of titration. 
Titration. This consists in neutralizing an acid with 
an alkali in the presence of an indicator which determines 
when the point of neutrality has been reached. 
Acids and alkalies are substances that have entirely 
opposite chemical properties. The acid in milk gives it 
its sour taste, and for our purpose, illustrates very well 
what we mean by an acid. Ordinary lime may be used 
to illustrate what we mean by an alkali. 
When lime is added to sour milk the acid unites with 
the lime forming a neutral substance which is neither 
alkaline nor acid. If we keep on adding lime to the milk 
we reach a point at which all the acid has combined 
with the lime. This is called the point of neutrality. The 
moment this point is passed is made visible to the eye 
by means of the indicator, (phenolphthalein) which is 
colorless in the presence of an acid but pink in the 
presence of an alkali. One drop of alkali added to milk 
after the acid has been neutralized will turn it pink, 
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