ACID TESTS 85 
and slowly run this from the burette into the cream, 
shaking the beaker after each addition of alkali. With 
the first few additions of alkali the pinkish color pro- 
duced quickly disappears. But when the point of neu- 
trality approaches, the color disappears very slowly and 
the neutralizer must be added drop by drop only. The 
moment the cream remains pink indicates that the acid 
has all been neutralized. The number of cubic centimeters 
of alkali added to the cream is then noted, and from this 
the percentage of acid is calculated according to the 
following formula: 
No. c.c. alkali x .009 
No. c.c. cream 
Per cent acid = x 100. 
Example: What is the percentage of acidity when 
30 c.c. of alkali are required to neutralize 50c.c. of cream? 
0 x .009 
Ss x 100 = .544. 
From the formula it is evident that any amount of 
cream may be used for a test. But more accurate results 
are obtained by using 50 c.c. than less. Where this 
amount of cream is always used the formula may be con- 
siderably simplified. 
Thus, by dividing the numerator and denominator by 50, the 
a No. c.c. alkali x .009 
expression 50 x 100) becomes (No. c.c. 
alkali x .009 x 2) or (No. cc. alkali x .018). The acidity in 
the problem above would therefore equal 30 x .018 = .54%. 
FARRINCTON’S ALKALINE TABLET TEST. 
In the Farrington test the same alkali is used as in 
Manns’, but in a dry tablet form in which it is more 
