ACID TESTS 87 
rotating the cup after each addition. As soon as a per- 
manent pink color appears, the graduate is read and the 
number of c.c. solution used will indicate the number 
of hundredths of one per cent of acid in the cream. Thus, 
if it required 50 c.c. of the tablet solution to neutralize the 
cream then the amount of acid would be .50%. From 
this it will be seen that with the Farrington test no calcu- 
lation of any kind is necessary. 
The acidity of milk may be determined in the same way 
as that of cream, except that the milk need not be diluted 
with water before adding the alkali. 
A Rapid Acid Test for Milk. Where milk is pasteur- 
ized it is often desirable to determine approximately the 
acidity of each lot as it arrives at the creamery. 
It has been found that milk that contains more than .2% 
acid cannot be satisfactorily pasteurized. Farrington and 
Woll have devised the following rapid method for testing 
the acidity of milk that is to be pasteurized: 
Prepare a tablet solution by adding two tablets for each 
ounce of water. When the tablets have dissolved, take 
the solution into the intake. Now, as each lot is 
dumped into the weigh can a sample of milk is taken 
with a No. Io brass cartridge shell and emptied into a 
teacup. With another, or the same, No. 10 shell add a 
measure of tablet solution to the cup. Mix the alkali and 
milk by giving the contents of the cup a rotary motion. If 
the milk remains white it contains more than .2% acid; 
if it is colored, there is less than .2% acid present. 
Where the tablet solution is prepared as above care 
must be taken to secure equal quantities of milk and 
solution for the test. 
