94 MODERN METHODS OF TESTING MILK 



pink color disappears more slowly, showing that the 

 acid is becoming more nearly neutralized. When the 

 color disappears quite slowly, the neutralizer should 

 be added a drop at a time. Finally a point is reached 

 when, after the addition of one drop of alkali, the 

 pink color does not disappear even after stirring lo 

 or 15 seconds. This indicates that the acid is com- 

 pletely neutralized. Add no more alkali. The pink 

 color will slowly disappear after standing some time, 

 even when the solution is alkaline. Some experience 

 enables one easily to know when the pink color is suf- 

 ficiently permanent. 



(3) Calculating results. — Having completed the ad- 

 dition of alkali, the burette is examined to see how 

 many cubic centimeters of neutralizer have been used. 

 The percentage of acid for 50 cc. or any amount of 

 sample taken is calculated from the following for- 

 mula: 



Per cent, of acid=g2-H_4iM|21^^09 ^^^ 

 No. cc. of sample taken 



When one uses 50 cc. of the sample, this formula 

 becomes 



Per cent, of acid = No. cc. of alkali X .018. 



From this last formula one can prepare a table which 

 gives the results and saves making calculations at 

 every test: 



