256 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



If the reaction is alkaline, i.e., if the milk or cream 

 becomes permanently pink when the phenolphthalein 

 solution is added, or if the pink color appears and remains 

 before the addition of the quantity of tenth-normal 

 sodium hydroxide solution required for normal milk, then 

 the rosolic acid test for alkalies should be applied (see 

 page 260). 



Acidity Test With Babcock Pipette. The test for 

 acidity may also be made by using a Babcock fat-test 

 pipette to measure the milk or cream. 17.6 c.c. of milk 

 or cream is placed in the cup or beaker, a few drops of 

 the phenolphthalein solution added and the tenth-normal 

 solution of sodium hydroxide run in slowly until the pink 

 color appears and remains permanently. The per cent, 

 of acid may be determined by dividing the number of c.c. 

 of tenth-normal sodium hydroxide solution used by two, 

 and expressing the quotient in tenths, thus: 



6 -T- 2 = 3, or 0.3 per cent. acid. 



Farringtorfs Alkaline Tablet Test. The special 

 feature of this test is the use of tablets of sodium car- 

 bonate for making the alkaline solution. Each tablet 

 contains sufficient alkali to neutralize 0.034 gramme of 

 acid. Five tablets are placed in a 100 c.c. graduated 

 cylinder and clean, soft water, preferably distilled, is 

 added up to the 97 c.c. mark. The cylinder is then 

 closed tightly with a stopper and laid on its side for sev- 

 eral hours to give the tablets an opportunity to dissolve. 

 Solution is never entirely complete, a slight flocculent 

 residue remaining. After thoroughly mixing by shaking, 

 17.6 c.c. of the milk or cream to be tested is measured 

 into the beaker or cup with a Babcock fat-test pipette. 

 The pipette is then filled with water to the 17.6 mark 



