600 TESTING MILK AND CREAM FOR ACID 



used ; stopper tightly and 'lay the cylinder horizontally. This insures 

 complete solution by the time the tablet solution is needed. When 

 ready for the test, pour with the pipette 17.6 c.c. cream into the 

 white cup and add tablet solution from the cylinder until the cream 

 remains faintly pink. Then read off the number of c.c. of tablet 

 solution used on the graduations of the cylinder. Each c.c. tablet 

 solution represents .01 per cent acid. 



Example. 60 c.c. tablet solution are required to neutralize the 

 cream, in the cup. 60 X .01 = .6 per cent acid. The Farrington 

 alkaline tablets are especially convenient because they contain both 

 the alkali and the indicator. They may be purchased from any 

 creamery supply house. They should be kept perfectly dry and in 

 the dark. Otherwise they will weaken and the indicator will bleach 

 out. For maximum accuracy an 18 c.c. pipette should be used for 

 cream. 



Marshall Acid Test. Apparatus Needed. One alkaline solu- 

 tion bottle with graduated burette, one 9 c.c. pipette, one white 

 cup, one bottle for indicator. 



Reagents Needed. Tenth normal solution of sodium hydro- 

 xide (neutralizer) and phenolphthalein indicator same as in 

 Mann's test. 



Making the Test. With the pipette pour 9 c.c. of cream into 

 the white cup ; add a few drops of indicator. Fill neutralizer bottle 



N 



with the -Tp solution of sodium hydroxide. Fill the graduated bur- 

 ette by tipping the bottle until the burette is full and run neutralizer 

 from the burette into the cream in the cup until the cream remains 

 slightly pink. The number of c.c. of neutralizer solution used, as 

 indicated on the graduation of the burette, represents per cent acid- 

 ity. 



Soxhlet-Henkel Acid Test This test is very similar to the 

 previous tests, but instead of expressing the results in number of 

 cubic centimeters of decinormal alkaline solution required, as is the 

 case in Mann's acid test, or in per cent of acid in the cream as is the 

 case of the Farrington Tablet test and the Marshall Acid test, the 

 Soxhlet-Henkel Acid test gives its results in degrees acid. One 

 degree is equivalent to approximately .045 per cent acid or to 2.5 c.c. 

 decinormal alkaline solution of Mann's acid test using 50 c.c. of 

 cream. In this test a one-fourth normal solution of sodium hydrate 

 is used for neutralizing the acid. 



