CREAM-RIPENING 



223 



indicator (phenolphthalein) are added. This indicator gives a 

 red color in an alkaline solution, and no color in an acid solution. 

 The tenth normal alkali solution is poured into a burette, and 

 allowed to run into the 50 c.c. or 25 c.c. of cream (which is kept 

 stirred thoroughly) until it begins to 

 turn pink in color. At this point it is 

 neutral. The number of cubic centi- 

 meters of alkali required to neutralize 

 the acid in 50 c.c. of cream indicates the 

 number of degrees of acid. For in- 

 stance, if it should require 32 c.c. of a 

 tenth normal alkali to neutralize the acid 

 in 50 c.c. of cream, the acidity of the 

 cream would be 32. (i c.c. of N/io 

 alkali = i Mann's Test.) 



Mann's test reading can be con- 

 verted so as to express the results in 

 percentage similar to the Farrington 

 test. As i c.c. of the tenth normal 

 alkali neutralizes .009 gram of pure lactic 

 acid, 32 c.c., as in the above case, would 

 neutralize 32 times .009. This would 

 give the amount of acid, calculated in 

 terms of lactic acid, present in the 50 c.c. 



of cream. This product divided by the 50, and multiplied by 

 100, would give the percentage of the acid present. 



Farrington Test. The same principle is involved in the Far- 

 rington test. The alkali is put up in small tablets, already 

 containing the indicator. These tablets contain a definite 

 amount of alkali, and are represented as retaining their strength. 

 They lose it, however, if they are exposed to the atmosphere. The 

 amount of alkali in each tablet is such that when five of them are 

 put into a graduated cylinder, the cylinder filled up with dis- 

 tilled water to the 97 c.c. mark, and the tablets thoroughly 

 dissolved in it, a solution is obtained, each cubic centimeter of 

 which represents .01 of i per cent of acid, provided 17.6 c.c. of 

 cream are taken. The tablets can be made up of different 



FIG. 76. Apparatus for 

 Mann's acid test. Instead 

 of the burette the alka'i 

 can be kept in a large 

 bottle, as shown in Figs. 

 77 and 78. 



