I4O MODERN METHODS OF TESTING MILK 



enables one easily to know when the pink color is 

 sufficiently permanent. It is very helpful in recogniz- 

 ing the point of neutralization to have some color- 

 standard with which to compare the pink color obtained 

 on neutralization; it also insures greater uniformity 

 in results. For this purpose a color-standard can be 

 prepared in the manner described on page 192. The 

 number of cubic centimeters of alkali used is then 

 read from the burette. 



Calculation of results. The percentage of lactic 

 acid in the material tested can be calculated from the 

 following rule : Multiply the number of cc. of alkali 

 used by the amount of lactic acid neutralized with i cc. 

 of alkali (0.009 in case of tenth-normal solutions, and 

 0.0018 in case of fiftieth-normal solutions) ; divide the 

 result by the amount of sample used in the test (9, 18, 

 etc.) and multiply the last result by 100. This rule 

 may be expressed by the following formula: 



Per cent, of acid = 



c.c. alkali X acid equivalent of I c.c. alkali 

 Amount of sample used for test 



XIOO 



It makes comparatively little difference in the results 

 whether the figure representing the .amount of sample 

 used is given in the form of grams or cubic centi- 

 meters. The difference amounts to only .02 or 0.03 per 

 cent, ordinarily. 



Some needless confusion has been introduced by 

 stating the results in the form of "degree of acidity," 

 one degree meaning I cc. of tenth-normal alkali solu- 

 tion neutralized when a certain amount of material is 

 taken for testing. In the dairy literature of Europe, 



