100 MODERN METHODS OF TESTING MILK 



has been completely neutralized, that is, changed into 

 sodium lactate. 



Having completed the neutralization of the acid, 

 we examine the burette or the graduated cylinder con- 

 taining the alkali to find exactly how much alkali so- 

 lution has been used in neutralizing the acid. The 

 lactic acid has required, say, 28 cc. of soda solution. 

 Each cubic centimeter of alkali neutralized by acid 

 corresponds to .009 gram of acid, and 28 cc. would 

 therefore correspond to .25 gram of lactic acid. This 

 amount of lactic acid in 100 cc. is .25 per cent. The 

 process of making a chemical determination by means 

 of a standard solution is known as titration. 



NEUTRALIZATION METHOD APPLIED TO TEST- 

 ING ACIDITY OF MILK AND MILK PRODUCTS 



In practical dairy work, one is freed from the ne- 

 cessity of preparing standard solutions, except in a 

 simple way, and the calculations needed to figure the 

 results are direct and easy. The caustic soda solution 

 is prepared in such strength that a certain amount of 

 it equals .1 per cent, of lactic acid, when a certain 

 amount of milk or other substance is used. All tests 

 for the acidity of milk and its products are based upon 

 the general principles previously described and differ 

 from one another simply in some of the details of 

 carrying out the process. There are now available sev- 

 eral forms of so-called acid tests, among which we 

 shall describe the following : "Mann's acid test," "Far- 

 rington's alkaline-tablet test," and the "Purdue alkali 

 test." 



