TESTING THE SANITARY CONDITIONS OF MILK 153 



milk in relation to its use either as food or as material 

 for the manufacture of dairy products ; and some of 

 these methods have not yet been utilized as fully as 

 they ought to be. 



The methods of testing milk in relation to its bio- 

 chemical or sanitary condition will be considered under 

 the following headings: (i) Acidity, (2) fermenta- 

 tion tests, (3) enzyms, (4) heated milk, (5) dirt in 

 suspension. 



RELATION OF ACIDITY TO SANITARY CONDI- 

 TION OF MILK 



The details of the quantitative methods of deter- 

 mining acidity in milk by titration with standardized 

 alkali solution have been given already (pp. 131-148), 

 For exact results, one of the methods given should 

 be used. There are, however, some very simple tests 

 which can be used for rough or preliminary work 

 under conditions that do not permit exact work. Three 

 of these tests we will describe, (i) the boiling test, 

 (2) the alcohol test, and (3) the alizarol test. 



Boiling test for acidity in milk. A small amount 

 of milk (10 to 20 cc.) is placed in a test-tube or beaker 

 and brought to boiling. If it coagulates, the presence 

 of more than 0.26 per cent, of acid is indicated, since 

 normal milk coagulates on boiling when it contains 

 about 0.26 per cent, of lactic acid. 



Alcohol test for acidity in milk. Equal parts (5 to 

 10 cc.) of milk and alcohol (specific gravity, 0.89) are 

 mixed in a test-tube, and shaken vigorously. Fresh, 

 normal milk shows no change, while old milk and milk 

 from diseased udders show more or less coagulation 



