142 



MODERN METHODS OF TESTING MILK 



FIG. 38 VAN NORMAN ACIDITY TEST 



Each cubic centimeter of alkali solution used corres- 

 ponds to o.oi per cent, of acid. Thus 40 cc. of alkali 

 solution equals .40 per cent, of acid in the material 

 tested. 



Farrington's alkali-tablet method (Fig. 38a) makes 

 use of tablets containing the alkali and indicator mixed 

 together ; one tablet contains enough alkali to neutralize 

 0.035 gram of lactic acid. When 5 tablets are dissolved 

 in 97 cc. of water, a fiftieth normal solution is fur- 

 nished, each cubic centimeter of which is equal to o.oi 

 per cent, of lactic acid when a 17.6 cc. sample of ma- 



