SOME PHYSICO-CHEMICAL MEASUREMENTS ON MILK. 



189 



of acid salts over alkaline ones. At a temperature of 30°C. 

 the H ion attained its maximum value after about twenty- 

 four hours, and in the samples examined this value varied 

 from 4*3 to 4*65. 



4-0. 



5-0 



6-0 



7-0 

 



/ 



10 20 



Fig. 3. — Time hours. 



30 



The curdling of the milk, which is brought about by the 

 precipitation of the caseinogen by the acid formed, took 

 place in the sample under observation at a temperature of 

 30° O. when the acidity calculated as lactic acid reached 

 a value of '73 per cent., which corresponded to a H ion 

 value of 4*9; this value was arrived at when the milk was 

 20 hours old. 



