40 MANUAL OF MILK PRODUCTS 



" These figures show that the acidity of fresh milk is the same as 

 that of its serum, which means that the constituents of the milk 

 causing acidity are soluble constituents contained in the serum. 

 Since the serum contains phosphates in amounts sufficient to 

 furnish two to four times as much acid phosphates as is required 

 to account for the acidity, and since, moreover, no other acid 

 constituents of the milk-serum are present in more than mi- 

 nute quantities and are wholly insufficient to cause the observed 

 degree of acidity, it appears a reasonable conclusion that the 

 acidity of fresh milk is due to soluble acid phosphates. This 

 conclusion is further strengthened by the results given in the 

 preceding pages, which go to show conclusively that the insol- 

 uble constituents of fresh milk are neutral in reaction, consist- 

 ing largely or wholly of neutral calcium caseinate (casein Ca 4 ), 

 neutral di-calcium phosphate (CaHPO 4 ), and fat. 



"Both fresh milk and the serum from fresh milk show a 

 slight acid reaction to phenolphthalein but are strongly alka- 

 line to methyl orange, indicating that acidity is due, in part at 

 least, to acid phosphates. In eight samples of fresh milk, the 

 acidity of the milk and of the milk-serum was determined after 

 treatment with neutral potassium oxalate. The results show 

 that the acidity of the whole milk is the same as that of the 

 serum and that, therefore, the constituents of the serum are 

 responsible for the acidity of milk. There is every reason to 

 believe that the phosphates of the serum cause the observed 

 acidity." 



