318 Report of the Department of Chemistry of the 



to casein or acid phosphates in the milk or to both. The fact that 

 fresh milk and its serum are strongly alkaline to methyl orange 

 indicates that the acidity is due to acid phosphates, though it does not 

 necessarily show that acid caseinates are not also responsible for 

 some of the acidity. The results of our work given in the preceding 

 pages furnish aid in determining to what compounds in milk the acid 

 reaction to phenolphthalein is due. 



A 1,000 c.c. sample of milk was obtained from each of eight cows 

 immediately after milking and chloroform (50 c.c.) was added to 

 this at once. The acidity of the milk and of the milk-serum was 

 determined after treatment with neutral potassium oxalate accord- 

 ing to the method of Van Slyke and Bosworth. 6 The results are 

 given below. 



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 minute 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 strength- 

 ened by the results given in the preceding pages which go to show 

 conclusively that the insoluble constituents of fresh milk are neutral 

 in reaction, consisting largely or wholly of neutral calcium caseinate 

 (casein Ca 4 ), neutral di-calcium phosphate (CaHP0 4 ) and fat. 



•N. Y. Agrl. Expt. Sta. Tech. Bui. No. 37, p. 5. 



