THE CHEMICAL COMPOSITION OF MILK 



39 



orange is the indicator, the reaction is alkaline, while with 

 phenolphthalein it is acid. Van Slyke and Bosworth explain 

 the reaction in fresh milk as follows : 



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

 slight acid reaction to phenolphthalein. This has been be- 

 lieved to be due 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 1000 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 according to the method of Van Slyke and Bosworth. 1 

 The results are given below : 



Acidity of Milk and Milk-serum 



Number op Sample 



Number of C.C. of^. Alkali Required to 

 Neutralize 100 C.C. of — 





Milk 



Milk-serum 



1 . . . . 



4.8 

 6.2 

 4.2 

 6.0 

 6.4 

 4.4 

 7.0 

 6.6 



5.0 



2 



6.2 



3 



4.2 



4 



5.8 



5 



6.4 



6 



4.4 



7 



6.8 



8 



6.4 







1 N. Y. Agr. Expt. Sta. Tech. Bui. No. 37, p. 5. 



