THE CHEMICAL COMPOSITION OF MILK 35 



with distilled water and filtering several times. The purified 

 material goes readily into suspension on shaking with water 

 and, if treated with a preservative, will remain indefinitely 

 without change other than the separation of fat-globules. It 

 has been held by some that the citrates of milk perform the 

 function of holding the insoluble phosphates in suspension, 

 but this is not supported by the behavior of the insoluble por- 

 tion shown in our experiments. 

 Reaction. 



A suspension of the insoluble constituents of milk, prepared 

 in the manner described above, is neutral to phenolphthalein. 

 We purified the deposit made from 1000 c.c. of milk, made a 

 suspension of it in water, and, after the addition of 10 c.c. of 



neutral solution of potassium oxalate, it was found to require 



tf 

 only 0.5 c.c. of solution of sodium hydroxide to make it 



neutral to phenolphthalein. We interpret this to mean that 

 there are no tri-basic (alkaline) phosphates in milk or in the 

 serum, because the serum, since it is acid, can contain none, and 

 the insoluble portion, being neutral, can therefore contain none. 

 Relation of inorganic constituents to casein in milk. 



Without going into a detailed discussion of the history of 

 the different views held by different investigators, it is suffi- 

 cient for our purpose to state that three general views have 

 been put forward in regard to the relation of inorganic con- 

 stituents to casein in milk: (1) That milk-casein is combined 

 with calcium (about 1.07 per cent) to form a salt, calcium 

 caseinate (which is neutral to litmus and acid to phenol- 

 phthalein) ; (2) that casein is chemically combined directly 

 with calcium phosphate ; (3) that casein is a double compound 

 consisting of calcium caseinate combined with calcium phos- 

 phate. 



We have attempted to learn what is the true condition of 

 casein in milk in relation to inorganic constituents, whether it 



