306 Report of the Department of Chemistry of the 



stituents 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. 



5. The data presented, with results of other work, furnish a 

 basis for suggesting an arrangement of the individual compounds 

 contained in milk, especially including the salts. 



INTRODUCTION. 



The chemistry of milk has been studied by many investigators. 

 Numerous facts have been accumulated relating to the amounts 

 and properties of the more prominent constituents of milk, including 

 various conditions affecting the composition; but much less atten- 

 tion has been given to thorough study of individual constituents, 

 owing largely to the difficulties involved in making such investigations. 



From the beginning of its existence, this Station has given much 

 attention to study of different phases of the composition of milk. 

 In connection with the study of the relation of the constituents of 

 milk to cheese-making, to fermented beverages made from milk, 

 and to the uses of milk in human nutrition, numerous chemical 

 questions have constantly arisen and continue to come up, to which 

 satisfactory answers can not be given, owing to our lack of knowledge 

 of the chemistry of some of the milk constituents. Until our 

 knowledge in this field becomes more complete, we cannot under- 

 stand fully, for example, the fundamental chemical facts involved 

 in the process of cheese-making and cheese-ripening, the chemical 

 changes taking place in its constituents when milk sours or when 

 it is made into fermented beverages such as kumyss, imitation butter- 

 milks, matzoon, zoolak, bulgarzoon, etc. 



We have in hand investigations relating to several of the fundamental 

 questions referred to. In the present bulletin, we shall present the 

 results of our work bearing on the following points: 



(1) Properties and composition of milk serum or constituents in 

 solution. 



(2) Properties and composition of portion of constituents not in 

 solution. 



(3) Acidity of milk and milk-serum. 



(4) The salts of milk. 



METHOD OF PREPARING MILK-SERUM. 



Before taking up the detailed results relating to these lines of 

 investigation, we will give a description of the method used in pre- 

 paring milk-serum from milk. 



That portion of the milk consisting of water and the compounds 

 in solution is known as the milk-serum. In studying the individual 

 constituents of milk, it is necessary to separate the serum. Various 

 methods have been used to separate milk-serum from the other con- 



