CHAPTEE I. 

 COMPOSITION OF MILK AND ITS PRODUCTS. 



Before taking up the discussion of the Babcock milk 

 test, a brief description of the chemistry of milk and its 

 products is given, so that the student may understand 

 what are the components of dairy products, and the re- 

 lation of these to each other. Only such points as have 

 a direct bearing upon the subject of milk testing and 

 the use of milk tests in butter and cheese factories or 

 private dairies will be treated in this chapter, and the 

 reader is referred to standard works on dairying for 

 more detailed information in regard to the composition 

 of dairy products. 



15. Composition of milk. Milk is composed of the 

 following substances: water, fat, casein, albumen, milk 

 sugar, and ash. A few other substances are present in 

 small quantities, but they are hardly of sufficient prac- 

 tical importance to be considered here. The com- 

 ponents of the milk less the water are known collect- 

 ively as mUk solids or total solids, and the total solids 

 less the fat, i. e., casein, albumen, milk sugar, and ash, 

 are often spoken of as solids not fat or the non-fatty 

 milk solids. The milk serum includes all components 

 of the milk less the fat; the serum solids are therefore 

 another name for the solids not fat; when given, they 

 are, however, generally calculated to per cent, of milk 

 serum, not of milk. If, e. g., a sample of milk contains 



