CHAPTER I. 

 COMPOSITION OF MILK AND ITS PRODUCTS. 



Before taking up the discussion of the Babcock niilk 

 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 rela- 

 tion of these to each other. Only such points as have a 

 direct bearing on 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 pro- 

 ducts. 



15. Composition of milk. Milk is composed of the fol- 

 lowing substances: water, fat, casein, albumen, milk sugar, 

 and ash. A few other substances are present in small 

 quantities, but they are hardly of any practical impor- 

 tance and will not be considered here. The components 

 of the milk less the water are known collectively as milk 

 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 calcu- 

 lated to per cent, of milk serum, not of milk. If, e. g., 

 a sample of milk contains nine per cent, of solids not fat, 



