2 A DAIRY LABORATORY GUIDE 



keeps its circular forni because of its power of con- 

 densing upon its surface the serum of the milk. 

 The size of the fat globules differ in milk from 

 dififerent breeds of cows, and it is supposed that the 

 larger the fat globules the more easily they rise to 

 the surface when the milk is left standing in a 

 vessel. 



Butter is composed largely of fat, so we speak of 

 the fat of milk as butter fat. 



Fat is the most important constituent of the 

 milk, because milk which contains a fair amount of 

 butter fat is more valuable as a food than a milk 

 which is poor in fat. The other food constituents 

 of the milk usually increase or decrease as the fat 

 increases or decreases. This is true, however, only 

 within certain limits. 



Fat is an important constituent of nearly all of 

 the products of milk, so that in most cases a milk 

 rich in fat is more valuable for manufacturing pur- 

 poses than a milk poor in fat. 



On account of the importance of the fat, it is 

 made oftentimes a basis of payment for milk. 



Butter fat is composed mainly of nine different 

 fats. There are a few fats which are present in 

 such minute quantities that they are of no prac- 

 tical importance. All of the fats have the same 

 basis, namely, glycerin, and the fat is made by the 

 chemical union of glycerin and the corresponding 

 fatty acid. For example, the fat butyrin is made 

 of glycerin and butyric acid. The fat stearin is 

 made of stearic acid and glycerin. While the com- 

 position of the different butter fats are known, yet 

 the chemist is unable to make them in the labora- 

 tory. 



The fats of butter fat are divided into two main 

 groups, the volatile and nonvolatile, and are so 



