4 MODERN METHODS OP' TESTING MILK 



from less than i to nearly 3 per cent, of each of the 

 glycerides of other acids. Milk-fat contains about 

 12.5 per cent, of glycerin in combination with the 

 acids. The proportions of these constituents of milk- 

 fat vary somewhat, and this variation influences the 

 character of the milk-fat. Thus, palmitin and myris- 

 tin tend to make milk-fat harder, while olein and buty- 

 rin have the opposite tendency. 



The acids contained in milk-fat or butter-fat may 

 be divided into two groups: (i) The acids in one 

 group (palmitic, oleic, myristic, stearic, lauric) are 

 insoluble in water and non-volatile, while (2) the 

 other acids (butyric, caproic, etc.,) are more or less 

 completely soluble in water and are volatile. These 

 differences afford a practical basis for distinguishing 

 pure butter from artificial butter. Of the fat-acids 

 contained in butter-fat, about 87.5 per cent, consists 

 of the insoluble fat-acids, while in other forms of 

 animal fat (beef- fat, lard, etc.,) the amount of these 

 insoluble fat-acids is considerably greater. The amount 

 of volatile fat-acids in milk-fat or butter-fat is much 

 greater than in other forms of animal fat. 



Fat-globules in milk. — ]\Iilk-fat is present in milk, 

 not in solution, but suspended in the form of very 

 small, transparent globules. Globules varying in size 

 between one twenty-five hundredth and one fifteen- 

 thousandth of an inch in diameter are the ones most 

 commonly present. The average size of fat-globules 

 in milk is somewhat more than one ten-thousandth of 

 an inch in diameter. The smaller globules are more 

 numerous than the larger ones. In one drop of aver- 

 age milk there are more than one hundred million fat- 



