THE CHEMICAL COMPOSITION OF MILK 



21 



tions with glycerin : Palmitic acid, oleic acid, myristic acid, and 

 butyric acid. The compounds or glycerides, formed by the 

 combination of glycerin and the acids, have special names 

 derived from the acids ; thus, we have palmitin (glycerin com- 

 bined with palmitic acid), butyrin (glycerin combined with 

 butyric acid), olein, etc. Milk-fat contains, on an average, 

 about 40 per cent of palmitin, 34 per cent of olein, 10 per cent 

 of myristin, 6 per cent of butyrin, and from less than 1 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 myristin tend to make milk- 

 fat harder, while olein and butyrin have the opposite tendency. 

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

 into two groups : (1) 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 dif- 

 ferences 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. 



Table Showing the Composition of Milk-fat (Babcock) 

 ' Olein 

 Palmitin 

 Stearin 

 Myristin 

 Butter-fat | Butin (trace) acids \ Fat 3.6 



3.6% Butyrin 

 Caproin 



Caprylin (trace) 

 Caprinin (trace) 



Glycerides of 





insoluble and 



> 3.3 



non-volatile 





acids 





Glycerides of 





soluble and 



0.3 



volatile acids 







, 



