10 BUTTER-MAKING AND COMPOSITION OF MILK 



of larger globules has a finer flavor, and a little more oily appear- 

 ance. 



From what has been said, it will be seen that the minute- 

 ness of the fat-globules is almost inconceivable. They were 

 first discovered in 1697 by A. von Leeuwenhoek. The minute 

 state of division, or the form of emulsion in which they exist 

 in milk, renders it easy to digest when consumed as a food. 



Properties of Fat. The specific gravity of pure butter-fat 

 at 15 C. is .93002. The refractive index of butter-fat at 22 C. is 

 on an average 1.459. The melting-point of pure butter-fat, as 

 now determined, varies between 32 and 37 C. (90 F. and 

 99 F.) 



When pure butter-fat is rapidly cooled, it solidifies into one 

 solid mass; but if allowed to cool gradually, part of it solidifies, 

 and part of it remains a liquid longer than other parts. This 

 seems to indicate that some fats with a high melting-point sepa- 

 rate out from the fats with a low melting-point. This behavior 

 of pure butter-fat is not well understood, as it contradicts the 

 now accepted theory that the different fats are in chemical com- 

 bination with each other, rather than a mechanical mixture of 

 different glycerides of fat. 



Glycerides of Fat. By this term we understand that the 

 fatty acid radicals are in chemical combination with the glycerol 

 (glycerine) radical, thus: 



Fatty acid radicals. 



C 4 H 7 O 2 (Butyric) 

 C 18 H 3 30 2 (Oleic) 



Glycerol radical. 

 C* TT 



(Stearic) 

 The chemical formula for glycerine is : 



Hydroxyl groups. 



Glycerol radical. 



C 3 H 5 



OH 

 OH 

 OH 



The difference and similarity of these two formulas are 

 easily observed, and the reason why the term " Glyceride of Fat " 

 has been applied to such a compound is evident. 



