8 BUTTER-MAKING. 



AVhen 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 

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

 behavior of pure butter-fat is not well understood, as it con- 

 tradicts the now accepted theory that the different fats are 

 in chemical combination with each other, rather than a me- 

 chanical mixture of different glycerides of fat. 



Glycerides of Fat. — By this term \\q understand that the 

 fatty acid radicals are in chemical combination with the glycerol 

 (glycerine) radical, thus: 



Fatty acid radicals. 

 Glycerol radical. [ C4H7O2 (Butyric) 

 C3H5 I C18H33O2 (Oleic) 

 [ C18H33O2 (Stearic) 



The chemical formula for glycerine is: 



Hydroxyl groups. 

 Glycerol radical. ' 'H 



C3H5 I OH 



[ OH 



Comparing these t^^'o formulas, their difference and .simi- 

 larity are easily ob.served, and the reason why the term "Gly- 

 ceride of Fat " has been applied to such a compound is evident. 



Condition of Fat. — Whether the fats in milk exist in chem- 

 ical comliinaticn, or whether they exist as glyceride of Ixityrin 

 stearin, olein, etc., in the form of a mechanical mixture, is a 

 question in dispute. If they exist in the latter form, the com- 

 position of the different fats nuist be thus: 



Butyrin. Olein. Stearin. 



[C4H7O2 [C.sHgsOa 



C3H5 } C4H7O2 C3H5 j 0i«H33O2 C3H5 



I C4H7O2 I C,8H3302 



C18H35O2 



t'i8H3502 etc. 



(^'l8H3502 



