1 8 NUTRITION OF FARM ANIMALS 



31. Chemical reactions. Of the chemical reactions of the 

 fats, the one of most importance physiologically is that known 

 as saponification, or more strictly as hydrolysis. It consists of 

 a cleavage and hydration of the molecule, yielding glycerol and 

 fatty acids. The most familiar instance of this reaction is in 

 the process of soap making. For example, if tri-stearin is acted 

 upon by potassium hydrate the final result is as represented 

 by the following equation : 



C 3 H 5 (C 18 H350 2 )3 + (KOH) 3 = (KC 18 H 35 2 )3 + C 3 H 8 O 3 



Tristearin Potassium hydrate Potassium tristearate Glycerol 



In this reaction, the alkali salt of the fatty acid, that is, a 

 soap, is obtained. By the action of water at temperatures con- 

 siderably above 100 C., essentially the same result is reached 

 except that the free acid is obtained instead of the salt. The 

 same decomposition may also be effected by means of acids, 

 which probably act as catalyzers. 



Of most importance physiologically is the hydrolysis of fat by 

 means of enzyms. Such enzyms are produced by certain plants 

 and are also found in various digestive juices, notably in the 

 secretion of the pancreas. These enzyms have received the 

 general name of Upases. The hydrolysis of fats by enzyms 

 appears to be a reversible reaction, at least with the glycerids 

 of low molecular weight. In other words, the same enzym 

 may effect the cleavage of a glycerid or the combination of 

 glycerol and the fatty acid, the reaction in either case reaching 

 an equilibrium at a certain stage.. 



32. Physical properties. Certain general properties are 

 common to all the fats. Their specific gravity is in all cases 

 less than one, so that they float on water. They have a fatty 

 feel and leave a permanent grease spot on paper or fabric. They 

 are almost insoluble in water, although water is soluble to a not 

 inconsiderable extent in fats. They are readily soluble in ether, 

 benzol, carbon disulphid and most of them in petroleum ether, 

 but only sparingly in alcohol. 



The melting point of the fatty acids increases with the 

 molecular weight. The exact melting point of a fat is diffi- 

 cult to determine, but for the three common glycerids and 

 the corresponding acids it may be stated approximately as 

 follows : 



