THE FATS 25 



Glycerin or Glycerol is a triatomic alcohol, C 3 H fi (OH) a i.e. three 

 atoms of hydroxyl united to a radical glyceryl (C 3 H 5 ). The hydrogen 

 in the hydroxyl atoms is replaceable by other organic radicals. As 

 an example take the radical of acetic acid called acetyl (CH 3 .CO). 

 The following formulae represent the derivatives that can be obtained 

 by replacing one, two, or all three hydroxyl hydrogen atoms in this 

 way : 



/OH i OH (OH ,O.CH 3 .CO 



C 3 H 5 OH C 3 H 5 -I OH C 3 H fi O.CH 3 .CO C S H 5 O.OH 8 .CO 



(OH (O.CH 3 .CO (O.CH 3 .CO lO.CH 3 .CO 



[glycerin] [monoacetin] [diaoetin] [triacetin] 



Triaoetin is a type of a neutral fat ; stearin, palmitin, and olein 

 ought more properly to be called tristearin, tripalmitin, and triolein 

 respectively. Each consists of glycerin in which the three atoms of 

 hydrogen in the hydroxyls are replaced by radicals of the fatty acid. 

 This is represented in the following formulae : 



Acid Eadical Fat 



Palmitic acid C 15 H 31 .COOH Palmityl C 15 H 31 .CO Palmitin C 3 H 5 (OC 15 H 31 .CO) 3 

 Stearic acid C 17 H 35 .COOH Stearyl C 17 H 35 .CO Stearin C 3 H 5 (OC 17 H 35 .CO) 3 

 Oleic acid C 17 H 33 .COOH Oleyl C 17 H 33 .CO Olein C 3 H 5 (OC 17 H 33 .CO) 3 



Decomposition Products of the Fats. The fats split up into the 

 substances out of which they are built up. 



Under the influence of superheated steam, mineral acids, and in 

 the body by means of certain ferments (for instance, the fat-splitting 

 ferment steapsin of the pancreatic juice), a fat combines with water 

 and splits into glycerin and the fatty acid. The following equation 

 represents what occurs in a fat, taking tripalmitin as an example : 



[palmitin a fat] [glycerin] [palmitic acid a fatty acid] 



In the process of saponification, much the same sort of reaction 

 occurs, the final products being glycerin and a compound of the base 

 with the fatty acid, which is called a soap. Suppose, for instance, 

 that potassium hydrate is used ; we get 



C 3 H 5 (O.C 15 H 31 CO) 3 -f3KHO=C 3 H 5 (OH) 3 



[palmitin a fat] [glycerin] [potassium palmitate a soap] 



Emulsification. Another change that fats undergo in the body is 

 very different from saponification. It is a physical rather than a 

 chemical change ; the fat is broken up into very small globules, such 

 as are seen in the natural emulsion milk. 



Lecithin (C 42 H 84 NP0 9 ). This is a very complex fat, which 



