en. XXVIIL] THE FATS 415 



the general formula is C n _iH 2tt _3.COOH. It is the eighteenth term 

 of the series, and its formula is CnH 



The first member of the group of alcohols from which this acrylic series of 

 acids is obtained is called allyl alcohol (CH 2 :CH.CH 2 OH); the aldehyde of 

 this is acrolein (CH 2 :CH.CHO), and the formula for the acid (acrylic acid) is 

 CH. 2 :CH.COOH. It will be noticed that two of the carbon atoms are united by 

 two valencies, and these bodies are therefore unsaturated ; they are unstable and 

 are prone to undergo by uniting with another element a conversion into bodies in 

 which the carbon atoms are united by only one bond. This accounts for their 

 reducing action, and it is owing to this that the colour reactions with osmic acid 

 and Sudan III. (red coloration) are due. Fat which contains any member of the 

 acrylic series, such as oleic acid, blackens osmic acid, by reducing it to a lower 

 (black) oxide. The fats palmitin and stearin do not give these reactions. 



Glycerin or Glycerol is a triatomic alcohol, C 3 H 5 (HO) 3 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 (OH (OH (O.CH,.CO 



C 3 HJOH C 3 HJOH C 3 HJO.CH 3 .CO C 3 H 5 J O.CH 3 .CO 



[OH tO.CH 3 .CO lO.CH 3 .CO lO.CH 3 .CO 



[Glycerin.] [Monoacetin.] [Diacetin.] [Triacetin.] 



Triacetin 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. Radical. Fat. 



Palmitic acid C 15 H 51 .COOH Palmityl C ]6 H 31 .CO Palmitin C 3 H 5 (OC 15 H 31 .CO) 3 



Stearicacid C 17 H 35 .COOH Stearyl C 17 H 35 .CO Stearin C,H 5 (OC 17 H., 5 .CO) 3 



Oleic acid C^H^COOH Oleyl C^H^CO Olein C-jH^OC^Hgg.CO), 



Decomposition Products of the Pats. 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 enzymes (for instance, the fat-splitting 

 enzyme, lipase, of the pancreatic juice), a fat combines with water 

 and splits into glycerin and the fatty acid. The following equa- 

 tion represents what occurs in a fat, taking tripalmitin as an 

 example : 



C 3 H 6 (O.C 15 H 31 CO) 3 + 3H 2 = C 3 H 5 (OH) 3 + 3C 15 H 31 CO.OH. 



[Tripalmititi a fat.] [Glycerin.] [Palmitic acid a 



fatty acid.] 



In the process of saponiflcation much the same sort of reaction 

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



