394 THE CHEMICAL COMPOSITION OF THE BODY [dl. XXV. 



Or in general terms : 



From the alcohol with formula C n H 2n +i.HO, the acid with 

 formula C n -iH 2 n-i.COOH is obtained. The sixteenth term of this 

 series has the formula Ci 5 H 31 .COOH, and is called palmitic acid; 

 the eighteenth has the formula Ci7H 35 .COOH, and is called stearic 

 acid. Each acid, as will be seen, consists of a radicle, C n _iH 2 n-iCO, 

 united to hydroxyl (OH). Oleic acid, however, is not a member of 

 this series, but belongs to a somewhat similar series known as the 

 acrylic series, of which the general formula is C n _iH 2 n_3.COOH. It 

 is the eighteenth term of the series, and its formula is Ci7H 33 .COOH. 



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 acrohin (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. are due. Fat which contains any member of the acrylic series like 

 oleic acid blackens osmic acid, by reducing it to a lower (black) oxide. Fats like 

 palmitin and stearin do not give this reaction. 



Glycerin or Glycerol is a triatomic alcohol, C 3 H 5 (HO) 3 i.e., three 

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

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

 an example, take the radicle 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 : 



fOH (OH (OH (O.CH 3 .CO 



C 3 HJ OH C 3 HJ OH C 3 HJ O.CH 5 .CO C 3 H 5 4 O.CH 3 .CO 



I OH lo.CHs.co lo.CH 3 .co io.GH 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 radicles of the fatty acid. 

 This is represented in the following formula : 



Acid. Radicle. Fat. 



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



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



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



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 ferments (for instance, the fat-splitting 

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



