196 FATTY ACIDS 



series possessing the general formula C n H 2n _ 1 .COOH and characterised 

 by containing some doubly linked carbon atoms. In such cases the 

 acids are said to be unsaturated, because under suitable conditions 

 they can combine with hydrogen or other element, the double link- 

 age between the carbon atoms being replaced by the usual single 

 linkage. The fatty acids can thus be divided into two great divisions 

 the saturated and the unsaturated acids. 



The following are a few of the more important fatty acids : 



SATURATED ACIDS. 



(a) Acetic or stearic acid series. General formula = C n H 2n+1 .COOH : 



(1) Formic acid, H.COOH, occurs in nettles, ants, etc. 



(2) Acetic acid, CH 3 .COOH, vinegar, etc. 



(3) Butyric acid, C 3 H 7 .COOH, butter. 



(4) Capric acid, C 9 H 19 .COOH, "butter and in cocoa- 



nut oil. 



(5) Myristic acid, C 13 H 27 .COOH, cocoanut oil and in 



spermaceti. 



(6) Palmitic acid, C 15 H 31 .COOH, palm oil. 



(7) Stearic acid, C 17 H 35 .COOH, tallow and many 



oils. 



UNSATURATED ACIDS. 



(ft) Oleic acid series. General formula = C n H 2n - r COOH : 



(1) Crotonic acid, C 3 H 5 .COOH, occurs in croton oil. 



(2) Oleic acid, C 17 H 33 .COOH, olive and other 



oils. 



(3) Brassic acid, G 21 H 41 .COOH, rape or colza oiL 



(4) Ricinoleic acid, C 17 H 32 (OH).COOH, castor oil. 

 (y) Linoleic acid series. General formula = CnH 2n _ 3 .COOH : 



(1) Linoleic acid, C 17 H 31 .COOH, occurs in linseed and other " dry- 

 ing " oils. 

 (8) Propiolic acid series. General formula = C n H 2n _ 5 .COOH : 



(1) Linolenic acid, C 17 H 29 .COOH, occurs in linseed and other dry- 

 ing oils. 



The essential difference between the saturated and unsaturated fatty 

 acids lies in their susceptibility to the action of external agencies. The 

 saturated compounds have no power to combine additively with oxygen, 

 chlorine, etc., while the unsaturated compounds, in many instances, 

 easily unite with these elements. The readiness with which the un- 

 saturated fatty acids absorb oxygen and the amount which they can 

 absorb, both increase with the number of doubly linked carbon atoms 

 contained in a molecule. Thus linolenic acid, C 17 H 29 .COOH, oxidises 

 more readily and to a greater extent than oleic acid, C 17 H 33 .COOH. As 

 the oxidation products are solid or stiff, viscid substances, oils contain- 

 ing much of these unsaturated acids are known as drying oils, whilst oils 

 containing chiefly saturated fatty acids or acids containing only one pair 

 of doubly linked carbon atoms, e.g., oleic acid, are known as non-drying 



