DRYING AND NON-DRYING OILS. 203 



UNSATURATED ACIDS. 



(/?) Oleic acid series. General formula = C n H 2n _ 1 .COOH : 



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



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



(3) Brassic acid, C 21 H 41 .COOH, ,, rape or colza oil. 



(4) Eicinoleic acid, C 17 H : ^(OH).COOH, occurs in castor oil. 

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



(1) Linoleic acid, C 17 H H1 .COOH, occurs in linseed and other 



" drying" 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 

 drying oils. 



The essential difference between the saturated and unsatu- 

 rated fatty acids lies in their susceptibility to the action of 

 external agencies. The saturated compounds have no power to 

 combine additively with oxygen, chlorine, &c., while the imsatu- 

 rated compounds in many instances easily unite with these 

 elements. The readiness with which the unsaturated 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^H^.COOH, 

 oxidises more readily and to a greater extent than oleic acid, 

 C 17 H.^.COOH. As the oxidation products are solid or stiff, 

 viscid substances, oils containing much of these unsaturated 

 acids are known as drying oils; while 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 oils. The former are used in the arts in the manu- 

 facture of oil-cloth, linoleum, paints, &c., the latter for lubri- 

 cation, &c. 



Glyceryl, C 8 H 6 '" = CH 2 .CH.CH. 2 is not known in the 

 free state, but its hydroxide, C 3 H 5 (OH) 3 , is the well-known 

 substance glycerine, or, as it is systematically called, glycerol. 



Glycerol, C 3 H 5 (OH) 8 , is a colourless, viscid liquid of sweetish 

 taste. It has a specific gravity of 1'27 and mixes with water 

 in all proportions. It is hygroscopic, and articles smeared 



