THE PLANT 89 



All acids of this series have the general formula 

 C,H2,+,.C00H, 

 and are saturated, because each carbon atom is united by four 

 combining affinities with other atoms, and the compound is 

 incapable of uniting by addition with other substances. 



The oils contain chiefly acids of high molecular weight. Thus 

 capric acid, CgHj^COOH, occurs in cocoa-nut oil ; myristic 

 acid, CjoHjiCOOH, also in cocoa-nut oil ; palmitic acid, 

 CijHgjCOOH, in palm oil ; stearic acid, Cj^Hg^COOII, in many 

 oils. These various acids are in combination with glyceryl. 

 But many oils contain also unsaturated fatty acids — i.e., acids 

 in which two or more carbon atoms are linked together by two 

 combining affinities. Such acids can combi:ie hy addition with 

 other substances — e.g.^ oxygen, chlorine, or iodine. 

 The following are examples of unsaturated acids: 

 Crotonic acid, CjHjCOOH, in croton oil. 

 Oleic acid, Cj^UgjCOOH, in olive and other oils. 

 Brassic acid, CgiH^iCOOH, in colza oil. 

 Kicinoleic acid, Oj7H32(OH)COOH, in castor oil. 



All these have the general formula CnHjn_jCOOH and con- 

 tain one pair of doubly linked carbon atoms. Another acid, 

 linoleic acid, CJ7H31COOH— i.e., CnHgn.jCOOH — and containing 

 two pairs of doubly linked carbon atoms, occurs in linseed and 

 other oils ; while a still more unsaturated acid, linolenic acid, 

 0„H2,C00H (i.e., C^H^n-sCOOH), containing three pairs of 

 doubly linked carbon atoms, also occurs in linseed oil. 



Oils containing glyceryl compounds of unsaturated acids 

 tend to absorb oxygen from the air and to become converted 

 into solid or stiff, viscid substances. This property is the more 

 marked the larger the number of doubly linked carbon atoms, 

 there are in the molecule. 



Oils which contain only saturated acids or acids contain- 

 ing only one pair of doubly linked carbon atoms {e.g., oleic 

 acid) are known as non-drying oih-y while those containing 

 much of the unsaturated acids are known as drying oils. Tli(# 



