FIXED OILS AND WAXES 75 



(b) Unsaturated Fatty Acids. — (1) With one double bondy 

 CnH 2n -iCOOII. Oleic acid, Ci 7 H 3 3< JOOH, melting point 14° C. 



CH 3 . (CH 2 )t . CH : CH . (CH 2 ) 7 . COOH 



(2) With two double bonds, CILh-sCOOII. Linoleic acid, 

 CnHsiCOOH, melting point below- 18° C. 



CH3.(CH2) 6 .CH:CH.CH:CH.(CH 2 )6.COOH 



(3) With three double bonds, C n H 2 n-5COOH. Linolenic 

 acid, CnH^COOH, liquid at ordinary temperatures. 



CH3.(CH 2 )5.CH:CH.CH:CH.CH:CH.(CH 2 )5.COOH 



The presence of more than one double bond in the fatty 

 acid is necessary for a true drying oil of commercial value. 

 One double bond in the acid radicle does not absorb oxygen 

 readily enough — does not harden sufficiently. 



The glycerides are named according to the fatty acid 

 radicle, thus: Olein for a glyceride of oleic acid, palmitin, 

 for one of palmitic acid, stearin for one of stearic acid, etc. 



In the above classification it is to be noted that palmitic 

 and stearic acids are solid at ordinary temperatures, and 

 oils containing a large proportion of these acids are solid 

 at ordinary temperatures. They are called fats. The other 

 acids mentioned are liquid at ordinary temperatures and oils 

 containing them are usually liquid. This property of being 

 solid is more or less characteristic of the saturated group, 

 and of being liquid more or less characteristic of the unsatu- 

 rated group, although not exclusively so. Some acids of the 

 first group are liquid at ordinary temperatures, and some 

 acids of the second group are solid. 



In most cases the plant fixed oils are liquid and contain 

 a larger proportion of the liquid fatty acids than do animal 

 fixed oils which are called fats. The latter contain as a 

 rule more stearic and palmitic acids. 



Oils containing oleic acid have a slight drying power. 

 Those containing linoleic and linolenic are much better 

 "driers." The "drying," it should be remembered, is an 



