THE COMPONENTS OF PLANTS AND ANIMALS 17 



30. Molecular structure. The simple neutral fats are tri- 

 glycerids, that is, they are esters of the triatomic alcohol 

 glycerol with monobasic fatty acids, the hydrogen atoms of 

 the three hydroxyls being replaced by the acid radicles. Their 

 general formula is as follows, RI, R 2 and R 3 representing the 

 acid radicles, which may or may not be the same : 



Glycerol CH 2 - OH CH . OH CH 2 . OH 

 Neutral fat CH 2 . ORi CH OR 2 CH 2 . OR 3 



The fatty acids may be divided into the saturated and the 

 unsaturated. The saturated fatty acids have the general for- 

 mula C ra H 2n O 2 and are the normal acids of the aliphatic series, 

 the two lower members of which are familiar as formic and 

 acetic acids. The general formula of these acids is as follows, 

 each carbon atom being united to the adjacent ones by a single 

 bond. 



CH 3 -(CH 2 ) n -COOH 



The two principal saturated acids contained in the animal fats 

 are stearic acid, Ci8H 36 O 2 , and palmitic acid, CieH 32 O 2 . Besides 

 these two, however, others are also found in small amounts. 

 In butter fat, especially, several of the lower acids of the series 

 are present, the principal ones being butyric, C4H 8 O 2 , caproic, 

 C6H i2 O 2 , caprylic, C 8 Hi 6 O 2 , capric, Ci H2oO 2 , lauric, Ci 2 H 24 O 2 

 and myristic, Ci4H 28 O 2 . In the body fats there have been 

 found also higher acids of the same series, particularly arachnic 

 acid, C 2 oH 4 oO 2 . 



The unsaturated fatty acids differ from the saturated acids 

 in containing two or more carbon atoms united by two bonds 

 instead of one and consequently in containing less hydrogen 

 than the saturated acids. Of the unsaturated acids, the most 

 abundant in animal fats is oleic acid, having the formula 



CH 3 -(CH 2 ) 7 -CH = CH-(CH 2 ) 7 -COOH 



The eruic acid of rape oil also belongs to this series, and the 

 linoleic acid, Ci 8 H 32 O 2 , of linseed oil and other drying oils belongs 

 to a related series of unsaturated acids of the general formula 

 C n H 2n _4O 2 with two double unions of carbon atoms. 



It is a noteworthy fact that nearly all the fatty acids occurring 

 in the animal body contain an even number of carbon atoms. 



