FATS 195 



ration, such as those of the Unoleic series, C„H(2„-3)COOH, 

 and the Unolenic series, C,iH(2«_r))C00H. 



As an example of the constitution of a fat we may give 

 glycerine tripalmitate : — 



CH2 



CH 



I 

 CH. 



OOCC13H31 

 OOCC15H31 

 OOCC13H31 



On boiling with alkahes {saponification) fats are hydro- 

 lysed, cleavage occurring, at the dotted Une above, into 

 glycerine and the sodium or potassium salt of the fatty 

 acids (soap). 



Saturated and unsaturated fatty acids differ from one 

 another physically and chemically, the most important 

 differences being — • 



1. The Melting-point. — Palmitic and stearic acids are 

 sohd at 60°, while oleic acid is liquid at 0°. When the 

 fatty acid is combined with glycerine to form a fat it 

 impresses upon that fat a melting-point which approaches 

 its own. 



2. Behaviour to the Halogens. — Unsaturated acids readily 

 combine with the halogens, forming saturated compounds. 

 Oleic acid, for instance, with iodine forms — 



CH3(CH2)7CHI - CHI(CH2),C00H. 



Since the iodine can be introduced at every double 

 hnkage, the amount of iodine thus taken up forms a 

 measure of the degree of unsaturation of the acid ; and 

 since the double hnkage remains unaffected in the synthesis 

 of a fatty acid with glycerine, the resulting fat will absorb 

 the same amount of iodine as the fatty acid of which it is 

 composed. The amount of iodine with which a fat can 

 combine is called its iodine number. 



Fats as they occur in the body are mixtures of different 



