202 THE CONSTITUENTS OF PLANTS. IX. 



the analyses of the earlier investigators having been called in 

 question by later observers (Tollens, &c.). 



II. THE FATS AND WAXES. 



The constitution of the fats has already been briefly de- 

 scribed (p. 11). They are glyceryl salts of the fatty acids. 

 The true fatty acids are members of a series of which formic 

 acid, H.COOH, is the first member, acetic acid, CH 8 .COOH, 

 the second, propionic acid, C. 2 H 5 .COOH, the third, and so on, 

 each member differing from its predecessor by CH 2 . The 

 general formula for a fatty acid would therefore be C n H 2n+1 . 

 COOH and its structure would be represented most simply 

 and generally by H (CH 2 ) n COOH. 



Such acids are saturated, i.e., cannot combine with other 

 chemical elements or radicals by addition. Included under 

 the title "fatty acids" and occurring in many vegetable fats 

 are acids of a different type, e.g., crotonic acid, C 8 H 5 .COOH 

 = CH 2 :CH.CH 2 .COOH, a member of a series possessing the 

 general formula CnH^-j.COOH and characterised by contain- 

 ing some doubly linked carbon atoms. In such cases the 

 acids are said to be itnsatiiratcd, because under suitable con- 

 ditions they can combine with hydrogen or other element, the 

 double linkage between the carbon atoms being replaced by the 

 usual single linkage. The fatty acids can thus be divided into 

 two great divisions the saturated and the unsaturated acids. 



The following are a few of the more important fatty acids : 



SATURATED ACIDS. 



(a) Acetic or stearic acid series. General formula = 

 C n H 2n+1 .COOH :- 



(1) Formic acid, H.COOH, occurs in nettles, ants, c. 



(2) Acetic acid, CH 3 .COOH, ,, vinegar, &c. 



(3) Butyric acid, C,H 7 .COOH, ,, butter. 



(4) Capric acid, C,H 19 . COOH, ,, butter and in cocoa- 



nut oil. 



(5) Myristic acid, C 18 H. 27 .COOH, ,, cocoa-nut oil and in 



spermaceti. 



(6) Palmitic acid, C 15 H 31 .CQOH, palm oil. 



(7) Stearic acid, C 17 H ;{5 .COOH, ,, tallow and many 



oils. 



