CHEMICAL BASIS OF THE ANIMAL BODY. 121, 



with most other bases are insoluble. It may be distinguished from 

 the acids of the acetic series by its reaction with nitrous acid which 

 converts it into a solid (elai'dic acid) and by the changes it undergoes 

 when exposed to the air. It may be converted into stearic acid 



C 17 H 33 . COOH + H 2 = C 17 H 35 . COOH. 



THE NEUTRAL FATS. 



These may be considered as ethereal salts formed by replacing the 

 exchangeable atoms of hydrogen in the triatomic alcohol glycerin (see 

 below), by the acid radicles of the acetic and oleic series. Since there 

 are three such exchangeable atoms of hydrogen in glycerin, it is possible 

 to form three classes of these ethereal salts ; only those, however, which 

 belong to the third class occur as natural constituents of the human 

 body : those of the first and second are of theoretical importance only. 



The following reaction which represents the formation of tri-pal- 

 mitin from glycerin and palmitic acid is typical for all the others. 



Glycerin. Palmitic acid. Tri-palmitin. 



C 3 H 5 (OH) 3 + 3 (C 15 H 31 .CO.OH) = C 3 H 5 (C 15 H 31 .CO.O) 3 + 3 H 2 O. 



They possess certain general characteristics. Insoluble in water 

 and but slightly in alcohol, they are readily soluble in ether, chloroform, 

 benzol, &c. ; they also dissolve one another. They are neutral bodies, 

 colourless and tasteless when pure ; they are not capable of being distilled 

 without undergoing decomposition, and yield as a result of this decom- 

 position, solid and liquid hydrocarbons, water, fatty acids, and a 

 peculiar substance, acrolein, resulting from the decomposition of the 

 glycerin. (See below.) 



They possess no action on polarised light. 



They may readily be decomposed into glycerin and their respective 

 fatty acids by the action of caustic alkalis, or of superheated steam. 



Palmitin (Tri-palmitin). C 3 H 5 (C 16 H 31 .CO.O) 3 . 



Palmitin is but slightly soluble in alcohol either cold or hot, readily 

 so in ether from which, when pure, it crystallises in fine needles; if 

 mixed with stearin, it generally forms shapeless lumps, although the 

 mixture may at times assume a crystalline form, and was then regarded 

 as a distinct body, namely margarin. When pure it melts at 62 and 

 solidifies again at 45. 



It is most conveniently obtained from palm-oil by removing the 

 free palmitic and oleic acids by alcohol and repeatedly crystallising 

 the residue from ether. 



