CHEMICAL BASIS OF THE ANIMAL BODY'. li'l 



glycerin (see below), by the acid radicles of the acetic and oleic 

 series. Since there are three such exchangeable atoms of hydro- 

 gen in glycerin, it is possible to form three classes of these eth<-- 

 real salts; only those, however, which belong to the third da-- 

 occur as natural constituent.- of the human body: those of the 

 tirst and second are of theoretical importance only. 



The following reaction which repivsrnt* the formation of tri- 

 palmitin from glycerin and palmitic acid is typical for all the 

 others. 



(ilvo-riii. Palmitic acid. Tri-palmitin. 



C.H. (OH), + 3 (C U H M . CO . OH) =C,H 6 (C 15 H 81 . CO . 0),+ 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 decomposition solid and liquid hydro- 

 carbons, water, fatty acids, and a peculiar substance, acrolein, 

 resulting from the decomposition of the glycerin. (See below.) 



They POS-I-.-S no action on polarised light. 



They may readily In- decomposed into glycerin and their respec- 

 tive fatty acids by the action of caustic alkalis, or of superheated 

 steam. 



Palmitin (Ti -i-palmitin). C 8 H 5 (C, 6 H 81 . CO . 0) 8 . 



1'almitin 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 wa- then regarded as a distinct body, namely margarin. 

 \Yhfii pun- it melts at 62 and solidifies again at 45. 



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

 free palmitic and oleic acids by alcohol and repeatedly crystallising 

 tin- residue from ether. 



Stearin (TH->t.-urin). C,H S (C 17 H 86 . CO . 0),. 



This is the hardest and least fusible of the ordinary fats of the 

 liody ; is also the least soluble, and hence is the first to crystallise 

 out from solutions of the mixed tats. Ueadily soluble in ether 

 and in Iniliny alcohol. It crystallises usually in square talilr- 

 or glittering plates. It present- pi-culiaritii-s in its fusing-points, 

 mdting tirst at "> , then solidifying as the temperature is further 

 1. and melting finally and permanently at 71. 



Preparation. From mutton suet, its separation from palmitin 

 and olfin In-ing effected by repeated crystallisation from ether, 

 stearin l>rin- th- loa-t soluble. It is, however, very difficult to 

 obtain it pure ly tin- process. 



