dlKMICAL BASIS OF T1IK ANIMAL BODY. IL':; 



Glycerin (< i hverol). C 3 H 6 (OH),. 



tlready stated, glycerin i-; ;i triutomic alcohol, the neutral fats 

 being ethereal salts rarmed from it with the radicles of the higher 

 fatty acids and oleic arid. 



When pure, glycerin is a viscid, colourless liquid, of a well-, 

 known sweet taste. It is soluble in water and in alcohol in all 

 proportions, insoluble in ether. Exposed to very low temperatures 

 it becomes almost solid; it boils at 290 and may be distilled 

 without decomposition in the absence of air. 



It dissolves the alkalis and alkaline earths, also many oxide-., 

 such as those of lead and copper; many of the fatty acids are 

 also soluble in glycerin. 



It possesses no rotatory power on polarised light. 



It is easily recognised by its ready solubility in both water and 

 alrohol, its insolubility in ether, its sweet taste, and its reaction 

 with liases. When sufficiently heated, especially in presence of a 

 dehydrating agent, glycerin is decomposed, loses two molecules of 

 water and yields acrolein. C|H 6 (OH), = ('.,II 4 < )+L'H 2 0. This 

 substance possesses an intensely penetrating, irritating and pungent 

 odour so that its formation enables glycerin to be readily idm ti- 

 tled. It is the cause of the peculiar smell arising from overheated 

 tats. Chemically it is the aldehyde of allyl alcohol (derived from 

 tin- oil-tines) and is intermediate between this substance and acry- 

 lir acid, which is a homologue of oleic acid. (.See above.) 



(Jlycerin is formed in traces during the alcoholic fermentation 

 of sugar \ It is prepared in bulk by distilling in a current of 

 superheated steam the fluid residue left after the saponification of 

 tat- with lime. 



Soaps. 



When iifittral fats are heated with lime or caustic alkalis under 

 ne they are decomposed, the metal combining with the free 

 fatty or oleic acid to form a salt, leaving the glycerin in solution. 

 These >;ilts are called soaps, being soluble in water if the metal is 

 an alkali, insoluble if it is calcium, lead, or other similar metal. 

 The reaction which takes place during the above saponitication is 



Tri -t.-riu. l'"t;isxium sterftte. (il\ci-rin 



CH,(Ci,H u . CO.O), -f 3KHO = 3(C 17 H 88 .COOK) -f C 3 H 6 (OH),. 



A similar decomposition into glycerin and free fully acid ran be 

 i-tle.-ted by pancreatic juice (see p. 64), the acid uniting with the 

 alkali of tin- juice or of the bile to form a son].. This drcomji.iv.j- 



tion is however quantitatively inconsiderable but qualitatively of 

 great importance for the absorption of fats, owing to the extra<>r- 



1 r.iM.-ur, Ann. <L <'lf m. >t. /'harm. IM. < \ i ( 1*58), S. 338. 



