APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 739 



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

 sweet taste. It is soluble in water and alcohol in all proportions, 

 insoluble in aether. Exposed to very low temperatures it becomes almost 

 solid ; it may be distilled in close vessels without decomposition, between 

 275 280 C. 



It dissolves the alkalis and alkaline earths, also many oxides, 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 recognized by its ready solubility in water and alcohol, 

 its insolubility in aether, its sweet taste, and its reaction with bases. 

 The production of acrolein is also characteristic of glycerin. 



C 3 H 8 8 - 2H,O = C,H 4 O (Acrolein). 



Preparation. By saponification of the various oils and fats. It is 

 also formed in small quantities during the alcoholic fermentation of 

 sugar 1 . 



Soaps. These may be formed by the action of caustic alkalis on fats. 

 The process consists in a substitution of the alkali for the radicle of 

 glycerin, the latter combining with the elements of water to form 

 glycerin. Thus 

 Tristearin. Potassic stearate. Glycerin. 



(oH.o),i ,K) _ gcg^.01 eystt 



C 3 H S j' +3 H/ C K P H,} " 



Pancreatic juice can split up fats into glycerin and free fatty acids (see p. 254), 

 and the bile is known to be capable of saponifying these fatty acids. The amount 

 of soaps formed in the alimentary canal is however small and unimportant. 



ACIDS OF THE GLY COLIC SERIES. 



Running parallel to the monatomic alcohols (C^H^^O) is the series 

 of diatomic alcohols or glycols (C n H n+2 O 2 ). Thus corresponding to ethyl 

 alcohol is the diatomic alcohol, ethyl-glycol. As from the monatomic 

 alcohols, so from the glycols, acids may be derived by oxidation ; from 

 the latter (glycols) however two series of acids can be obtained, known 

 respectively as the glycolic and oxalic series. The iirst stage of oxi- 

 dation of the glycol gives a member of the glycolic series, thus : 



Ethyl-glycol. Glycolic- acid. 



C 2 H 6 O 2 + O 2 = C 2 H 4 O 3 + H 2 O, or more generally 

 C.H^ A + 2 p. CJF^O, + H 2 0. 



1 Pasteur, Ann. d. Chem. u. Pharm. Bd. 106, S. 338. 



472 



