CHEMICAL BASIS OF THE ANIMAL BODY. 1231 



Preparation. From olive oil, either by cooling to C. and press- 

 ing out the olein that remains fluid, or by dissolving in hot alcohol 

 and cooling, when the olein remains in solution while the other fats 

 crystallize out. 



The fats which occur in the animal body are mixtures of 

 the above three substances in varying proportions. The nor- 

 mal fat of each animal or class of animals is however character- 

 ized by the constant preponderance of one of the three ; thus 

 in the fat of man and carnivora palmitin is in excess over the 

 other two. In the fat of herbivora stearin predominates and 

 in that of fishes olein. Butter contains, in addition to the 

 above, several fats formed by the union of glycerin with the 

 radicles of the lower acids of the acetic series. 



Glycerin (Glycerol). C 3 H 5 (OH) 3 . 



As already stated, glycerin is a triatomic alcohol, the neu- 

 tral fats being ethereal salts formed from it with the radicles 

 of the higher fatty acids and oleic acid. 



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 tempera- 

 tures it becomes almost solid ; it boils at 290 and may be dis- 

 tilled without decomposition in the absence of air. 



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 polarized light. 



It is easily recognised by its ready solubility in both water 

 and alcohol, its insolubility in ether, its sweet taste, and its 

 reaction with bases. When sufficiently heated, especially in 

 presence of a dehydrating agent, glycerin is decomposed, loses 

 two molecules of water and yields acrolein. C 3 H 5 (OH) 3 

 = C 3 H 4 O + 2H 2 O. This substance possesses an intensely pene- 

 trating, irritating and pungent odour, so that its formation 

 enables glycerin to be readily identified. It is the cause of 

 the peculiar smell arising from overheated fats. Chemically 

 it is the aldehyde of allyl alcohol (derived from the defines) 

 and is intermediate between this substance and acrylic acid, 

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



Glycerin is formed in traces during the alcoholic fermenta- 

 tion of sugar. It is prepared in bulk by distilling in a current 

 of superheated steam the fluid residue left after the saponifica- 

 tion of fats with lime. 



Soaps. 



When neutral fats are heated with lime or caustic alkalis 

 under pressure they are decomposed, the metal combining with 



