GLYCERIN. 169 



fats occurring in nature, in the vegetable as well as 

 the animal kingdom. It is formed in small quantities 

 as a product of the fermentation of sugar. 



Preparation. "When a fat is decomposed (saponified) 

 by boiling with an excess of alkali or with lime, the 

 salts of the acids (soaps) contained in the fat are thrown 

 down, as the salts of the alkalies are insoluble in the 

 alkaline liquid and the calcium salts are insoluble in 

 water; the glycerin, however, remains dissolved, and, 

 after saturating the alkali with sulphuric acid and 

 evaporating, can be extracted from the mass. It is 

 most easily obtained by boiling a fat with lead oxide 

 and water. The lead salts (lead plaster) formed are 

 insoluble; in the water remains glycerin with a little 

 lead oxide, which is removed by sulphuretted hydro- 

 gen. Treatment with superheated steam also decom- 

 poses fats. In this case there is obtained an aqueous 

 solution of glycerin, upon which the acids float. 



Properties. Colorless, syrupy liquid, of a pure sweet 

 taste, easily soluble in water and alcohol. Under cer- 

 tain circumstances, as it appears, by continued shaking 

 at a low winter-temperature, it congeals, forming a 

 solid crystalline mass. Can be distilled in a vacuum 

 without decomposition; in the air only with partial 

 decomposition. When sodium is dissolved in alcohol 

 and glycerin added, a crystallizing substance C 3 H 5 

 (OH) 2 (ONa) + C 2 H 6 is formed. In an aqueous solu- 

 tion, in contact with yeast, it is gradually converted 

 at 20-30 into propionic acid, with rotten cheese and 

 chalk at 40 into alcohol and butyric acid. Heated 

 with dehydrating substances (concentrated sulphuric 

 or phosphoric acid, potassium bisulphite) it is converted 

 into acrolein (p. 128). 



Chlorhydrine, C 3 H 7 C10 2 = C 3 H 5 C1(OH) 2 , is pro- 

 duced when glycerin is saturated with hydrochloric 

 acid and heated for some time at 100 ; and by direct 

 union of allyl alcohol with hypochlorous acid. Oil of 

 an ethereal odor, boils at 225-230. Is converted into 

 propylene alcohol by treatment with sodium-amalgam. 

 15 



