GLYCERIN. 877 



in cold water, of which the solution has a magnificent blue 

 colour (Stass, An. de Chim. Ixix. 367). 



CHAPTER VIII. 



GLYCERIN. 



Glyceryl, C 6 H 7 =G1; a hypothetical radical admitted by 

 Liebig to exist in the substance long known as glycerin, which 

 is found combined with various acids in the fat oils. Glycerin 

 is considered as a compound of glyceryl with 5 atoms of 

 oxygen and 1 atom of water, or the hydrated oxide of 

 glyceryl. 



Hydrate of oocide of glyceryl, glycerin; C 6 H 7 O 5 + HO. 

 This substance was first observed by Scheele, and distinguished 

 by him as the sweet principle of oils, its function in the constitu- 

 tion of oils and fats was developed by Chevreul, and its compo- 

 sition carefully determined by Pelouze*. It forms a base to the 

 oleic, stearic, and margaric acids of the fat oils and tallow, and 

 is separated when those acids are made to combine with an 

 alkali or any metallic oxide, in the saponification of the oils. 

 It is conveniently prepared in saponifying oil of olives with 

 oxide of lead and a little water, by boiling them together ; the 

 liberated glycerin dissolves in the water, while the soap of 

 oxide of lead is insoluble. The glycerin is accompanied by a 

 small quantity of oxide of lead in solution, which may be pre- 

 cipitated by sulphuretted hydrogen. Or when an oil is con- 

 verted into a soap by boiling it with water and an excess of 

 alkali, the soap comes to the surface being insoluble in the 

 alkaline liquor. The latter, which contains the glycerine in 

 solution, may be drawn off, the free alkali be neutralised with 

 sulphuric acid, and the solution evaporated to a syrup, from 

 which strong alcohol dissolves out the glycerin. If the 

 product is coloured it may be purified by means of animal 

 charcoal, evaporated by a water-bath, and afterwards in vacuo 

 over sulphuric acid. 



* Ann. de Chim. et de Phys. t. 63. p. 19. 



