ALCOHOLS. 487 



Allyl alcohol is a colorless liquid possessing a disagreeable penetrating odor. 

 It is soluble in water in all proportions ; B. P. 96.5 C. 



Glycerin, Glycerinum, C 3 H 5 (OH) 3 = 91.37 (Glycerol). This is 

 a triatomic alcohol, in which three OH groups have replaced three 

 hydrogen atoms in propane, CH 3 .CH 2 .CH 3 . Synthetic methods have 

 shown the glycerin to be CH 2 OH.CHOH.CH 2 OH. 



Glycerin is a normal constituent of all fats, which are glycerin in which the 

 three atoms of hydrogen of the hydroxyl have been replaced by radicals of 

 fat acids. It is obtained as a by-product in the manufacture of soap, but it is 

 also largely manufactured by passing steam under 120 to 150 pounds pressure 

 into fats contained in large copper digesters. By this treatment the fats are 

 decomposed into glycerin, which remains dissolved in the water; non-volatile 

 fatty acids, floating on the surface of the solution ; and volatile fatty acids, 

 which escape with the steam. The aqueous solution of glycerin is first con- 

 centrated by evaporation, and then treated with superheated steam, with which 

 glycerin volatilizes and is condensed in suitably constructed vessels. 



Pure glycerin is a clear, colorless, odorless liquid of a syrupy con- 

 sistence, smooth to the touch, hygroscopic, very sweet, and neutral in 

 reaction, soluble in water and alcohol in all proportions, but insoluble 

 in ether, chloroform, benzol, and fixed oils ; its specific gravity is 

 1.246 at 25 C. ; it cannot be distilled by itself without decomposition, 

 but is volatilized in the presence of water or when steam is passed 

 through it. 



Glycerin is a good solvent for a large number of organic and inorganic sub- 

 stances ; the solutions thereby obtained are often termed glycerites ; official are 

 the glycerites of starch, carbolic acid, tannic acid, and a few others. 



Boroglycerin is made by heating a mixture of boric acid and gly- 

 cerin, when an ether of the composition C 3 H 5 BO 3 is obtained. It is 

 used as a mild antiseptic agent. 



Analytical reactions. 



1. A borax bead immersed for a few minutes in a solution of 

 glycerin (made slightly alkaline with potassium hydroxide) imparts 

 a green color to a non-luminous flame, owing to the liberation of 

 boric acid. 



2. Glycerin slightly warmed with an equal volume of sulphuric 

 acid should not turn dark, but, on further heating, the characteristic, 

 irritating odor of acrolein is noticed. 



Glycerin trinitrate, C 3 H 5 (NO 3 ) 3 (Nitro-glycerin, Glonoin). When 

 glycerin is treated with nitric acid, or, better, with a mixture of con- 

 centrated sulphuric and nitric acids, chemical action takes place 



