DI-, TRI- AND POLYHYDRIC ALCOHOLS. 



In compounds containing two or more carbon atoms in their mole- 

 cule not only can one of the hydrogen atoms be replaced by OH 

 groups, but also 2, 3, 4, etc., so long as two OH groups are not 

 attached to I carbon atom (see aldehydes). Thus : 



These compounds have the properties of primary and secondary 

 alcohols. 



Glycol. 



Glycol is the first member of the series of polyhydric alcohols, and 

 is prepared from ethylene dibromide : 



CH 2 



2KOH = 2 KBr 



Br 



| 

 CH 2 OH. 



Glycol is a colourless syrupy liquid with a sweet taste ; it boils 

 at 198 and has a sp. gr. of 1-1297 at o. It is miscible with water 

 and alcohol in all proportions, but is very slightly soluble in ether. It 

 is very hygroscopic and takes up water from the atmosphere forming 

 a hydrate C 2 H 6 O 2 . 2H 2 O. 



Glycerol. 



Glycerol, a trihydric alcohol, is the chief member of the series. It 

 occurs in nature in the free state, but mainly in combination with fatty 

 acids in the form of esters the fats or glycerides from which it is pre- 

 pared by hydrolysis (p. 177). 



Glycerol is a thick, colourless, very hygroscopic liquid without 

 smell but with a sweet taste. It boils and distils under atmospheric 

 pressure at 290 but undergoes slighti decomposition ; in vacua it can 

 be distilled without decomposition. If kept at o for some time it 

 crystallises and the crystals melt at 17. It has a sp. gr. of 1*265 

 at H. 



