Structure of Simpler Organic Compounds. 77 



can be obtained. The glycols have the general formula 

 C n H 2n (OH) 2 . They are named after the members of the 

 olefine series to which they belong, being designated 

 ethylene, propylene, butylene glycols, etc. The isomerism 

 will depend not only on the hydrocarbons from which 

 they are derived, but also on the position in which the 

 hydroxyl groups are substituted. Thus, from normal 

 propane, two propylene glycols can be derived, namely, 

 CH 2 (OH) . CH 2 CH 2 (OH) and CH 3 - CH(OH)CH 2 (OH). 

 The former is known as a-y and the latter as a-/3 pro- 

 pylene glycol, the letters a, /3, y, etc., being employed to 

 indicate the position of the carbon atom to which the 

 hydroxyl group is attached the terminal carbon atom 

 being indicated by a, the contiguous carbon atom by ft, 

 and so on. The glycols are neutral thick liquids, similar 

 in properties to glycol. 



Glycerol, which is more generally called glycerine,* 

 is the most important of the polyhydroxy alcohols. It 

 is trihydroxy propane, CH 2 (OH)CH(OH)CH 2 (OH), and 

 is prepared on a large scale by the hydrolysis of fats 

 and oils. When such substances are heated with water 

 under high pressure, they undergo decomposition, yielding 

 glycerol and fatty acids. The latter are insoluble in the 

 water, and can be filtered off. The aqueous solution on 

 concentration yields glycerol, which can be purified by 

 fractional distillation under reduced pressure. As ordi- 

 narily prepared, it is a thick syrup of sp. gr. T26, but by 

 careful purification it can be obtained in the form of crystals 

 which have a melting point of 17. These are very hygro- 

 scopic, and readily take up moisture from the atmosphere 

 to form a syrup. Glycerol is readily soluble in water and 

 alcohol, but not in ether a property which it shares 



* The termination ol is employed to indicate the presence in the substance 

 of a hydroxyl group. 



