642 APPENDICES 



saturated, but if two hydrogen atoms are let go, the unocGupied hands of 

 the carbon may join and form an unsaturated molecule, thus : — 



Ethane becomes Ethylene H H 



! I 

 H— C = C— H 



When one hydrogen atom is taken away, and the molecule has a hand 

 ready to link with some other substance, a radicle is constituted, and these 

 are known as Methyl, Ethyl, etc. 



Alcohols- — If one of the hydrogen atoms of Methane is oxidised to 

 hydroxyl ( -OH), an alcohol is formed — 



The hydroxyl group ( — OH) is characteristic of alcohols. 



H 



I 



H— 0— OH Methyl Alcohol. 



I 

 H 



Similarly Ethane gives — 

 H H 



H— C— C— OH Ethvl Alcohol, 



I I 

 H H 



and so on for compounds having a longer carbon chain. 



If only one — H is oxidised to — OH, the alcohol formed is termed 

 Monohydric. 



If two — H atoms are oxidised, the alcohol is Dihydric. 



If more than two — OH groups are present, the alcohol is Polyhydric, e.g. 



H H H 



I I I 

 HO— C— C— C— OH Glycerol (Glycerine). 



H OH H 



Propane C^Hg, and comijounds having more than three carbon atoms, 

 may form more than one monohydric alcohol, according to the C atom on 

 which the — OH is placed. 



Thus, there are two propyl, four butyl, and eight amyl alcohols. 



Primary Alcohols are those in whicli a terminal carbon is oxidised. 



Secondary Alcohols have one or more of the middle carbons oxidised. 



Polyhydric alcohols may contain primary or secondary groups or 

 both. 



Aldehydes — When, from a Primary Alcohol, two hydrogens are 



