62 



LIFE S BEGINNING ON THE EARTH 



as petroleum. Gasoline, which is so important for the 



world on wheels, contains such carbon-chain compounds 



with only hydrogen attached from pentane (see above) up 



to decane, a ten-membered chain. Octane, the well known 



motor test-fuel is one of the series. Solid paraffine which 



also belongs in this series contains compounds with chains 



of 21 to 27 carbon atoms. 



The diversity of carbon-hydrogen compounds becomes 



greater due to the existence of ramified chains such as that 



of iso-butane : 



H H H 



H— C^C— C— H 



H 



H 



H C— H 



I 

 H 



Moreover, carbon atoms can be linked together not only by 

 the simple linkages, as they appear in the carbon-hydrogen 

 compounds mentioned so far, but also by the so-called 

 double links or triple links. Still another possibility is the 

 arrangement of carbon atoms in rings. The most stable 

 ring system is the six-membered ring as it appears in the 

 hydro-carbon benzene, also known as benzol, which has the 

 following arrangement of atoms in its molecule: 



II 



lie 



Ha 



:CH 



^CH 



H 



Countless other ring structures are known, as for ex- 

 ample, one consisting of two six-membered rings, very 

 closely linked together; (his arrangement is peculiar to the 



