FUELS AND CARBON COMPOUNDS 



263 



gen, and a small percentage of other hydrocarbons : 

 acetylene, ethylene, and benzene. 



Natural gas is largely used for heating and lighting 

 purposes in certain localities and is reached by drilling. 

 Natural gas consists mainly of hydrogen and marsh gas 

 and is excellent for heating purposes. Since it burns 

 with almost no flame, it has little illuminating power. 



rtirr 



U. S. Geological Survey. 

 FIG. 228. Oil Derricks, Beaumont, Texas. 



For lighting purposes it is used to heat a mantle to in- 

 candescence. 



Petroleum. Petroleum is a dark, oily liquid obtained 

 from oil wells in certain localities, especially in Pennsyl- 

 vania, Ohio, Texas, California, and near Baku in Russia 

 (Figure 228). All petroleums are mixtures of hydrocar- 

 bons. Nearly all the petroleum produced is refined. The 



