LIGHT 



243 



illuminating purposes petroleum is sprayed into the hot 

 carburetor of the gas-producing apparatus. The heat 

 breaks the oil into gases which give illuminating power 

 to the water gas. 



As illuminating gas reaches the consumer, it burns 

 with a bright yellow flame. To prevent smoking, 

 it is burned from a narrow slit burner in order 

 that more of its surface will come in contact with 

 the air. 



This gas is stored by the gas companies in large tanks 

 inverted in water. The tanks are quite heavy and 

 cause the gas pressure in the distributing lines. As gas 

 is used the tanks sink into the water, and as more gas is 

 pumped into them they rise again. 



Natural Gas. In some regions large pools of natural 

 gas are found. So far as is known the United States 

 has a greater supply of this gas than any 

 other nation. It is a most perfect fuel and 

 may be used for lighting purposes if an 

 incandescent mantle is used. To use a 

 mantle we simply burn the gas in a Bun- 

 sen burner and suspend the mantle over 

 the colorless flame. The light comes from 

 the materials of the mantle which are 

 heated to incandescence (Figure 219). 



The best mantles are made by soaking 

 the little knitted sack in a solution of 

 cerium and thorium salts. When the sack 

 is dry, the solid salts fill the spaces between 

 the threads. The mantlets now set on fire. The thread 

 burns, leaving a thin shell of the oxides of the metals. 

 Other gases besides natural gas may be used with in- 

 candescent mantles. 



FIG. 219. A Gas 

 Mantle. 



