GAS BURNERS AND GAS MANTLES 277 



this explains the danger of turning a lamp wick too high and 

 producing more carbon particles than can be oxidized by the air 

 admitted at the bottom of the lamp chimney. 



One great disadvantage of oil lamps and oil stoves is that 

 they cannot be carried safely from place to place. It is almost 

 impossible to carry a lamp without jarring it and without spill- 

 ing oil over the edges. The flame soon spreads from the wick 

 to the overflowing oil, and in consequence the lamp blazes and 

 an explosion may result. Candles, on the other hand, are safe 

 from explosion ; the grease which drops from them is unpleasant 

 but not dangerous. 



The illumination from a shaded oil lamp is soft and agreeable, 

 but the trimming of the wicks, the refilling of the bowls, and 

 the cleaning of the chimneys require time and labor. For this 

 reason the introduction of gas met with widespread success. 

 The illumination trom an ordinary gas jet is also stronger than 

 that from an ordinary lamp, and the stronger illumination 

 added to the greater convenience made gas a very popular 

 source of light. 



Gas burners and gas mantles. For a long time, the only 

 gas flame used was that from a fishtail burner (Fig. 141). 

 Recently, however, the fishtail burner has been 

 widely replaced by incandescent mantles, such 

 as the Welsbach. The principle of the incan- 

 descent mantle is very simple. When certain 

 substances, such as thorium and cerium, are 

 heated, they do not melt or vaporize, but 

 glow with an intensely bright light. Mr. Wels- 

 1 bach made use of this fact to secure a burner 

 in which the illumination depends upon the FIG. 141. Fishtail 

 1 glowing of an incandescent, solid mantle, rather 

 1 than upon the blazing of a burning gas. He made a cylindri- 

 cal mantle of thin fabric (Fig. 142), and then soaked it in a 



