Artificial Lighting 



161 



and in Brazil. The other is the metal cerium, which is found 

 in the same places. These two metals are combined in the 

 exact proportion of 99 per cent of thorium to 1 per cent of 

 cerium. The exact one per cent of cerium multiplies the light 

 from a thorium mantle nearly ten times, yielding a whiter, 

 brighter light than any other proportion. 



Thorium and cerium are dissolved in nitric acid. Mantles 

 made of mercerized cotton or other suitable material sewed 



Carbon Fish-tail Kerosene 

 electric, burner gas. 



Tungsten 

 electric. 



Gas Mantle. Hours 



FIG. 45. Graphical representation of hours of light of twenty candle power 

 purchasable for ten cents. Compare carbon with tungsten incandescent, and 

 fish-tail burner with gas mantle ; which of each set is more economical ? Why ? 



into the desired shape with asbestos thread are dipped into 

 and thoroughly saturated with this solution. The mantles 

 are then burned to remove the gauze and to convert the metals 

 into thorium oxid or thoria and cerium oxid or ceria. The 

 mantles after burning are dipped into collodion and dried to 

 insure their safety in distribution through the market. This 

 dried film is burned away after the mantle is placed on a gas 

 jet. The oxids remain as ash in the original form of the mantle. 

 The economy of gas by the use of mantles is considerable, a 

 good mantle consuming about one half the gas needed for the 

 ordinary gas burner, and giving five to seven times the amount 

 of light. 



62. Artificial gas. Artificial gas is to-day usually coal gas 

 or what is generally called illuminating gas. The latter is an 



