Ignition of Gases by Hot Wires. 



G25 



In methane, Table IV., the current is also the same in all 

 mixtures, but here *2 mm. tungsten wires were used, platinum 



melting. 



10 A. 



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FIG. 4-. 



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PLAT! HUM WIRES. 



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This current, 5'25 amperes, is the same as in hydrogen, 

 fig. 2, and in carbon monoxide. The curves of hydrogen, 

 ethylene, and coal gas, drawn to the same scale in fig. 5, 

 have the same small slope of base. Ignition fails with sur- 

 prising suddenness at the lower limit. It may be noted that 

 the slope of the base is uniform ; it is therefore not due to 

 any change in the influence of the heating effect of the wire, 

 which would vary as the square of the current. Ignition 

 increases in difficulty as the oxygen percentage diminishes 

 and the point of perfect combustion is passed through with- 

 out notice. Excess of oxygen is here favourable to ignition. 

 In carbon monoxide, however, the igniting current has a 

 quite constant value from 30 to 55 per cent., as in methane. 



Hydrogen, methane, and carbon monoxide are the chief 

 constituents of coal gas. Since each of these lias the same 

 igniting current it was to be expected that coal gas would 

 not be different. Its igniting current was found on trial to 

 be 5"3 amperes. 



The ignition of ethane resembles that of merhane in no! 

 being affected by change of composition, and having sharp 

 limits. It took 1*11 amperes from 3 to 8*5 per cent, with a 

 '1 mm. platinum wire which was then red before surface 



