100 MODERN SCIENCE READER 



was that the burning hydrogen, carbon monoxide and 

 hydrocarbons furnished the heat necessary to raise carbon 

 to incandescence. In that year Lewes advanced his "latent 

 heat" theory. This theory declared that the latent heat 

 set free when acetylene is decomposed instantly heats the 

 carbon particles thus set free to incandescence. 



After showing that the heat of combustion of a flame is 

 only sufficient to render carbon faintly luminous, Lewes 

 compared the temperatures of flames burning coal gas, the 

 unsaturated hydrocarbon gas, ethylene, and the still less 

 saturated acetylene, and also the amount of light given by 

 each when burning equal volumes of gas per hour from 

 burners best suited to each. He likewise studied the 

 temperatures developed when acetylene is exploded and 

 the localization of the heat set free by its decomposition. 

 His experiments were ingenious and convincing. By com- 

 paring ethylene, C 2 H 4 , with acetylene, C 2 H 2 (where for 

 equal consumption the same number of carbon atoms were 

 present), and also with coal gas, it was seen that the lumi- 

 nous portion of the acetylene flame is not as hot as that of 

 either ethylene or coal gas, while the illuminating powers 

 of the flames were : acetylene, 240.0 candle power, ethylene, 

 65.5 c.p. and coal gas, 16.8 c.p. Evidently the heat of 

 combustion does not account for the incandescence of the 

 carbon ; for if it did the cooler acetylene flame would give 

 less light, while, as a matter of fact, it gives twice as much 

 as the ethylene and about fourteen times as much light as 

 the very much hotter coal gas flame. It was evident that 

 our temperature measuring instruments do not detect the 

 heat of the carbon particles themselves. 



To see if luminosity be even partly due to the latent heat 

 of acetylene, Lewes exploded that gas in a closed tube. 

 This was done by wrapping a bit of fulminate of mercury 

 in tissue paper and suspending it by copper wires joined 

 by platinum in contact with the fulminate, and passing an 

 electric current. There followed a brilliant flash of light 

 and a complete decomposition of the gas, and of the eudio- 



