462 Prof. V. B. Lewes. The Cause of Luminosity [Mar. 21, 



A. Heat derived from the decomposition of the acetylene molecule. 



B. Heat derived from the combustion of hydrogen, carbon mon- 



oxide, and some hydrocarbons in the flame. 



C. Heat derived from the combustion of the carbon particles 



themselves, 



whilst in the tube experiments the heat of the walls of the tube 

 and the heat of decomposition alone are acting, and it is evident 

 that the intensity of the heat finding its way through the walls of 

 the tube will be very different to that exercised by the walls of burn- 

 ing gas which enclose the luminous portion of the flame, and there 

 can be but little doubt that the temperature of the carbon particles 

 will vary enormously with the rate at which the acetylene decom- 

 poses, as the more quickly the action takes place, the greater will be 

 the localising action upon the heat evolved, and the higher the incan- 

 descence of the carbon particles . 



That this is so seems certain from the whiteness of the flash of 

 light emitted when the acetylene is detonated, and experiments 

 were made in order, if possible, to gain an idea as to how much 

 of the incandescence of the carbon particles was due to the 

 endothermicity of the decomposing acetylene, and how much to 

 the action of heat and combustion on the carbon particles after 

 formation. 



In order to do this, a non-luminous flat flame of large size wa& 

 desired, and was obtained by using coal gas de-illuminated by slowly 

 passing it through bromine, well washing with sodic hydrate solution 

 and water, and then passing it through strong sulphuric acid, the 

 gas so treated having an illuminating value of 1*2 candles for 5 cubic 

 feet when burnt in the London argand at such a rate as to give a 

 3-in. flame, whilst in a fish-tail burner it gave a non-luminous- 

 flame. This gas gave on analysis the following percentage compo- 

 sition : 



Carbon dioxide O'OO 



Unsaturated hydrocarbons . . O'OO 



Carbon monoxide 5*50 



Saturated hydrocarbons 33*28 



Hydrogen 55*25 



Nitrogen 5*49 



Oxygen 0*48 



100-00 



so that its combustion would give practically the same temperature 

 and flame reactions as those in an ordinary gas flame. 



A very fine platinum tube was now obtained, closed at one end, and 

 with five minute holes bored in a line close to the sealed end, and 



