the Theory of Luminous Flames. 



103 





Light-intensity, in candles. 



Gras-consumption. 



Increase in light- 

 intensity*, 

 in per cents., in hot 

 tubes, heated 



In cold 

 tubes. 



In hot tubes, 

 heated 



In cold 

 tubes. 



In hot tubes, 

 heated 



near the 

 orifice. 



at some 



distance 



back. 



near the 

 orifice. 



at some 



distance 



back. 



near the 

 orifice. 



at some 



distance 



back. 



X. | Platinum 

 XI. j tube. 



r o-4 



1 2-0 



0-9 

 3-4 



0-6 



2-8 



19 



48 



19 



46 



19 

 45-5 



125 



78-9 



50 

 555 



These experiments prove that a much smaller increase in 

 luminosity is brought about by heating the tube of the burner at 

 some distance from its orifice than just at that orifice. These 

 results confirm those of the former Tables, inasmuch as they 

 show that the increase in luminosity occasioned by heating 

 the burner-tube is more marked when the gas-consumption is 

 small than when it is large. The fact that the luminosity of 

 a flame produced by a large gas-consumption was increased in 

 a proportionally greater degree than the luminosity of a small 

 flame, when the tube was heated in the 7niddle, is to be accounted 

 for by remembering that in this experiment the rapid current 

 of gas would give up proportionally less heat to the cold 

 parts of the tube than the slowly moving stream would. 



The maximum luminosity, then, is attained when the anterior 

 part of the tube is heated : the cooling-down of the heated 

 stream of gas is hereby prevented ; and the cooling action of 

 the cold burner upon the flame itself is at the same time 

 removed. 



The question now arises, Is the increased luminosity which 

 is brought about by heating the tube to be traced merely to the 

 increase in temperature of the gas, or to a change in the che- 

 mical composition of the gas itself? It may be supposed that 

 heating the gas brings about the formation of new compounds 

 which are very ready to suffer decomposition attended with 

 separation of carbon in the flame. In order to determine 

 whether this was so or not, coal-gas was passed through a 

 heated platinum tube and then through a tube many times 

 bent and surrounded with water maintained at 15°. 



To this tube a steatite burner was attached. There was no 

 observable alteration in the intensity of light from gas burn- 

 ing at the orifice of this apparatus. 



It might be supposed that new compounds were actually 

 produced in this experiment, but that the increased luminosity 

 * Calculated for constant consumption. 



