102 



Dr. Karl Heumann's Contributions to 



VII. 



VIIL 



IX. 



Intensity of light, in 

 candles. 



Cold tubes. Hot tubes 



1-3 



2-6 



4-7 



2-2 

 3-5 

 5-8 



Gas-consumption, in 

 litres. 



Cold tubes. Hot tubes 



38 

 55 

 90 



35 



51-5 



81 



5. 



Increase in 

 light-in- 

 tensity, in 

 per cents. 



69-2 

 34-6 

 23-4 



VII. 



VIIL 



IX. 



Decrease in 

 gas-consump- 

 tion, in 

 per cents. 



6-3 

 10-0 



7. 8. 



Light-intensity for decreased 



gas- consumption 



(column 4). 



Calculated. 



Cold tubes. 



1-2 

 2-4 

 4-2 



Found. 



Hot tubes. 



2-2 

 3-5 



5-8 



9. 



Gain in 

 light- 

 intensity, 

 in per cents. 



83-3 

 45-8 

 38-0 



From these results it is again apparent that heating the 

 tube causes a marked increase in the luminosity of the flame, 

 and that this increase is the greater the less gas is passed 

 through the tube. The very considerable decrease in the 

 quantity of gas consumed occasioned by heating the tube is 

 most remarkable, and shows that when the gas makes its exit 

 through a narrow opening the expansion caused by heating- 

 exercises a greater retarding effect upon the Telocity of issue 

 than when a wide exit-tube is employed. 



In the first part of this paper, when describing the increase 

 in luminosity brought about in a non-luminous flame of mixed 

 coal-gas and carbon dioxide by heating the tube through 

 which the mixture passed, I stated that this increase was no 

 longer noticeable if the tube were heated at some distance 

 from its orifice ; and I accounted for this fact by the cooling 

 action exercised on the hot gas by that part of the tube the 

 temperature of which had not been increased. 



A similar action might be anticipated to occur in the 

 cases just described, wherein heating the platinum tube which 

 served as a burner caused an increase in luminosity. Expe- 

 riments justify this anticipation, and show that the increase 

 in luminosity is materially affected by the position of the 

 source of heat employed for raising the temperature of the 

 platinum tube. The following numbers were obtained : — 



