1894.] Atmospheres which extinguish Flame. 5 



Characteristic differences were observed between the behaviour of 

 wick-fed flames and that of gas- fed flames when they were introduced 

 into an atmosphere which extinguished them. The wick-fed flames 

 gradually diminished in size until they vanished. The gas-fed flames, 

 on the other hand, gradually increased in size, becoming pale and 

 apparently lower in temperature, and then suddenly expired. The 

 extinction of the flame is apparently due in both cases to the lower- 

 ing of its temperature. This primary cause, however, seems to 

 operate directly in the case of the gas- fed flame, whilst in the case of 

 the wick-fed flame it operates by gradually reducing the amount of 

 combustible gas and vapour produced, and leads ultimately to the 

 flame dying from lack of combustible material. The large expansion 

 of the gas-fed flame is evidently due to an attempt to obtain the 

 necessary supply of oxygen in the diluted atmosphere by increasing 

 its own surface. 



6. Theoretical Considerations. 



The following deductions seem to be warranted by the results 

 arrived at in these experiments : 



1. That the extinction of a flame is not determined only by the 



proportion which the inert gas bears to the oxygen of the atmo- 

 sphere into which it is introduced, but that the nature of the 

 inert gas present also influences the result. 



2. That carbon dioxide uniformly exerts a more powerful extinc- 



tive effect upon flame than nitrogen does. 



3. That there is a remarkable uniformity in the proportions of 



inert gas which must be mingled .with air in order to just 

 extinguish wick-fed flames. 



4. That this uniformity does not apply to the flames of com- 



bustible gases burnt from a jet. 



5. That the flames of gases burnt from a jet show no simple 



relation, as regards the proportion of oxygen present in the 

 extinctive atmosphere, to the relative proportions of oxygen 

 required for their complete combustion. 



With regard to the superior extinctive power of carbon dioxide 

 over that of nitrogen, it has been stated that the greater the density 

 of an inert gas which is introduced into air, the less will be the 

 quantity which suffices to arrest combustion. Waldie suggests that 

 this is due to the cooling effect produced upon the flame by the 

 rapidity of diffusion of its heated products increasing as the sur- 

 rounding atmosphere increases in density. But it is probable that 

 carbon dioxide also surpasses nitrogen in its extinctive effect upon 

 flame in virtue of its higher specific heat, and because of its slower 

 movement owing to its high molecular weight and density. When 



