Dr. "Frankland on Combustion in Rarefied Air. 549 



March 7. — Major-General Sabine, R.A., Treasurer and Vice- 

 President, in the Chair. 



The following communications were read : — 



" On Combustion in Rarefied Air." By Dr. Edward Frankland, 

 F.R.S. 



In the autumn of 1859, whilst accompanying Dr. Tyndall to the 

 summit of Mont Blanc, I undertook at his request some experiments 

 on the effect of atmospheric pressure upon the amount of combustible 

 matter consumed by a common candle. I found that, taking the 

 average of five experiments, a stearine candle diminished in weight 

 9*4 grammes when burnt for an hour at Chamounix ; whilst its igni- 

 tion for the same length of time on the summit of Mont Blanc, 

 perfectly protected from currents of air, reduced its weight to the 

 extent of 9*2 grammes. 



This close approximation to the former number under such a 

 widely different atmospheric pressure, goes far to prove that the 

 rate of combustion is entirely independent of the density of the at- 

 mosphere. 



It is impossible to repeat these determinations in a satisfactory 

 manner with artificially rarefied atmospheres, owing to the heating 

 of the apparatus which surrounds the candle, and the consequent 

 guttering and unequal combustion of the latter ; but an experiment 

 in which a sperm candle was burnt first in air under a pressure of 

 28 - 7 inches of mercury, and then in air at 9 inches pressure, other 

 conditions being as similar as possible in the two experiments, the 

 consumption of sperm was found to be, — ■ 



At pressure of 28*7 inches 7'85 grms. of sperm per hour, 

 9-0 „ 9-10 

 thus confirming, for higher degrees of rarefaction, the result pre- 

 viously obtained. 



In burning the candles upon the summit of Mont Blanc, I was 

 much struck by tne comparatively small amount of light which they 

 emitted. The lower and blue portion of the flame, which under 

 ordinary circumstances scarcely rises to within a quarter of an inch 

 of the apex of the wick, now extended to the height of -i-th of an inch 

 above the cotton, thus greatly reducing the size of the luminous 

 portion of the flame. 



On returning to England, I repeated the experiments under cir- 

 cumstances which enabled me to ascertain, by photometrical measure- 

 ments, the extent of this loss of illuminating effect in rarefied air. 

 The results prove that a great reduction in the illuminating power of 

 a candle ensues when the candle is transferred from air at the ordi- 

 nary atmospheric pressure to rarefied air. It was, however, found that, 

 owing to the circumstances mentioned above, no satisfactory quan- 

 titative experiments could be made with candles in artificially rarefied 

 air, and recourse was therefore had to coal-gas, which, although also 

 liable to certain disturbing influences, yet yielded results, during an ex- 

 tensive series of experiments, exhibiting sufficient uniformity to render 

 them worthy of confidence. The gas was in all cases passed through a 

 governor to secure uniformity of pressure in the delivery tubes. A 

 single jet of gas was employed as the standard of comparison, and 



