1861.] PTof, Frankland on Combustion in Rarefied Air, 331 



WEEKLY EVENING MEETING, 



Friday, March 8, 1861. 



The Rev. John Barlow, M.A. F.R.S. Vice-President, 

 in the Chair. 



EdWAKD FBANKIiAND, F.R.S. 



On some Phenomena attending Comhitstion in Rarefied Air. 



The investigation forming the subject of this discourse had its origin 

 in some experiments which the speaker made upon the summit of 

 Mont Bl^jinc, in the autumn of 1859, for the purpose of ascertaining 

 the effect of atmospheric pressure upon the amount of combustible 

 matter consumed by a common candle. He found, as the average 

 of five experiments, that a stearin candle diminished in weight 

 9 • 4 grammes, when burnt for an hour at Chamonix ; whilst it con- 

 sumed 9 • 2 grammes, when ignited for the same length of time on the 

 summit of Mont Blanc. This close approximation in the quantity of 

 combustible matter consumed under such widely different atmospheric 

 pressures, goes far to prove that the rate of combustion is entirely 

 independent of the density of the atmosphere. This result was subse- 

 quently confirmed by a repetition of the experiments in air, artificially 

 rarefied, until it supported a column of only 9 inches of mercury. 



In burning the candles upon the top of the mountain, it was 

 noticed, in the subdued light of the tent in which the operation 

 was performed, that their luminosity was much less than usual. The 

 lower and blue portion of the flame, which, under ordinary cir- 

 cumstances, scarcely rises to within a quarter of an inch of the apex 

 of the wick, now extended to the height of one-eighth of an inch above 

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

 the flame ; and, on subsequently repeating the experiments in arti- 

 ficially rarefied atmospheres, and measuring the amount of light 

 emitted in each case, it was found that as the rarefaction proceeded, 

 the blue or non-luminous portion of the flame gradually extended 

 upwards until it finally expelled, as it were, the yellow or luminous 

 part even from the apex of the flame. During the progress of the 



