The Romance of Modern Chemistry

FLAME: WHAT IS IT? its luminosity, once took the trouble to carry candles up to the top of Mont Blanc, and was much struck by the comparatively small amount of light which they emitted when burning there. He traced this decrease of luminosity to the small atmospheric pressure prevailing at such a high level, and was able to show subsequently in his laboratory that the illuminating power of a candle is much reduced when it is burning in a partially exhausted vessel. Since diminution of pressure reduces the luminosity of a flame, it might fairly be expected that increase of pressure would have the opposite effect; and so it turns out. A spirit-lamp, which, as the reader knows, gives practically no light when burning in air under ordinary conditions, gives a highly luminous flame when placed under a pressure of four atmospheres; and Frankland estimated that under a pressure of five or six atmospheres its luminosity would be equal to that of sperm oil burn- ing under ordinary atmospheric pressure. The influence of pressure on the luminosity of a flame is most strikingly illustrated by the effect of compres- sion on burning hydrogen. This gas bums under ordinary conditions with a pale flame, absolutely useless for illumi- nating purposes, and it might be supposed that the want of luminosity is due to the absence of any solid product of combustion; water, the compound which results from the union of hydrogen and oxygen, is, of course, a vapour at the temperature of the flame. But if hydrogen is burned in oxygen at ten atmospheres pressure, the light emitted by the flame is sufficient to enable the observer to read a newspaper two feet away. Plainly, therefore, the presence of solid particles is not the only thing on which the luminosity of flame 159