Some new Researches on Flame. 15 
believe, that when phasphuretted hydrogen explodes in very rare 
air, it is only the phosphorus which is consumed. Any other 
substance that produces solid matter in combustion would pro- 
bably be luminous in air as rare, or in mixtures as diluted, as 
phosphorus, provided the heat was elevated sufficiently for its 
combustion. I have found that this is actually the case with 
respect to zinc. 1 threw some zinc filings into an ignited iron 
erucible fixed on the stand of an air-pump under a receiver, and 
exhausted until only 1-60th of the original quantity of air re- 
tained. When I judged that the red het crucible must be full 
of the vapour of zinc, I admitted about 1-6Uth more of air, 
when a bright flash of light took place in and above the cruci- 
ble, similar to that which is produced by admitting air to the 
vapour of phosphorus in vacuo. 
The cooling power of mixtures of elastic fluids in preventing 
combustion must increase with their condensation, and diminish 
with their rarefaction ; at the same time, the quantity of matter 
entering into combustion in given spaces, is relatively increased 
and diminished. ‘The experiments on flame in rarefied atmo- 
spherical air, show that the quantity of heat produced in com- 
bustion is very slowly diminished by rarefaction, the diminution 
of the cooling power of the azote being apparently in a higher - 
ratio than the diminution of the heating powers of the burning 
bodies. I endeavoured to ascertain what would be the effect of 
condensation on flame in atmospheric air, and whether the cool- 
ing power of the azote would increase in a lower ratio, as might 
be expected, than the heat produced by the increase of the quan- 
tity of matter entering into combustion ; but I found consider- 
able difficulties in making the experiments with precision. I 
ascertained, however, that both the light and heat of the flames 
of the taper, of sulphur and hydrogen, were increased by acting 
on them by air condensed four times; but not more than they 
would have been by an addition of 1-5th of oxygen. 
I condensed air nearly five times, and ignited iron wire to 
whiteness in it by the voltaic apparatus; but the combustion took 
place with very little more brightness than in the common at- 
mosphere, and would not continue as in oxygen, nor did char- 
coal burn much more brightly in this compressed air than in 
common air. | intend to repeat these experiments, if possible, 
with higher condensing powers: they show sufficiently that (for 
certain limits at least) as rarefaction does not diminish consider- 
ably the heat of flame in atmospherical air, so neither does con- 
densation considerably increase it; a circumstance of great im- 
portance in the constitution of our atmosphere, which at all the 
heights or depths at which man can exist still preseryes the 
same relations to combustion. 
It 
