Some new Researches on Flame. ll 
the following circumstance. When the heat is greatest, and 
before the invisible combination is completed, if an iron wire 
heated to whiteness be placed upon the coal within the vessel, 
the mixture instantly explodes. 
Light carburetted hydrogen, or pure fire-damp, as has been 
shown, requires a very strong heat for its inflammation; it there- 
fore offered a good substance for an experiment on the effect of 
high degrees of rarefaction by heat on combustion. I mixed to- 
gether one part of this gas and eight parts of air, and introduced 
them into a bladder furnished with a capillary tube. 1 heated 
this tube till it began to melt, and then slowly passed the mix- 
ture through it into the flame of a spirit-lamp, when it took fire 
and burned with its own peculiar explosive light beyond the 
flame of the amp, and when withdrawn, though the aperture 
was quite white hot, it continued to burn vividly. 
That the compression in one part of an explosive mixture 
produced by the sudden expansion of another part by heat, or 
the electric spark, is not the cause of combination, as has been 
supposed by Dr. Higgins, M. Berthollet, and others, appears to 
be evident from what has been stated, and it is rendered still 
more so by the following facts. A mixture of hydro-phosphoric 
gas (bi-phosphuretted hydrogen gas) and oxygen, which explode 
at a heat a little above that of boiling water, was confined by 
mercury, and very gradually heated on a sand-bath: when the 
temperature of the mercury was 242°, the mixture exploded. 
A similar mixture was placed in a receiver communicating with 
a condensing syringe, and condensed over mercury till it oc- 
eupied only 1-5th of its original volume. No explosion took 
place, and no chemical change had occurred; for when its volume 
was restored, it was instantly exploded by the spirit-lamp. 
It would appear, then, that the heat given out by the com- 
pression of gases is the real cause of the combustion which it 
produces, and that at certain elevations of temperature, whether 
in rarefied or compressed atmospheres, explosion or combustion 
co 2.@. bodies combine with the production of heat and 
ight. 
Ili. On the Effects of the Mixture of different Gases in Ex- 
plo 
sion and Combustion. 
In my first paper on the fire-damp of coal mines, I have men- 
tioned that carbonic acid gas has a greater power of destroying 
the explosive power of mixtures of fire-damp and air than azote, 
and I have ventured to suppese the cause to be its greater den- 
sity and capacity for heat, in consequence of which it might exert 
a greater cooling agency, and prevent the temperature of the 
mixture from being raised to that degree necessary for com - 
bustion, 
