58 Sir H. Davy’s researches on flame. 
hydro-phosphoric gas ( bi-phosphuretted hydrogene gas) and 
oxygene, 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 occupied only -f- 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, whe- 
ther in rarefied 'or compressed atmospheres, explosion or 
combustion occurs, i, e. bodies combine with the production 
of heat and light. 
III. On the effects of the mixture of different gases in explosion 
and combustion. 
In my first Paper on the fire-damp of coal mines, I have 
mentioned 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 suppose the cause to 
be its greater density and capacity for heat, in consequence 
of which it might exert a greater cooling agency, and pre- 
vent the temperature of the mixture from being raised to that 
degree necessary for combustion. I have lately made a series 
of experiments with the view of determining how far this idea 
