48 Sir H. Davy’s researches on flame. 
extinguished in rarefied atmospheres, only when the heat it 
produces is insufficient to keep up the combustion, which 
appears to be when it is incapable of communicating visible 
ignition to metal, and as this is the temperature required for 
the inflammation of hydrogene at common pressures, it 
appears that its combustibility is neither diminished nor in- 
creased by rarefaction from the removal of pressure. 
According to this view with respect to hydrogene, it should 
follow that amongst other combustible bodies, those which 
require least heat for their combustion, ought to burn in more 
rarefied air than those that require more heat, and those that 
produce much heat in their combustion ought to burn, other 
circumstances being the same, in more rarefied air than those 
that produce little heat: and every experiment I have made 
confirms these conclusions. Thus olefiant gas which ap- 
proaches nearly to hydrogene in the heat produced by its 
combustion, and which does not require a much higher tem- 
perature for its inflammation, when its flame was made by a 
jet of gas from a bladder connected with a small tube fur- 
nished with a wire of platinum, under the same circumstances 
as hydrogene, ceased to burn when the pressure was dimi- 
nished between 10 and it times: and the flames of alcohol 
and of the wax taper which require a greater consumption of 
heat for the volatilization and decomposition of their combus- 
tible matter, were extinguished when the pressure was 5 or 
6 times less without the wire of platinum, and 7 or 8 times 
less when the wire was kept in the flame. Light carburetted 
hydrogene, which produces, as will be seen hereafter, 
less heat in combustion than any of the common combus- 
tible gases, except carbonic oxide, and which requires a 
higher temperature for its inflammation than any other, had 
