64 Sir H. Davy’s researches on flame. 
this is actually the case with respect to zinc. I threw some 
zinc filings into an ignited iron crucible fixed on the stand of 
an air pump under a receiver, and exhausted until only ~ of 
the original quantity of air remained. When I judged that the 
red hot crucible must be full of the vapour of zinc, I admitted 
about more of air, when a bright flash of light took place 
in and above the crucible, 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 prevent- 
ing combustion must increase with their condensation, and 
diminish with their rarefaction ; at the same time, the quan- 
tity of matter entering into combustion in given spaces, is 
relatively increased and diminished. The experiments on 
flame in rarefied atmospherical air, show that the quantity of 
heat produced in combustion 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 cooling power of the 
azote would increase in a lower ratio, as might be expected, 
than the heat produced by the increase of the quantity of 
matter entering into combustion, but I found considerable 
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 hydrogene, were in- 
creased by acting on them by air condensed four times ; but 
not more than they would have been by an addition of - 5 of 
oxygene. 
I condensed air nearly five times, and ignited iron wire to 
