Sir H. Davy's researches on flame. % 
whiteness in it by the voltaic apparatus, but the combustion 
took place with very little more brightness than in the com- 
mon atmosphere, and would not continue as in oxygene, nor 
did charcoal burn much more brightly in this compressed air 
than in common air. I intend to repeat these experiments, if 
possible, with higher condensing powers: they show suffi- 
ciently that, (for certain limits at least) as rarefaction does 
not diminish considerably the heat of flame in atmospherical 
air, so neither does condensation considerably increase it ; a 
circumstance of great importance in the constitution of our 
atmosphere, which at all the heights or depths at which man 
can exist, still preserves the same relations to combustion. 
It may be concluded from the general law, that at high 
temperatures, gases not concerned in combustion will have less 
powers of preventing that operation, and likewise, that steam 
and vapours, which require a considerable heat for their for- 
mation, will have less effect in preventing combustion, parti- 
cularly of those bodies requiring low temperatures, than 
gases at the common heat of the atmosphere. 
I have made some experiments on the effects of steam, and 
their results were conformable to these views. I found that a 
very large quantity of steam was necessary to prevent sul- 
phur from burning. Oxygene and hydrogene exploded by 
the electric spark when mixed with five times their volume 
of steam ; and even a mixture of air and carburetted hydro- 
gene gas, the least explosive of all mixtures, required a third 
of- steam to prevent its explosion, whereas ~ of azote produced 
the effect. These trials were made over mercury ; heat was 
applied to water above the mercury, and 37.5 for 100 parts 
was regarded as the correction for the expansion of the gases,, 
MBCCCXVII. K 
