ender it elastic, great part of which,
during the low combustion which it supports, and in which heat is
visible or perceptible, and light in an invisible state developed,
three parts of this oxygen, with about one third of its weight of
carbon, is converted into an elastic state, under the form of fixed
air, that separates from the decomposing mass; a circumstance attending
also on the combustion of coal and other combustible substances during
their decomposition by that process, which supported in them by the
external air of the atmosphere, where heat and light are both visible
from the intensity and velocity of the combustion; and wholly invisible
in the former, not from exclusion of external air, but from the length
of time elapsed in low combustion; the one being performed
instantaneously, and the other taking several days from its
decomposition. Although fixed air is known to extinguish a lighted
candle, and destroy animal life, that is, to be equally unfit for the
combustion of inflammable bodies, or the support of animal respiration,
it is also known to be as successfully employed as atmospheric air, or
even dephlogisticated air, to melt glass, &c., when applied to the
clear flame of a wax candle, by passing a current of it through a
blow-pipe, to direct that flame on the glass to be melted.[4]

[4] Count Rumford on the Economy of Fuel.

This will not be so much to be wondered at, when we consider that the
proportion of vital air in fixed air is as twenty-seven to nine, and in
atmospheric air, the proportion of azotic gas or phlogisticated air, to
vital air, is as seventy-three to twenty-seven; therefore, the former
contains three fourths of vital air, and the latter little better than
one fourth; but the fixed air is in a combined, and the phlogisticated
air in an uncombined state. Among the processes made use of by nature
for the decomposition of vegetable and animal substances, fermentation,
or low combustion, is a principle one. Air, in a fixed or unelastic
state, may be as necessary here as air in an elastic state is known to
be in the active combustion of inflammable bodies. Chemists and
philosophers are no strangers to two sorts of combustion, one in
external air, and the other in close vessels.

But this is not the combustion alluded to in fermentation, where all
the requisites for complete decomposition is to be found independent of
contact with the atmosphere; here one part is oxygenated at the