emptying during the process, that there may be no interruption to the
combustion; 4, 5, is a tube of glass filled with deliquescent salts, for
drying the air as much as possible in its passage; and the weight of
this tube and its contained salts, at the beginning of the experiment,
being known, it is easy to determine the quantity of water absorbed by
them from the air. From this deliquescent tube the air is conducted
through the pipe 5, 6, 7, 8, 9, 10, to the lamp 11, where it spreads on
both sides of the wick, as before described, and feeds the flame. One
part of this air, which serves to keep up the combustion of the oil,
forms carbonic acid gas and water, by oxygenating its elements. Part of
this water condenses upon the sides of the pitcher A, and another part
is held in solution in the air by means of caloric furnished by the
combustion. This air is forced by the compression of the gazometer to
pass through the tube 12, 13, 14, 15, into the bottle 16, and the worm
17, 18, where the water is fully condensed from the refrigeration of the
air; and, if any water still remains in solution, it is absorbed by
deliquescent salts contained in the tube 19, 20.
All these precautions are solely intended for collecting and determining
the quantity of water formed during the experiment; the carbonic acid
and azotic gas remains to be ascertained. The former is absorbed by
caustic alkaline solution in the bottles 22 and 25. I have only
represented two of these in the figure, but nine at least are requisite;
and the last of the series may be half filled with lime-water, which is
the most certain reagent for indicating the presence of carbonic acid;
if the lime-water is not rendered turbid, we may be certain that no
sensible quantity of that acid remains in the air.
The rest of the air which has served for combustion, and which chiefly
consists of azotic gas, though still mixed with a considerable portion
of oxygen gas, which has escaped unchanged from the combustion, is
carried through a third tube 28, 29, of deliquescent salts, to deprive
it of any moisture it may have acquired in the bottles of alkaline
solution and lime-water, and from thence by the tube 29, 30, into a
gazometer, where its quantity is ascertained. Small essays are then
taken from it, which are exposed to a solution of sulphuret of potash,
to ascertain the proportions of oxygen and azotic gas it contains.
In the combustion of oils the wick becomes charred at last, and
obstructs the rise of the oil; besides, if we raise the wick above a
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