_Of the Combustion of Alkohol._
The combustion of alkohol may be very readily performed in the apparatus
already described for the combustion of charcoal and phosphorus. A lamp
filled with alkohol is placed under the jar A, Pl. IV. Fig. 3. a small
morsel of phosphorus is placed upon the wick of the lamp, which is set
on fire by means of the hot iron, as before directed. This process is,
however, liable to considerable inconveniency; it is dangerous to make
use of oxygen gas at the beginning of the experiment for fear of
deflagration, which is even liable to happen when common air is
employed. An instance of this had very near proved fatal to myself, in
presence of some members of the Academy. Instead of preparing the
experiment, as usual, at the time it was to be performed, I had disposed
every thing in order the evening before; the atmospheric air of the jar
had thereby sufficient time to dissolve a good deal of the alkohol; and
this evaporation had even been considerably promoted by the height of
the column of mercury, which I had raised to EF, Pl. IV. Fig. 3. The
moment I attempted to set the little morsel of phosphorus on fire by
means of the red hot iron, a violent explosion took place, which threw
the jar with great violence against the floor of the laboratory, and
dashed it in a thousand pieces.
Hence we can only operate upon very small quantities, such as ten or
twelve grains of alkohol, in this manner; and the errors which may be
committed in experiments upon such small quantities prevents our placing
any confidence in their results. I endeavoured to prolong the
combustion, in the experiments contained in the Memoirs of the Academy
for 1784, p. 593. by lighting the alkohol first in common air, and
furnishing oxygen gas afterwards to the jar, in proportion as it
consumed; but the carbonic acid gas produced by the process became a
great hinderance to the combustion, the more so that alkohol is but
difficultly combustible, especially in worse than common air; so that
even in this way very small quantities only could be burnt.
Perhaps this combustion might succeed better in the oil apparatus, Pl.
XI.; but I have not hitherto ventured to try it. The jar A in which the
combustion is performed is near 1400 cubical inches in dimension; and,
were an explosion to take place in such a vessel, its consequences would
be very terrible, and very difficult to guard against. I have not,
however, despaired of making the attempt.
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