quantity and quality of gas remaining after combustion may be
determined, as it is received, either in another gazometer, or in jars,
in a pneumato-chemical apparatus; the weight of ashes remaining in the
ash-hole is readily ascertained; and, finally, the additional weight
acquired by the bottles of alkaline solution gives the exact quantity of
carbonic acid formed during the process. By this experiment we may
likewise determine, with sufficient accuracy, the proportions in which
charcoal and oxygen enter into the composition of carbonic acid.
In a future memoir I shall give an account to the Academy of a series of
experiments I have undertaken, with this instrument, upon all the
vegetable and animal charcoals. By some very slight alterations, this
machine may be made to answer for observing the principal phenomena of
respiration.
SECT. IV.
_Of the Combustion of Oils._
Oils are more compound in their nature than charcoal, being formed by
the combination of at least two elements, charcoal and hydrogen; of
course, after their combustion in common air, water, carbonic acid gas,
and azotic gas, remain. Hence the apparatus employed for their
combustion requires to be adapted for collecting these three products,
and is consequently more complicated than the charcoal furnace.
The apparatus I employ for this purpose is composed of a large jar or
pitcher A, Pl. XII. Fig. 4. surrounded at its upper edge by a rim of
iron properly cemented at DE, and receding from the jar at BC, so as to
leave a furrow or gutter xx, between it and the outside of the jar,
somewhat more than two inches deep. The cover or lid of the jar, Fig. 5.
is likewise surrounded by an iron rim f g, which adjusts into the
gutter xx, Fig. 4. which being filled with mercury, has the effect of
closing the jar hermetically in an instant, without using any lute; and,
as the gutter will hold about two inches of mercury, the air in the jar
may be made to sustain the pressure of more than two feet of water,
without danger of its escaping.
The lid has four holes, T h i k, for the passage of an equal
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