extremity, s, through which we can see
if the charcoal be on fire.

I neglected to observe above, that the furnace, and its appendages, are
plunged in water in the cistern, TVXY, Fig. 11. Pl. XII. to which ice
may be added to moderate the heat, if necessary; though the heat is by
no means very considerable, as there is no air but what comes from the
gazometer, and no more of the charcoal burns at one time than what is
immediately over the grate.

As one piece of charcoal is consumed another falls down into its place,
in consequence of the declivity of the sides of the furnace; this gets
into the stream of air from the grate, d e, and is burnt; and so on,
successively, till the whole charcoal is consumed. The air which has
served the purpose of the combustion passes through the mass of
charcoal, and is forced by the pressure of the gazometer to escape
through the tube, o p, and to pass through the bottles of alkaline
solution.

This experiment furnishes all the necessary data for a complete analysis
of atmospheric air and of charcoal. We know the weight of charcoal
consumed; the gazometer gives us the measure of the air employed; the
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