I have employed for this process consists of a small
conical furnace of hammered copper, represented in perspective, Pl. XII.
Fig. 9. and internally displayed Fig. 11. It is divided into the
furnace, ABC, where the charcoal is burnt, the grate, d e, and the
ash-hole, F; the tube, GH, in the middle of the dome of the furnace
serves to introduce the charcoal, and as a chimney for carrying off the
air which has served for combustion. Through the tube, l m n, which
communicates with the gazometer, the hydrogen gas, or air, intended for
supporting the combustion, is conveyed into the ash-hole, F, whence it
is forced, by the application of pressure to the gazometer, to pass
through the grate, d e, and to blow upon the burning charcoal placed
immediately above.

Oxygen gas, which forms 28/100 of atmospheric air, is changed into
carbonic acid gas during combustion with charcoal, whilst the azotic gas
of the air is not altered at all. Hence, after the combustion of
charcoal in atmospheric air, a mixture of carbonic acid gas and azotic
gas must remain; to allow this mixture to pass off, the tube, o p, is
adapted to the chimney, GH, by means of a screw at G, and conveys the
gas into bottles half filled with solution of caustic potash. The
carbonic acid gas is absorbed by the alkali, and the azotic gas is
conveyed into a second gazometer, where its quantity is ascertained.

The weight of the furnace, ABC, is first accurately determined, then
introduce the tube RS, of known weight, by the chimney, GH, till its
lower end S, rests upon the grate, d e, which it occupies entirely; in
the next place, fill the furnace with charcoal, and weigh the whole
again, to know the exact quantity of charcoal submitted to experiment.
The furnace is now put in its place, the tube, l m n, is screwed to
that which communicates with the gazometer, and the tube, o p, to that
which communicates with the bottles of alkaline solution. Every thing
being in readiness, the stop-cock of the gazometer is opened, a small
piece of burning charcoal is thrown into the tube, RS, which is
instantly withdrawn, and the tube, o p, is screwed to the chimney, GH.
The little piece of charcoal falls upon the grate, and in this manner
gets below the whole charcoal, and is kept on fire by the stream of air
from the gazometer. To be certain that the combustion is begun, and goes
on properly, the tube, q r s, is fixed to the furnace, having a piece
of glass cemented to its upper