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Art. II.

Essays, Political, Economical, and
Philosophical. By Benjamin Count
Rumford. The first American,
from the third London Edition.

[Continued from p. 453 of vol. i.]

COUNT Rumford proceeds to
enumerate various circumstan-
ces in which the due operation of
fire-places depends.

Though it be not known how
much heat it is possible to produce
in the combustion of fuel, yet it is
probable that the quantity chiefly
depends on the management of the
fire. It is likewise probable that
the heat produced is furnished, not
merely by the fuel, but chiefly by
the air by which the fire is fed. Air
is necessary to combustion; the
pure part of common air, or that
part of it (amounting to about one
fifth) capable of supporting com-
bustion, is decomposed in that pro-
cess. As, in this decomposition, a
great quantity of heat is set loose,
it has been supposed by many, that
by far the greater part, if not all the
heat produced, is derived from this
source.

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It is, at least, certain, that the
quantity furnished depends much
upon the management of the fire, and
that the quantity is greater as the
combustion or decomposition of the
fuel is more complete.

The consumption of fuel is much
accelerated, and the intensity of the
heat augmented, by causing the air
by which the combustion is excited,
to flow into the fire-place in a con-
tinued stream, and with a certain
degree of velocity. Hence, blow-
ing a fire, when the current of air
is properly directed, and when not
too strong, serves to accelerate the
combustion, and to increase the
heat; but when too strong or im-
properly directed, it tends rather to
impede the combustion than to for-
ward it; and when too strong, it
will totally extinguish it.

Fire-places may be so construct-
ed that the fire may blow itself, that
is, may cause a current of air to
flow into the fire. Furnaces thus
constructed, have been called air-
furnaces; but every perfect fire-
place ought to be an air-furnace,
and that even when intended for the
smallest sauce-pan.

An Argand's lamp is a fire-place
of this kind; for the glass tube
which surrounds the wick, serves
merely as a blower. The circular
form of the wick is not of moment;
for, by applying a flatted glass tube
as a blower to a lamp with a flat or
ribband wick, it may be made to
give as much light as an Argand's
lamp, in proportion to the size of
the wick, and to the quantity of oil
consumed.

In these lamps, the fire-place is
closed on all sides, and the current
of air which feeds the fire, rises per-
pendicularly from below the fire-
place into the fire. By surround-
ing the fire with a wall, the cold
atmosphere is prevented from rush-
ing in laterally to supply the place
of the heated air which continually
rises from the fire, and this causes

the current of air below to be very
strong.

But, that a fire-place may be per-
fect, it should be so contrived that
the combustion of fuel, and the
generation of heat, may occasion-
ally be accelerated or retarded with-
out adding to or diminishing the quan-
tity of fuel; and, when the fire-
place is closed, this may be done
by means of a register in the door,
which closes the passage leading to
the ash-pit; for, as the rapidity of
the combustion depends on the
quantity of air by which the fire is
fed, by opening the register more
or less, more or less air will be ad-
mitted, and more or less fuel will
consequently be consumed, and
more or less heat generated in a
given time, though the quantity of
fuel be much greater than would
otherwise be sufficient.

That this register may produce
the proper effect, a valve, or dam-
per, should be placed in the chim-
ney or canal by which the smoke is
carried off; which damper should
be opened more or less, as the quan-
tity of air admitted into the fire-
place is more or less. This register
and this damper will be found very
useful in putting out the fire when
no longer needed; for, on closing
them entirely, the fire will be im-
mediately extinguished, and the half-
consumed fuel, instead of burning
out to no purpose, will be saved.

Nearly the same effects may be
produced without a damper, by
causing the smoke, after having
quitted the fire-place, to descend
several feet below the level of the
grate on which the fuel is burned,
before it goes up the chimney.

Another circumstance is of much
importance, namely, the proper
disposition of the fuel. It is neces-
sary that the solid parts of the fuel
be of a just size, and that they be
not placed too near each other, so
as to prevent the free passage of air
between them, nor too far asunder.

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The fire-place should be so con-
trived, that solid pieces of the in-
flamed fuel, as they go on to be
diminished in size, may naturally
fall together in the centre of the
fire-place without assistance. This
may be done, in small fire-places,
by burning the fuel on a grate in
the form of a section of a hollow
sphere, or of a dish. Instead of a
grate of iron, we may use hollow
dishes or pans, of earthen ware,
perforated with a great number of
holes for giving passage to the air.
Earthen pans are cheaper, and, on
the whole, better than metalic
grates. The holes should be wider
below than above, to prevent ob-
structions by ashes or coals.

For large fire-places, grates may
be used, the bars of which consist
of common brick placed edgewise.

When the fire-place is closed on
all sides by a wall, and when the
opening by which the fuel is intro-
duced is kept closed, no air can
press in laterally upon the fire; but
yet, when the grate is larger than
the heap of burning fuel, a great
quantity of air may insinuate itself
by the sides of the grate into the
fire-place, without going through
the fire; but when, instead of an
iron-grate, a perforated hollow
earthen pan is used, by making its
bottom two, three, or four inches
thick, and making all the air-holes
point to the focus or centre of the
fire, this furtive entrance of cold
air will, in a great measure, be pre-
vented.

This evil may likewise be pre-
vented when iron grates are used,
by narrowing the fire-place under
the grate, in the form of an invert-
ed, truncated, hollow cone, the
opening of which above, being
equal to the internal diameter of
the circular rim of the grate, and
that below, by which the air rises
into the fire-place about one-third of
that diameter. This opening be-
low must be under the exact cen-

tre of the grate, and as near to ti as
possible; a small space, however,
must be left between the outside or
underside of the iron bars which
form the hollow grate, and the in-
side surface of this hollow cone, that
the ashes may slide down into the
ash-pit.

The ash-pit should be large
enough to give free passage to the
air necessary for feeding the fire,
and the only passage into it should
be closed by a door furnished with
a register.

These fire-places serve equally
well for every kind of fuel. Wood,
pitcoal, charcoal, turf, &c. may
indifferently be used, or any two,
or more of them, may be used at
the same time without inconve-
nience; or the fire having been
lighted with dry wood, or any very
inflammable material, the heat may
afterwards be kept up by cheaper
or less combustible fuel. Some
kinds of fuel will perhaps be found
most useful for making the pot
boil, and others for keeping it boil-
ing. When the fire-place is so con-
trived as to serve equally well for
all kinds of fuel, this may easily be
done.

By narrowing that part of the
fire-place which lies below the
grate, the air is made to enter the
fire in a more advantageous man-
ner. But this structure produces
another benefit; the heat which is
projected downwards through the
openings between the bars of the
grate, instead of escaping into the
ash-pit, strikes against the sides of
this inverted hollow cone, is there
stopped, and afterwards rises into
the fire-place again with the cur-
rent of air which feeds the fire, or
it is immediately reflected by this
conical surface, and, after several
bounds from side to side, is thrown
up against the bottom of the boiler.

To form clear conceptions on
this subject, it is necessary to ex-
amine all the circumstances attend-

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ing the generation of heat in com-
bustion, and to ascertain under
what form the heat generated mani-
fests itself, and how it may be col-
lected, accumulated, confined, and
directed.

The heat generated in combus-
tion manifests itself in two ways;
namely, in the hot vapour which
rises from the fire, with which it
may be said to be combined, and in
the calorific rays which are thrown
off from the fire in all directions.

The quantity of heat which goes
off in the heated elastic fluids, visi-
ble and invisible, which rise from
a fire, is much greater than that
which all the calorific rays united
is capable of producing. But though
the quantity of radiant heat be less
than that existing in the hot vapour,
(and which may be called combined
heat) the former is still too con-
siderable to be neglected.

That the heat thus generated is
considerable, appears from the heat
which is felt in a room warmed by
a chimney fire; for as all the heat,
combined with the smoke and hot
vapour, goes up the chimney, it
follows that the increase of heat in
the room, occasioned by the fire, is
wholly owing to the calorific rays
thrown into it from the burning fuel.

It is not, however, burning bo-
dies alone that emit calorific rays.
All bodies throw off these rays
when made red hot.

As they generate heat in the body
by which they are stopped or absorb-
ed, and not in the medium through
which they pass, it is necessary to
dispose those obstructing bodies so
that they may necessarily commu-
nicate the heat thus acquired to the
body which it is intended that such
heat should operate; and this pur-
pose is thoroughly effected by closed
fire-places. The fire being closed
on all sides except where the bot-
tom of the boiler presents itself to
the fire, none of these rays can es-
cape; and as the materials of the
fire-place, bricks and mortar, are
bad conductors of heat, a small
part only of the heat will be absorb-
ed and transmitted by them into the
interior parts of the wall, there to
be dispersed and lost.

Inquiries into the means of con-
fining and directing heat, has led
the author into many curious spe-
culations and experiments on the
qualities of different bodies, to
conduct, transmit, and detain heat.
These we shall notice hereafter.

(To be continued.)