will be a great improvement, as I have found by
experience. This may be done, in fmall fire-places,
(and in thefe it is more particularly neceffary) by
burning the Fuel upon a grate in the form of a
fegment of a hollow fphere, or of a difh. (See the
Figures. 3 and 4. Plate I.) All thofe I now ufe,
except it be for fire-places which are very large in
deed, are of this form ; and where wood is made
ufe of for Fuel, it is cut into fmall billets from 4
to 6 inches in length. Inftead of a grate of iron,
I have lately introduced grates, or rather hollow
diihes or pans, of earthen ware, perforated with a
great number of holes for" giving a paffage to the
air.
Vo*. II. G Thefe



42 Of the Management of Firs,

Thefe perforated earthen pans, which are made
very thick and flrong, are incomparably cheaper
than iron grates ; and judging from the experience
I have had of them, I am inclined to think they
anfwer even better than the grates ; indeed it ap
pears to me not difficult to affign a reafon why
they ought to be better.

For large fire-places I have fometimes ufed
grates, the bars of which were common bricks
placed edgewife, and thefe have been found to
anfwer very well.

As only that part of the air which, entering the
fire-place in a proper manner, and in a juft quan
tity, and coming into actual contact with the burn*
ing Fuel, is decomfofed, contributes to the genera
tion of heat ; it is evident that all the air that
finds its way into the fire-place, and out of it again,
without being decompofed, is a thief; that it not
only contributes nothing to the heat, but being itfelf
heated at the expenfe of the Fire., and going off
hot into the atmofphere by the chimney, occaiions
an actual lofs of heat j and this lofs is often very
conllderable, and the prevention of it is fuch an
object, that too much attention cannot be paid to
it in the conftruction of fire-places.

When the fire-place is clofed on all fides by a
wall, and when the opening by which the Fuel is
introduced is kept clofed, no air can prefs in late
rally upon the Fire ; but yet, when the grate is
larger than the heap of burning Fuel, which muft
often be the cafe, a great quantity of air may in-

finuate



and tie Economy of Fuel. 43

finuate itfelf by the fides of the grate into the fire
place, without going through the Fire : But when,
inftead of an iron-grate, a perforated hollow earth-
en pan is ufed, by making the bottom of the pan
of a certain thicknefs, 2, 3, or 4 inches, for in-
ftance, and making all the air-holes point to one
common centre, (to the focus or centre of the Fire)
this furtive entrance of cold air into the fire-place
will, in a great meafure, be prevented.

This evil may likewife be prevented when circu
lar hollow iron grates are ufed, by narrowing the
fire-place immediately under the grate, in the form
of an inverted, truncated, hollow cone, the open
ing or diameter of which above being equal to the
internal diameter of the circular rim of the grate,
and that below (by which the air rifes to enter the
fire-place) about one-third of that diameter. (See
the Figure 5. Plate I.) This opening below,
through which the air rifes, muft be immediately
under the centre of the grate, and as near to it as
poffible ; care muft be taken, however, that a fin all
fpace be left between the outfide or under fide of
the iron bars which form the hollow grate, and the
infide furface of this inverted hollow cone, in or
der that the afhes may flide down into the aih-pit.

As to the form and fize of the afh-pit, thefe
are matters of perfect indifference, provided, how
ever, that it be large enough to give a free pafiage
to the air nexeilary for feeding the Fire, and that
the only pJRTage into it, by which air can enter, is
clofed by a good door furnifhed with a regifter.

The



44 Of the Management of Fire,

The neceffity of being completely matter of the
paffage, by which the air enters the fire-place, has
already been fufficiently explained.

It is perhaps unneceffary for me to obferve, that
where perforated earthen pans are ufed inftead of
iron grates, the air holes in the pans ought to be
rather fmaller above than below, in order that they
may not be choked up by the fmall pieces of coal,
and the afhes which occafionally fall through them
Into the afh~pit.

One great advantage attending fire-places on tfc
conftru&ion here propofed, is, that they ferve
equally well for every kind of Fuel. Wood, pit-
coal, charcoal, turf, &c. may indifferently be ufed,
and all of them with the fame facility, and with the
fame advantages ; or any two, or more, of thefe
different kinds of Fuel, may be ufed at the fame
time without the fmalleft inconvenience ; or the
Fire having been lighted with dry wood, or any
other very inflammable material, the heat may af
terwards be kept up by cheaper or more ordinary
Fuel of a more difficult and flow combuftion.
Some kinds of Fuel will perhaps be found moil ad
vantageous for making the pot boil, and others
for keeping it boiling ; and a very confiderable
faving will probably be found to refult from paying
due attention to this circumftance. When the
fire-place is fo contrived as to ferve equally well for
all kinds of Fuel, this may be done without the
leaft difficuly or trouble,

I have



and the Economy of FucL 45

I have juft fhown, that narrowing that part of
the fire-place which lies below the grate, ferves to
make the air enter the fire in a more advantageous
manner. This conftruc~tion has another advan
tage, perhaps ftill more important ; the heat which
is projected downwards through the openings be
tween the bars of the grate, inftead of being per
mitted to efcape into the afh-pit, (where it would
be loft) ftriking againft the iides of this inverted
hollow cone, it is there flopped, and afterwards rifes
yito the fire-place again with the current of air
which feeds the Fire, or it is immediately reflected
by this conical furface, and, after two or three
bounds from fide to fide, is thrown up againft the
bottom of the boiler.

But in order to be able to form a clear and
diftinct idea upon this fubjecl, it is necelTary to
examine with care all the circumftances attending
the generation of heat in the combuftion of in
flammable bodies, and to fee in what manner, or
under what form, the heat generated manifefts it-
felf, and how it may be collected, accumulated,
confined, and directed.

This opens a wide field for philofophical inquiry ;
but as thefe inveftigations are not only curious and
entertaining, but alfo ufeful and important in a
high degree, I truft my reader will pardon me for
requefting his particular attention while I endeavour
to do juftice to this moft interefting, but, at the
fame time, moft abftrufe and moft difficult part of
the fubjecl: I have undertaken to treat.

The



46 Of the Management of Fire,

The heat generated in the combuftion of Fuel
manifefts itfelf in two ways ; namely, in the hot va
pour which rifes from the Fire, with which it may
be faid to be combined, and in the calorific rays
which are thrown off from the Fire in all direc
tions. Thefe rays may, with greater propriety, be
faid to be calorific, or capable of generating heat, in
any body by which they are flopped, than to be
called hot ; for when they pafs freely through any
medium, (as through a mafs of air, for inftance)
they are not found to communicate any heat what
ever to fuch medium ; neither do they appear to
excite any confiderable degree of heat in bodies
from whofe furfaces they are reflected ; and in
thefe refpects they bear a manifeft xefemblance to
the rays emitted by the fun.

What proportion this radiant heat (if I may be
allowed to ufe fo inaccurate an expreffion) bears to
that which goes off from burning bodies in the
fmoke and heated vapour, is not exactly known ;
it is certain, however, that the quantity of heat
which goes off in the heated elaftic fluids, viiible
and invifible, which rife from a Fire, is much
greater than that which all the calorific rays united
would be capable of producing. But though the
quantity of radiant heat islefs than that exiftingin
the hot vapour, (and which, for the fake of diftinc-
tion, may be called combined heat) the former is
flill much too confiderable to be neglefted.

That the heat generated, or excited, by the calo
rific rays which proceed from burning bodies, is in

fad



and the Economy of Fuel. 47

facl confiderable, is evident from the heat which is
felt in a room warmed by a chimney Fire ; for as
all the heat, combined with the fmoke and hot va
pour, goes up the chimney, it is certain that the
increafe of heat in the room, occafioned by the Fire,
is entirely owing to the calorific rays thrown into
it from the burning Fuel.

The activity of thefe rays may be mown in va
rious ways, but in no way in a more ftriking man
ner than by the following fimple Experiment :
When the Fire burns bright upon the hearth, let
the arm be extended in a ftraight line towards the
centre of the Fire, with the hand open, and all the
fingers extended and pointing to the Fire. If the
hand is not nearer the Fire than the diftance of
two or three yards, except the Fire be very large
indeed, the heat will fcarcely be perceptible ; but
if, without moving the arm, the wrift be bent up
wards fo as to prefent the infide or flat of the hand
perpendicular to the Fire, the heat will not only be
very fenfibly felt, but, if the Fire be large, and if it
burns clear and bright, it will be found to be fo
intenfe as to be quite infupportable.

It is not, however, burning bodies alone that
emit calorific rays. All bodies, thofe which are
fixed and incombuftible, as well as thofe which are
inflammable, fluids as well as folids, are found
to throw off thefe rays in great abundance, as foon
as they are heated to that degree which is nqceffary
to their becoming luminous in the dark, or till
they are red-hot.

Bodies



48 Of tie Management of JF/n%

Bodies even which arc heated to a lefs degree than
that which is necelfary to their emitting vifible light,
fend off calorific rays in all directions. This is a
master of fad, which has been proved by experi
ment. Do all bodies, at all temperatures, freez
ing mercury as well as melting iron, continually
emit thefc rays in greater or lefs quantities, or with
greater or lefs velocities ? Are bodies cooled in
confequence of their emitting thefe rays ? Do
thefc calorific rays always generate heat, even when
the body by which they are flopped or abforbed,
is hotter than that from which the rays proceed
ed ? But I forget that I promifed not to involve
myfelf in abflrufe fpeculation. To return then :
Whatever may be the nature of the rays emitted
by burning Fuel, as one of their known properties is
to generate heat, they ought certainly to be very
particularly attended to in every arrangement in
which the Economy of Heat, or of Fuel, is a prin
cipal object in view.

As thefe calorific rays generate heat in the body
by which they are flopped or abforbed, and not in the
medium through w r hich they pafs, it is neceffary to
difpofe thofe bodies which are defigned for flopping
them, in fuch a manner that they may eafiiy and
ncccflarily communicate the heat they thus acquire
to the body upon which it is intended that it
fhould operate.

The clofed fire-places which I have recommend
ed, and which will hereafter be more particularly
defcribed, will anfwer this purpofe completely.

The



and the Economy of Fuel. 49

The Fire being clofed in thefe fire-places, on every
fide, as well below the grate as laterally, and in
fhort every where, except where the bottom of the
boiler prefents itfelf to the Fire, none of thefe rays
can poffibly efcape ; and as the materials of which
the fire-place is conftructed, (bricks and mortar)
are bad conductors of heat, but a fmall part of the
heat generated in the combuftion of the fuel will
be abforbed and tranfmitted by them into the inte
rior parts of the wall, there to be difperfed and
loft. But the confining of heat is a matter of fuf-
ficient importance to deferve being treated in a fe~
parate Chapter.



VOL. II, H



50 Of the Management cf Fire,



CHAP. III.

Of the Means of CONFINING HEAT, and DIRECT
ING ITS OPERATIONS. Of Conductors and Non-
conductors of Heat. Common Atmofpheric Air a
good Non-conduclor of Heat, and may be employed
with great Advantage for confining it is employed
by Nature for that purpofe, in many Inflames is
the principal Caufe of the Warmth of Natural and
Artificial Clothing is the f ole Caufe of the Warmth
of Double Windows. Great Utility of Double
Windows and Double Walls they are equally ufe-
ful in Hot Countries as in Cold. ALL ELASTIC
FLUIDS Non-CQnduftors of Heat. STEAM proved
by Experiment to be a Nonconduclor of Heat.
FLAME is alfo a Non-conduclor of Heat.

THAT HEAT paiTes more freely through fome
bodies than through others, is a fact well
known ; but the caufe of this difference in the
conducing powers of bodies, with refpecl to Heat,
has not yet been difcovered.

The utility of giving a wooden ha.ndle to a tea
pot or coffee-pot of metal, or of covering its metallic
handle with leather, or with wood, is well known :
But the difference in the conducting powers of va
rious bodies with regard to Heat, may be fliown by
a great number of very fimple experiments j fuch

as



and the Economy of Fuel. 51

as are in the power of every one to make at all
times and in all places, and almoft without either
trouble or expenfe.

If an iron nail and a pin of wood, of the fame
form and dimenfions, be held fucceffively in the
flame of a candle, the difference in the conducting
powers of the metal and of wood will manifeft it-
felf in a manner in which there will be no room-
left for doubt. As foon as the end of the nail,
which is expofed in the flame of the candle, begins
to be heated, the other end of it will grow fo hot as
to render it impoflible to hold it in the hand with*
out being burnt ; but the wood may be held any
length of time in the fame fituation without the leaft
inconvenience ; and, even after it has taken fire,
it may be held till it is almoft entirely confumed ;
for the uninflamed wood will not grow hot, and,
till the flame actually comes in contact with the
fingers, they will not be burnt. If a fmall flip or
tube of glafs be held in the flame of the candle in
the fame manner, the end of the glafs by which it
is held will be found to be more heated than the
wood, but incomparably lefs fo than the pin or nail
of metal ; and among all the various bodies that
can be tried in this manner, no two of them will
be found to give a paflage to Heat through their
fubftances with exactly the fame degree of faci
lity.*

To

* To fhow the relative conducing power of the different metals, Do&or
Ingenhouz contrived a very pretty experiment. He took equal cylinders

of



5 Of the Management of Fire,

To confine Heat is nothing more than to prevent
its efcape out of the hot body in which it exifts,
and in which it is required to be retained ; and this
can only be done by furrounding the hot body by
fome covering compofed of a fubftance through
which Heat cannot pafs, or through which it pafles
With great difficulty. If a covering could be found
perfectly impervious to Heat, there is reafon to be
lieve that a hot body, completely furrounded by it,
would remain hot forever ; but we are acquainted
with no fuch fubftance ; nor is it probable that any
fuch exifts.

Thofe bodies in which Heat pafles freely or ra
pidly, are called Conductors of Heat ; thofe in which
it makes its way with great difficulty, or very (low
ly, Nm*condatfon 9 or bad Conductors of Heat. The
epithets, good, bad, indifferent, excellent, &c. are
Applied indifferently to conductors and to non-con-
dutfors. A good conductor, for inftance, is one in
which Heat pafles very freely ; a good non-con-
ducter is one, in which it pafles with great difficulty;
and an indifferent conductor may likewife be called,
without any impropriety, an indifferent non-con
ductor.

Thofe

of the different metals, (being ftraight pieces of flout wire, drawn through
the fame hole, and of the fame length) and dipping them into melted
wax, covered them with a thin coating of the wax. He then held one
end of each of thefe cylinders in bpiling water, and obferved how far the
coating of wax was melted by the Heat communicated through the metal,
ind with what celerity the Heat patted.



ttnd the Economy of Fuel, 53

Thofe bodies which are the worft conductors, or
rather the belt non-conductors of Heat, are befl
adapted for forming coverings for confining Heat.

All the metals are remarkably good conductors
of heat ; wood, and in general all light, dry, and
fpungy bodies, are non-conductors : Glafs, though
a very hard and compact body, is a non-conductor.
Mercury, water, and liquids of all kinds, are con-?
ductors ; but air, and in general all elaftic fluids,
Jleam even not excepted, are non-conductors.

Some experiments which I have lately made, and
which have not yet been publiflied, have induced
me to fufpect, that water ^ mercury, and all other
non-elafiic fluids, do not permit Heat to pals
through them from particle to particle, as it un
doubtedly paffes through folid bodies, but that
their apparent conducting powers depend effen-
tially upon the extreme mobility of their parts ; in
fliort, that they rather tranfport Heat than allow it
a paffage. But I will not anticipate a fubject which
I propofe to treat more fully at fome fut^we
period.

The conducting power of any folid body in one
folid mafs, is much greater than that of the fame
body reduced to a powder, or divided into many
fmaller pieces : An iron bar, or an iron plate, for
inftance, is a much better conductor of Heat than
iron filings \ and faw-duft is a better non-conductor
than wood. Dry wood-afhes is a better non-con
ductor than either ; and very dry charcoal reduced
to a fine powder is one of the belt non-conductors

known j



54 Of the Management of Fire,

known ; and as charcoal is perfectly incombuftible
when confined in a fpace where frefh air can have
no accefs, it is admirably well calculated for form
ing a barrier for confining Heat, where the Heat to
be confined is intenfe.

But among all the various fubftances of which
coverings may be formed for confining Heat, none
can be employed with greater advantage than com
mon atmofpheric air. It is what Nature employs
for that purpofe ; and we cannot do better than to
imitate her.

The warmth of the wool and fur of beafts, and
of the feathers of bif ds, is undoubtedly owing to
the air in their intereftices ; which air, being
flrongly attraded by thefe fubftances, is con
fined, and forms a barrier, which not only prevents
the cold winds from approaching the body of the
animal, but which oppofes an almoft infurmount-
able obflacle to the efcape of the Heat of the animal
into the atmofphere. And in the fame manner the
air^n fnow ferves to preferve the Heat of the earth
in winter. The warmth of all kinds of artificial
clothing may be ihown to depend on the fame
caufe ; and were this circumftance more generally
known, and more attended to, very important im
provements in the Management of Heat could not
fail to refult from it. A great part of our lives is
fpent in guarding ourfelves againfl the extremes of
heat and of cold, and in operations in which the
ufe of Fire is indifpenfable ; and yet how little
progrefs has been made in that moft ufeful and

moft



and the Economy of Fuel. 55

moft important of the arts, die Management of
Heat !

Double windows have been in ufe many years
in moil of the northern parts of Europe, and their
great utility, in rendering the houfes furniflied with
them warm and comfortable in winter, is univer-
fally acknowledged, but I have never heard that
any body has thought of employing them in hot
countries to keep their apartments cool in fum-
me r ; yet how eafy and natural is this application
of fo iimple and fo ufeful * .an invention ! If a
double window can prevent the Heat which is in a
room from palling out of it, one would imagine it
could require no great effort of genius to difcover
that it would be equally efficacious for preventing
the Heat without from coming in. But natural as
this conclufion may appear, I believe it has never
yet occurred to any body ; at leaft, lam quite cer
tain that I have never feen a double window either
in Italy, or in any other hot country I have had oc-
cafion to vilit.

But the utility of double windows and double
walls, in hot as well as in cold countries, is a mat
ter of fo much importance that I mall take occafion
to treat it more fully in another place. In the
mean time, I mall only obferve here, that it is the
confined air fhut up between the two windows, and
not the double glafs plates, that renders the paflage
of Heat through them fo difficult. Were it owing
to the increafed thicknefs of the glafs, a fingle pane
of glafs twice as thick would anfwer the fame pur-

pofe;



5 5 Of the Management of Fire,

pofe : but the increafed thicknefs of the glafs of
which a window is formed, is not found to have
any fenfible effect in rendering a room w r armer.

But air is not only a non-conductor of heat, but
its non-conducting power may be greatly increafed.
To be able to form a juft idea of the manner in
which air may be rendered a worfe conductor of
Heat, or, which is the fame thing, a better non
conductor of it than it is in its natural unconfined
ftate, it will be neceffary to confider the manner in
which Heat pafles through air. Now it appears
from the refult of a number of Experiments which
I made with a view to the inveftigation of this fub-
ject, and which are publifhed in a paper read be
fore the Royal Society,* that though the particles
of air, each particle for* itfe/f, can receive Heat from
ether bodies, or communicate it to them, yet there is
no communication of Heat between one particle of
air and another particle of air. And from hence it
follows, that though air may, and certainly does,
carry off Heat, and tranfport it from one place, or
from one body to another, yet a mafs of air in a
quiefcent ftate, or with all its particles at reft,
could it remain in this Jiate, would be totally im
pervious to Heat ; or fuch a mafs of air would be a
perfect non-conductor.

Now if Heat paffes in a mafs of air merely in con-
fequence of the motion it occafions in that air, if
it is tranfported, not fuffered to pafs, in that cafe,

it

* See the Philofophical Tranfadion$, 1793.



and the Economy of Fuel. 57

it is clear that whatever can obftrucl and impede
the internal motion of the air, muft tend to dimi-
nifli its conducting power : And this I have found
to be the cafe in fad:. I found that a certain quan
tity of Heat which was able to make its way through
a wall, or rather a fheet of confined air an inch
thick in 9^ minutes, required 2 1 \ minutes to make
its way through the fame wall, when the internal
motion of this air was impeded by mixing with it
part of its bulk of eider-down, of very fine fur,
or of fine filk, as fpun by the worm.

But in mixing bodies with air, in order to im
pede its internal motion, and render it more fit for
confining Heat, fuch bodies only muft be chofen as
are themfelves non-conduclors of Heat, otherwife
they will do more harm than good, as I have found
by experience. When, inftead of making ufe of
eider-down, fur, or fine filk, for impeding the inter
nal motion of the confined air, I ufed an equal
volume of exceedingly fine filver-wire flatted, (be
ing the ravellings of gold or filver lace) the paflage
of the Heat through the barrier, fo far from being
impeded, was remarkably facilitated by this addi
tion ; the Heat pafling through this compound of
air and fine threads of metal much fooner than it
would have made its way through the air alone.

Another circumftance to be attended to in the
choice of a fubftance to be mixed with air, in order
to form a covering or barrier for confining Heat, is
the finenefs or fubtility of its parts ; for the finer
they are, the greater will be their furface in propor-
VOL. II. I tion



5 8 Of the Management of Fire,

tion to their folidity , and the more will they Impede
the motions of the particles of the air. Coarfe
horfe-hair would be found to anfwer much worfe
for this purpofe than the fine fur of a beaver,
though it is not probable that there is any effential
difference in the chymical properties of thofe two
kinds of hair.