edges of the hollow, and over the top of the partition: then lay
down your bottom plate in its place (with the rods in it) and tread
it till it lies firm. Then put a little fine mortar (made of loam
and lime, with a little hair) into its joints, and set in your back
plate, leaning it for the present against the false back: then set
in your air-box, with a little mortar in its joints; then put in the
two sides, closing them up against the air-box, with mortar in their
grooves, and fixing at the same time your register: then bring up
your back to its place, with mortar in its grooves, and that will
bind the sides together. Then put in your front plate, placing it
as far back in the groove as you can, to leave room for the sliding
plate: then lay on your top plate, with mortar in its grooves also,
screwing the whole firmly together by means of the rods. The capital
letters A B D E, &c. in Plate VIII., shew the corresponding parts of
the several plates. Lastly, the joints being pointed all round on the
outside, the fire-place is fit for use.
When you make your first fire in it, perhaps if the chimney be
thoroughly cold, it may not draw, the work too being all cold and
damp. In such case, put first a few shovels of hot coals in the
fire-place, then lift up the chimney-sweeper's trap-door, and putting
in a sheet or two of flaming paper, shut it again, which will set
the chimney a drawing immediately, and when once it is filled with a
column of warm air, it will draw strongly and continually.
The drying of the mortar and work by the first fire may smell
unpleasantly, but that will soon be over.
In some shallow chimneys, to make more room for the false back and
its flue, four inches or more of the chimney back may be picked away.
Let the room be made as tight as conveniently it may be, so will the
outer air, that must come in to supply the room and draught of the
fire, be all obliged to enter through the passage under the bottom
plate, and up through the air-box, by which means it will not come
cold to your backs, but be warmed as it comes in, and mixed with the
warm air round the fire-place, before it spreads in the room.
But as a great quantity of cold air, in extreme cold weather
especially, will presently enter a room if the door be carelessly
left open, it is good to have some contrivance to shut it, either by
means of screw hinges, a spring, or a pulley.
When the pointing in the joints is all dry and hard, get some
powder of black lead (broken bits of black lead crucibles from the
silver-smiths, pounded fine, will do) and mixing it with a little rum
and water, lay it on, when the plates are warm, with a hard brush,
over the top and front-plates, part of the side and bottom-plates,
and over all the pointing; and, as it dries, rub it to a gloss with
the same brush, so the joints will not be discerned, but it will look
all of a piece, and shine like new iron. And the false back being
plaistered and white-washed, and the hearth reddened, the whole will
make a pretty appearance. Before the black lead is laid on, it would
not be amiss to wash the plates with strong lee and a brush, or soap
and water, to cleanse them from any spots of grease or filth that may
be on them. If any grease should afterwards come on them, a little
wet ashes will get it out.
If it be well set up, and in a tolerable good chimney, smoke will
draw in from as far as the fore part of the bottom plate, as you may
try by a bit of burning paper.
People are at first apt to make their rooms too warm, not imagining
how little a fire will be sufficient. When the plates are no hotter
than that one may just bear the hand on them, the room will generally
be as warm as you desire it.
_Soon after the foregoing piece was published, some persons in
England, in imitation of Mr. Franklin's invention, made what they
call_ Pensylvanian Fire-places, with improvements; _the principal of
which pretended improvements is, a contraction of the passages in the
air-box, originally designed for admitting a quantity of fresh air,
and warming it as it entered the room. The contracting these passages
gains indeed more room for the grate, but in a great measure defeats
their intention. For if the passages in the air-box do not greatly
exceed in dimensions the amount of all the crevices by which cold air
can enter the room, they will not considerably prevent, as they were
intended to do, the entry of cold air through these crevices._
FOOTNOTES:
[44] Body or matter of any sort, is said to be _specifically_ heavier
or lighter than other matter, when it has more or less substance or
weight in the same dimensions.
[45] As the writer is neither physician nor philosopher, the reader
may expect he should justify these his opinions by the authority of
some that are so. M. Clare, F. R. S. in his treatise of _The Motion
of Fluids_, says, page 246, &c. "And here it may be remarked, that
it is more prejudicial to health to sit near a window or door, in
a room where there are many candles and a fire, than in a room
without; for the consumption of air thereby occasioned, will always
be very considerable, and this must necessarily be replaced by cold
air from without. Down the chimney can enter none, the stream of
warm air always arising therein absolutely forbids it, the supply
must therefore come in wherever other openings shall be found. If
these happen to be small, _let those who sit near them beware_; the
smaller the floodgate, the smarter will be the stream. Was a man,
even in a sweat, to leap into a cold bath, or jump from his warm bed,
in the intensest cold, even in a frost, provided he do not continue
over-long therein, and be in health when he does this, we see by
experience that he gets no harm. If he sits a little while against a
window, into which a successive current of cold air comes, his pores
are closed, and he gets a fever. In the first case, the shock the
body endures, is general, uniform, and therefore less fierce; in the
other, a single part, a neck, or ear perchance, is attacked, and that
with the greater violence probably, as it is done by a successive
stream of cold air. And the cannon of a battery, pointed against a
single part of a bastion, will easier make a breach than were they
directed to play singly upon the whole face, and will admit the enemy
much sooner into the town."
That warm rooms, and keeping the body warm in winter, are means of
preventing such diseases, take the opinion of that learned Italian
physician Antonino Parcio, in the preface to his tract _de Militis
Sanitate tuenda_, where, speaking of a particular wet and cold
winter, remarkable at Venice for its sickliness, he says, "Popularis
autem pleuritis quæ Venetiis sæviit mensibus _Dec. Jan. Feb._ ex
cæli, aërisque inclementia facta est, quod non habeant hypocausta
[_stove-rooms_] & quod non soliciti sunt Itali omnes de auribus,
temporibus, collo, totoque corpore defendendis ab injuriis aëris; et
tegmina domorum Veneti disponant parum inclinata, ut nives diutius
permaneant super tegmina. E contra, Germani, qui experiuntur cæli
inclementiam, perdidicere sese defendere ab aëris injuria. Tecta
construunt multum inclinata, ut decidant nives. Germani abundant
lignis, domusque _hypocaustis_; foris autem incedunt pannis
pellibus, gossipio, bene mehercule loricati atque muniti. In Bavaria
interrogabam (curiositate motus videndi Germaniam) quot nam elapsis
mensibus pleuritide vel peripneumonia fuissent absumti: dicebant vix
unus aut alter illis temporibus pleuritide fuit correptus."
The great Dr. Boerhaave, whose authority alone might be sufficient,
in his _Aphorisms_, mentions, as one antecedent cause of pleurisies,
"A cold air, driven violently through some narrow passage upon the
body, overheated by labour or fire."
The eastern physicians agree with the Europeans in this point;
witness the Chinese treatise entitled, _Tschang seng_; i.e. _The
Art of procuring Health and long Life_, as translated in Pere Du
Halde's account of China, which has this passage. "As, of all the
passions which ruffle us, anger does the most mischief, so of all
the malignant affections of the air, a wind that comes through any
narrow passage, which is cold and piercing, is most dangerous; and
coming upon us unawares insinuates itself into the body, often
causing grievous diseases. It should therefore be avoided, according
to the advice of the ancient proverb, as carefully as the point of an
arrow." These mischiefs are avoided by the use of the new-invented
fire-places, as will be shown hereafter.
[46] The shutter is slid up and down in this manner, only in those
fire-places which are so made as that the distance between the top of
the arched opening, and the bottom plate, is the same as the distance
between it and the top plate. Where the arch is higher, as it is in
the draught annexed (which is agreeable to the last improvements) the
shutter is set by, and applied occasionally; because if it were made
deep enough to close the whole opening when slid down, it would hide
part of it when up.
[47] My Lord Molesworth, in his account of Denmark, says, "That few
or none of the people there are troubled with coughs, catarrhs,
consumptions, or such like diseases of the lungs; so that in the
midst of winter in the churches, which are very much frequented,
there is no noise to interrupt the attention due to the preacher.
I am persuaded (says he) their _warm stoves_ contribute to their
freedom from these kind of maladies." page 91.
[48] People who have used these fire-places, differ much in their
accounts of the wood saved by them. Some say five-sixths, others
three-fourths, and others much less. This is owing to the great
difference there was in their former fires; some (according to the
different circumstances of their rooms and chimneys) having been used
to make very large, others middling, and others, of a more sparing
temper, very small ones: while in these fire-places (their size
and draught being nearly the same), the consumption is more equal.
I suppose, taking a number of families together, that two-thirds,
or half the wood, at least, is saved. My common room, I know, is
made thrice as warm as it used to be, with a quarter of the wood I
formerly consumed there.
[49] Mr. Boyle, in his experiments and observations upon cold,
_Shaw's Abridgement_, Vol. I. p. 684, says, "It is remarkable, that
while the cold has strange and tragical effects at Moscow, and
elsewhere, the Russians and Livonians should be exempt from them, who
accustom themselves to pass immediately from a great degree of heat,
to as great an one of cold, without receiving any visible prejudice
thereby. I remember being told by a person of unquestionable credit,
that it was a common practice among them, to go from a hot stove,
into cold water; the same was also affirmed to me by another who
resided at Moscow. This tradition is likewise abundantly confirmed by
Olearius."--"It is a surprising thing, says he, to see how far the
Russians can endure heat; and how, when it makes them ready to faint,
they can go out of their stoves, stark naked, both men and women, and
throw themselves into cold water; and even in winter wallow in the
snow."
[50] See page 240, where the trap-door is described that ought to be
in this closing.
TO DR. INGENHAUSZ, PHYSICIAN TO THE EMPEROR, AT VIENNA[51].
_On the Causes and Cure of Smoky Chimnies._
_At Sea, Aug., 28, 1785._
DEAR FRIEND,
In one of your letters, a little before I left France, you desire
me to give you in writing my thoughts upon the construction and use
of chimneys, a subject you had sometimes heard me touch upon in
conversation. I embrace willingly this leisure afforded by my present
situation to comply with your request, as it will not only show my
regard to the desires of a friend, but may at the same time be of
some utility to others; the doctrine of chimneys appearing not to
be as yet generally well understood, and mistakes respecting them
being attended with constant inconvenience, if not remedied, and with
fruitless expence, if the true remedies are mistaken.
Those who would be acquainted with this subject should begin by
considering on what principle smoke ascends in any chimney. At first
many are apt to think that smoke is in its nature and of itself
specifically lighter than air, and rises in it for the same reason
that cork rises in water. These see no case why smoke should not rise
in the chimney, though the room be ever so close. Others think there
is a power in chimneys to _draw_ up the smoke, and that there are
different forms of chimneys which afford more or less of this power.
These amuse themselves with searching for the best form. The equal
dimensions of a funnel in its whole length is not thought artificial
enough, and it is made, for fancied reasons, sometimes tapering and
narrowing from below upwards, and sometimes the contrary, &c. &c. A
simple experiment or two may serve to give more correct ideas. Having
lit a pipe of tobacco, plunge the stem to the bottom of a decanter
half filled with cold water; then putting a rag over the bowl, blow
through it and make the smoke descend in the stem of the pipe, from
the end of which it will rise in bubbles through the water; and being
thus cooled, will not afterwards rise to go out through the neck of
the decanter, but remain spreading itself and resting on the surface
of the water. This shows that smoke is really heavier than air, and
that it is carried upwards only when attached to, or acted upon, by
air that is heated, and thereby rarefied and rendered specifically
lighter than the air in its neighbourhood.
Smoke being rarely seen but in company with heated air, and its
upward motion being visible, though that of the rarefied air that
drives it is not so, has naturally given rise to the error.
I need not explain to you, my learned friend, what is meant by
rarefied air; but if you make the public use you propose of this
letter, it may fall into the hands of some who are unacquainted with
the term and with the thing. These then may be told, that air is a
fluid which has weight as well as others, though about eight hundred
times lighter than water. That heat makes the particles of air recede
from each other and take up more space, so that the same weight of
air heated will have more bulk, than equal weights of cold air which
may surround it, and in that case must rise, being forced upwards by
such colder and heavier air, which presses to get under it and take
its place. That air is so rarefied or expanded by heat may be proved
to their comprehension, by a lank blown bladder, which, laid before a
fire, will soon swell, grow tight and burst.
[Illustration: (remedies for smoky chimnies)
_Plate IX._ _Vol. II. page 269._
_Published as the Act directs, April 1, 1806, by Longman, Hurst, Rees
& Orme, Paternoster Row._]
Another experiment may be to take a glass tube about an inch in
diameter, and twelve inches long, open at both ends and fixed upright
on legs, so that it need not be handled, for the hands might warm it.
At the end of a quill fasten five or six inches of the finest light
filament of silk, so that it may be held either above the upper
end of the tube or under the lower end, your warm hand being at a
distance by the length of the quill. (Plate IX. fig. 1.) If there
were any motion of air through the tube, it would manifest itself
by its effect on the silk; but if the tube and the air in it are
of the same temperature with the surrounding air, there will be no
such motion, whatever may be the form of the tube, whether crooked
or strait, narrow below and widening upwards, or the contrary; the
air in it will be quiescent. Warm the tube, and you will find, as
long as it continues warm, a constant current of air entering below
and passing up through it, till discharged at the top; because the
warmth of the tube being communicated to the air it contains rarefies
that air and makes it lighter than the air without, which therefore
presses in below, forces it upwards, and follows and takes its place,
and is rarefied in its turn. And, without warming the tube, if you
hold under it a knob of hot iron, the air thereby heated will rise
and fill the tube, going out at its top, and this motion in the
tube will continue as long as the knob remains hot, because the air
entering the tube below is heated and rarefied by passing near and
over that knob.
That this motion is produced merely by the difference of specific
gravity between the fluid within and that without the tube, and not
by any fancied form of the tube itself, may appear by plunging it
into water contained in a glass jar a foot deep, through which such
motion might be seen. The water within and without the tube being
of the same specific gravity, balance each other, and both remain
at rest. But take out the tube, stop its bottom with a finger and
fill it with olive oil, which is lighter than water, then stopping
the top, place it as before, its lower end under water, its top a
very little above. As long as you keep the bottom stopt, the fluids
remain at rest, but the moment it is unstopt, the heavier enters
below, forces up the lighter, and takes its place. And the motion
then ceases, merely because the new fluid cannot be successively made
lighter, as air may be by a warm tube.
In fact, no form of the funnel of a chimney has any share in its
operation or effect respecting smoke, except its height. The longer
the funnel, if erect, the greater its force when filled with heated
and rarefied air, to _draw_ in below and drive up the smoke, if one
may, in compliance with custom, use the expression _draw_, when in
fact it is the superior weight of the surrounding atmosphere that
_presses_ to enter the funnel below, and so _drives up_ before it the
smoke and warm air it meets with in its passage.
I have been the more particular in explaining these first principles,
because, for want of clear ideas respecting them, much fruitless
expence has been occasioned; not only single chimneys, but in some
instances, within my knowledge, whole stacks having been pulled down
and rebuilt with funnels of different forms, imagined more powerful
in _drawing_ smoke; but having still the same height and the same
opening below, have performed no better than their predecessors.
What is it then which makes a _smoky chimney_, that is, a chimney
which, instead of conveying up all the smoke, discharges a part of it
into the room, offending the eyes and damaging the furniture?
The causes of this effect, which have fallen under my observation,
amount to _nine_, differing from each other, and therefore requiring
different remedies.
1. _Smoky chimneys in a new house, are such, frequently from mere
want of air._ The workmanship of the rooms being all good, and just
out of the workman's hand, the joints of the boards of the flooring,
and of the pannels of wainscotting are all true and tight, the more
so as the walls, perhaps not yet thoroughly dry, preserve a dampness
in the air of the room which keeps the wood-work swelled and close.
The doors and the sashes too, being worked with truth, shut with
exactness, so that the room is as tight as a snuff-box, no passage
being left open for air to enter, except the key-hole, and even that
is sometimes covered by a little dropping shutter. Now if smoke
cannot rise but as connected with rarefied air, and a column of such
air, suppose it filling the funnel, cannot rise, unless other air
be admitted to supply its place; and if, therefore, no current of
air enter the opening of the chimney, there is nothing to prevent
the smoke coming out into the room. If the motion upwards of the
air in a chimney that is freely supplied, be observed by the rising
of the smoke or a feather in it, and it be considered that in the
time such feather takes in rising from the fire to the top of the
chimney, a column of air equal to the content of the funnel must be
discharged, and an equal quantity supplied from the room below, it
will appear absolutely impossible that this operation should go on
if the tight room is kept shut; for were there any force capable of
drawing constantly so much air out of it, it must soon be exhausted
like the receiver of an air-pump, and no animal could live in it.
Those therefore who stop every crevice in a room to prevent the
admission of fresh air, and yet would have their chimney carry up
the smoke, require inconsistencies, and expect impossibilities.
Yet under this situation, I have seen the owner of a new house, in
despair, and ready to sell it for much less than it cost, conceiving
it uninhabitable, because not a chimney in any one of its rooms would
carry off the smoke, unless a door or window were left open. Much
expence has also been made, to alter and amend new chimneys which
had really no fault; in one house particularly that I knew, of a
nobleman in Westminster, that expence amounted to no less than three
hundred pounds, _after_ his house had been, as he thought, finished
and all charges paid. And after all, several of the alterations were
ineffectual, for want of understanding the true principles.
_Remedies._ When you find on trial, that opening the door or a
window, enables the chimney to carry up all the smoke, you may be
sure that want of air _from without_, was the cause of its smoking.
I say _from without_, to guard you against a common mistake of those
who may tell you, the room is large, contains abundance of air,
sufficient to supply any chimney, and therefore it cannot be that the
chimney wants air. These reasoners are ignorant, that the largeness
of a room, if tight, is in this case of small importance, since it
cannot part with a chimney full of its air without occasioning so
much vacuum; which it requires a great force to effect, and could not
be borne if effected.
It appearing plainly, then, that some of the outward air must be
admitted, the question will be, how much is _absolutely necessary_;
for you would avoid admitting more, as being contrary to one of your
intentions in having a fire, viz. that of warming your room. To
discover this quantity, shut the door gradually while a middling
fire is burning, till you find that, before it is quite shut, the
smoke begins to come out into the room, then open it a little till
you perceive the smoke comes out no longer. There hold the door, and
observe the width of the open crevice between the edge of the door
and the rabbit it should shut into. Suppose the distance to be half
an inch, and the door eight feet high, you find thence that your room
requires an entrance for air equal in area to ninety-six half inches,
or forty-eight square inches, or a passage of six inches by eight.
This however is a large supposition, there being few chimneys, that,
having a moderate opening and a tolerable height of funnel, will not
be satisfied with such a crevice of a quarter of an inch; and I have
found a square of six by six, or thirty-six square inches, to be a
pretty good medium, that will serve for most chimneys. High funnels,
with small and low openings, may indeed be supplied thro' a less
space, because, for reasons that will appear hereafter, the _force
of levity_, if one may so speak, being greater in such funnels, the
cool air enters the room with greater velocity, and consequently
more enters in the same time. This however has its limits; for
experience shows, that no increased velocity, so occasioned, has
made the admission of air through the key-hole equal in quantity to
that through an open door; though through the door the current moves
slowly, and through the key-hole with great rapidity.
It remains then to be considered how and where this necessary
quantity of air from without is to be admitted so as to be least
inconvenient. For if at the door, left so much open, the air thence
proceeds directly to the chimney, and in its way comes cold to your
back and heels as you sit before your fire. If you keep the door
shut, and raise a little the sash of your window, you feel the same
inconvenience. Various have been the contrivances to avoid this, such
as bringing in fresh air through pipes in the jams of the chimney,
which, pointing upwards, should blow the smoke up the funnel; opening
passages into the funnel above, to let in air for the same purpose.
But these produce an effect contrary to that intended: for as it
is the constant current of air passing from the room _through the
opening of the chimney_ into the funnel which prevents the smoke
coming out into the room, if you supply the funnel by other means or
in other ways with the air it wants, and especially if that air be
cold, you diminish the force of that current, and the smoke in its
effort to enter the room finds less resistance.