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and yet at no very great price; which could circumstances of your chimney considered. not have been, if they had not universally If the fire-place is to be put up in a chamber, used stoves, but consumed it as we do, in great you may have this communication of outer air quantities, by open fires. By the help of this from the staircase; or sometimes more easisaving invention our wood may grow as fastly from between the chamber floor, and the as we consume it, and our posterity may warm ceiling of the lower room, making only a small themselves at a moderate rate, without being hole in the wall of the house entering the obliged to fetch their fuel over the Atlantic; space betwixt those two joists with which as, if pit-coal should not be here discovered your air-passage in the hearth communicates. (which is an uncertainty) they must necessa- If this air-passage be so situated as that mice rily do.*
may enter it, and nestle in the hollow, a litWe leave it to the political arithmetician tle grate of wire will keep them out. This to compute how much money will be saved passage being made, and, if it runs under any to a country, by its spending two thirds less part of the hearth, tiled over securely, you of fuel; how much labour saved in cutting may proceed to raise your false back. This and carriage of it; how much more land may may be of four inches or two inches thickbe cleared by cultivation ; how great the pro- ness, as you have room, but let it stand at fit by the additional quantity of work done, in least four inches from the true chimney-back. those trades particularly that do not exercise In narrow chimneys this false back runs from the body so much, but that the workfolks are jamb to jamb, but in large old-fashioned chimobliged to run frequently to the fire to warm neys, you need not make it wider than the themselves : and to physicians to say, how back of the fire-place. To begin it, you may much healthier thick-built towns and cities form an arch nearly flat, of three bricks end will be, now half suffocated with sulphury to end, over the hollow, to leave a passage smoke, when so much less of that smoke shall the breadth of the iron fire-place, and five or be made, and the air breathed by the inhabi- six inches deep, rounding at bottom, for the tants be consequently so much purer. These smoke to turn and pass under the false back, things it will suffice just to have mentioned; and so behind it up the chimney. The false let us proceed to give some necessary direc-back is to rise till it is as high as the breast tions to the workman who is to fix or set up of the chimney, and then to close over the these fire-places.
breast;* always observing, if there is a wooden Directions to the Bricklayer.
mantel-tree, to close above it. If there is no
wood in the breast, you may arch over and The chimney being first well swept and close even with the lower part of the breast. cleansed from soot, &c. lay the bottom plate By this closing the chimney is made tight, down on the hearth, in the place where the that no air or smoke can pass up-it, without fire-place is to stand, which may be as for- going under the false back. Then from side ward as the hearth will allow. Chalk a line to side of your hollow, against the marks you from one of its back corners round the plate made with chalk, raise a tight partition, brickto the other corner, that you may afterwards on-edge, to separate the air from the smoke, knows its place when you come to fix it; and bevelling away to half an inch the brick that from those corners, two parallel lines to the comes just under the air-hole, that the air back of the chimney: make marks also on may have a free passage up into the air-box: each side, that you may know where the par- lastly, close the hearth over that part of the tition is to stand, which is to prevent any hollow that is between the false back and the communication between the air and smoke. place of the bottom plate, coming about half Then, removing the plate, make a hollow un- an inch under the plate, which piece of holder it and beyond it, by taking up as many of low hearth may be supported by a bit or two the bricks or tiles as you can, within your of old iron-hoop; then is your chimney fitted chalked lines, quite to the chimney-back. Dig to receive the fire-place. out six or eight inches deep of the earth or
To set it, lay first a little bed of mortar all rubbish, all the breadth and length of your round the edges of the hollow, and over the hollow; then make a passage of four inches top of the partition : then lay down square (if the place will allow so much) lead- tom plate in its place (with the rods in it) and
boting from the hollow to some place communi- tread it till it lies firm. Then put a little fine cating with the outer air ; by outer air we mortar (ináde of loam and lime, with a little mean air without the room you intend to coarse hair) into its joints, and set in your
This passage may be made to enter back plate, leaning it for the present against your hollow on either side, or in the fore the false back: then set in your air-box, with part, just as you find most convenient, the a little mortar in its joints ; then put in the two
* Pitcoal has been discovered since in great abundance sides, closing them up against the air-box, with in various parts of the United States, The mountains mortar in their grooves, and fixing at the same of Pennnsylvania contain vast treasures, which only require canals and roads to convey them in quantities * See page 396, where the trap.door is described that sufficient for the supply of the whole continent. ought to be in this closing.
time your register : then bring up your back to them from any spots of grease or filth that may its place, with mortar in its grooves, and that be on them. If any grease should afterwards will bind the sides together. Then put in come on them, a little wet ashes will get it your front plate, placing it as far back in the out. groove as you can, to leave room for the slid If it be well set up, and in a tolerable good ing plate: then lay on your top plate, with chimney, smoke will draw in from as far as mortar in its grooves also, screwing the whole the fore part of the bottom plate, as you may firmly together by means of the rods. The try by a bit of burning paper. capital letters A B D E, &c. in the annexed People are at first apt to make their rooms cut, show the corresponding parts of the se. too warm, not imagining how little a fire will veral plates. Lastly, the joints being pointed be sufficient. When the plates are no hotter all around on the outside, the fire-place is fit than that one may just bear the hand on them,
the room will generally be as warm as you deWhen you make your first fire in it, per- sire it. haps if the chimney be thoroughly cold, it may Soon after the foregoing piece was pubnot draw, the work too being all cold and lished, some persons in England, in imidamp. In such case, put first a few shovels tation of Dr. Franklin's invention, of hot coals in the fire-place, then lift up the what they call Pennsylvanian Fire-Places, chimney-sweeper's trap-door, and putting in a with improvements; the principal of which sheet or two of flaming paper, shut it again, pretended improvements is, a contraction of which will set the chimney a drawing imme- the passages in the air-box, originally dediately, and when once it is filled with a co signed for admitting a quantity of fresh air, lumn of warm air, it will draw strongly and and warming it as it entered the room. The continually.
'contracting these passages gains indeed more The drying of the mortar and work by the room for the grate, but in a great measure first fire may smell unpleasantly, but that will defeats their intention. For if the passages soon be over.
in the air-box do not greatly exceed in diIn some shallow chimneys, to make more mensions the amount of all the crevices by room for the false back and its flue, four inches which cold air can enter thè, room, they will or more of the chimney back may be picked not considerably prevent, as they were intendo away.
ed to do, the entry of cold air through these Let the room be made as tight as conve- crevices. niently 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 To Dr. Ingenhausz, Physician to the Empepassage under the bottom plate, and up
ror, at Vienna.* through the air-box, by which means it will on the Causes and Cure of Smoky Chimneys.not come cold to your backs, but be warmed
Read in the American Philosophical Society, as it comes in, and mixed with the warm air
Oct. 21, 1785. round the fire-place, before it spreads in the
At Sea, Aug. 28, 1785.
DEAR FRIEND,—In one of your letters, a But as a great quantity of cold air, in ex- little before I left France, you desired me to treme cold weather especially, will present give you in writing my thoughts upon the ly enter a room if the door be carelessly left construction and use of chimneys, a subject open, it is good to have some contrivance to you had sometimes heard me touch upon in shut it, either by means of screw hinges, a conversation. I embrace willingly this leispring, or a pulley.
sure afforded by my present situation to comWhen the pointing in the joints is all dry ply with your request, as it will not only show and hard, get some powder of black lead my regard to the desires of a friend, but may (broken bits of black lead crucibles from the at the same time be of some utility to others; silversmiths, pounded fine, will do) and mix- the doctrine of chimneys appearing not to be ing it with a little rum and water, lay it on, as yet generally well understood, and miswhen the plates are warm, with a hard brush, takes respecting them being attended with over the top and front plates, part of the side constant inconvenience, if not not remedied, and bottom plates, and over all the pointing; and with fruitless expense, if the true remeand, as it dries, rub it to a gloss with the dies are mistaken. same brush, so the joints will not be discerned, Those who would be acquainted with this but it will look all of a piece, and shine like subject should begin by considering on what new iron. And the false back being plaster principle smoke ascends in any chimney. At ed and white-washed, and the hearth redden- first many are apt to think that smoke is in ed, the whole will make a pretty appearance. Before the black lead is laid on, it would not * This letter has been published in a separate be amiss to wash the plates with strong lee pamphlet, in Germany, England, and America; it has
also appeared in the Transactions of the American Phiand a, brush, or soap and water, to cleanse I losophical Society. VOL. II....3 E
its nature and of itself specifically lighter than | der the lower end, your warm hand being at air, and rises in it for the same reason that a distance by the length of the quill(See cork rises in water. These see no case why the plate, fig. 1.) If there were any motion of smoke should not rise in the chimney, though air through the tube, it would manifest itself the room be ever so close. Others think there by its effect on the silk; but if the tube and is a power in chimneys to draw up the smoke, the air in it are of the same temperature with and that there are different forms of chimneys the surrou ling air, there will be no such mowhich afford more or less of this power. tion, whatever may be the form of the tube, These amuse themselves with searching for whether crooked or strait, narrow below and the best form. The equal dimensions of a widening upwards, or the contrary; the air funnel in its whole length is not thought arti- | in it will be quiescent. Warm the tube, and ficial enough, and it is made, for fancied rea- you will find, as long as it continues warm, a sons, sometimes tapering and narrowing from constant current of air entering below and below upwards, and sometimes the contrary, passing up through it, till discharged at the &c. A simple experiment or two may serve top; because the warmth of the tube being to give more correct ideas. Having lit a pipe communicated to the air it contains, rarefies of tobacco, plunge the stem to the bottom of a that air and makes it lighter than the air decanter half filled with cold water; then without, which therefore presses in below, putting a rag over the bowl, blow through it forces it upwards, and follows and takes its and make the smoke descend in the stem of place, and is rarefied in its turn. And, withthe pipe, from the end of which it will rise in out warming the tube, if you hold under it a bubbles through the water; and being thus knob of hot iron, the air thereby heated will cooled, will not afterwards rise to go out rise and fill the tube, going out at its top, through the neck of the decanter, but remain and this motion in the tube will continue as spreading itself and resting on the surface of long as the knob remains hot, because the air the water. This shows that smoke is really entering the tube below is heated and rarefied heavier than air, and that it is carried up by passing near and over that knob. wards only when attached to, or acted upon, That this motion is produced merely by the by air that is heated, and thereby rarefied and difference of specific gravity between the fluid rendered specifically lighter than the air in its within and that without the tube, and not by neighbourhood.
any fancied form of the tube itself, may apSmoke being rarely seen but in company pear by plunging it into water contained in a with heated air, and its upward motion being glass jar a foot deep, through which such movisible, though that of the rarefied air that tion might be seen. The water within and drives it is not so, has naturally given rise to without the tube being of the same specific the error.
gravity, balance each other, and both remain 1. I need not explain to you, my learned friend, at rest. But take out the tube, stop its bottom what is meant by rarefied air; but if you with a finger and fill it with olive oil, which make the public use you propose of this letter, is lighter than water, then stopping the top, it
may fall into the hands of some who are un- place it as before, its lower end under water, acquainted with the terin and with the thing: its top a very little above. As long as you These then may be told, that air is a fluid keep the bottom stopt, the fluids remain at which has weight as well as others, though rest, but the moment it is unstopt, the heavier about eight hundred times lighter than water. enters below, forces up the lighter, and takes That heat makes the particles of air recede its place. And the motion then ceases, merely from each other and take up more space, so because the new fluid cannot be successively that the same weight of air heated will have made lighter, as air may be by a warm tube. more bulk, than equal weights of cold air In fact, no form of the funnel of a chimney which may surround it, and in that case must has any share in its operation or effect respectrise, being forced upwards by such colder and ing smoke, except its height. The longer the heavier air, which presses to get under it and funnel, if erect, the greater its force when take its place. That air is so rarefied or ex- filled with heated and rarefied air, to draw in panded by heat may be proved to their com- below and drive up the smoke, if one may, in prehension, by a lank blown bladder, which, compliance with custom, use the expression laid before a fire, will soon swell, grow tight, draw, when in fact it is the superior weight and burst.
of the surrounding atmosphere that presses to Another experiment may be to take a glass enter the funnel below, and so drives up betube about an inch in diameter, and twelve fore it the smoke and warm air it meets with inches long, open at both ends and fixed up in its passage. right on legs, so that it need not be handled, I have been the more particular in explainfor the hands might warm it. At the end of ing these first principles, because, for want of a quill fastén five or six inches of the finest clear ideas respecting them, much fruitless exlight filament of silk, so that it may be held pense has been occasioned ; not only single either above the upper end of the tube or un- chimneys, but in some instances, within my
knowledge, whole stacks having been pulled expense amounted to no less than three hundown and rebuilt with funnels of different dred pounds, after his house had been, as he forms, imagined more powerful in drawing thought, finished, and all charges paid. And smoke; but having still the same height and after all, several of the alterations were inefthe same opening below, have performed no fectual, for want of understanding the true better than their predecessors.
principles. What is it then which makes a smoky chim Remedies. When you find on trial, that ney, that is, a chimney which, instead of con- opening the door or a window, enables the veying up all the smoke, discharges a part of chimney to carry up all the smoke, you may it into the room, offending the eyes and da- be sure that want of air from without was the maging the furniture ?
cause of its smoking. I say from without, to The causes of this effect, which have fallen guard you against a common mistake of those under my observation, amount to nine, differ- who may tell you, the room is large, contains ing from each other, and therefore requiring abundance of air, sufficient to supply any different remedies.
chimney, and therefore it cannot be that the 1. Smoky chimnies in a new house, are chimney wants air. These reasoners are igsuch, frequently from mere want of air. The norant, that the largeness of a room, if tight, workmanship of the rooms being all good, and is in this case of small importance, since it just out of the workman's hand, the joints of cannot part with a chimney full of air withthe boards of the flooring, and of the pannels out occasioning so much vacuum; which it of wainscoting are all true and tight, the more requires a great force to effect, and could not so as the walls, perhaps not yet thoroughly be borne if effected. dry, preserve a dampness in the air of the room It appearing plainly, then, that some of the which keeps the wood-work swelled and close. outward air must be admitted, the question The doors and the sashes too, being worked will be, how much is absolutely necessary ; with truth, shut with exactness, so that the for you would avoid admitting more, as being room is as tight as a snuff box, no passage be- contrary to one of your intentions in having a ing left open for air to enter, except the key- fire, viz. that of warming your room. To dishole, and even that is sometimes covered by a cover this quantity, shut the door gradually little dropping shutter. Now if smoke cannot while a middling fire is burning, till you find rise but as connected with rarefied air, and a that, before it is quite shut, the smoke begins column of such air, suppose it filling the fun- to come out into the room,
it a little nel, cannot rise, unless other air be admitted till you perceive the smoke comes out no to supply its place; and if, therefore, no cur- longer. There hold the door, and observe the rent of air enter the opening of the chimney, width of the open crevice between the edge there is nothing to prevent the smoke coming of the door and the rabbit it should shut into. out into the room. If the motion upwards of Suppose the distance to be half an inch, and the air in a chimney that is freely supplied, the door eight feet high, you find thence that be observed by the raising of the smoke or a your room requires an entrance for air equal feather in it, and it be considered that in the in area to ninety-six half inches, or forty-eight time such feather takes in rising from the fire square inches, or a passage of six inches by to the top of the chimney, a column of air equal eight. This, however, is a large supposition, to the content of the funnel must be discharged, there being few chimneys, that, having a moand an equal quantity supplied from the room derate opening and a tolerable height of funnel, below, it will appear absolutely impossible that will not be satisfied with such a crevice of a this operation should go on if the tight room quarter of an inch; and I have found a square is kept shut; for were there any force capable of six by six, or thirty-six square inches, to be of drawing constantly so much air out of it, it a pretty good medium that will serve for most must soon be exhausted like the receiver of chimneys. High funnels, with small and low. an air-pump, and no animal could live in it. openings, may indeed be supplied through a Those therefore who stop every crevice in a less space, because for reasons that will appear room to prevent the admission of fresh air, and hereafter, the force of levity, if one may so yet would have their chimney carry up the speak, being greater in such funnels, the cool smoke, require inconsistencies, and expect im- air enters the room with greater velocity, and possibilities. Yet under this situation, I have consequently more enters in the same time.seen the owner of a new house, in despair, This however has its limits, for experience and ready to sell it for much less than it cost, shows, that no increased velocity, so occasioned, conceiving it uninhabitable, because not a has made the admission of air through the keychimney in any one of its rooms would carry hole equal in quantity to that through an off the smoke, unless a door or window were open door; though through the door the curleft open. Much expense has also been made, rent moves slowly, and through the keyhole to alter and amend new chimneys which had with great rapidity. really no fault; in one house particularly that It remains then to be considered how and I knew, of a nobleman in Westminster, that I where this necessary quantity of air from with
out is to be admitted so as to be least incon- outward air is best admitted, with which bevenient. For if at the door, left so much open, ing mixed, its coldness is abated, and its inthe air thence proceeds directly to the chim- convenience diminished so as to become ney, and in its way comes cold to your back scarce observable. This may be easily done, and heels as you sit before your fire. If you by drawing down about an inch the upper keep the door shut, and raise a little the sash sash of a window; or, if not moveable, by of your window, you feel the same inconveni- cutting such a crevice through its frame; in
Various have been the contrivances both which cases, it will be well to place a to avoid this, such as bringing in fresh air thin shelf of the length, to conceal the openthrough pipes in the jambs of the chimney, ing, and sloping upwards to direct the enterwhich, pointing upwards, should blow the ing air horizontally along and under the ceil, smoke up the funnel; opening passages into ing. In some houses the air may be admitted the funnel above, to let in air for the same pur- by such a crevice made in the wainscot, corpose. But these produce an effect contrary to nish, or plastering, near the ceiling and over that intended; for as it is the constant current the opening of the chimney. This, if practiof air passing from the room through the open- cable, is to be chosen, because the entering ing of the chimney into the funnel which pre-cold air will there meet with the warmest vents the smoke coming out into the room, if you rising air from before the fire, and be soonest supply the funnel by other means or in other tempered by the mixture. The same kind ways with the air it wants, and especially if of shelf should also be placed here. Another that air be cold, you diminish the force of that way, and not a very difficult one, is to take current, and the smoke in its effort to enter out an upper pane of glass in one of your the room finds less resistance.
sashes, set in a tin frame, (Plate, Fig. 2.) givThe wanted air must then indispensably be ing it two springing angular sides, and then admitted into the room, to supply what goes replacing it, with hinges below on which it off through the opening of the chimney. M. may be turned to open more or less above. It Gauger, a very ingenious and intelligent will then have the appearance of an internal French writer on the subject, proposes with skylight. By drawing this pane in, more or judgment to admit it above the opening of the less, you may admit what air you find neceschimney; and to prevent inconvenience from sary. Its position will naturally throw that its coldness, he directs its being made to pass air up and along the ceiling. This is what is in its entrance through winding cavities made called in France a Was ist das ? As this is a behind the iron back and sides of the fire- German question, the invention is probably of place, and under the iron hearth-plate; in that nation, and takes its name from the frewhich cavities it will be warmed, and even quent asking of that question when it first heated, so as to contribute much, instead of appeared. In England, some have of late cooling, to the warming of the room. This years cut a round hole about five inches diainvention is excellent in itself, and may be meter in a pane of the sash and placed against used with advantage in building new houses; it a circular plate of tin hung on an axis, and because the chimney may then be so disposed cut into vanes, which, being separately bent as to admit conveniently the cold air to enter a little obliquely, are acted upon by the ensuch passages: but in houses built without tering air, so as to force the plate continually such views, the chimneys are often so situated round like the vanes of a windmill. This ad. as not to afford that convenience, without mits the outward air, and by the continual great and expensive alterations. Easy and whirling of the vanee, does in some degree cheap methods, though not quite so perfect in disperse it. The noise only, is a little inconthemselves, are of more general utility; and venient. such are the following.
2. A second cause of the smoking of chimIn all rooms where there is a fire, the body neys is, their openings in the room being of air warmed and rarefied before the chim- too large; that is, too wide, too high, or both. ney is continually changing place, and mak- Architects in general have no other ideas of ing room for other air that is to be warmed proportion in the opening of a chimney, than in its turn. Part of it enters and goes up the what relate to symmetry and beauty, respectchimney, and the rest rises and takes place ing the dimensions of the room :* while its true near the ceiling. If the room be lofty, that proportion, respecting its function and utility, warm air remains above our heads as long as depends on quite other principles; and they it continues warm, and we are little benefit- might as properly proportion the step in a ed by it, because it does not descend till it is stair-case to the height of the story, instead cooler. Few can imagine the difference of of the natural elevation of men's legs in climate between the upper and lower parts of mounting. The proportion then to be regardsuch a room, who have not tried it by the ed, is what relates to the height of the funnel. thermometer, or by going up a ladder till their For as the funnels in the different stories of heads are near the ceiling. It is then among this warm air that the wanted quantity of * See Notes at the end of this paper, No.