and yet at no very great price; which could circumstances of your chimney considered.— not have been, if they had not universally used stoves, but consumed it as we do, in great quantities, by open fires. By the help of this saving invention our wood may grow as fast as we consume it, and our posterity may warm themselves at a moderate rate, without being obliged to fetch their fuel over the Atlantic; as, if pit-coal should not be here discovered (which is an uncertainty) they must necessarily do.* If the fire-place is to be put up in a chamber, you may have this communication of outer air from the staircase; or sometimes more easily from between the chamber floor, and the ceiling of the lower room, making only a small hole in the wall of the house entering the space betwixt those two joists with which your air-passage in the hearth communicates. If this air-passage be so situated as that mice may enter it, and nestle in the hollow, a litThis We leave it to the political arithmetician tle grate of wire will keep them out. 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 these fire-places. Directions to the Bricklayer. The chimney being first well swept and cleansed from soot, &c. lay the bottom plate down on the hearth, in the place where the fire-place is to stand, which may be as forward as the hearth will allow. Chalk a line from one of its back corners round the plate to the other corner, that you may afterwards knows its place when you come to fix it; and from those corners, two parallel lines to the back of the chimney: make marks also on each side, that you may know where the partition is to stand, which is to prevent any communication between the air and smoke. Then, removing the plate, make a hollow under it and beyond it, by taking up as many of the bricks or tiles as you can, within your chalked lines, quite to the chimney-back. Dig out six or eight inches deep of the earth or rubbish, all the breadth and length of your hollow; then make a passage of four inches square (if the place will allow so much) leading from the hollow to some place communicating with the outer air; by outer air we mean air without the room you intend to warm. This passage may be made to enter your hollow on either side, or in the fore part, just as you find most convenient, the * Pitcoal has been discovered since in great abundance in various parts of the United States. The mountains of Pennnsylvania contain vast treasures, which only require canals and roads to convey them in quantities sufficient for the supply of the whole continent. of the chimney, and then to close over the breast; always observing, if there is a wooden mantel-tree, to close above it. If there is no wood in the breast, you may arch over and close even with the lower part of the breast. By this closing the chimney is made tight, that no air or smoke can pass up it, without going under the false back. Then from side to side of your hollow, against the marks you made with chalk, raise a tight partition, brickon-edge, to separate the air from the smoke, bevelling away to half an inch the brick that comes just under the air-hole, that the air may have a free passage up into the air-box: lastly, close the hearth over that part of the hollow that is between the false back and the place of the bottom plate, coming about half an inch under the plate, which piece of hollow hearth may be supported by a bit or two of old iron-hoop; then is your chimney fitted to receive the fire-place. To set it, lay first a little bed of mortar all round the 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 coarse 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 * See page 396, where the trap-door is described that ought to be in this closing. 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 the annexed cut, show the corresponding parts of the several plates. Lastly, the joints being pointed all around on the outside, the fire-place is fit for use. 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. When you make your first fire in it, perhaps 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, made 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. continually. '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. 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. ror, at Vienna.* ̈ The 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 To Dr. Ingenhausz, Physician to the Empepassage 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 silversmiths, 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 plastered 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 VOL. II.... 3 E 34* On the Causes and Cure of Smoky Chimneys.— At Sea, Aug. 28, 1785. DEAR FRIEND,-In one of your letters, a little before I left France, you desired 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 not remedied, and with fruitless expense, 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 * This letter has been published in a separate pamphlet, in Germany, England, and America; it has also appeared in the Transactions of the American Philosophical Society. 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 arti ficial enough, and it is made, for fancied reasons, sometimes tapering and narrowing from below upwards, and sometimes the contrary, &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 up wards 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 terin 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. der the lower end, your warm hand being at a distance by the length of the quill. (See the plate, 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 ap pear 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. 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, 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 fasten 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 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. 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 air without occasioning so much vacuum; which it requires a great force to effect, and could not be borne if effected. 1. Smoky chimnies 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 wainscoting 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 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, then open 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 I knew, of a nobleman in Westminster, that It remains then to be considered how and where this necessary quantity of air from with outward air is best admitted, with which be ing mixed, its coldness is abated, and its inconvenience diminished so as to become scarce observable. This may be easily done, by drawing down about an inch the upper sash of a window; or, if not moveable, by cutting such a crevice through its frame; in both which cases, it will be well to place a thin shelf of the length, to conceal the opening, and sloping upwards to direct the entering air horizontally along and under the ceiling. In some houses the air may be admitted by such a crevice made in the wainscot, cornish, or plastering, near the ceiling and over the opening of the chimney. This, if practicable, is to be chosen, because the entering out 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 jambs 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 pre-cold air will there meet with the warmest vents 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. The wanted air must then indispensably be admitted into the room, to supply what goes off through the opening of the chimney. M. Gauger, a very ingenious and intelligent French writer on the subject, proposes with judgment to admit it above the opening of the chimney; and to prevent inconvenience from its coldness, he directs its being made to pass in its entrance through winding cavities made behind the iron back and sides of the fireplace, and under the iron hearth-plate; in which cavities it will be warmed, and even heated, so as to contribute much, instead of cooling, to the warming of the room. This invention is excellent in itself, and may be used with advantage in building new houses; because the chimney may then be so disposed as to admit conveniently the cold air to enter such passages: but in houses built without such views, the chimneys are often so situated as not to afford that convenience, without great and expensive alterations. Easy and cheap methods, though not quite so perfect in themselves, are of more general utility; and such are the following. In all rooms where there is a fire, the body of air warmed and rarefied before the chimney is continually changing place, and making room for other air that is to be warmed in its turn. Part of it enters and goes up the chimney, and the rest rises and takes place near the ceiling. If the room be lofty, that warm air remains above our heads as long as it continues warm, and we are little benefited by it, because it does not descend till it is cooler. Few can imagine the difference of climate between the upper and lower parts of such a room, who have not tried it by the thermometer, or by going up a ladder till their heads are near the ceiling. It is then among this warm air that the wanted quantity of rising air from before the fire, and be soonest tempered by the mixture. The same kind of shelf should also be placed here. Another way, and not a very difficult one, is to take out an upper pane of glass in one of your sashes, set in a tin frame, (Plate, Fig. 2.) giving it two springing angular sides, and then replacing it, with hinges below on which it may be turned to open more or less above. It will then have the appearance of an internal skylight. By drawing this pane in, more or less, you may admit what air you find necessary. Its position will naturally throw that air up and along the ceiling. This is what is called in France a Was ist das? As this is a German question, the invention is probably of that nation, and takes its name from the frequent asking of that question when it first appeared. In England, some have of late years cut a round hole about five inches diameter in a pane of the sash and placed against it a circular plate of tin hung on an axis, and cut into vanes, which, being separately bent a little obliquely, are acted upon by the entering air, so as to force the plate continually round like the vanes of a windmill. This admits the outward air, and by the continual whirling of the vanes, does in some degree disperse it. The noise only, is a little inconvenient. 2. A second cause of the smoking of chimneys is, their openings in the room being too large; that is, too wide, too high, or both. Architects in general have no other ideas of proportion in the opening of a chimney, than what relate to symmetry and beauty, respecting the dimensions of the room :* while its true proportion, respecting its function and utility, depends on quite other principles; and they might as properly proportion the step in a stair-case to the height of the story, instead of the natural elevation of men's legs in mounting. The proportion then to be regarded, is what relates to the height of the funnel. For as the funnels in the different stories of See Notes at the end of this paper, No. I. |