Chimney Fireplaces Chapter III

Buckley Rumford Company

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CHAP. III.

Of the Cause of the Ascent of Smoke. - Illustration of the Subject by familiar Comparisons and Experiments. - Of Chimneys which affect and cause each other to smoke. - Of Chimneys which smoke from Want of Air. - Of the Eddies of Wind which sometimes blow down Chimneys, and cause them to smoke.
THOUGH it was my wish to avoid all abstruse philosophical investigations in this essay, yet I feel that it is necessary to say a few words upon a subject generally considered as difficult to be explained, which is too intimately connected with the matter under consideration to be passed over in silence. - A knowledge of the cause of the ascent of smoke being indispensably necessary to those who engage in the improvement of fireplaces, or who are desirous of forming just ideas relative to the operations of fire and the management of heat, I shall devote a few pages to the investigation of that curious and interesting subject. And as many of those who may derive advantage from these inquiries are not much accustomed to philosophical disquisitions, and would not readily comprehend either the language or the diagrams commonly used by scientific writers to explain the phenomena in ques-
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tion, I shall take pains to express myself in the most familiar manner, and to use such comparisons for illustration as may easily be understood.
If small leaden bullets, or large goose-shot, be mixed with peas, and the whole well shaken in a bushel, the shot will separate from the peas, and will take its place at the bottom of the bushel; forcing, by its greater weight, the peas, which are lighter, to move upwards, contrary to their natural tendency, and take their places above.
If water and linseed oil, which is lighter than water, be mixed in a vessel by shaking them together, upon suffering this mixture to remain quiet the water will descend and occupy the bottom of the vessel, and the oil, being forced out of its place by the greater pressure downwards of the heavier liquid, will be obliged to rise and swim on the surface of the water.
If a bottle containing linseed oil be plunged in water with its mouth upwards, and open, the oil will ascend out of the bottle, and, passing upwards through the mass of water, in a continued stream, will spread itself over its surface.
In like manner, when two fluids of any kind, of different densities, come into contact, or are mixed with each other, that which is the lightest will be forced upwards by that which is the heaviest.
And as heat rarefies all bodies, fluids as well as solids, air as well as water or mercury, it follows that two portions of the same fluid, at different temperatures, being brought into contact with each
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other, that portion which is the hottest, being more rarified, or specifically lighter than that which is colder, must be forced upwards by this last. - And this is what always happens in fact.
When hot water and cold water are mixed, the hottest part of the mixture will be found to be at the surface above; - and when cold air is admitted into a warmed room, it will always be found to take its place at the bottom of the room, the warmer air being in part expelled, and in part forced upwards to the top of the room.
Both air and water being transparent and colourless fluids, their internal motions are not easily discovered by the sight; and when these motions are very slow, they make no impression whatever on any of our senses, consequently they cannot be detected by us without the aid of some mechanical contrivance: - But where we have reason to think that those motions exist, means should be sought, and may often be found, for rendering them perceptible.
If a bottle containing hot water tinged with logwood, or any other colouring drug, be immersed, with its mouth open, and upwards, into a deep glass jar filled with cold water, the ascent of the hot water from the bottle through the mass of cold water will be perfectly visible through the glass. - Now, nothing can be more evident than that both of these fluids are forced or pushed, and not drawn upwards. - Smoke is frequently said to be drawn up the chimney, - and that a chimney draws well or ill; - but
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these are careless expressions, and lead to very erroneous ideas respecting the cause of the ascent of smoke, and consequently tend to prevent the progress of improvements in the management of fires. - The experiment just mentioned with the coloured water is very striking and beautiful, and it is well calculated to give a just idea of the cause of the ascent of smoke. The cold water in the jar, which, in consequence of its superior weight or density, forces the heated and rarefied water in the bottle to give place to it, and to move upwards out of its way, may represent the cold air of the atmosphere, while the rising column of coloured water will represent the column of smoke which ascends from a fire.
If smoke required a chimney to draw it upwards, how happens it that smoke rises from a fire which is made in the open air, where there is no chimney?
If a tube, open at both ends, and of such a length that its upper end be below the surface of the cold water in the jar, be held vertically over the mouth of the bottle which contains the hot coloured water, the hot water will rise up through it, just as smoke rises in a chimney.
If the tube be previously heated before it is plunged into the cold water, the ascent of the hot coloured water will be facilitated and accelerated, in like manner as smoke is known to rise with greater facility in a chimney which is hot, than in one in which no fire has been made for a long time. - But in neither of these cases can it, with any
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propriety, be said that the hot water is drawn up the tube. - The hotter the water in the bottle is, and the colder that in the jar, the greater will be the velocity with which the hot water will be forced up through the tube; and the same holds of the ascent of hot smoke in a chimney. - When the fire is intense, and the weather very cold, the ascent of the smoke is very rapid; and under such circumstances chimneys seldom smoke.
As the cold water of the jar immediately surrounding the bottle which contains the hot water will be heated by the bottle, while the other parts of the water in the jar will remain cold, this water so heated, becoming specifically lighter than that which surrounds it, will be forced upwards; and if it finds its way into the tube will rise up through it with the coloured hot water. - The warmed air of a room heated by an open chimney fireplace has always a tendency to rise (if I may use that inaccurate expression), and, finding its way into the chimney, frequently goes off with the smoke.
What has been said will, I flatter myself, be sufficient to explain and illustrate, in a clear and satisfactory manner, the cause of the ascent of smoke; and just ideas upon that subject are absolutely necessary in order to judge, with certainty, of the merit of any scheme proposed for the improvement of fireplaces, or to take effectual measures, in all cases, for curing smoking chimneys. - For, though the perpetual changes and alterations which are produced by accident, whim, and caprice, do sometimes lead to useful discoveries, yet the progress
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of improvement under such guidance must be exceedingly slow, fluctuating, and uncertain.
As to the causes of the smoking of chimneys, they are very numerous and various; but as a general idea of them may be acquired from what has already been said upon that subject in various parts of this essay, and as they may, in all cases (a very few only excepted) be completely remedied by making the alterations in fireplaces here pointed out, I do not think it necessary to enumerate them all in this place, or to enter into those long details and investigations which would be required to show the precise manner in which each of them operates, either alone or in conjunction with others.
There is, however, one cause of smoking chimneys which I think it is necessary to mention more particularly. - In modern-built houses, where the doors and windows are generally made to close with such accuracy that no crevice is left for the passage of the air from without, the chimneys in rooms adjoining to each other, or connected by close passages, are frequently found to affect each other; and this is easy to be accounted for. - When there is a fire burning in one of the chimneys, as the air necessary to supply the current up the chimney where the fire burns cannot be had in sufficient quantities from without, through the very small crevices of the doors and windows, the air in the room becomes rarefied, not by heat, but by subtraction of that portion of air which is employed in keeping up the fire, or supporting the com-

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bustion of the fuel, and, in consequence of this rarefaction, its elasticity is diminished and being at last overcome by the pressure of the external air of the atmosphere, this external air rushes into the room by the only passage left for it, namely, by the open chimney of the neighbouring room; - And the flow of air into the fireplace, and up the chimney where the fire is burning, being constant, this expense of air is supplied by a continued current down the other chimney.
If an attempt be made to light fires in both chimneys at the same time, it will be found to be very difficult to get the fires to burn, and the rooms will both be filled with smoke.
One of the fires, - that which is made in the chimney where the construction of the fireplace is best adapted to facilitate the ascent of the smoke; or, if both fireplaces are on the same construction, that which has the wind most favourable, or in which the fire happens to be soonest kindled, - will overcome the other, and cause its smoke to be beat back into the room by the cold air which descends through the chimney. - The most obvious remedy in this case is to provide for the supply of fresh air necessary for keeping up the fires by opening a passage for the external air into the room by a shorter road than down one of the chimneys; and when this is done, both chimneys will be found to be effectually cured.
But chimneys so circumstanced may very frequently be prevented from smoking, even without opening any new passage for the external air,

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merely by diminishing the draught (as it is called) up the chimneys; which can best be done by altering both fireplaces upon the principles recommended and fully explained in the foregoing chapters of this essay.
Should the doors and windows of a room be closed with so much nicety as to leave no crevices by which a supply of air can enter sufficient for maintaining the fire, after the current of air up the chimney has been diminished as much as possible by diminishing the throat of the fireplace, in that case there would be no other way of preventing the chimney from smoking but by opening a passage for the admission of fresh air from without; - but this, I believe, will very seldom be found to be the case.
A case more frequently to be met with is, where currents of air set down chimneys in consequence of a diminution and rarefaction of the air in a room, occasioned by the doors of the room opening into passages or courts where the air is rarefied by the action of some particular winds. In such cases the evil may be remedied, either by causing the doors in question to close more accurately, or (which will be still more effectual) by giving a supply of air to the passage or court which wants it by some other way.
Where the top of a chimney is commanded by high buildings, by cliffs, or by high grounds, it will frequently happen, in windy weather, that the eddies formed in the atmosphere by these obstacles will blow down the chimney, and beat

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down the smoke into the room. - This, it is true, will be much less likely to happen when the throat of the chimney is contracted and properly formed than when it is left quite open, and the fireplace badly constructed; but as it is possible that a chimney may be so much exposed to these eddies in very high winds as to be made to smoke sometimes when the wind blows with violence from a certain quarter, it is necessary to show how the effects of those eddies may be prevented.
Various mechanical contrivances have been imagined for preventing the wind from blowing down chimneys, and many of them have been found to be useful; there are, however, many of these inventions, which, though they prevent the wind from blowing down the chimney, are so ill-contrived on other accounts as to obstruct the ascent of the smoke, and do more harm than good.
Of this description are all those chimney-pots with flat horizontal plates or roofs placed upon supporters just above the opening of the pot; and most of the caps which turn with the wind are not much better. - One of the most simple contrivances that can be made use of, and which in most cases will be found to answer the purpose intended as well or better than more complicated machinery, is to cover the top of the chimney with a hollow truncated pyramid or cone, the diameter of which above, or opening for the passage of the smoke, is about 10 or l 1 inches. - This pyramid, or cone (for either will answer), - should be of earthenware or of cast-iron; - its perpendicular height

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may be equal to the diameter of its opening above, and the diameter of its opening below equal to three times its height. - It should be placed upon the top of the chimney, and it may be contrived so as to make a handsome finish to the brick-work. - Where several flues come out near each other, or in the same stack of chimneys, the form of a pyramid will be better than that of a cone for these covers.
The intention of this contrivance is, that the winds and eddies which strike against the oblique surface of these covers may be reflected upwards, instead of blowing down the chimney. - The invention is by no means new, but it has not hitherto been often put in practice. - As often as I have seen it tried, it has been found to be of use; I cannot say, however, that I was ever obliged to have recourse to it, or to any similar contrivance; and if I forbear to enlarge upon the subject of these inventions, it is because I am persuaded that when chimneys are properly constructed in the neighbourhood of the fireplace, little more will be necessary to be done at the top of the chimney than to leave it open.
I cannot conclude this essay without again recommending, in the strongest manner, a careful attention to the management of fires in open chimneys; for not only the quantity of heat produced in the combustion of fuel depends much on the manner in which the fire is managed, but even of the heat actually generated a very small part

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only will be saved, or usefully employed, when the fire is made in a careless and slovenly manner.
In lighting a coal fire, more wood should be employed than is commonly used, and fewer coals; and as soon as the fire burns bright, and the coals are well lighted, and not before, more coals should be added to increase the fire to its proper size.*
* Kindling-balls, composed of equal parts of coal, charcoal, and clay, the two former reduced to a fine powder, well mixed and kneaded together with the clay moistened with water, and then formed into balls of the size of hens eggs, and thoroughly dried, might be used with great advantage instead of wood for kindling fires. These kindling balls may be made so inflammable as to take fire in an instant, and with the smallest spark, by dipping them in a strong solution of nitre and then drying them again; and they would neither be expensive nor liable to be spoiled by long keeping. Perhaps a quantity of pure charcoal, reduced to a very fine powder and mixed with the solution of nitre in which they are dipped, would render them still more inflammable.
I have often wondered that no attempts should have been made to improve the fires which are made in the open chimneys of elegant apartments, by preparing the fuel; for nothing surely was ever more dirty, inelegant, and disgusting than a common coal fire.
Fire-balls, of the size of goose-eggs, composed of coal and charcoal in powder, mixed up with a due proportion of wet clay, and well dried, would make a much more cleanly, and in all respects a pleasanter, fire than can be made with crude coals; and I believe would not be more expensive fuel. In Flanders and in several parts of Germany, and particularly in the Duchies of Juliers and Bergen, where coals are used as fuel, the coals are always prepared before they are used, by pounding them to a powder, and mixing them up with an equal weight of clay, and a sufficient quantity of water to form the whole into a mass which is kneaded together and formed into cakes; which cakes are afterwards well dried and kept in a dry place for use. And it has been found by long experience, that the expense attending this preparation is amply replid by the improvement of the fuel. The coals, thus mixed with clay, not only burn longer, but give much more heat than when they are burned in their crude state.
It will doubtless appear extraordinary to those who have not considered the subject with some attention, that the quantity ot heat produced in the combustion of any given quantity of coals should be increased by mixing the coals with clay, which is certainly an incombustible body; but the phenomenon may, I think, be explained in a satisfictory manner.
The heat generated in the combustion of any small particle of coal existing under two distinct forms, namely, in that which is combincd with the flame and smoke which rise from the fire, and which, if means are not found to stop it, goes off immediately by the chimney and is lost, and the radiant heat which is sent off from the fire, in all directions, in right lines; I think it reasonable to conclude, that the particles of clay, which are surrounded on all sides by the flame, arrest a part at least of the combined heat, and prevent its escape; and this combined heat so arrested, heating the clay red-hot, is retained in it, and, being changed by this operation to radiant heat, is afterwards emitted, and may be directed and employed to useful purposes.
In composing fire-balls, I think it probable that a certain proportion of chaff of straw cut very fine, or even of saw-dust might be employed with great advantage. I wish those who have leisure would turn their thoughts to this subject, for I am persuaded that very important improvements would result from a thorough investigation of it.
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The enormous waste of fuel in London may be estimated by the vast dark cloud which continually hangs over this great metropolis, and frequently overshadows the whole country, far and wide; for this dense cloud is certainly composed almost entirely of unconsumed coal, which, having stolen wings from the innumerable fires of this great city, has escaped by the chimneys, and continues to sail about in the air, till, having lost the heat which gave it volatility, it falls in a dry shower of extremely fine black dust to the ground, obscuring the atmosphere in its descent, and frequently changing the brightest day into more than Egyptian darkness.
I never view from a distance, as I come into town, this black cloud which hangs over London,
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without wishing to be able to compute the immense number of caldrons of coals of which it is composed; for, could this be ascertained, I am persuaded so striking a fact would awaken the curiosity and excite the astonishment of all ranks of the inhabitants, and perhaps turn their minds to an object of economy to which they have hitherto paid little attention.

Conclusion.

Though the saving of fuel which will result from the improvements in the forms of chimney fireplaces, here recommended, will be very considerable, yet I hope to be able to show in a future essay that still greater savings may be made, and more important advantages derived, from the introduction of improvements I shall propose in kitchen fireplaces.
I hope, likewise, to be able to show in an essay on cottage fireplaces, which I am now preparing for publication, that three quarters, at least, of the fuel which cottagers now consume in cooking their victuals and in warming their dwellings, may with great ease, and without any expensive apparatus, be saved.

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