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ESSAYS, Political, Economical and Philosophical. Volume 1.
by Benjamin Rumford
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The whole of the combined heat escapes by the Chimney, and is totally lost; and, indeed, no part of it could ever be brought into a room from an open Fire-place, without bringing along with it the smoke with which it is combined; which, of course, would render it impossible for the room to be inhabited. There is, however, one method by which combining heat, and even that which arises from an open Fire-place, may be made to assist in warming a room; and that is by making it pass through something analogous to a German stove, placed in the Chimney above the fire.—But of this contrivance I shall take occasion to treat more fully hereafter; in the mean time I shall continue to investigate the properties of open Chimney Fire-places, constructed upon the most simple principles, such as are now in common use; and shall endeavour to point out and explain all those improvements of which THEY appear to me to be capable. When fuel is burnt in Fire-places upon this simple construction, where the smoke escapes immediately by the open canal of the Chimney, it is quite evident that all the combined heat must of necessity be lost; and as it is the radiant heat alone which can be employed in heating a room, it becomes an object of much importance to determine how the greatest quantity of it may be generated in the combustion of the fuel, and how the greatest proportion possible of that generated may be brought into the room.

Now the quantity of radiant heat generated in the combustion of a given quantity of any kind of fuel depends very much upon the management of the fire, or upon the manner in which the fuel is consumed. When the fire burns bright, much radiant heat will be sent off from it; but when it is SMOTHERED UP, very little will be generated; and indeed very little combined heat, that can be employed to any useful purpose: most of the heat produced will be immediately EXPENDED in giving elasticity to a thick dense vapour or smoke which will be seen rising from the fire; — and the combustion being very incomplete, a great part of the inflammable matter of the fuel being merely rarefied and driven up the Chimney without being inflamed, the fuel will be wasted to little purpose. And hence it appears of how much importance it is, whether it be considered with a view to economy, or to cleanliness, comfort, and elegance, to pay due attention to the management of a Chimney Fire.

Nothing can be more perfectly void of common sense, and wasteful and slovenly at the same time, than the manner in which Chimney Fires, and particularly where coals are burned, are commonly managed by servants. They throw on a load of coals at once, through which the flame is hours in making its way; and frequently it is not without much trouble that the fire is prevented from going quite out. During this time no heat is communicated to the room; and what is still worse, the throat of the Chimney being occupied merely by a heavy dense vapour, not possessed of any considerable degree of heat, and consequently not having much elasticity, the warm air of the room finds less difficulty in forcing its way up the Chimney and escaping, than when the fire burns bright;—and it happens not unfrequently, especially in Chimneys and Fire-places ill constructed, that this current of warm air from the room which presses into the Chimney, crossing upon the current of heavy smoke which rises slowly from the fire, obstructs it in its ascent, and beats it back into the room; hence it is that Chimnies so often smoke when too large a quantity of fresh coals is put upon the fire. So many coals should never be put on the fire at once as to prevent the free passage of the flame between them. In short, a fire should never be smothered; and when proper attention is paid to the quantity of coals put on, there will be very little use for the poker; and this circumstance will contribute very much to cleanliness, and to the preservation of furniture.

Those who have feeling enough to be made miserable by any thing careless, slovenly, and wasteful which happens under their eyes,—who know what comfort is, and consequence are worthy of the enjoyments of a CLEAN HEARTH and a CHEERFUL FIRE, should really either take the trouble themselves to manage their fires, (which, indeed, would rather be an amusement to them than a trouble,) or they should instruct their servants to manage them better.

But to return to the subject more immediately under consideration. As we have seen what is necessary to the production or generation of radiant heat, it remains to determine how the greatest proportion of that generated and sent off from the fire in all directions may be made to enter the room, and assist in warming it. How as the rays which are thrown off from burning fuel have this property in common with light, that they generate heat only WHEN and WHERE they are stopped or absorbed, and also in being capable of being reflected WITHOUT GENERATING at the surfaces of various bodies, the knowledge of these properties will enable us to take measures, with the utmost certainty, for producing the effect required,—that is to say, for bringing as much radiant heat as possible into the room.

This must be done, first, by causing as many as possible of the rays, as they are sent off from the fire in straight lines, to come DIRECTLY into the room; which can only be effected by bringing the fire as far forward as possible, and leaving the opening of the Fire-place as wide and as high as can be done without inconveniences; and secondly, by making the sides and back of the Fire-place of such form, and constructing them of such materials, as to cause the direct rays from the fire, which strike against them, to be sent into the room BY REFLECTION in the greatest abundance.

Now it will be found, upon examination, that the best form for the vertical sides of a Fire-place, or the COVINGS, (as they are called,) is that of an upright plane, making an angle with the plane of the back of the Fire-place, of about 135 degrees.— According to the present construction of Chimnies this angle is 90 degrees, or forms a right angle; but as in this case the two sides or covings of the Fire-place (AC, BD, Fig. 1.) are parallel to each other, it is evident that they are very ill contrived for throwing into the room by reflection the rays from the fire which fall on them.

To have a clear and perfect idea of the alterations I propose in the forms of Fire-places, the reader need only observe, that, whereas the backs of Fire-places, as they are now commonly constructed, are as wide as the opening of the Fire-place in front, and the sides of it are of course perpendicular to it, and parallel to each other,—in the Fire-places I recommend, the back (i k, Fig. 3) is only about one-third of the width of the opening of the Fire-place in front (a,b), and consequently that the two sides of covings of the Fire-place (a i and b k), instead of being perpendicular to the back, are inclined to it at an angle of about 135 degrees; and in consequence of this position, instead of being parallel to each other, each of them presents an oblique front towards the opening of the Chimney, by means of which the rays which they reflect are thrown into the room. A bare inspection of the annexed drawings (Fig. 1. and Fig. 3.) will render this matter perfectly clear and intelligible.

In regard to the materials which it will be most advantageous to employ in the construction of Fire-places, so much light has, I flatter myself, already been thrown on the subject we are investigating, and the principles adopted have been established on such clear and obvious facts, that no great difficulty will attend the determination of that point.—As the object in view is to bring radiant heat into the room, it is clear that that material is best for the construction of a Fire-place which reflects the most, or which ABSORBS THE LEAST of it; for that heat which is ABSORBED cannot be REFLECTED—Now as bodies which absorb radiant heat are necessarily heated in consequence of that absorption, to discover which of the various materials that can be employed for constructing Fire-places are best adapted for that purpose, we have only to find out by an experiment, very easy to be made, what bodies acquire LEAST HEAT when exposed to the direct rays of a clear fire;—for those which are least heated, evidently absorb the least, and consequently reflect the most radiant heat. And hence it appears that iron, and, in general, metals of all kinds, which are well known to GROW VERY HOT when exposed to the rays projected by burning fuel, are to be reckoned among the VERY WORST materials that it is possible to employ in the construction of Fire-places.

The best materials I have hitherto been able to discover are fire-stone, and common bricks and mortar. Both these materials are, fortunately, very cheap; and as to their comparative merits, I hardly know to which of them the preference ought to be given.

When bricks are used they should be covered with a thin coating of plaster, which, when it is become perfectly dry, should be white-washed. The fire-stone should likewise be white washed, when that is used; and every part of the Fire-place, which is not exposed to being soiled and made black by the smoke, should be kept as white and clean as possible. As WHITE reflects more heat, as well as more light than any other colour, it ought always to be preferred for the inside of a Chimney Fire-place, and BLACK, which reflects neither light nor heat should be most avoided.

I am well aware how much the opinion I have have ventured to give, respecting the unfitness of iron and other metals to be employed in the construction of open Fire-places, differs from the opinion generally received upon that subject;—and I even know that the very reason which, according to my ideas of the matter, renders them totally unfit for the purpose, is commonly assigned for making use of them, namely, that they soon grow very hot. But I would beg leave to ask what advantage is derived from heating them?

I have shown the disadvantage of it, namely, that the quantity of radiant heat thrown into the room is diminished;—and it is easy to show that almost the whole of that absorbed by the metal is ultimately carried up the Chimney by the air, which, coming into contact with this hot metal, is heated and rarefied by it, and forcing its way upwards, goes off with the smoke; and as no current of air ever sets from any part of the opening of a Fire-place into the room, it is impossible to conceive how the heat existing in the metal composing any part of the apparatus of the Fire-place, and situated within its cavity, can come, or be brought into the room.

This difficulty may be in part removed, by supposing, what indeed seems to be true in a certain degree, that the heated metal sends off rays, the heat it acquires from the fire, even when it is not heated red hot; but still, as it never can be admitted that the heat, absorbed by the metal and afterwards thrown off by it in rays, is INCREASED by this operation, nothing can be gained by it; and as much must necessary be lost in consequence of the great quantity of heat communicated by the hot metal to the air in contact with it, which, as has already been shown, always makes its way up the Chimney, and flies off into the atmosphere, the loss of heat attending the use of it is too evident to require being farther insisted on.

There is, however, in Chimney Fire-places destined for burning coals, one essential part, the grate, which cannot well be made of any thing else but iron; but there is no necessity whatever for that immense quantity of iron which surrounds grates as they are now commonly constructed and fitted up, and which not only renders them very expensive, but injures very essentially the Fire-place. If it should be necessary to diminish the opening of a large Chimney in order to prevent its smoking, it is much more simple, economical, and better in all respects, to do this with marble, fire-stone, or even with bricks and mortar, than to make use of iron, which, as has already been shown, is the very worst material that can possibly be employed for that purpose; and as to registers, they not only are quite unnecessary, where the throat of a Chimney is properly constructed, and of proper dimensions, but in that case would do much harm. If they act at all, it must be by opposing their flat surfaces to the current of rising smoke in a manner which cannot fail to embarrass and impede its motion. But we have shown that the passage of the smoke through the throat of a Chimney ought to be facilitated as much as possible, in order that it may be enabled to pass by a small aperture.

Register-stoves have often been found to be of use, but it is because the great fault of all Fire-places constructed upon the common principles being the enormous dimensions of the throat of the Chimney, this fault has been in some measure corrected by them; but I will venture to affirm, that there never was a Fire-place so corrected that would not have been much more improved, and with infinitely less expence, by the alterations here recommended, and which will be more particularly explained in the next Chapter.

CHAPTER. II.

Practical directions designed for the use of workmen, showing how they are to proceed in making the alterations necessary to improve chimney fire-places, and effectually to cure smoking chimnies.

All Chimney Fire-places, without exception, whether they are designed for burning wood or coals, and even those which do not smoke, as well as those which do, may be greatly improved by making the alterations in them here recommended; for it is by no means MERELY to prevent Chimnies from smoking that these improvements are recommended, but it is also to make them better in all other respects as Fire-places; and when the alterations proposed are properly executed, which may be very easily be done with the assistance of the following plain and simple directions, the Chimnies will never fail to answer, I will venture to say, even beyond expectation. The room will be heated much more equally and more pleasantly with LESS THAN HALF THE FUEL used before, the fire will be more cheerful and more agreeable; and the general appearance of the Fire-place more neat and elegant, and the Chimney WILL NEVER SMOKE.

The advantages which are derived from mechanical inventions and contrivances are, I know, frequently accompanied by disadvantages which it is not always possible to avoid; but in the case in question, I can say with truth, that I know of no disadvantage whatever that attends the Fire-places constructed upon the principles here recommended. —But to proceed in giving directions for the construction of these Fire-places.

That what I have to offer on this subject may be the more easily understood, it will be proper to begin by explaining the precise meaning of all those technical words and expressions which I may find it necessary or convenient to use.

By the THROAT of a Chimney, I mean the lower extremity of its canal, where it unites with the upper part of its open Fire-place. —This throat is commonly found about a foot above the level of the lower part of the mantle, and it is sometimes contracted to a smaller size than the rest of the canal of the Chimney, and sometimes not.

Fig. 5. shows the section of a Chimney on the common construction, in which d e is the throat.

Fig. 6. shows the section of the same Chimney altered and improved, in which d i is the reduced throat.

The BREAST of a Chimney, is that part of it which is immediately behind the mantle.—It is the wall which forms the entrance from below into the throat of the Chimney in front, or towards the room.—It is opposite to the upper extremity of the back of the open Fire-place, and parallel to it; in short it may said to be the back part of the mantle itself.—In the figures 5 and 6, it is marked by the letter d. The WIDTH of the throat of Chimney (d e fig. 5, and d i fig. 6,) is taken from the breast of the Chimney to the back, and its LENGTH is taken at right angles to its width, or in a line parallel to the mantle (a fig. 5. and 6.).

Before I proceed to give particular directions respecting the exact forms and dimensions of the different parts of a Fire-place, it may be useful to make such general an practical observations upon the subject as can be clearly understood without the assistance of drawings; for the more complete the knowledge of any subject is which can be acquired without drawings, the more easy will it be to understand the drawings when it becomes necessary to have recourse to them.

The bringing forward of the Fire into the room, or rather bringing it nearer to the front of the opening of the Fire-place;—and the diminishing of the throat of the Chimney, being two objects principally had in view in the alterations in Fire-places here recommended, it is evident that both these may be attained merely by bringing forward the back of the Chimney. —The only question therefore is, how far it should be brought forward?—The answer is short, and easy to be understood;—bring it forward as far as possible, without diminishing too much the passage which must be left for the smoke. Now as this passage, which, in its narrowest part, I have called the THROAT OF THE CHIMNEY, ought, for reasons which are fully explained in the foregoing Chapter, to be immediately, or perpendicularly over the Fire, it is evident that the back of the Chimney must always be built perfectly upright.—To determine therefore the place for the new back, or how far precisely it ought to be brought forward, nothing more is necessary than to ascertain how wide the throat of the Chimney ought to be left, or what space must be left, between the top of the breast of the Chimney, where the upright canal of the Chimney begins, and the new back of the Fire-place carried up perpendicularly to that height.

In the course of my numerous experiments upon Chimnies, I have taken much pains to determine the width proper to be given to this passage, and I have found, that, when the back of the Fire-place is of a proper width, the best width for the throat of a Chimney, when the Chimney and the Fire-place are at the usual form and size, is FOUR INCHES.—Three inches might sometimes answer, especially where the Fire-place is very small, and the Chimney good, and well situated: but as it is always of much importance to prevent those accidental puffs of smoke which are sometimes thrown into rooms by the carelessness of servants in putting on suddenly too many coals at once upon the fire, and as I found these accidents sometimes happened when the throats of Chimneys were made very narrow, I found that, upon the whole, all circumstances being well considered, and advantages and disadvantages compared and balanced, FOUR INCHES is the best width that can be given to the throat of a chimney; and this, whether the Fire-place be destined to burn wood, coals, turf, or any other fuel commonly used for heating rooms by an open fire.

In Fire-places destined for heating very large halls, and where very great fires are kept up, the throat of the Chimney may, if it should be thought necessary, be made four inches and an half, or five inches wide;—but I have frequently made Fire-places for halls which have answered perfectly well where the throats of the Chimnies have not been wider than four inches.

It may perhaps appear extraordinary, upon the first view of the matter, that Fire-places of such different sizes should all require the throat of the Chimney to be of the same width; but when it is considered that the CAPACITY of the throat of a Chimney does not depend on its width alone, but on its width and LENGTH taken together; and that in large Fire-places, the width of the back, and consequently the length of the throat of the Chimney, is greater than in those which are smaller, this difficulty vanishes.

And this leads us to consider another important point respecting open Fire-places, and that is, the width which it will, in each case, be proper to give to the back.—In Fire-places as they are now commonly constructed, the back is of equal width with the opening of the Fire-place in front;—but this construction is faulty on two accounts.—First, in a Fire-place, so constructed, the sides of the Fire-place, or COVINGS, as they are called, are parallel to each other, and consequently ill-contrived to throw out into the room the heat they receive from the fire in the form of rays;—and secondly, the large open corners which are formed by making the back as wide as the opening of the Fire-place in front occasion eddies of wind, which frequently disturb the fire, and embarrass the smoke in its ascent in such a manner as often to bring it into the room.—Both these defects may be entirely remedied by diminishing the width of the back of the Fire-place. —The width which, in most cases, it will be best to give it, is ONE THIRD of the width of the opening of the Fire-place in front.—But it is not absolutely necessary to conform rigorously to this decision, nor will it always be possible.—It will frequently happen that the back of a Chimney must be made wider than, according to the rule here given, it ought to be.—This may be, either to accommodate the Fire-place to a stove, which being already on hand, must, to avoid the expense of purchasing a new one, be employed; or for other reasons;—and any small deviation from the general rule will be attended with no considerable inconvenience.—It will always be best, however, to conform to it as far as circumstances will allow.

Where a Chimney is designed for warming a room of a middling size, and where the thickness of the wall of the Chimney in front, measured from the front of the mantle to the breast of the Chimney, is nine inches, I should set off four inches more for the width of the throat of the Chimney, which, supposing the back of the Chimney to be built upright, as it always ought to be, will give thirteen inches for the depth of the Fire-place, measured upon the hearth, from the opening of the Fire-place in front, to the back.—In this case thirteen inches would be a good size for the width of the back; and three times thirteen inches, or thirty-nine inches, for the width of the opening of the Fire-place in front; and the angle made by the back of the Fire-place and the sides of it, or covings, would be just 135 degrees, which is the best position they can have for throwing heat into the room.

But I will suppose that in altering such a Chimney it is found necessary, in order to accommodate the Fire-place to a grate or stove already on hand, to make the Fire-place sixteen inches wide. — In that case, I should merely increase the width of the back, to the dimensions required, without altering the depth of the Chimney, or increasing the width of the opening of the Chimney in front. —The covings, it is true, would be somewhat reduced in their width, by this alteration; and their position with respect to the plane of the back of the Chimney would be a little changed; but these alterations would produce no bad effects of any considerable consequence, and would be much less likely to injure the Fire-place, than an attempt to bring the proportions of its parts nearer to the standard, by increasing the depth of the Chimney, and the width of its opening in front;—or than an attempt to preserve that particular obliquity of the covings which is recommended as the best, (135 degrees,) by increasing the width of the opening of the Fire-place, without increasing its depth.

In order to illustrate this subject more fully, we will suppose one case more.—We will suppose that in the Chimney which is to be altered, the width of the Fire-place in front is either wider or narrower than it ought to be, in order that the different parts of the Fire-place, after it is altered, may be of the proper dimensions. In this case, I should determine the depth of the Fire-place, and the width of the back of it, without any regard to the width of the opening of the Fire-place in front; and when this is done, if the opening of Fire-place should be only two or three inches too wide, that is to say, only two or three inches wider than is necessary in order that the covings may be brought into their proper position with respect to the back, I should not alter the width of this opening, but should accommodate the covings to this width, by increasing their breadth, and increasing the angle they make with the back of the Fire-place; but if the opening of the Fire-place should be more than three inches too wide; —I should reduce it to the proper width by slips of stone, or by bricks and mortar.

When the width of the opening of the Fire-place, in front, is very great, compared with the depth of the Fire-place, and with the width of the back, the covings in that case being very wide, and consequently very oblique, and the Fire-place very shallow, any sudden motion of the air in front of the Fire-place, (that motion, for instance, which would be occasioned by the clothes of a woman passing hastily before the fire, and very near it,) would be apt to cause eddies in the air, WITHIN THE OPENING OF THE FIRE-PLACE, by which puffs of smoke might easily be brought into the room. Should the opening of the Chimney be too narrow, which however will very seldom be found to be the case, it will, in general, be advisable to let it remain as it is, and to accommodate the covings to it, rather to attempt to increase its width, which would be attended with a good deal of trouble, and probably a considerable expence.

From all that has been said it is evident, that the points of the greatest importance, and which ought most particularly to be attended to, in altering Fire-places upon the principles here recommended, are, the bringing forward the back to its proper place, and making it of a proper width.—But it is time that I should mention another matter upon which it is probable that my reader is already impatient to receive information.—Provision must be made for the passage of the Chimney-sweeper up the Chimney.—This may easily be done in the following manner:— In building up the new back of the Fire-place; when this wall, (which need never be more than the width of a single brick in thickness,) is brought up so high that there remains no more than about ten or eleven inches between what is then the top of it, and the inside of the mantle, or lower extremity of the breast of the Chimney, an opening, or door-way, eleven or twelve inches wide, must be begun in the middle of the back, and continued quite to the top of it, which, according to the height to which it will commonly be necessary to carry up the back, will make the opening about twelve or fourteen inches high; which will be quite sufficient to allow the Chimney-sweeper to pass. When the Fire-place is finished, this door-way is to be closed by a few bricks, by a tile, or a fit piece of stone, placed in it, dry, or without mortar, and confined in its place by means of a rabbet made for that purpose in the brick-work.—As often as the Chimney is swept, the Chimney-sweeper takes down this temporary wall, which is very easily done, and when he has finished his work, he puts it again into its place.—The annexed drawing (No. 6.) will give a clear idea of this contrivance; and the experience I have had of it has proved that it answers perfectly well the purpose for which it is designed.

I observed above, that the new back, which it will always be found necessary to build in order to bring the fire sufficiently forward, in altering a Chimney constructed on the common principles, need never be thicker than the width of a common brick.—I may say the same of the thickness necessary to be given to the new sides, or covings, of the Chimney; or if the new back and covings are constructed of stone, one inch and three quarters, or two inches in thickness will be sufficient.—Care should be taken in building up these new walls to unite the back to the covings in a solid manner.

Whether the new back and covings are constructed of stone, or built of bricks, the space between them, and the old back and covings of the Chimney ought to be filled up, to give greater solidity to the structure.—This may be done with loose rubbish, or pieces of broken bricks, or stones provided the work be strengthened by a few layers or courses of bricks laid in mortar; but it will be indispensably necessary to finish the work, where these new walls end, that is to say, at the top of the throat of the Chimney, where it ends abruptly in the open canal of the Chimney by a horizontal course of bricks well secured with mortar. —This course of bricks will be upon a level with the top of the door-way left for the Chimney-sweeper.

From these descriptions it is clear that where the throat of the Chimney has an end, that is to say, where it enters into the lower part of the open canal of the Chimney, THERE the three walls which form the two covings and the back of the Fire-place all end abruptly.—It is of much importance that they should end in this manner; for were they to be sloped outward and raised in such a manner as to swell out the upper extremity of the throat of the Chimney in the form of a trumpet, and increase it by degrees to the size of the canal of the Chimney, this manner of uniting the lower extremity of the canal of the Chimney with the throat would tend to assist the winds which may attempt to blow down the Chimney, in forcing their way through the throat, and throwing the smoke backward into the room; but when the throat of the Chimney ends abruptly, and the ends of the new walls form a flat horizontal surface, it will be much more difficult for any wind from above, to find, and force its way through the narrow passage of the throat of the Chimney.

As the two walls which form the new covings of the Chimney are not parallel to each other; but inclined, presenting an oblique surface towards the front of the Chimney, and as they are built perfectly upright and quite flat, from the hearth to the top of the throat, where they end, it is evident that an horizontal section of the throat will not be an oblong square; but its deviation from that form is a matter of no consequence; and no attempts should ever be made, by twisting the covings above, where they approach the breast of the Chimney, to bring it to that form.—All twists, bends, prominences, excavations, and other irregularities of form, in the covings of a Chimney, never fail to produce eddies in the current of air which is continually passing into, and through an open Fire-place in which a fire is burning;—and all such eddies disturb, either the fire, or the ascending currents of smoke, or both; and not unfrequently cause the smoke to be thrown back into the room.—Hence it appears, that the covings of Chimneys should never be made circular, or in the form of any other curve; but always quite flat.

For the same reason, that is to say, to prevent eddies, the breast of the Chimney, which forms that side of the throat that is in front, or nearest to the room, should be nearly cleaned off, and its surface made quite regular and smooth.

This may easily be done by covering it with a coat of plaster, which may be made thicker or thinner in different parts as may be necessary in order to bring the breast of the Chimney to be of the proper form.

With regard to the form of the breast of a Chimney, this is a matter of very great importance, and which ought always to be particularly attended to.—The worst form it can have is that of a vertical plane, or upright flat;—and next to this the worst form is an inclined plane.—Both these forms cause the current of warm air from the room, which will, in spite of every precaution, sometimes find its way into the Chimney, to cross upon the current of smoke, which rises from the fire, in a manner most likely to embarrass it in its ascent, and drive it back. —The inclined plane which is formed by a flat register placed in the throat of a Chimney produces the same effects; and this is one reason, among many others, which have induced me to disapprove of register stoves.

The current of air, which, passing under the mantle, gets into the Chimney, should be made GRADUALLY TO BEND ITS COURSE UPWARDS, by which means it will be QUIETLY with the ascending current of smoke, and will be less likely to check it, or force it back into the room.—Now this may be effected with the greatest ease and certainty, merely by ROUNDING OFF the breast of the Chimney or back part of the mantle, instead of leaving it flat, or full of holes and corners; and this of course ought always to be done.

I have hitherto given no precise directions in regard to the height to which the new back and covings ought to be carried:— This will depend not only on the height of the mantle, but also, and more especially, on the height of the breast of the Chimney, or of that part of the Chimney where the breast ends and the upright canal begins.—The back and covings must rise a few inches, five or six for instance, higher than this part, otherwise the throat of the Chimney will not be properly formed:—but I know of no advantages that would be gained by carrying them up still higher.

I mentioned above, that the space between the walls which form the new back and covings, and the old back and sides of the Fire-place, should be filled up:—but this must not be understood to apply to the space between the wall of dry bricks, or the tile which closes the passage for the Chimney-sweeper, and the old back of the Chimney; for that space must be left void, otherwise, though this tile (which at most will not be more than two inches in thickness,) were taken away, there would not be any room sufficient for him to pass.

In forming this door-way, the best method of proceeding is to place the tile or flat piece of stone destined for closing it, in its proper place; and to build round it, or rather by the sides of it; taking care not to bring any mortar near it, in order that it may be easily removed when the door-way is finished.—With regard to the rabbet which should be made in the door-way to receive it and fix it more firmly in its place, this may either be formed at the same time when the door-way is built, or it may be made after it is finished, by attaching to its bottom and sides, with strong mortar, pieces of thin roof tiles. Such as are about half an inch in thickness will be best for this use; if they are thicker, they will diminish too much the opening of the door-way, and will likewise be more liable to be torn away by the Chimney-sweeper in passing up and down the Chimney.

It will hardly be necessary for me to add, that the tile, or flat stone, or wall of dry bricks, which is used for closing up the door-way, must be of sufficient height to reach quite up to a level with the top of the walls which form the new back and covings of the Chimnies.

I ought, perhaps, to apologize for having been so very particular in these description and explanations, but it must be remembered that this chapter is written principally for the information of those who, having had few opportunities of employing their attention in abstruse philosophical researches, are not sufficiently practised in these intricate investigations, to seize, with facility, new ideas;—and consequently, that I have frequently been obliged TO LABOUR to make myself understood.

I have only to express my wishes that my reader may not be more FATIGUED with this labour than I have been;—for we shall them most certainly be satisfied with each other.—But to return once more to the charge.

There is one important circumstance respecting Chimney Fire-places, destined for burning coals, which still remains to be farther examined;—and that is the Grate.

Although there are few grates that may not be used in Chimneys constructed or altered upon the principles here recommended, yet they are not, by any means, all equally well adapted for that purpose.—Those whose construction is the most simple, and which of course are the cheapest, are beyond comparison the best, ON ALL ACCOUNTS.—Nothing being wanted in these Chimnies but merely a grate for containing the coals, and in which they will burn with a clear fire;—and all additional apparatus being, not only useless, but very pernicious, all complicated and expensive grates should be laid aside, and such as more simple substituted in the room of them.—And in the choice of a grate, as in every thing else, BEAUTY and ELEGANCE may easily be united with the MOST PERFECT SIMPLICITY.—Indeed they are incompatible with every thing else.

In placing the grate, the thing principally to be attended to is, to make the back of it coincide with the back of the Fire-place;— but as many of the grates now in common use will be found to be too large, when the Fire-places are altered and improved, it will be necessary to diminish their capacities by filling them up at the back and the sides with pieces of fire-stone. When this is done, it is the front of the flat piece of fire-stone which is made to form a new back to the grate, which must be made to coincide with, and make part of the back, of the Fire-place.— But in diminishing the capacities of grates with pieces of fire-stone, care must be taken not to make them TOO NARROW.

The proper width for grates destined for rooms of a middling size will be from six to eight inches, and their length may be diminished more or less, according as the room is heated with more or less difficulty, or as the weather is more or less severe. —But where the width of a grate is not more than five inches, it will be very difficult to prevent the fire from going out.

It goes out for the same reason that a live coal from the grate that falls upon the hearth soon ceases to be red hot;—it is cooled by the surrounding cold air of the atmosphere.— The knowledge of the cause which produces this effect is important, as it indicates the means which may be used for preventing it. —But of this subject I shall treat more fully hereafter.

It frequently happens that the iron backs of grates are not vertical, or upright, but inclined backwards.—When these grates are so much too wide as to render it necessary to fill them up behind with fire-stone, the inclination of the back will be of little consequence; for by making the piece of stone with which the width of the grate is to be diminished in the form of a wedge, or thicker above than below, the front of this stone, which in effect will become the back of the grate, may be made perfectly vertical; and the iron back of the grate being hid in the solid work of the back of the Fire-place, will produce no effect whatever; but if the grate be already so narrow as not to admit of any diminution of its width, in that case it will be best to take away the iron back of the grate entirely, and fixing the grate firmly in the brick-work, cause the back of the Fire-place to serve as a back to the grate.—This I have very frequently done, and have always found it to answer perfectly well.

Where it is necessary that the fire in a grate should be very small, it will be best, in reducing the grate with fire-stone, to bring its cavity, destined for containing the fuel, to the form of one half of a hollow hemisphere; the two semicircular openings being one above, to receive the coals, and the other in front, or towards the bars of the grate; for when the coals are burnt in such a confined space, and surrounded on all sides, except in the front and above, by fire-stone, (a substance peculiarly well adapted for confining heat,) the heat of the fire will be concentrated, and the cold air of the atmosphere being kept at a distance, a much smaller quantity of coals will burn, than could possibly be made to burn in a grate where they would be more exposed to be cooled by the surrounding air, or to have their heat carried off by being in contact with iron, or with any other substance through which heat passes with greater facility than through fire-stone.

Being persuaded that if the improvements in Chimney Fire-places here recommended should be generally adopted, (which I cannot help flattering myself will be the case,) that it will become necessary to reduce, very considerably, the sizes of grates, I was desirous of showing how this may, with the greatest safety and facility, be done.

Where grates, which are designed for rooms of a middling size, are longer than 14 or 15 inches, it will always be best, not merely to diminish their lengths, by filling them up at their two ends with fire-stone, but, forming the back of the Chimney of a proper width, without paying any regard to the length of the grate, to carry the covings through the two ends of the grate in such a manner as to conceal them, or at least to conceal the back corners of them in the walls of the covings.

I cannot help flattering myself that the directions here given in regard to the alterations which it may be necessary to make in Fire-places, in order to introduce the improvements proposed, will be found to be so perfectly plain and intelligible that no one who reads them will be at any loss respecting the manner in which the work is to be performed; — but as order and arrangement tend much to facilitate all mechanical operations, I shall here give a few short directions respecting the manner of LAYING OUT THE WORK, which may be found useful, and particularly to gentlemen who may undertake to be their own architects, in ordering and directing the alterations to be made for the improvement of their Fire-places.

Directions for laying out the Work.

If there be a grate in the Chimney which is to be altered, it will always be best to take it away; and when this is done, the rubbish must be removed, and the hearth swept perfectly clean.

Suppose the annexed figure No. 1. to represent the ground plan of such a Fire-place; A B being the opening of it in front, A C and B D the two sides or covings, and C D the back.

Figure 2. shows the elevation of this Fire-place.

First draw a strait line, with chalk, or with a lead pencil, upon the hearth, from one jamb to the other,—even with the front of the jambs. The dotted line A B, figure 3, may represent this line.

From the middle C of this line, (A B) another line c d, is to be drawn perpendicular to it, across the hearth, to the middle d, of the back of the Chimney.

A person must now stand upright in the Chimney, with his back to the back of the Chimney, and hold a plumb-line to the middle of the upper part of the breast of the Chimney (d, fig. 5,) or where the canal of the Chimney begins to rise perpendicularly;— taking care to place the line above in such a manner that the plumb may fall on the line c d, draw on the hearth from the middle of the opening of the Chimney in front to the middle of the back, and an assistant must mark the precise place e, on that line where the plumb falls.

This being done, and the person in the Chimney having quitted his station, four inches are to be set off the line c d, from e, towards d; and the point f, where these four inches end, (which must be marked with chalk, or with a pencil,) will show how far the new back is to be brought forward.

Through f, draw the line g h, parallel to the line A B, and this line g h will show the direction of the new back, or the ground line upon which it is to be built.

The line c f will show the depth of the new Fire-place; and if it should happen that c f is equal to about ONE-THIRD of the line A B; and if the grate can be accommodated to the Fire-place instead of its being necessary to accommodate the Fire-place to the grate, in that case, half the length of the line c f, is to be set off from f on the line g f h, on one side to k, and on the other to i, and the line i k will show the ground line of the fore part of the back of the Chimney.

In all cases where the width of the opening of the Fire-place in front (A B) happens to be not greater, or not more than two or three inches greater than THREE TIMES the width of the new back of the Chimney (i k), this opening may be left, and lines drawn from i to A, and from k to B, will show the width and position of the front of the new covings;—but when the opening of the Fire-place in front is still wider, it must be reduced; which is to be done in the following manner:

From c, the middle of the line A B, c a and c b, must be set off equal to the width of the back (i k), added to half its width (f i), and lines drawn from i to a, and from k to b, will show the ground plan of the fronts of the new covings.

When this is done, nothing more will be necessary than to build up the back and covings; and if the Fire-place is designed for burning coals, to fix the grate in its proper place, according to the directions already given.—When the width of the Fire-place is reduced, the edges of the covings a A and b B are to make a finish with the front of the jambs.—And in general it will be best, not only for the sake of the appearance of the Chimney, but for other reasons also, to lower the height of the opening of the Fire-place, whenever its width in front is diminished.

Fig. 4. shows a front view of the Chimney after it has been altered according to the directions here given.—By comparing it with fig. 2. (which shows a front view of the same Chimney before it was altered), the manner in which the opening of the Fire-place in front is diminished may be seen.—In fig. 4. the under part of the door-way by which the Chimney-sweeper gets up the Chimney is represented by white dotted lines. The door-way is represented closed.

I shall finish this chapter with some general observations relative to the subject under consideration; with directions how to proceed where such local circumstances exist as render modifications of the general plan indispensably necessary.

Whether a Chimney be designed for burning wood upon the hearth, or wood, or coals in a grate, the form of the Fire-place is in my opinion, most perfect when THE WIDTH OF THE BACK is equal to the DEPTH OF THE FIRE-PLACE, and the opening of the Fire-place in front equal to THREE TIMES the width of the back, or, which is the same thing, to THREE TIMES THE DEPTH OF THE FIRE-PLACE.

But if the Chimney be designed for burning wood upon the hearth, upon hand irons, or dogs, as they are called, it will sometimes be necessary to accommodate the width of the back to the length of the wood; and when this is the case, the covings must be accommodated to the width of the back, and the opening of the Chimney in front.

When the wall of the Chimney in front, measured from the upper part of the breast of the Chimney to the front of the mantle, is very thin, it may happen, and especially in Chimnies designed for burning wood upon the hearth, or upon dogs, that the depth of the Chimney, determined according to the directions here given, may be too small.

Thus, for example, supposing the wall of the Chimney in front, from the upper part of the breast of the Chimney to the front of the mantle, to be only four inches, (which is sometimes the case, particularly in rooms situated near the top of a house,) in this case, if we take four inches for the width of the throat, this will give eight inches only for the depth of the Fire-place, which would be too little, even were coals to be burnt instead of wood.—In this case I should increase the depth of the Fire-place at the hearth to 12 or 13 inches, and should build the back perpendicular to the height of the top of the burning fuel, (whether it be wood burnt upon the hearth, or coals in a grate,) and then, sloping the back by a gentle inclination forward, bring it to its proper place, that is to say, PERPENDICULARLY UNDER THE BACK OF THE THROAT OF THE CHIMNEY. This slope, (which will bring the back forward four or five inches, or just as much as the depth of the Fire-place is encreased,) though it ought not to be too abrupt, yet it ought to be quite finished at the height of eight or ten inches above the fire, otherwise it may perhaps cause the Chimney to smoke; but when it is very near the fire, the heat of the fire will enable the current of rising smoke to overcome the obstacle which this slope will oppose to its ascent, which it could not do so easily were the slope situated at a greater distance from the burning fuel[2].

Fig. 7, 8, and 9, show a plan, elevation, and section of a Fire-place constructed or altered upon this principal.—The wall of the Chimney in front at a, fig. 9, being only four inches thick, four inches more added to it for the width of the throat would have left the depth of the Fire-place measured upon the hearth b c only eight inches, which would have been too little;—a niche c and e, was therefore made in the new back of the Fire-place for receiving the grate, which niche was six inches deep in the center of it, below 13 inches wide, (or equal in width to the grate,) and 23 inches high; finishing above with a semicirular arch, which, in its highest part, rose seven inches above the upper part of the grate.—The door-way for the Chimney-sweeper, which begins just above the top of the niche, may be seen distinctly in both the figures 8 and 9.—The space marked g, fig. 9, behind this door-way, may either be filled with loose bricks, or may be left void.—The manner in which the piece of stone f, fig. 9, which is put under the mantle of the Chimney to reduce the height of the opening of the Fire-place, is rounded off on the inside in order to give a fair run to the column of smoke in its ascent through the throat of the Chimney, is clearly expressed in this figure.

The plan fig. 7, and elevation fig. 8, show how much the width of the opening of the Fire-place in front is diminished, and how the covings in the new Fire-place are formed.

A perfect idea of the form and dimension of the Fire-place in its original state, as also after its alteration, may be had by careful inspection of these figures.

I have added the drawing fig. 10, merely to show how a fault, which I have found workmen in general whom I have employed in altering Fire-places are very apt to commit, is to be avoided. —In Chimneys like that represented in this figure, where the jambs A and B project far into the room, and where the front edge of the marble slab, o which forms the coving, does not come so far forward as the front of the jambs, the workmen in constructing the new covings are very apt to place them,—not in the line c A, which they ought to do,—but in the line c o, which is a great fault.—The covings of a Chimney should never range BEHIND the front of the jambs, however those jambs may project into the room;—but it is not absolutely necessary that the covings should MAKE A FINISH with the internal front corners of the jambs, or that they should be continues from the back c, quite to the front of the jambs at A.—They may finish in front at a and b, and small corners A, o, a, may be left for placing the shovels, tongs, etc.

Were the new coving to range with the front edge of the old coving o, the obliquity of the new coving would commonly be too great;—or the angle d c o would exceed 135 degrees, WHICH IT NEVER SHOULD DO,—or at least never by more than a very few degrees.

No inconvenience of any importance will arise from making the obliquity of the covings LESS than what is here recommended; but many cannot fail to be produced by making it much greater;— and as I know from experience that workmen are very apt to do this, I have thought it necessary to warn them particularly against it.

Fig. 11. shows how the width and obliquity of the covings of a Chimney are to be accommodated to the width of the back, and to the opening in front and depth of the Fire-place, where the width of the opening of the Fire-place is less than three times the width of the new back. As all those who may be employed in altering Chimneys may not, perhaps, known how to set off an angle of any certain numbers of degrees,—or may not have at hand the instruments necessary for doing it,—I shall here show how an instrument may be made which will be found to be very useful in laying out the work for the bricklayers.

Upon a board about 18 inches wide and four feet long, or upon the floor or a table, draw three equal squares A, B, C, fig. 12. of about 12 or 14 inches each side, placed in a strait line, and touching each other.—From the back corner c of the center square B, draw a diagonal line across the square A, to its outward front corner f, and the adjoining angle formed by the lines d c and c f will be equal to 135 degrees,—the angle which the plane of the back of a Chimney Fire-place ought to make with the plane of its covings.—And a bevel m, n, being made to this angle with thin slips of hard wood, this little instrument will be found to be very useful in marking out on the hearth, with chalk, the plans of the walls which are to form the covings of Fire-places.

As Chimneys which are apt to smoke will require the covings to be placed less obliquely in respect to the back than others which have not that defect, it would be convenient to be provided with several bevels;—three or four, for instance, forming different angles.—That already described, which may be called No. 1. will measure the obliquity of the covings when the Fire-place can be made of the most perfect form:—another No. 2. may be made to a smaller angle, d c e,—and another No. 3. for Chimnies which are very apt to smoke at the still smaller angle d c i.—Or a bevel may be so contrived, by means of a joint, and an arch, properly graduated, as to serve for all the different degrees of obliquity which it may ever be necessary to give to the covings of Fire-places.

Another point of much importance, and particularly in Chimneys which are apt to smoke, is to form the throat of the Chimney properly, by carrying up the back and covings to a proper height. This, workmen are apt to neglect to do, probably on account of the difficulty they find in working where the opening of the canal of the Chimney is so much reduced.—But it is absolutely necessary that these walls should be carried up five or six inches at least above the upper part of the breast of the Chimney, or to that point where the wall which forms the front of the throat begins to rise perpendicularly. —If the workman has intelligence enough to avail himself of the opening which is formed in the back of the Fire-place to give a passage to the Chimney-sweeper, he will find little difficulty in finishing his work in a proper manner.

In placing the plumb-line against the breast of the Chimney, in order to ascertain how far the new back is to be brought forward, great care must be taken to place it at the very top of the breast, where the canal of the Chimney BEGINS TO RISE PERPENDICULARLY; otherwise, when the plumb-line is placed too low, or against the slope of the breast, when the new back comes to be raised to its proper height, the throat of the Chimney will found to be too narrow.

Sometimes, and indeed very often the top of the breast of a Chimney lies very high, or far above the fire (see the figures 13 and 14, where d shows the top of the breast of the Chimney); when this is the case it must be brought lower, otherwise the Chimney will be very apt to smoke.—So much has been said in the First Chapter of this Essay of the advantages to be derived from bringing the throat of a Chimney near to the burning fuel, that I do not think it necessary to enlarge on them in this place,— taking it for granted that the utility and necessity of that arrangement have already been made sufficiently evident;— but a few directions for workmen, to show them how the breast (and consequently the throat) of a Chimney can most readily be lowered, may not be superfluous.

Where the too great height of the breast of a Chimney is owing to the great height of the mantle, (see fig. 13,) or, which is the same thing, of the opening of the Fire-place in front, which will commonly be found to be the case; the only remedy for the evil will be to bring down the mantle lower;—or rather, to make the opening of the Fire-place in front lower, by throwing across the top of this opening, from one jamb to the other, and immediately under the mantle, a very flat arch;—a wall of bricks and mortar, supported on straight bars of iron;—or a piece of stone (h, fig. 13).—When this is done, the slope of the old throat of the Chimney, or of the back side of the mantle, is to be filled up with plaster, so as to form one continued flat, vertical, or upright plane surface with the lower part of the wall of the canal of the Chimney, and a new breast is to be formed lower down, care being taken to round it off properly, and make it finish at the lower surface of the new wall built under the mantle;—which wall forms in fact a new mantle.

The annexed drawing fig. 13, which represents the section of a Chimney in which the breast has been lowered according to the method here described, will show these various alterations in a clear and satisfactory manner. In this figure, as well as in most of the others in this Essay, the old walls are distinguished from the new ones by the manner in which they are shaded;— the old walls being shaded by diagonal lines, and the new ones by vertical lines. The additions, which are formed of plaster, are shaded by dots instead of lines.

Where the too great height of the breast of a Chimney is occasioned, not by the height of the mantle, but by the too great width of the breast, in that case, (which however will seldom be found to occur,) this defect may be remedied by covering the lower part of the breast with a thick coating of plaster, supported, if necessary, by nails or studs, driven into the wall which forms the breast, and properly rounded off at the lower part of the mantle.—See fig. 14.

CHAPTER. III.

Of the cause of the ascent of smoke. Illustration of the subject by familiar comparisons and experiments. Of chimnies which affect and cause each other to smoke. Of chimnies which smoke from want of air. Of the eddies of wind which sometimes blow down chimnies, and cause them to smoke. Explanation of the figures.

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 Fire-places, 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 phaenomena in question, 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 quite, 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 ascent 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 other, that portion which is the hottest being more rarefied 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 log-wood, 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 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 a 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 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 Fire-place 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 Fire-places; or to take effectual measures, in all cases, for curing smoking Chimnies.—For though the perpetual changes and alterations which are produced by accident, whim, and caprice, do sometimes lead to useful discoveries, yet the progress of improvement under such guidance must be exceedingly slow, fluctuating, and uncertain.

As to the causes of the smoking of Chimnies, 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 Fire-places 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 Chimnies 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 Chimnies 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 Chimnies, 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 combustion 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 Fire-place, and up the Chimney where the fire is burning being constant, this expence of air is supplied by a continued current down the other Chimney.

If an attempt be made to light fires in both Chimnies 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 Fire-place is best adapted to facilitate the ascent of the Smoke,—or if both Fire-places 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 Chimnies; and when this is done, both Chimnies will be found to be effectually cured.

But Chimnies so circumstanced may very frequently be prevented from smoking even without opening any new passage for the external air, merely by diminishing the draught, (as it is called,) up the Chimnies; which can best be done by altering both Fire-places 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 FIRE-PLACE; 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 Chimnies 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 clifts, 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 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 Fire-place 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 Chimnies, 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 11 inches. —This pyramid, or cone, (for either will answer,)—should be of earthen ware, or of cast iron;—its perpendicular height 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 flews come out near each other, or in the same stack of Chimnies, 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 Chimnies are properly constructed IN THE NEIGHBOURHOOD OF THE FIRE-PLACE 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 Chimnies; for not only the quantity of heat produced on 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 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[3].

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 Chimnies, 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, without wishing to be able to compute the immense number of chaldrons 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 FIRE-PLACES 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 FIRE-PLACES.

I hope likewise to be able to show in an Essay on COTTAGE FIRE-PLACES, 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.

END OF THE FOURTH ESSAY.

EXPLANATION OF THE FIGURES

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Fig. 1. The plan of a Fire-place on the common construction. A B, the opening of the Fire-place in front. C D, the back of the Fire-place. A C and B D, the covings. See page 341.

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Fig. 2. This figure shows the elevation, or front view of a Fire-place on the common construction. See page 341.

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Fig. 3. This Figure shows how the Fire-place represented by the Fig. 1, is to be altered in order to its being improved.

A B is the opening in front,—C D, the back, and A C and B D, the covings of the Fire-place in its original state.

a b, its opening in front,—i k, its back,—and a i and b k, its covings after it has been altered, e is a point upon the hearth upon which a plum suspended from the middle of the upper part of the breast of the Chimney falls. The situation for the new back is ascertained by taking the line e f equal to four inches. The new back and covings are represented as being built of bricks;—and the space between these and the old back and covings as being filled up with rubbish. See page 342.

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Fig. 4. This Figure represents the elevation or front view of the Fire-place Fig. 3. after it has been altered. The lower part of the door-way left for the Chimney-sweeper is shown in this Figure by white dotted lines. See page 344.

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Fig. 5. This Figure shows the section of a Chimney Fire-place and of a part of the canal of the Chimney, on the common construction.

a b is the opening in front; b c, the depth of the Fire-place at the hearth; d, the breast of the Chimney.

d e, the throat of the Chimney, and d f, g e, a part of the open canal of the Chimney.

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Fig. 6. Shows a section of the same Chimney after it has been altered.

k l is the new back of the Fire-place; l i, the tile or stone which closes the door-way for the Chimney-sweeper; d i, the throat of the Chimney, narrow to four inches; a, the mantle, and h, the new wall made under the mantle to diminish the height of the opening of the Fire-place in front.

N.B. These two Figures are sections of the same Chimney which is represented in each of the four preceding Figures.

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Fig. 7.

This Figure represents the ground plan of a Chimney Fire-place in which the grate is placed in a niche, and in which the original width A B of the Fire-place is considerably diminished.

a b is the opening of the Fire-place in front after it has been altered, and d is the back of the niche in which the grate is placed. See page 347.

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Fig. 8. Shows a front view of the same Fire-place after it has been altered; where may be seen the grate, and the door-way for the Chimney-sweeper. See page 347.

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Fig. 9. Shows a section of the same Fire-place, c d e being a section of the niche, g the door-way for the Chimney-sweeper, closed by a piece of the fire-stone, and f the new wall under the mantle by which the height of the opening of the Fire-place in front is diminished. See page 347.

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Fig. 10. This Figure shows how the covings are to be placed when the front of the covings (a and b) do not come so far forward as the front of the opening of the Fire-place, or the jambs (A and B). See page 348.

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Fig. 11. This Figure shows how the width and obliquity of the covings are to be accommodated to the width of the back of a Fire-place, in cases where it is necessary to make the back very wide. See page 349.

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Fig. 12. This Figure shows how an instrument called a bevel (m n), useful in laying out the work, in altering Chimney Fire-places, may be constructed. See page 349.

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Fig. 13. This shows how, when the breast of a Chimney (d) is too high, it may be brought down by means of a wall (h) placed under the mantle, and a coating of plaster, which in this Figure is represented by the part marked by dots. See page 351.

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Fig. 14. This shows how the breast of a Chimney may be brought down merely by a coating of plaster. See page 351.

Footnotes for essay IV.

[1] Eves and Sutton, bricklayers, Broad Sanctuary, Westminster, have alone altered above 90 Chimnies.—The experiment was first made in London at Lord Palmerston's house in Hanover-square;—then two Chimnies were altered in the house of Sir John Sinclair, Baronet, President of the Board of Agriculture; one in the room in which the Board meets, and the other in the Secretary's room; which last being much frequented by persons from all parts of Great Britain, it was hoped that circumstances would tend much to expedite the introduction of these improvements in various parts of the kingdom. Several Chimnies were altered in the house of Sir Joseph Banks, Baronet, K. B. President of the Royal Society. Afterwards a number were altered in Devonshire-house;—in the house of Earl Besborough, in Cavendish-square, and at his seat at Roehampton;—at Holywell-house, near St. Alban's, the seat of the Countess Dowager Spencer:—at Melbourne-house;—at Lady Templeton's in Portland-place; —at Mrs Montagu's in Portman-square;— at Lord Sudley's, in Dover-street:—at the Marquis of Salisbury's seat at Hatfield, and at his house in town;—at Lord Palmerston's seat at Broadlands, near Southampton, and at several gentlemen's houses in that neighbourhood;—and a great many others; but it would be tiresome to enumerate them all; and even these are mentioned merely for the satisfaction of those who may wish to make inquiries respecting the success of the experiments.

[2] Having been obliged to carry backward the Fire-place in the manner here described, in order to accommodate it to a Chimney whose walls in front were remarkably thin,—I was surprised to find upon lighting the fire that it appeared to give out more heat into the room than any Fire-place I had ever constructed.— This effect was quite unexpected; but the cause of it was too obvious not to be immediately discovered.—The flame rising from the fire broke against the part of the back which sloped forward over the fire, and this part of the back being soon very much heated, and in consequence of its being very hot, (and when the fire burnt bright it was frequently quite red hot,) it threw off into the room a great deal of radiant heat.—It is not possible that this oblique surface (the slope of the back of the Fire-place) could have been heated red-hot MERELY by the radiant heat projected by the burning fuel, for other parts of the Fire-place nearer the fire, and better situated for receiving radiant heat, were never found to be so much heated;—and hence it appears that the combined heat in the current of smoke and hot vapour which rises from an open fire MAY BE, at least IN PART, stopped in its passage up the Chimney, changing into radiant heat, and afterwards thrown into the room.—This opens up a new and very interesting field for experiment, and bids fair to lead to important improvements in the construction of Fire-places.—I have of late been much engaged in these investigations, and am now actually employed daily in making a variety of experiments with grates and Fire-places, upon different constructions, in the room I inhabit in the Royal Hotel in Pall Mall;—and Mr. Hopkins of Greek-street Soho, Ironmonger to his Majesty, and Mrs. Hempel, at her Pottery at Chelsea, are both at work in their different lines of business, under my direction, in the construction of Fire-places upon a principle entirely new, and which, I flatter myself, will be found to be not only elegant and convenient, but very economical.—But as I mean soon to publish a particular account of these Fire-places,—with drawings and ample directions for constructing them, I shall not enlarge farther on the subject in this place.—It may however not be amiss just to mention here, that these new-invented Fire-places not being fixed to the walls of the Chimney, but merely set down upon the hearth, may be used in any open Chimney: and that Chimnies altered or constructed on the principles here recommended are particularly well adapted for receiving them.

The Public in general, and more particularly those Tradesmen and Manufacturers whom it may concern, are requested to observe, that as the Author does not intent to take out himself, or to suffer others to take out, any patent for any invention of his which may be of public utility, all persons are at full liberty to imitate them, and vend them, for their own emolument, when and where, and in any way they may think proper; and those who may wish for any further information respecting any of those inventions or improvements will receive (gratis) all the information they can require by applying to the Author, who will take pleasure in giving them every assistance in his power.

[3] 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 Chimnies 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 particular in the Dutchies 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 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 repaid by the improvement of the fuel. The coals, thus mixed with the clay, not only burn longer, but give much more heat than when they are burnt in their crude state.

It will doubtless appear extraordinary to those who have not considered the subject with some attention, that the quantity of heat produced in the combustion of any 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 satisfactory manner.

The heat generated in the combustion of any small particle of coal existing under two distinct forms, namely, in that which is COMBINED 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 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.

CONTENTS of ESSAY V.

A SHORT ACCOUNT of SEVERAL PUBLIC INSTITUTIONS Lately formed in Bavaria. together with the APPENDIX to the FIRST VOLUME.

Account I A Short Account of the military academy at munich

Account II An account of the means used to improve the bread of horses, and horned cattle, in Bavaria and the Palatinate.

Account III An account of the measures adopted for putting an end to usury at Munich.

Account IV An account of a scheme for employing the soldiery in Bavaria in repairing the highways and public roads.

APPENDIX

No. I Address and petition to all inhabitants and citizens of Munich, in the name of the real poor and distressed.

No. II Subscription lists distributed among the inhabitants of Munich, in the month of January 1790, when the establishment for the relief of the poor in that city was formed.

No. III An account of the receipts and expenditures of the institution for the poor at Munich during five years.

No. IV Certificate relative to the expence of fuel in the public kitchen of the military workhouse at Munich.

No. V Printed form for the descriptions of the poor.

No. VI Printed form for spin-tickets, such as are used at the military workhouse at Munich.

No. VII An Account of experiments made at the bakehouse of the military workhouse at Munich, November the 4th and 5th, 1794.

No. VIII Account of the persons in the house of industry in Dublin the 30th of April 1796, and of the details of the manner and expence of feeding them.

No. IX An account of an experiment made (under the direction of the author,) in the kitchen of the house of industry at Dublin, in cooking for the poor.

ESSAY V.

A short Account of the MILITARY ACADEMY at MUNICH.

Though it is certain that too much learning is rather disadvantageous than otherwise to the lower classes of the people;—that the introduction of a spirit of philosophical investigation,—literary amusement,—and metaphysical speculation among those who are destined by fortune to gain their livelihood by the sweat of their brow, rather tends to make them discontented and unhappy, than to contribute any thing to their real comfort and enjoyments; yet there appears, now and then, a native genius in the most humble stations, which it would be a pity not to be able to call forth into activity. It was principally with a view to bring forward such extraordinary talents, and to employ them usefully in the public service, that the Military Academy at Munich was instituted. This Academy, which consists of 180 eleves or pupils, is divided into three classes. The first class, which is designed for the education of orphans and other children of the poorer class of Military Officers, and those employed in the Civil Departments of the State, consists of thirty pupils, who are received gratis, from the age of eleven to thirteen years, and who remain in the Academy for years. The second class, which is designed to assist the poorer nobility, and less opulent among the merchants, citizens, and servants of government, in giving their sons a good general education, consists of sixty pupils, who are received from the age of eleven to fifteen years, and who pay to the Academy twelve florins a month; for which sum they are fed, clothed, and instructed. The third class, consisting of ninety pupils, from the age of fifteen to twenty years, who are all admitted gratis, is designed to bring forward such youths among the lower classes of the people as show evident signs of UNCOMMON TALENTS and genius, joined to a sound constitution of body, and a good moral character.

All Commanding Officers of regiments, and Public Officers in Civil departments, and all Civil Magistrates, are authorised and INVITED to recommend subjects for this class of the Academy, and they are not confined in their choice to any particular ranks of society, but they are allowed to recommend persons of the lowest extraction, and most obscure origin. Private soldiers, and the children of soldiers, and even the children of the meanest mechanics and day-labourers, are admissible, provided they possess the necessary requisites; namely, VERY EXTRAORDINARY NATURAL GENIUS, a healthy constitution, and a good character; but if the subject recommended should be found wanting in any of these requisite qualifications, he would not only be refused admittance into the Academy, but the person who recommended him would be very severely reprimanded.

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