Popular Science Monthly/Volume 29/June 1886/The Principles of Domestic Fireplace Construction
| THE PRINCIPLES OF DOMESTIC FIREPLACE CONSTRUCTION.[1] |
By T. PRIDGIN TEALE, F. R. C. S.
IF there be a place in the kingdom in which a lecture on the subject selected for to-night could appropriately be given, surely it is the theatre in which we are assembled. Some of my hearers may be aware of the mutual fitness of subject and place. Many, perhaps, are not aware, as, indeed, was the case with myself three months ago, that the principles of fireplace construction which will be laid before you to-night, and which I have been working out and teaching for the last three or four years, were urged, written about, and acted upon at the end of the last century by your founder, Count Rumford, and that a great portion of his time, his writings, and his work was devoted to this very question.
Hardly any subject would be more in harmony with the aims which he set before him in founding this society, as we may learn from the following quotation from the "Prospectus of the Royal Institution," published at the end of the fifth volume of Rumford's works: "But if it should be proved, as in fact it may, that in the applications of fire, in the management of heat, and in the production of light, we do not derive half the advantage from combustion which might be obtained, it will readily be admitted that these subjects must constitute a very important part of the useful information to be conveyed in the public lectures of the Royal Institution."
And why should it be necessary, at the end of this nineteenth century, to give a lecture on "The principles of fireplace construction"? Why should such a title draw together an audience? Clearly from the fact that correct principles have been habitually, and, until the last few years, almost universally violated, and because the rules so ably worked out, so earnestly and forcibly advocated by Rumford, have lain dormant, lingering here and there, chiefly in old-fashioned houses, and almost forgotten.
Again, why should a layman, whose profession lies outside that of the architect, the builder, and the manufacturer, take upon himself to teach principles that are to guide other professions than his own? Mainly for two reasons: one, that there are principles which a medical man may work out without reproach, as tending to contribute to the happiness, the comfort, and the health of mankind; the other, that when principles have to be insisted upon, and to be made a subject of public instruction, they can be urged with more effect by those who are hampered by no relations to any patents, and have no pecuniary interest in the success or failure of the application of the principles in question. On this point we have a good example in Count Rumford, who says in a note: "The public in general and particularly those tradesmen and manufacturers whom it may concern, are requested to observe that, as the author does not intend 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."
Three evils result from the prevalence of bad principles in construction: 1. Waste of fuel and loss of heat. 2. Excessive production of soot and smoke. 3. Large addition to ash-pit refuse by cinders, which are really unburned, and therefore wasted fuel. These are matters of national concern, and it has been the main object of my labors on this question during the last four years to endeavor to convince the public that it is the interest no less than the duty of every house-holder to burn his fuel on correct principles, and to do his part toward the diminution of these evils.
On the first point, "waste of fuel and heat," let us listen to Rumford, whose words are as true to-day as when written eighty years ago: "Though it is generally acknowledged that there is a great waste of fuel in all countries, arising from ignorance and carelessness in the management of fire, yet few—very few, I believe—are aware of the real amount of this waste. . . . From the result of all my inquiries upon this subject, I have been led to conclude that not less than seven eighths of the heat generated, or which with proper management might be generated, from the fuel actually consumed, is carried up into the atmosphere with the smoke, and totally lost. . . . And with regard to the economy of fuel, it has this in particular to recommend it, that whatever is saved by an individual is at the same time a positive saving to the whole community."
Heat is wasted in three ways—either by combustion under the impulse of strong draught, which means rapid escape of heat up the chimney; or by imperfect combustion of the gases which are generated during the burning of the coals; or by escape of heat through the iron sides and back into the space between the range and the brickwork, and so into the chimney. The greatest offenders are the ordinary register grates. Iron all over, back, and sides, and roof, they are usually set in a chamber open above to the chimney, and imperfectly filled in, or not filled in at all, with brickwork. The heat escapes through the iron to this chamber, and thence is lost. Another fault is that the "register-opening," in other words the "throat of the chimney," being immediately above the coal, submits the burning fuel to the full concentrated force of the current to the chimney, converting the fire into a miniature blast-furnace. On this point Rumford says: "But there are, I am told, persons in this country who are so fond of seeing what is called a great roaring fire, that even with its attendant inconveniences, of roasting and freezing opposite sides of the body at the same time, they prefer it to the genial and equable warmth which a smaller fire, properly managed, may be made to produce, even in an open-chimney fireplace."
The second result of faulty construction in fireplaces is "undue production of smoke and soot." Smoke and soot imply imperfect combustion, and to this two defects in a fire mainly contribute, one, too rapid a draught through the fire which hurries away and chills below burning-point the gas rising from the heated fuel. The other defect is too cold a fire, i. e., too small a body of heat in and around the fuel, so that the temperature of the gases is not raised to a point at which they will burn. On the smoke question Rumford waxes eloquent: "The enormous waste of fuel in London may be estimated by the vast dark cloud which continually hangs over this great metropolis, and frequently overshadows the whole country, far and wide; for this dense cloud is certainly composed almost entirely of unconsumed coal, which, having stolen wings from the innumerable fires of this great city, has escaped by the chimneys, and continues to sail about in the air till, having lost the heat which gave it volatility, it falls in a dry shower of extremely fine black dust to the ground, obscuring the atmosphere in its descent, and frequently changing the brightest day into more than Egyptian darkness."
A few years ago the prevalence of unusually dense fogs roused the metropolitan public to a sense of this great evil. The Smoke Abatement Society was formed, and under its auspices exhibitions of smoke-consuming apparatus and improved fireplaces were held in London and Manchester. Beyond the fact that certain grates were pronounced to be good in point of economy, and moderate in the production of smoke, and that the public has been led to take an interest in and inquire into the relative value and economy of various patent fireplaces, there has been but little advance in the education of the public in the principles which lie at the root of the whole question.
A third result of bad construction is the "production of cinders." With good coal, cinders are inexcusable. They are unconsumed carbon—coke—and imply a faulty fireplace. If thrown into the ash-pit, as is the case in ninety-nine times out of a hundred, they are shameful waste, and more than waste, for they entail a great cost for their removal. The town of Leeds pays about fourteen thousand pounds a year for the scavenging of the streets and the emptying of ash-pits. Nearly every house in Leeds supplies in the way of cinders at least twice as much ash-pit refuse as it might do, were the fireplaces properly constructed. The ash-pit refuse of Leeds is burned in a "destructor," and the cinders in the refuse provide not only heat enough for its reduction to a mineral residue, but spare heat for driving two sixty-horse-power engines, and for consuming a reasonable amount of pigs, etc., killed by or on account of disease.
These three great evils, evils affecting not only individuals, but the community, waste of fuel and heat, production of soot, production of cinders, are a direct result of the violation of the correct principles in fireplace construction.
Let us next inquire what are the principles which promote good combustion in an open fireplace—i. e., what are the conditions which are essential to enable fuel to give out to a room "good money's worth in heat." That such a result may be obtained, fuel must burn well but not rapidly. Two things in combination are essential to the combustion of fuel—a supply of oxygen, and a high temperature—i. e., plenty of heat around the fuel. If fuel be burned with a hot jacket around it, a very moderate amount of oxygen will sustain combustion, and, if the supply of oxygen be moderate, combustion is slow. Burn coal with a chilling jacket around it, a rapid conductor like iron, and it needs a fierce draught of oxygen to sustain combustion, and this means rapid escape of actual heat, and also of potential heat in unburned gases and smoke, up the chimney. This is the key to the whole position; this is the touchstone by which to test the principles of fireplace construction.
Few people probably realize the exact conditions of combustion, which may be well illustrated from the process of manufacture of coal-gas. In coal we have three kinds of constituents: One mineral, incombustible, seen in the ash residue, which for good coal amounts to barely three per cent. The second, volatile, and which, under the influence of heat becoming gaseous, appears in an open fire as tall flame and smoke, and, where combustion is imperfect, produces soot. The third constituent is carbon or charcoal, familiarly known as coke or cinder, and when burning gives a short, shallow, bluish flame. The carbon and the volatile portions can be raised to a high temperature, and still will not burn unless oxygen be brought into contact with them.
In the manufacture of gas, coal is raised to a high temperature, and the gases are driven off by roasting the coal in an oven from which air, i. e., oxygen, is shut out. The gases are conducted away, cooled, purified, and stored for future use in a gasometer; the combined carbon and mineral residue, being non-volatile, is cooled down before being exposed to the air, and is sold as coke. Here we have a striking proof of the fact that high temperature in fuel does not of itself involve combustion. If air were admitted to the red-hot coke, or to the gases as they escape in their heated condition from the furnace, they would burn. But when coke has become cold, and the gases are cold, as in a gasometer, no amount of oxygen will of itself start combustion.
The deduction from all this is, that complete oxidation, i. e., good combustion, is possible only when the fuel and gases are at a high temperature, and that high temperature of fuel does not produce combustion until oxygen is introduced: therefore we can have a high temperature of fuel, without rapid combustion, provided we control and limit the supply of oxygen. If we have thoroughly grasped these elementary facts, we shall be in a position to understand the points to be aimed at in the construction of a fireplace.
My attention was first directed to the question of waste of fuel at the time of the coal-famine some twelve years ago. I read in the "Times," and acted upon the suggestion, to economize coal by inserting an iron plate on the grid under the fuel so as to cut off all draught through the fire. This undoubtedly induced slow combustion, and economized fuel, but the fire was dull, cold, and ineffective. The plan was abandoned. It taught me, however, the fact that combustion could be controlled by cutting off the under-draught, but I did not then see why combustion was spoiled. The reason was that the under surface of the fire was chilled, and the fuel lost its incandescence owing to the rapid loss of heat through the iron toward the open-hearth chamber. To some persons even now "slow-combustion stoves" are an abomination, and are supposed to by synonymous with bad combustion.
The next stage in my fireplace education was the adoption of the Abbotsford grate. I thereby learned that the reason why an Abbotsford grate was an advance upon the iron plate lay in the fact that the solid fire-brick bottom stored up heat and enabled the fuel to burn more brightly resting upon a hot surface—not upon a cooling iron plate. But Abbotsford grates, and the other class of grates with solid fire-brick bottoms, the Parson's grates, have disadvantages. They are apt to become dull and untidy toward the end of the day, and do not burn satisfactorily with inferior coal. There is a better thing than a solid fire-brick bottom, and that is the chamber under the fire closed in front by an "Economizer."
The history of the next, the most important stage of my fireplace education, was as follows:
Some five years ago I made, somewhat accidentally, the discovery that the burning of coal in an ordinary fireplace could be controlled and retarded by the adoption of a very simple and inexpensive contrivance, applicable to nearly every existing grate, and that this result could be attained without impairment of, and often with increase of, the heating power of the fire. This contrivance, which I have named an "Economizer," was simply a shield of iron, standing on the hearth, and rising as high as the level of the grid at the bottom of the grate, converting the hearth-space under the fire into a chamber closed by a movable door.
The effect was twofold: The stream of air, which usually rushes through the bottom of the fire, and causes for a short time rapid combustion at a white heat, was thereby cut off, and the air under the fire was kept stagnant, the heated coal being dependent for its combustion on the air passing over the front and the upper surface. The second point was that this boxing up rendered the chamber hotter, and this increased temperature beneath the fire-grate, i. e., under the fuel, added so materially to the temperature of the whole, even of the cinders coming into contact with the iron grid, that the very moderate supply of oxygen reaching the front and upper surface of the fuel was sufficient to maintain every portion in a state of incandescence. Moreover, I observed that combustion was going on at an orange, not at a white, heat.
Let us contrast a white with the orange heat. A white heat in a fire means rapid combustion, owing to the strong current of air, oxygen, which passes under the grate, through the center of the fire, and up the chimney. As soon as the heart of the fire has been rapidly burned away at a white heat, the fuel cools; the iron grid cools also; and the cinders in contact with the grid are chilled below combustion point. They then cease to burn, and the bottom of the fire becomes dead and choked. The poker must now be brought into play to clear away the dead cinders, and to reopen the slits in the choked grid. New coal is added to the feeble remnant of burning embers, with no reserve of heat in the iron surroundings; and in time, and perhaps very slowly, the fire revives, and rapid combustion sets in afresh under the influence of the renewed current of oxygen passing through the heart of the fire. An orange heat means that the coke, i. e., the red-hot cinder, is burning with a slowly applied stream of oxygen, a degree of combustion which is only possible when the coal is kept warm by the hot chamber beneath, and by a reasonable limitation of loss of heat at the back and sides by fire-brick, either in contact with the fuel, or at least close behind the iron surrounding it. This effect is seen, partially, in the grates with solid fire-brick bottom, but far more perfectly in the grates with the chamber closed by the "Economizer."
This hot chamber has the following effects: The incandescent coal remains red-hot from end to end of the grate, until nearly all is consumed, thus maintaining a larger body of the fuel in a state to radiate effective heat into a room. The cinders on coming into contact with the iron grid also remain red-hot, and so continue to burn away until they fall through the grid as a fine powder. This allows the fire to burn clearly all day long almost without poking. When the fire is low, and new coal is added, the reserve of heat in the hot chamber is such that the addition of cold fresh fuel does not temporarily quench the embers, and the fire is very quickly in a blaze after being mended.
Having made the discovery by the observation of a grate supplied to me with an "Economizer," the value of which, I suspect, was hardly appreciated by the makers, I applied "Economizers" one by one to all my grates, kitchen included. The result surpassed my expectations. There was a saving of at least a fourth of my coal. The experience of many friends, who, at my advice, adopted the system, confirmed my own results. It was, therefore, clear to me that I was bound to make widely known a discovery which was fraught with such benefit to myself, and was likely to prove a great boon to the public.
My chief aim hitherto has been to persuade the public to apply the "Economizer" to existing fireplaces. After steady exertions for four years, some impression has been made on the inertia of the public, and extensive trials of the "Economizer" are taking place in many parts of the country. To-day, however, my aims are more complete. It is my wish to advocate not one principle alone, although that is the cardinal one, but to urge all the best principles which enter into the construction of a really effective fireplace, and to induce those whom it may concern to replace bad by an entirely new construction, right in every point.
The rules of construction which I shall lay down have been arrived at entirely by my own observation of what appeared to be the best points in various fireplaces. It was, therefore, no less a satisfaction to me than a surprise to discover, on reading Rumford's work in preparation for this lecture, that nothing which I have to advocate is new, but that every principle, and the "Economizer" is hardly an exception, was advocated no less enthusiastically by him at the very commencement of this century.
Having considered the principles that should guide us, we are now prepared to lay down strict rules which should be acted upon in the construction of fireplaces. I trust that what I have said has so far commended itself to your judgment that the fourteen rules here drawn up will command your hearty assent, and in due time will win their way into the confidence of our architects, our builders, and the public:
Rule I. "As little iron as possible."—The only parts of a fireplace that are necessarily made of iron are the grid on which the coal rests, and the bars in front. The "Economizer," though usually made of iron, from convenience in construction, might be of earthenware, and so would be more perfectly in harmony with this rule. On this point Rumford speaks most emphatically: "Those (grates) 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 chimneys but merely a grate for containing coals, and additional apparatus being not only useless but very pernicious, all complicated and expensive grates should be laid aside, and such as are simple substituted in their stead. In the choice of a grate, beauty and elegance may easily be united with perfect simplicity. Indeed, they are incompatible with everything else." Again he says, "Iron, and in general metals of all kinds, are to be reckoned among the very worst materials that it is possible to employ in the construction of a fireplace."
Rule II. "The back and sides of the fireplace should be of brick, or fire-brick."—Brick retains, stores, and accumulates heat, and radiates it back into the room, and keeps the fuel hot. Iron lets heat slip through it up the chimney, gives very little back to the room, and chills the fuel. On this point also Rumford speaks very strongly. "The best materials I have hitherto been able to discover are firebrick and common bricks and mortar. . . . The fuel, instead of being employed to heat the room directly or by the direct rays from the fire, should be so disposed or placed as to heat the back and sides of the grate, which must always be constructed of fire-brick or fire-stone, and never of iron or any other metal."
Rule III. "The fire-brick back should lean over the fire, not lean away from it," as has been the favorite construction throughout the kingdom. The lean-over not only increases the power of absorbing heat from rising flame—otherwise lost up the chimney—but the increased temperature accumulated in the fire-brick raises the temperature of gases to combustion-point, which would otherwise pass up the chimney unconsumed, and thus be lost. Rumford discovered accidentally the value of this "lean-over," and at once realized its immense importance. He does not, however, seem to have carried out his intention of working out for general adoption this form of back.
He first of all condemns to alteration all fire-backs which lean away from the fire. "It frequently happens that the iron backs of grates are not vertical, but inclined backward. Where the grates are wide, and can be filled up with fire-brick, the inclination of the back will be of little consequence, since, by making the fire-brick in the form of a wedge, the front may be made perfectly vertical, the iron back being hid in the solid work of the fireplace. If the grate be too shallow to admit of any diminution, it will be best to take away the iron back entirely, and cause the vertical back of the fireplace to serve as the back to the grate."
He next describes his discovery of the value of the "lean-over": "In this case I should increase the depth of the fireplace at the hearth to twelve or thirteen inches, and should build the back perpendicular to the height of the top of the burning fuel, and then, sloping the back by a gentle inclination forward, bring it to its proper place, that is to say, perpendicularly under the back part 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 fireplace is increased), 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.
"Having been obliged to carry backward the fireplace 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 fireplace 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 burned 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 fireplace) could have been heated red-hot merely by the radiant heat projected by the burning fuel; for other parts of the fireplace 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 vapor which rises from an open fire may be, at least in part, stopped in its passage up the chimney, changed into radiant heat, and afterward thrown into the room.
"This opens a new and very interesting field for experiment, and bids fair to lead to important improvements in the construction of fireplaces. . . . But, as I mean soon to publish a particular account of these fireplaces, with drawings and ample directions for constructing them, I will not enlarge further on the subject in this place. It may, however, not be amiss just to mention here that these new invented fireplaces not being fixed to the walls of the chimney, but merely set down upon the hearth, may be used in any open chimney; and the chimneys altered or constructed on the principles here recommended are particularly well adapted for receiving them."
Of recent years "lean-over" backs have been reinvented and sparingly used. The "Milner" back is excellent. It burns fuel well, and gives out a great heat. But it is extravagant in consumption, unless controlled by the "Economizer."
Captain Douglas Galton saw the virtue of the "lean-over," and adopted it in the grate which goes by his name. The "Bee-hive" back was the same in principle and very good, and, having a very small grid, was economical.
The "Rifle" back gives an admirable fire, little short of perfection; but observation shows that the "tall" flame extends far beyond the bend, and is therefore soon lost as a heating factor, the heat being wasted in the chimney.
From the commencement of my study of the fireplace question the value of the "lean-over" has not only taken firm hold of my fancy, but my sense of its importance has been growing in intensity, until I saw that the best construction must show the greatest possible extent of "lean-over" that could be obtained without sacrifice of other important details of construction. How to accomplish this will appear in considering the fifth rule.
Rule IV. "The bottom of the fire, or grating, should be deep from before backward, probably not less than nine inches for a small room, nor more than eleven inches for a large room." This is a corollary to Rule III. We can not possibly have the back of the fireplace over-hanging the fire when there is a shallow grid. If for no other reason than the demands of the "lean-over," depth of fire-space is essential. But there is gain, thereby, in another direction. It affords plenty of room for the burning fuel to lie down close to the grid, and away from swift air-currents, and prevents the tendency of the fire to burn hollow.
On this point Rumford has a word to say: "But as many of the grates now in common use will be found too large when the fireplaces are altered and improved, it will be necessary to diminish their capacities by filling up with pieces of fire-brick. But, in diminishing the capacities of grates, care must be taken not to make them too narrow, i. e., too shallow.
"The proper depth for grates for rooms of middling size will be from six to eight inches. But, where the width (i. e., depth) is not more than five inches, it will be very difficult to prevent the fire going out."
"Where grates designed for rooms of middling size are longer (and broader) than fourteen or fifteen inches, it will always be best to diminish their length by filling them up at their two ends by fire-brick."
Rule V. "The sides or 'covings' of the fireplace should be inclined to one another as the sides of an equilateral triangle" (Fig. 2). The working out of this rule has cost me much thought and experiment. It was worked out more or less empirically with a view to attain certain objects, and, having attained them, I discovered that I had unwittingly selected the sides of an equilateral triangle. It is of some importance, and may be of interest, to tell how the question arose. In my earlier fireplaces the sides or "covings" were parallel to each other, and had the defect that they radiated most of their heat from one to the other, not into the room, with the probable result that much of such heat would eventually escape up the chimney.
It was clear, then, that the sides must be set at an angle with the back, so as to face toward the room. But at what angle? My first experiments were determined by the shape of the corner bricks which were in the market. These determined the inclination of the sides to be such that, if prolonged, they would meet at a right angle. This is the angle laid down by Rumford as the angle of selection, but as the largest angle admissible in a good fireplace. This angle, however, brought me into difficulties with my "lean-over" back. The openness of the angle made the back, as it ascended, spread out so rapidly that what was gained in width was lost in height. Moreover, my critics objected to its appearance as ugly. What, then, should determine the inclination of the sides? The point was thus determined: Seeing that a heated brick throws off the greatest amount of radiant heat at a right angle with its surface, the "covings" should be at such an inclination to each other that the perpendicular line from the inner margin of one "coving" should just miss the outer margin of the opposite "coving." Where the "covings," as in my earlier attempts and in Count Rumford's fireplaces, are at a right angle to each other, this perpendicular line misses the opposite margin by several inches. It was clear, therefore, that the inclination might be made more acute. Guided by this idea, and having determined the principle on which the shape of the grate should depend, an inclination was arrived at which turned out to be an angle of 60°, i. e., the inclination of the sides of an equilateral triangle.
Count Rumford came very nearly to the same conclusions: "I have said, in my essay on chimney fireplaces, that where chimneys are well constructed and well situated, and have never been apt to smoke, in altering them the 'covings' may be placed at an angle of 135° with the back; but I have expressly said that they should never exceed that angle, and have stated at large the bad consequences that must follow from making the opening of a fireplace very wide, when its depth is very shallow."
Rule VII. "The 'lean-over' at the back should be at an angle of 70°" (Fig. 1).—Commencing at a level (A) corresponding with the top of the front bars, and leaning forward at an angle of 70° with the horizontal line of the hearth, the back should rise to such a point that the angle where it returns toward the chimney (B) should be vertically over the insertion (C) of the cheeks of the fire-grate. This angle (B) will be about twenty-eight inches from the hearth, or sixteen inches from the top of the fire, and about three and a half to four and a half inches from the front line of the fireplace, according to the size of the grate. These points will be obvious from the vertical section of the fireplace here shown, and from C, Fig. 2.
So far, in the fireplaces built after my rules, the height of the grid from the hearth has been taken at two bricks, or six inches, and the height of the bars from the grid also at two bricks, or six inches. It follows, therefore, that the lean-over commences at twelve inches from the hearth. It is possible that a better angle than 70° may eventually be found—such as an angle of 60°—but commencing a few inches above the fire so as not to lower the angle B where the lean-over returns to the chimney.
Fig. 1.
Rule VIII. "The shape of the grate should be based upon a square described within an equilateral triangle, the size to vary in constant proportion to the side of the square" (Fig. 2).—The shape of the grate, or grid, is arrived at in the following way: Describe a square, D, of which the sides shall be eight, nine, or ten inches, according to the size of the room, within an equilateral triangle, E, the two sides of which shall represent the "covings" of the fireplace, and the base the front line of the fireplace. From each front angle of the square carry a line from D to C, to the "covings" or sides of the triangle, at an angle of 45° with the front line of the fireplace. These two lines, with the side of the square from which they are drawn, form the front of the grid. The back line of the grid does not correspond with the corresponding side of the square, but is carried one and a half inch farther back, so as to give greater depth to the grate, and allow the fire-brick back to overhang the back of the grid to the extent of one and a half inch (see A, Fig. 1) before it ascends as the "lean-over."
Fig. 2.
The diagram of the grate, with the square and triangle on which it is based in dotted lines, will, I hope, make this description sufficiently intelligible. Whenever a grate on this principle proves too hot for a room, and in summer when a smaller fire is needed, the size should be reduced in width by triangular fire-bricks at each side, which reduce the fire-space to a square, with the addition of the one-and-a-half-inch space under the back. This rule secures sufficient depth from front to back, and a constant proportion between depth and width, whatever be the size of grate.
Rule IX. "The slits in the grating, or grid, should be narrow, perhaps one fourth inch for a sitting-room grate and good coal, three eighths for a kitchen-grate and bad coal."—When the slits are larger, small cinders fall through and are wasted.
Rule X. "The front bars should be vertical, that ashes may not lodge and look untidy; narrow, perhaps one fourth inch in thickness, so as not to obstruct heat and close together, perhaps three fourths of an inch apart, so as to prevent coal and cinder from falling on the hearth" (Fig. 3).—It is too soon to judge as to the lasting powers of one-fourth inch bars. Those in one of my own grates are round, and, after four and a half months' daily wear, show no sign of burning away. Flat bars, one fourth inch by one half inch, or even by two thirds of an inch, might perhaps resist fire better, if the one-fourth-inch round bars burn away. The bars are so arranged that, if one fails, it can easily be renewed. I have round bars about one third of an inch in diameter at present on trial in my kitchen-range.
Fig. 3.
Rule XI. "There should be a rim one inch or one and a half inch in depth round the lower insertion of the vertical bars" (Fig. 3).—The object of this is to conceal the ash at the bottom of the fire, and to enable the front cinders to burn away completely by protecting them from the cold air. This rim (F) contributes greatly to tidiness, and as a rule will prevent the need of any sweeping up of the hearth during the day. Rule XII. "The chamber under the fire should be closed by a shield or economizer" (G, Figs. 1 and 3).—This has been already spoken of, and described as the central principle which enhances greatly the value of all the rest.
Rule XIII. "Whenever a fireplace is constructed on these principles, it must be borne in mind that a greater body of heat is accumulated about the hearth than in ordinary fireplaces. If there be the least doubt whether wooden beams may possibly run under the hearthstone, then an ash-pan should be added, with a double bottom, the space between the two plates being filled with artificial asbestus, 'slag-wool,' two inches in thickness?
Rule XIV. "A fireplace on this construction must not be put up in a party wall, where there is no projecting chimney-breast, lest the heated back should endanger woodwork in a room at the other side."
Having now worked up rules for the construction of an effective fireplace, let us consider what benefits result.
1. Economy of Fuel.—I have already stated that my own experience of the application of the "Economizer" to all my original fireplaces, including kitchen and scullery, was a saving of more than one fourth. Friends who have followed my advice report variously from a sixth to one third. The saving in the Leeds Infirmary, according to returns supplied to me by Mr. Blair, the general manager, has been nearly a sixth, amounting to nearly one hundred tons in the year. What the saving in the fireplaces constructed on the best rules may be I can not say, probably about the same degree of saving, with a large increase of heat given into the room. My conviction is that such fireplaces make one ton of coal give out as much heat into a room as two tons would yield if burned in the worst forms of the nearly obsolete register-stove.
2. Reduction of Soot.—This is, perhaps, from a national point of view, the most important point in connection with our subject—and yet it is the portion of it in which my evidence is the most defective. I can only offer you my general impression that there is a very important reduction in the amount of soot, an impression based upon observation of the smoke issuing from chimneys where "Economizers" are in use, and of the diminution of soot falling about my own house, which is confirmed by the testimony of Miss Gordon, Lady Superintendent of the Leeds Infirmary, as to the lessened amount of soot which finds its way into the wards.
3. Reduction of Ash-pit Refuse.—This point is clearly proved by the fine, snuff-like powder, free from cinders, which I show; and by the fact that the whole produce in the ash-pit of my kitchen fireplace for one week was contained in one ash-pan, and weighed fifteen pounds.
Danger of Fire.—Seeing that improved fireplace construction involves increased heat about the hearth, an actual danger of fire will be created where the hearthstone rests on wood, unless the hearth itself be protected. It was therefore my duty to find out a means of protecting the hearth. With this view, experiments have been made with ash-pans with double bottoms and a small air-space between the ash-pan and the hearth. The results are shown in the specimens of cotton-wool, wood, etc., which have been exposed under ash-pans of various constructions. My conclusion is that two inches of artificial asbestus at the bottom of an ash-pan would render any hearth safe. Such an ash-pan may be named a "Hearth-Protector." Another caution should be given against erecting one of these improved fireplaces where there is no projecting chimney-breast, lest there should be insufficient depth of brick between the back of the fire and the wood-work of a room at the other side.
"Kitchen Refuse"—In some households there are certain portions of kitchen refuse which are apt to find their way into the dust-bin, instead of the pig-tub. You here see the remains of refuse, consisting of celery-stalks, potato-parings, etc., which have been roasted in a wire cage underneath my kitchen-fire in the chamber closed by the "Economizer." The wire cage is necessary to allow the heat to reach the under surface of the refuse.
Having now for four years done my best to persuade the public to take measures in reference to fireplaces which will confer upon them a saving in the cost of fuel, a saving in the labor of servants, an increase in the warmth and comfort of rooms, a lessening of the soot in the atmosphere of towns, and a possibility of reduction of scavenging rates, it is no little satisfaction to feel that my views are at last making way, and acquiring a momentum of their own.
It only remains for me now to bring my address to a conclusion with the words of the Roman poet—
"Nonfumum ex fulgore, sed ex fumo dare lucem."
Hor., Ars. Poet.
—which I will translate in the words of one of our greatest Latin scholars, the late Professor Conington:
"Not smoke from fire my object is to bring,
But fire from smoke, a very different thing."
- ↑ A lecture delivered at the Royal Institution of Great Britain, February 5, 1886.