to take an impression from a common tread: it is lastly stamped with beaters until the surface is uniform. The cake, now 8 or 9 inches thick, is divided by means of long laths into squares of about 4 inches, and these are gradually removed. The thickness of the cake is the length of the bricks, which are kept upright. In drying the cakes, the first one taken out is laid transversely upon the second; the third is laid upon the fourth, and so on; this order being reversed when the pieces are piled up. In some places the peat mud is scooped out with buckets on to a dry place, and when the water has drained off, it is made into bricks with moulds. Too large an amount of water in the peat may completely destroy its value, and render it incapable of being piled. Its value increases in rapid proportion to its dryness, density, and firmness. If it possess these properties only in an inferior degree, it suffers by carriage and by keeping, the upper layers of the heap compressing and breaking the lower layers, which thus become valueless. The porosity and brittleness of peat prevent its application in all cases where fuel and matters to be heated are piled up to a height one above the other. Besides this, dense peat comprises in a like bulk much more combustible matter than porous peat. Hence the use of presses for condensing the peat. In one experiment, a brick weighing 8 lbs. lost 2.5 lbs. of water under the press. The longer peat is allowed to dry in appropriate sheds, the more it will improve as a heating agent. In some cases the quantity of ash yielded by peat is so large as to render the peat useless as fuel. This ash consists, first, of salts peculiar to vegetable matter, and which have not been dissolved out by the bog-water; and secondly, of the earthy matter collected during the deposition of the peat. Indeed, peat of various districts has been found to contain from 1 per cent. to one-third of its weight of ash. Carbonates of the alkalies are never found in it, but phosphates, sulphates, &c. In 100 parts of ash Einhof found 15-25 lime, 20-5 alumina, 55 oxide of iron, 41 silica, 15 phosphate of lime, 1:55 common salt and gypsum. Schübler found 34 per cent. of phosphates in the ash of peat from Schwenningen, thus making it valuable as a manure. The ash is otherwise injurious as causing dust and taking up much room, decreasing the quantity of combustible matter, and in smelting processes acting chemically. COAL has already been treated of under that head: its value as a fuel will be more fully considered in the present article: COKE and CHARCOAL have been noticed in the article CARBON. In the Introductory Essay, p. lxxxiii., that description of fuel made from a mixture of coal-dust and pitch, and known as PATENT FUEL, was slightly noticed. The advantages of this kind of fuel are economy of money and of space: for waste and refuse coal is used, such as from its pulverulent state is unfit for the ordinary | purposes of combustion. This invention, although new to us, is an ancient one, for the Chinese have been accustomed for ages to mix their powdered fuel with a compost of soft clay just sufficient to make it cohere; cow-dung or other refuse vegetable matter is also used: balls are then formed of this mixture, which are dried in the sun or open air. This method is not adopted on account of the scarcity of fuel, for coal is abundant in China; but the Chinese, unlike the English, know how to take care of it. These fireballs during combustion give out very little smoke: they are largely manufactured in the coal districts, and are distributed by canal over a large portion of the empire. Powdered fuel mixed with clay is also sold in some parts of continental Europe as combustible bricks. Peat has also been converted into patent fuel: by Hill's process the peat is distilled dry, and the pyroligneous spirit and tar collected: the tar is converted into pitch, which is mixed while hot with the peat charcoal. Wylam's method of making patent fuel involves several distinct branches: 1st, the separation of coal tar by distillation into naphtha, dead oil, and pitch; the pitch is mixed with small coal and moulded into bricks, as will be described presently. 2. The naphtha is rectified, and sold as such. 3. The dead oil is converted into ivory black, and is also used for other purposes. 4. The pitch, having become hard, is ground under edge stones, and mixed with small coal in the proportion of 1 to 4. This mixture of coal and pitch is carried up into a large hopper, from which it gradually passes into the receivers, M M, Fig. 1010, at the bottom of which a pair of plain that the Mammoth Steam-packet, of 1,000 horse-power, requires rollers o, Fig. 1011, are kept in motion by the shaft (1) Its importance in this respect may be judged of from the fact for one journey 81,884 cubic feet, or 2,210 tons of coal. N, Fig. 1010; and in this way a regular supply is thrown into the retort R. An Archimedean screw Q, Fig. 1011, inside the retort, is also made to revolve by means of the shaft N. The retort is kept at a dull red heat by the hot air of the flue T, and the fuel passes through the whole length of the retort, which is about 15 feet, in about 3 minutes. The mass of coal and pitch is discharged at the opposite end of the retort in a pasty state, and carried by an endless chain into the receiver s, Fig. 1012, where it is kept in motion by the arms rr, so as to prevent it from hardening into lumps. From this cylinder or receiver it runs into large moulds, where it is subjected to a heavy pressure in the following manner: A is a movable oval table upon which the moulds B B are fixed; s the vessel which receives the fuel paste; u and x, two cylinders similar to the cylinders of a steam engine, but worked by water; y, the pistons, to which two rams are attached, each having 6 arms fitting accurately into the moulds BB; and z is a lever, worked by means of the piston y. The moulds are filled from the vessel s as the table is made to revolve by the movement of the lever z. As the moulds approach the cylinder u the piston descends and compresses the fuel with enormous force; and after the piston rises, another set of moulds take their places, while the piston y of the cylinder z, having descended at the other end of the table, the six bricks are forced out of the moulds, and are received below ready to be stamped with the maker's name. The composition of these bricks appears to be― Coke { Ashes Carbon Gaseous matter. 61.67 7:08 31.25 100·001 caused the heat of their calorimeter to act upon ice, and they measured the heat by the quantity of ice melted. Rumford used water instead of ice, and measured the quantity of heat by the increase of temperature in a given quantity of water. Both methods are similar, if we bear in mind that the same quantity of heat which will melt 1lb. of ice at the zero of the centigrade thermometer, is just sufficient to raise the temperature of as much water 79° Cent., or, what is the same thing, to raise 0.79lb. of water 100° Cent. When it is also remembered that an equal weight of aqueous vapour, whatever its temperature and tension, is always formed from one and the same amount of heat, and, consequently, always contains the same quantity, and that the quantity of heat which water at 100° Cent. absorbs or renders latent in order to become vapour, would be 5.5 times sufficient to heat the same weight of water from 0° to 100° Cent.: hence, it is easy to calculate how much water would be converted into vapour by the heat required to melt 1 lb. of ice: it is found to be the 55th part of the same lb., or in other words, it is capable of converting into vapour 0-154 lb. of water. Despretz and Welter found that those quantities of a combustible body which require equal amounts of oxygen for combustion, evolve also equal quantities of heat, and this was made the measure of the heating power. [See COMBUSTION.] Indeed, considering that the heat evolved must bear some relation to the mass of the body burned, so the oxygen may also be regarded as the combustible as much as the fuel with which it combines. When, therefore, oxygen burns by means of carbon, wood, hydrogen, &c., the heat evolved must increase with the quantity of The relative values of fuel is a very important inquiry. founded a practical process for detecting by one exoxygen consumed. On this supposition Berthier Different kinds of fuel produce very different amounts of heat, and various methods have been adopted for periment the quantity of oxygen required for comascertaining their maximum effect. To find the theo-bustion, and thus the heating power of the combustiretical effect of any fuel, we must know the quantity of heat which a certain amount of such fuel is capable of producing, and the time required for effecting that object. These two points furnish the heating power, on which its value as fuel (in conjunction, of course, with its market price) depends. But as heat cannot be weighed or measured, it is impossible to ascertain the quantity of heat produced by a body during combustion; but it is not difficult to ascertain the effect of one kind of fuel compared with another kind; how much one kind exceeds or falls short of the other. This gives a relative value to the fuels, although the actual quantity of heat produced by each is altogether unknown. One of the methods of making this comparison is to cause the whole quantity of heat evolved by the fuel under examination to act upon a third body, which producing different effects under the action of different kinds of fuel, thus affords a standard of comparison. Lavoisier and Laplace (1) Appendix to Knapp's Technology, by Dr. E. Ronalds and Dr. T. Richardson. Vol. I. 1848. The work itself has also furnished us with considerable information in the preparation of this article. ble. This process is, to heat to redness a weighed quantity of the combustible with a large excess of pure litharge, until the combustible is completely conwould be by the oxygen of the air. Every equivasumed by the oxygen of the oxide of lead, as it lent of oxygen thus consumed leaves an equivalent of reduced metallic lead, and it is only necessary to weigh this reduced lead in order to discover the amount of oxygen consumed, and consequently the heating power, the object being merely a comparison of the relative powers of the different kinds of fuel. The lighter kinds of woods contain more hydrogen than the heavier, so that the first stage of their combustion with flame is increased at the expense of the second-viz. the incandescence of the charcoal; hence they burn with greater facility, and evolve their heat in a shorter time than the hard woods; hence, also, lighter woods are more combustible than harder, and give out more heat, inasmuch as 1 equivalent of hydrogen requires 3 times as much oxygen (evolving 3 times as much heat) as 1 equivalent of carbon. The state of division of a fuel is a point of im and continued experiment. Their qualities, so far as portance. A cwt. of wood in the state of shavings | of qualities which could only be elicited by careful will expose a much greater amount of surface to the air than when in the form of a log. Numerous portions of wood will be burning at one time in the former case, while in the latter the surface is only, or chiefly acted on; and while the log will maintain a moderate temperature for hours, the shavings may produce a red heat in the sides of the furnace in a few minutes. But as the amount of combustion, or quantity of fuel, consumed in a given time, increases by a state of division, so if this state is increased beyond a certain limit, it acts in an opposite manner, and destroys combustion altogether. Thus saw-dust, charcoal, or peat in powder, crushed coal, &c., cease to be combustible under ordinary circumstances, because the small particles lie so close together that the air necessary for combustion cannot penetrate. If coal be of a caking quality, its dust can be converted into compact coke; but fuel which falls to pieces in the fire without caking, has many of the objections of powdered fuel. The pulverulent waste from peat, wood charcoal, and pit-coal may now be converted into patent fuel, and on the continent small fuel is often used in glass-works and for boiler fires, the grate-bars having been previously covered with lumps of sandstone, limestone, &c., to prevent the powder falling through the grate, and to distribute the supply of air through the fuel. An ingenious application of clinkers to the same purpose is described in the article COPPER, p. 428. The above conditions are never united in one coal. Anthracite, for example, has very high evaporative power, but not being easily ignited, is not suited for quick action. It has great cohesion in its particles, and is not easily broken up by attrition, but it is not a caking coal, and, therefore, would not cohere in the furnace when the ship rolled in a gale of wind. It emits no smoke, but from the intensity of its combustion, causes the iron of the grate-bars and boilers to oxidize, or waste away, rapidly. Thus, with many advantages, anthracite has several defects which under ordinary circumstances preclude its use. It was thought that the above conditions might be united in some of the fuels prepared from coals possessing the various qualities, after the manner of patent fuels, and with this object experiments were The quantity of heat obtained from fuel in the useful arts and manufactures falls very far short of the theoretical value. A considerable portion of the heat is either not evolved, or is lost without any useful effect. The application of fuel to practical purposes is called heating or warming, [see WARMING,] and its object is to evolve the heat from the fuel as completely as possible, and to apply it without loss to the purpose it is intended to serve, as in the pro-directed to be made with the view of preparing such cesses of boiling, roasting, smelting and forging operations, the warming of dwellings, &c. Some valuable information respecting fuel, especially as regards the coals of our own country, is contained in the reports "on the coals suited to the steam navy, by Sir H. De la Beche and Dr. Lyon Playfair." This inquiry was undertaken at the public cost, on the establishment of a steam navy, and the reports are published under the authority of the Government. We propose to lay before our readers as full an abstract of these valuable documents as our limits will allow. Considering the purposes to which the coal was to be applied, the chief test of the value of any particular coal was its evaporalice power, or power of converting water into steam. Thus, if a given weight of coal in a certain time converted a larger portion of water into steam than a similar weight of another coal, the evaporative power of the first would be greater than that of the second. It is shown, however, by this inquiry, that the true practical value of coals for steam purposes depends upon a combination (1) Date of the first Report, 1848; of the second, 1849. a fuel. Hence, in order to obtain a knowledge of the coals of different districts, Wales was first selected for examination, as producing coals of all kinds, varying from bituminous to anthracite. The result of these experiments was not favourable. The cementing tar, though partially carbonized by the heat of the coking-ovens in which the prepared fuels are heated, was so much more combustible than the dense and difficultly burning anthracite, that the latter remained after the combustion of the former, and either accumulated on the bars in the state of powder, obstructing the draught, or falling through the grate escaped combustion. If thrown again on the fire, it choked the air-way and impeded the proper action of the fuel. The evaporative power of the fuels thus prepared was found to increase according as the proportion of fixed carbon was augmented; but this would appear to arise from the fuel then assuming more of the characters of the anthracite or coke from which it was made. The results of the experiments indicated the necessity of keeping a uniform character in the fuel manufactured. In the selection of the coals for trial careful inquiries was made at the different ports in the | Civil Engineers, at Putney, by Professor John Wilson neighbourhood of the coal-fields as to the kind of coal exported for steam purposes. Information from steam-ship companies, in the habit of using the coals of that district, was collected, and the local character of the fuel was ascertained. Circulars were then forwarded to the owners of such coals, explaining the object of the inquiry, and requesting them to furnish 2 tons for experiment. In most instances the coal was sent, but in a few cases the owners declined to do so; and as it was contrary to the spirit of the inquiry to report on the merits of coals contrary to the wishes of the owners, no coal was examined except such as was delivered free of expense to the commissioners, under the certificate of the owner or his agent.1 The method of testing the cohesive power of the coals, was by means of a wooden cylinder, 3 feet in diameter, and about 4 feet long, each end with a bearing or gudgeon attached to it; in the interior were fixed 3 shelves, each 6 inches wide, tending to the axis, for the purpose of forming a lodgment for the coals, and of carrying them up towards the top of the cylinder during its revolution, thus ensuring a certain amount of fall. The coals being put in at a door at one end, the cylinder was supported by a tressle at one end, the other gudgeon resting on a block let into the wall, and motion was communicated by a band passing round its circumference. The coals to be tested were first broken to the size employed in the experiments on their evaporating power, then thrown on a sieve, the meshes of which were 1 inch square. Of the coals left on the sieve 100 lbs. were put into the cylinder, which was then turned a certain number of times. The coals were again sifted on the same sieve, and the weight remaining gave the per centage of large coals found in the tables. These values are the mean of 2 trials with each coal, with 50 revolutions. Each coal was subjected to experiment for 3 successive days, the draught being differently arranged for each day, either in the proportions of 4: 5: 8 or 1:2:4. In this way it was easy to ascertain when the gases escaping from the coals were most economically consumed. The coals most liable to be influenced by the different adjustments for the admission of air, are those which from their bituminous characters are most apt to generate a large quantity of gaseous products on the first application of heat, such as the coals from the Northumberland, Durham, and Lancashire coal-fields; and it was, therefore, found that the experiments made with them under different areas for the admission of air, vary much more considerably than the less bituminous coals of the South Wales coal-field. It was soon found necessary in the highly gas-giving coals, such as the Cannel coal of Wigan, to allow air to enter behind the fire-bridge, so as to complete the combustion of the escaping gases. The experiments were conducted at the College for (1) In the article CoAL, p. 384, the elementary analysis and economic value of some of the coals examined are exhibited in a tabular form. See also the Table at page 722. and Mr. J. Arthur Phillips, assisted by some other gentlemen of scientific attainments. The boiler-house is described as a rectangular building, 35 feet in length, and 16 feet 6 inches in breadth. The brickwork of the boiler is built against one of the end walls; its width being 7 feet 8 inches, and length 15 feet; the side is separated from one side wall by an interval of 18 inches, for the purpose of preventing loss of heat from the boilers by conduction through the external wall; by this means, also, ready access is gained to the base of the chimney D, Fig. 1013. The tanks E F for supplying the boiler with water, are made of wrought-iron plates, riveted together and placed outside the roof, the cast-iron pipe which supplies them with water being brought up inside the building to defend it from frost. The extremity of the pipe is furnished with the means of directing the flow of water into either tank at pleasure, and a twoway cock, b, connected with the tanks, directs in a similar way the supply from them to the boiler. A cock on the feed-pipe a short distance below this regulates the quantity of water admitted to the boiler. The boiler is cylindrical in form, 12 feet in length and 4 feet in diameter, with flat ends, and an internal flue 2 feet 6 inches in diameter, in one end of which the grate is placed. This is the usual form of Cornish boilers. The flues are on the split or bridle draught plan, in which the column of heated air, after leaving the fire, passes through the internal flue to the rear of the boiler, where it divides, returning along the outside of the boiler on both sides to the front; the two branches, which are each 2 feet 6 inches deep, then turn down at right angles to their former course, and uniting under the boiler in the bottom flue, which is 2 feet 6 inches wide, traverse its whole length again and finally enter the base of the chimney, after exposing, during a course of about 36 feet, an area of 1976 square feet of boiler surface to the heating action. In the horizontal part of the flue at K, just before entering the chimney, a damper is placed sliding vertically in a cast-iron frame, which is worked by means of a rod passing through a stuffing-box and attached to a cord K' carried over two pullies, and furnished with a balance weight, so that a person standing near the fire-door can easily regulate the amount of draught. The internal dimensions of the chimney, 1824 square inches; the whole height, 35 feet 6 inches. Apertures were made in the chimney about 6 feet from its base, for the purpose of making observations on the temperatures of the currents, and of obtaining samples of the gases for analysis. Openings were also made at the end of each of the side flues, and at the base of the chimney, for the purpose of drawing out the soot at the end of each set of experiments. The floor of the flues is laid in fire-tiles, to facilitate its removal. When the furnace is in action, the apertures at the end are closed, and loss of heat prevented by means of stone doors 4 inches thick; then an interval for air about 1 inch thick; and, finally, cast-iron hanging doors lined with fire-clay. The fire-grate is 2 feet 6 inches wide and 2 feet long, thus giving an area of 5 square feet of grate surface; the bars are inch in thickness, with inch spaces between them. In the front end of the grate, near the fire-door, is an iron plate (named a dead-plate), for the purpose of gradually heating the coals; it is 10 inches wide, and slopes down to the grate; beside this is another plate 8 inches wide, sloping upwards to the fire-door, contracting it in its width to 15 inches, which is the width of the aperture for the introduction of fuel. The fire-doors used for closing the entrances to the grate and ash-pit, were on Mr. Sylvester's plan, and well adapted for preventing the loss of heat, regulating the direct supply of air to the fire, and the convenient application of fuel. In this arrangement, cd, Fig. 1014, is a large cast-iron plate let into the brick-work, and having 4 projecting brackets, e e, ff, in which are secured the ends of stout cylindrical bars which are to carry the doors. The apertures to the grate and ash-pit are surrounded with an iron rim or edge, about inch wide, the lower part being continued backward along the plate, forming a kind of guide, gh. The fire-door, which exactly resembles the ashpit door, consists of a rectangular cast-iron box, having its edge ground so as to fit accurately the iron rim before described, and the interior is filled Fram Fig. 1013. THE BOILER AND ITS ASSOCIATED APPARATUS USED IN THE EXPERIMENTS ON STEAM COAL.. |