Abbildungen der Seite
PDF
EPUB

degree of heat to be inflammable. As soon as it has acquired that degree, the approach of a candle will inflame the whole body, and the difference of the heat which it gives will be very sensible. A still easier experiment may be made with a candle itself. Hold your hand near the side of its flame, and observe the heat it gives: then blow it out, the hand remaining in the same place, and observe what heat may be given by the smoke that rises from the still burning snuff; you will find it very little and yet the smoke has in it the substance of so much flame, and will instantly produce it, if you hold another candle above it so as to kindle it. Now the smoke from the fresh coals, laid on this stove, instead of ascending and leaving the fire, while too cold to burn, being obliged to descend through the burning coals, receives among them that degree of heat which converts it into flame: and the heat of that flame is communicated to the air of the room, as above explained.

The flame from the fresh coals laid on in this stove, descending through the coals already ignited, preserves them long from consuming, and continues them in the state of red coals, as long as the flame continues that surrounds them, by which means the fires made in this stove are of much longer duration than in any other, and fewer coals are therefore necessary for the day. This is a very material advantage indeed. That flame should be a kind of pickle to preserve burning coals from consuming, may seem a paradox to many, and very unlikely to be true, as the doctor tells us it appeared to himself the first time he observed the fact; he therefore relates the circumstances, and mentions an easy experiment, by which his reader may be in possession of every thing necessary to the understanding of it. In the first trial he made of this kind of stove, which was constructed of thin iron plate, he had, instead of the vase, a kind of inverted pyramid, like a mill-hopper; and fearing at first that the small grate contained in it might be clogged by cinders, and the passage of the flame sometimes obstructed, he ordered a little door near the grate, by means of which he could occasionally clear it; though after the stove was made, and before he had tried it, he began to think this precaution superfluous, from an imagination that the flame, being contracted in the narrow part where the grate was placed, would be more powerful in consuming what it should there meet with, and that any cinders between or near the bars would be presently destroyed and the pasage opened. After the stove was fixed, and in action, he had a pleasure now and then in opening that door a little, to see through the crevice how the flame descended among the red coals, and, observing once a single coal lodged on the bars in the middle of the focus, he observed by a watch in what time it would be consumed: he looked at it long without perceiving it to be at all diminished, which surprised him greatly. At length it occurred to him that he had seen the same thing a thousand times, in the conversion of the red coal formed in the snuff of a burning candle, which, while enveloped in flame, and thereby prevented from the contact of the passing air, is long continued, and augments instead of

diminishing, so that we are often obliged to remove it by the snuffers, or bend it out of the flame into the air, where it presently consumes to ashes. He then supposed, that to consume a body of fire, passing air was necessary to receive and carry off the separated particles of the body: and that the air passing in the flame of the stove, and in the flame of a candle, being already saturated with such particles, could not receive more, and therefore left the coal undiminished as long as the outward air was prevented from coming to it by the surrounding flame, which kept in a situation somewhat like that of charcoal in a well luted crucible, which, though long kept in a strong fire, comes out unconsumed.

Mr. Craigie has a patent fire-grate of a very peculiar construction. It consists of a foundation or basis of about four feet in length by about two feet eight inches in breadth, and about twenty inches in height; at one end in the front is to be placed the chimney grate, eighteen inches wide and six deep. On the foundation in the centre, at nineteen inches distant from each other, are to be raised two sides in stone or brick, the whole length thereof, about eight inches in height; on these sides is to be placed a pan of cast iron, of size to cover the whole, with rims to rest on the sides, but leaving a small space vacant, say about half an inch from each side below; the depth of the pan may be about five or six inches, and will be raised above the basis, so as to leave an aperture throughout of about an inch and a half; at the end of the furnace, opposite to the firegrate, the aperture will terminate in a flue of brick or iron to convey the smoke into the chimney of the house, which flue should be furnished with a register or damper.

A plate projecting from the lower end of the pan will form the top of the fire-place, of eighteen inches by six or eight; the sides will be formed of fire-bricks; the back of the fire-brick will ascend towards the top in a sloping direction under the pan. A frame of iron will be placed to receive the door or front, which will be in the clear about eighteen inches in width by about sixteen inches in depth, that is to say, to cover the ash-pit four inches, and about twelve inches above the grate for the fire-place, in front of which there should be an inner grate of about five or six inches high; this door must have in the lower part of it, about an inch and a half from the bottom, a small door of about three inches wide by two in depth, to furnish air through the ash-pit. When wood is used for fuel, the depth of the fire-place may be twelve inches instead of six. The iron pan being filled with dry sand, will form a sand bath, with heat sufficient according to the depth to which the vessel is placed in it for all ordinary purposes, and being once heated will retain the heat for a considerable time, especially if the doors are kept close shut; the plate or front will serve for broiling or frying. Roasting may be performed to perfection before the door in front even with the doors shut; an oven for baking may be fixed at the flue. Convenience will be found in having the meat, &c., to be roasted suspended from a moveable fire-screen.

The great numbers of manufactories destroyed

by fire in consequence of the large quantities of loose shavings in carpenters' and joiners' shops, induced Mr. Davis to contrive a fire-grate for a safe and economical mode of burning shavings; the object of which is to employ these useful combustible materials as fuel, instead of coal, by such a construction of the grate, that they will not burn too fast, as they do in an open fire, 1..aking an intense heat, but only of a momentary duration. This is effected by putting the shavings into a sheet iron cylinder, closed at top, which is fitted into the top of a grate, very similar to those used for burning coals; and the flame produced by the shavings passes through flues conducted in the usual manner; the air which supports the combustion being supplied through the bars of the grate.

The fire-grate is twelve inches wide, and one foot three inches high; it is of cast iron, and lined with fire tiles, having a door with an ashpit beneath, in the usual manner; the sheet iron pipe conveys the smoke and flame from the fireplace into a brick flue, and this leads into the chimney; there is an iron door opening into the chimney for the sweeping machine, or boy, to pass through to sweep the chimney; the sheet iron cylinder, in which the shavings are put to be consumed, is about nine inches in diameter, and sixteen inches high: it is placed over a circular aperture in the top of the fire-grate, and has a neck to prevent the sparks of the shavings from flying out into the workshop. The cylinder is covered at top with a lid, having also a neck, which is removed at pleasure by a handle, to put in a supply of shavings; this fits very close, and, as no air can pass by it, a sufficient draught to burn the shavings, but slowly, is afforded by the air passing through the bars of the grate, which is impeded by the ashes that may be therein; but this flame may be increased to a rapid combustion, when necessary, by opening the door of the stove; the flame passes along the flues, and gives out an equable heat to the room. Iron bearers are fixed across the flue, which may be used to support any work which requires drying, or for any other purpose of this kind. The supply of this stove with fuel from shavings is attended with so little trouble, and is such an advantage to the workmen, that they will always prefer burning the shavings to coals; so much so, that where ten men are at work, there is a difficulty to collect shavings sufficient even to light the fire the next morning. By this means the danger of fire, which has been fatal to so many manufactories, is greatly removed; the loose shavings being consumed as soon as they are made, and that in lieu of more expensive fuel; and so slowly are the shavings consumed, that the iron cylinder will hold enough, when completely filled, to supply the fire for upwards of half an hour. To guard the workshops still more effectually from danger, the stove and its iron flue is supported upon a mass of brick-work, which prevents any sparks from falling on the floor; and the sides of the brick-work afford very convenient shelves on which to lay any wood-work that requires heating or drying; and when a greater heat is required to extend to a considerable length horizontally, as, for instance,

four or five feet, by merely putting a few shavings into the cylinder frequently, in place of filling it, they become converted into flame, which is carried the whole length of the iron flue, heating it uniformly throughout. No soot lodges in the flue, but merely light ashes, which can be easily cleared out from time to time, as may be necessary.

The Swedish or Russian mode of warming buildings is thus described by M. Guyton in the Annales de Chimie. The construction of the apparatus which is there recommended may be improved, to adapt it to our use in England, where pit coal is used; but the following principles, which the author lays down, are very useful as guides in making all kinds of stoves for warming apartments. 1. Heat is produced only in proportion to the volume of air consumed by the fuel. 2. The quantity of heat produced is greatest (the quantity and quality of the fuel being the same) when the combustion is most complete. 3. The combustion is the more complete, in proportion as the fuliginous part is longer retained in channels where it may undergo a second combustion. 4. The only useful heat is that sent out into, and retained in, the space intended to be heated. The temperature of that space will be higher in proportion as the current, which must be renewed from without to support the combustion, is less enabled to take up in its passage the heat produced.

Hence the following inferences evidently arise: -1. The fire-place ought to be insulated from all bodies that are rapid conductors of heat. All the heat that goes out of the apartment is absolutely lost, unless intentionally directed into another apartment. 2. Heat being produced only by combustion, and combustion being sustained only by a current of air, the current should be brought in by channels, where the needful rapidity may be preserved without being too distant from the space to be warmed, so that the heat it there deposits may be gradually accumulated in the whole of the insulated surface, in order afterwards to flow out of it slowly, according to the laws of the equilibrium of that fluid. 3. The wood being so far consumed as to give no more smoke, it is advantageous to close the mouth of these channels, in order to retain there the heat that would otherwise be carried off through the upper flue, by the continuance of a current of fresh air, necessarily of a low temperature. 4. Lastly, it follows from these maxims, that, all things being equal, a higher temperature will be obtained, and supported during a much longer time, by forming in the internal parts of the stove, or under the hearth of a chimney, and in their vicinity, tubes in which the air that comes from without may be warmed before it enters the apartment, to serve the purpose of combustion, or replace that which has been consumed. These have been called bouches de chaleur (mouths or apertures of heat), because, instead of contemplating their principal use and intention, it is commonly imagined that they are only made in order to give, by their issues, a more rapid current to the heat produced. Nor is this idea absolutely devoid of foundation, since the air that issues from them has only changed its temperature, by carrying

off a portion of the heat that would have remained in the interior. Those, however, who would proscribe them, as opposing the most important object, which is the retaining of the heat as long as possible, do not consider that they may be closed, and all communication with the external air cut off by a simple slide, and, therefore, it is easy to derive from them every possible advantage without any inconvenience. And we may add that in small apartments, or such as are accurately closed, they are often indispensably requisite, if we would avoid being exposed to currents of cold air. Dr. Franklin very justly quotes a Chinese proverb to this effect: Shun a current of air from a narrow passage as you would the point of an arrow.'

The Swedish or Russian stoves, which have chambers for the reception of the flame and smoke, are little known in this country: but those which are in common use in the halls and vestibules of our great houses are French stoves. They differ from the others in having a very great length of small flues or winding passages, through which the smoke passes, and communicates its heat to the air, which circulates in similar passages, until it becomes warmed, and makes its exit through the mouths into the apartment. This method is not so simple as the small chambers or apartments of the Russian stoves, nor is it so good in the long run; because the passages are very liable to become clogged with soot; and, even before they are so clogged as to intercept the passage of the smoke, the transmission of the heat is much impaired, because the interior surfaces of the flues, becoming coated with soot, do not conduct the heat so rapidly, and, in consequence, a great part will still pass out into the chimney. Also, these flues with small passages require a stronger draught in the chimney to make the air pass through the passages, than when chambers are used.

The Holland iron stove, which has a flue proceeding from the top, the fire-place and ash-pit being closed by small iron doors opening into the room, comes next to be considered. It is frequently made of iron plate, and is most commonly called a German stove. Its conveniences are, that it makes a room warm all over, for the chimney being wholly closed, except the flue of the stove, very little air is required to supply that, and therefore not much rushes in at crevices, or at the door when it is opened. Little fuel serves, the heat being nearly all saved; for it radiates almost equally from the four sides, and the bottom and top, into the room, and presently warms the air around it, which, being rarefied, rises to the ceiling, and its place is supplied by the lower air of the room, which flows gradually towards the stove, and is there warmed and rises in its turn, so that there is a continual circulation, till all the air in the room is warmed. The air, too, is gradually changed by the stove-doors being in the room, through which part of it is continually passing, and that makes these stoves more wholesome, or at least more pleasant, than the German stoves. But they have the inconvenience that there is no sight of the fire, which is, in itself, a pleasant thing, nor can any other use be conveniently made of the fire but that of warming the room.

FIRE, GREEK, a kind of factitious fire, called by the Greeks, who were the inventors and principal users of it, the maritime fire; and which burns with greater violence in water than out of it. It is said to have been composed of naphtha, bitumen, pitch, sulphur, and gum, and was only to be extinguished by vinegar mixed with sand and urine. Leonard da Vinci describes the composition as formed by mixing over the fire, the charcoal of willow, nitre, brandy, resin, sulphur, pitch, and camphor. A woollen cord is then plunged in the mixture, and made into balls, which, when set on fire, are thrown into the enemy's vessels. This fire was employed principally in the wars of the Greeks with their Saracen neighbours; and the Eastern Romans retained the secret for above 400 years; and even at the end of the eleventh century, the Pisans, to whom every science and art were familiar, suffered the effects, without understanding the composition of the Greek fire. It was at length either discovered or stolen by the Mahommedans, and in the holy wars of Syria and Egypt they retorted the invention on the heads of the Christians.

It might be used with equal effect by sea or land, in battles or in sieges. It was either poured from the ramparts in large boilers, or launched in red hot balls of stone and iron, or darted in arrows and javelins, twisted round with flax which had deeply imbibed the inflammable oil: sometimes it was deposited in fireships, or most commonly blown through long tubes of copper, planted on the prow of a galley. The modern discoveries respecting combustion have disclosed the whole secret of compositions which burn without access to the atmosphere, by means of oxygen afforded from nitre.

FIRE-LOCK, in military affairs, the arms of a foot soldier, so called because it produces fire of itself by flint and steel, in contradistinction from a match-lock, which requires a lighted match. Firelocks were formerly three feet eight inches in the barrel, and weighed fourteen pounds, at present the length of the barrel is from three feet three inches to three feet six inches, and the weight of the piece only twelve pounds. They carry a leaden bullet, of which twenty-nine make two pounds, its diameter is 550 of an inch, and that of the barrel one-fiftieth part of the shot. See MUSKET.

FIRE-POTS, in the military art, small earthen pots, into which is put a charged grenade, and over that powder enough to cover the grenade; the pot is then covered with a piece of parchment, and two pieces of lighted match placed across; this being thrown by a handle of matches where it is designed, it breaks and fires the powder, and burns all that is near it, and likewise fires the powder in the grenade, which ought to have no fuse, that its operations may be the quicker.

FIRE-REEDS, reeds used in fire-ships. They are made up in small bundles of about a foot in circumference, cut even at both ends, and tied together in two places. They are distinguished into two kinds, viz. the long and short; the former of which are four feet, and the latter two feet five inches in length. One part of them are singly dipped, i. e. at one end the rest are

dipped at both ends in a kettle of melted composition. After being immersed about seven of eight inches in this preparation, and then drained, they are sprinkled over with pulverised sulphur upon a tanned hide.

FIRE-SHIPS are generally old vessels filled with combustibles, fitted with grappling irons to hook, and set fire to, the enemies ships in battle, &c. As there is nothing particular in the construction of this ship, except the apparatus by which the fire is instantly conveyed from one part to another, and thence to the enemy, it is sufficient to describe the fire-room, where these combustibles are enclosed, together with the instruments necessary to grapple the ship intended to be destroyed. The fire-room is built between decks, and limited on the afterpart by a bulkhead, L, behind the main mast, from which it extends quite forward, as represented in the diagram at the foot of this article. The train enclosed in this apartment is contained in a variety of wooden troughs, D, G, which intersect each other in different parts of the ship's length; being supported at proper distances by cross pieces and stanchions. On each side of the ship are six or seven ports, H, about eighteen inches broad and fifteen inches high; and having their lids to open downward, contrary to the usual method. Against every port is placed an iron chamber, which, at the time of firing the ship, blows out the port-lid, and opens a passage for the flame. The iron chambers are ten inches long and 3-5 in diameter. They are breeched against a piece of wood fixed across the ports, and let into another a little higher. When loaded they are almost filled with corn-powder, and have a wooden tompion well driven into their muzzles. They are primed with a small piece of quick-match thrust through their vents into the powder, with a part of it hanging out. When the ports are blown open by means of the iron chambers, the port-lids either fall downward, or are carried away by the explosion. Immediately under the main and fore shrouds is fixed a wooden funnel M; whose lower end communicates with a fire-barrel, by which the flame passing through the funnel is conducted to the shrouds. Between the funnels, which are likewise called fire-trunks, are two scuttles, or small holes in the upper deck, serving also to let out the flames. Both funnels must be stopped with plugs, and have sail-cloth or canvas nailed close over them, to prevent any accident from above to the combustibles laid below. The ports, funnels, and scuttles, not only communicate the flames to the outside and upper works of the ship and her rigging; but likewise open a passage for the inward air, confined in the fire-room, which is thereby expanded so as to force impetuously through those outlets, and prevent the blowing up of the decks, which must of necessity happen from such a sudden and violent rarefaction of the air as will then be produced. On each side of the bulk head behind is cut a hole L, of sufficient size to admit a trough of the same dimensions as the others. A trough, L, I, whose foremost end communicates with another trough within the fire-room, is laid close to this opening,

whence it extends obliquely to a sally port I, cut through the ship's side. The decks and troughs are well covered with melted resin. At the time of the firing either of the leading troughs, the flame is immediately conveyed to the opposite side of the ship, whereby both sides burn together. The spaces N, O, behind the fire-room, represent the cabins of the lieutenant and master, one of which is on the starboard, and the other on the larboard side. The captain's cabin, which is separated from these by a bulk-head, is exhibited also by P. Four of the eight fire-barrels are placed under the four fire-trunks; and the other four between them, two on each side of the fire scuttles, where they are securely cleated to the deck. The longest fire-reeds are put into the fore and aft troughs, and tied down: the shortest reeds are laid in the troughs athwart, and tied down also. The firebavins, dipped at one end, are tied fast to the troughs over the reeds, and the curtains are nailed up to the beams, in equal quantities, on each side of the fire-room. The remainder of the reeds are placed in a position nearly upright, at all the angles of every square in the fire-room, and there tied down. If any reeds are left, they are to be put round the fire-barrels, and other vacant places, and there tied fast.

The following instructions are given in the regulations for a fire-ship of 150 tons burden:

The fire-barrels are to be two feet four inches high, and one foot six inches in diameter. Each barrel must have four holes of about six inches square, cut in its sides, with a square piece of canvas nailed over each of them. They are then filled with the carcass-composition, and four plugs, of about one inch diameter and three inches long, and well greased, are thrust into the top, and then left to dry. When dry, these plugs are taken out, and the holes filled with fuse-composition, and quick-match at the top, which goes from one hole to the other; after this, the top is smeared over with mealed powder, mixed up with spirits of wine. When dry again, a sheet or two of brown paper is laid over the top, and then one of the canvas covers, which is made secure by the upper hoop of the barrel.

The composition for dipping reeds, bavins, and curtains, is

[blocks in formation]

In order to produce an additional external fire, forty-four boxes are filled with the carcasscomposition, and distributed on the three masts in the following manner :-One suspended from each of the cat-heads and davits, on each side of the bow; eight slung across the bowsprit; four across each of the out-riggers abaft; two from the grapplings of each of the lower yardarms; one from the dead-eyes on each side of the three round-tops; and one from the middle of the inside of the main, fore, and mizen shrouds.

Besides the boxes, there are fire-barrels arranged as follows:-Two half barrels on the forecastle; two abaft the main-deck, and four on the main-deck; two in each round-top, placed against the masts; and four large firebarrels, under fire-trunks, to convey fire to the curtains on the shrouds. All these fire-barrels and boxes are to be fired by separate leaders of quick-match, or port-fire, in order that any part of the ship may be fired, to cover its approach by the smoke; and the remaining part instantaneously upon quitting the ship. It has been found, by experiment, that two men, with lighted port-fires, can set fire to the whole of the leaders on the deck, bowsprit, cat-heads, out-riggers, &c., in less than a minute; therefore, the risk of trusting to one main leader to the whole may be avoided. The leaders are laid in painted canvas hose, made for the purpose.

The proportion of combustible stores for a fire-ship of 150 tons, is as follows:

8 Fire-barrels, filled with composition.
12 Iron chambers, to blow open the ports.
250 Bavins, single-dipped.
24 Port-fires.

31 Priming composition barrels.
1 Quick-match ditto.

48 Dipped curtains.

150 Long reeds, single-dipped.
75 Short reeds, single-dipped.
75 Short reeds, double-dipped.
60 Hand grenades.

When ordered to prime, the captain is to take up all his reeds, one after another, and strow a bitle composition at the bottom of all the troughs under the reeds, and then tie them gently down again; next to strow composition upon the upper part of the reeds throughout the fireroom; and upon the composition to lay double quick-match upon all the reeds, in all the troughs: the remainder of the composition to be spread over all the fire-room. He is then to cast off all the covers of the fire-barrels, and bang the quick-match loose over their sides, and place leaders of quick-match from the reeds into the barrels, and thence into the vent of the chambers, in such a manner as to be certain of their blowing open the ports, and setting fire to the barrels. The troughs of communication from each door of the fire-room to the sallyports must be laid with a strong leader of quickmatch, four or five times double: also a crosspiece to go from the sally-port, when the ship is

fired, to the communication through the trough, laid with leaders of quick-match, that the fire may be communicated on both sides at once. What quick-match is left must be placed so that the fire may be communicated to all parts of the room at once, especially about the ports and fire-barrels. The port-fire used for hiring the ship burns about twelve minutes; great care must be taken to have no powder on board when the ship is fired. Sheer-hooks are fitted so as to fasten on the yard-arms of the fire-ship, where they hook the enemy's rigging. The firegrapplings are either fixed on the yard-arms, or thrown by hand, having a chain to confine the ships together, or fasten those instruments whereever necessary. Whenever the commanding officer of a fleet displays the signal to prepare for action, the fire-ships fix their sheer-hooks, and dispose their grapplings in readiness. The battle being begun, they proceed immediately to prime, and prepare their fire-works. When they are ready for grappling, they inform the avoid being disabled by the enemy's cannon admiral thereof by a particular signal. during a general engagement, the fire-ships continue sufficiently distant from their line-ofbattle, either to windward or leeward. They cautiously shun the openings or intervals of the line, where they would be directly exposed to the enemy's fire, from which they are covered by lying on the opposite side of their own ships. They are attentively to observe the signals of the admiral or his seconds, in order to put their designs immediately into execution. Although no ship of the line should be previously appointed to protect any fire-ship, except a few of the smallest particularly destined to this service, yet the ship before whom she passes in order to approach the enemy, should escort her thither, and assist her with an armed boat, or whatever succour may be necessary in her situation.

To

Among the most formidable contrivances ever used, either as a fire-ship or explosion-vessel, is that which was used to destroy the bridge of boats at the siege of Antwerp, in the year 1585; which an author of that period states to have been a ship strongly timbered, containing a vulted arch of stone or mortar, filled with 200 barrels of gunpowder, over which were placed large stones of all forms, cannon-shot, iron chains, &c., sufficient to destroy a whole city, that were exploded by a secret fusee, contrived so as not to set fire to the charge till the vessel came in contact with the bridges, which it blew to atoms

[graphic][subsumed][merged small][merged small][subsumed][ocr errors][ocr errors]
« ZurückWeiter »