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PROMOTION OF COMBUSTION BY FORCED AIR.

such chamber and external cylinder, the valves at the bottom of the four pipes F are lifted, and the products of combustion begin to flow regularly into the water, and will continue to

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do so as long as the pumps supply the fire with air. Hence none of the heat evolved can possibly escape without passing through the water and being turned to profitable account.

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The elastic fluid thus formed being a compound of gases and vapours, is of course not wholly condensible, and therefore only fitted for high-pressure

engines: but the great strength of the above-described generator will probably seldom be required, as rivetted plates are sufficiently secure for most

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PROMOTION OF COMBUSTION BY FORCED AIR.

purposes; nor need the same form be followed.

With respect to combustion under great pressure, I have never discovered but that it proceeded as well in that way as by common drafts under the ordinary atmospheric pressure. As

to the expense of power required to force the air, I may observe, that that part of the atmospheric air-nitrogen -which does not enter into combustion, but separates itself from the oxygen during the process, though it does not itself evolve heat, must of necessity become charged with a considerable portion of heat in passing through any fire. Now, while in fires worked by a common chimney-draft the nitrogen thus charged with heat is almost wholly carried into the atmosphere and lost-in passing through a close fire and into the water in the manner before-mentioned, it must ultimately pass through the engine, in consequence of this charge of heat, with greater elasticity and power than the resistance it could oppose while being forced. Hence there is at least a favourable preponderance.

Then as to the oxygen, we will sup pose (leaving out other products formed by combustion, for the sake of simplicity) that every 659 cubic feet of oxygen forced into the fire unites with 1355 cubical feet of hydrogen-the composition of one cubic foot of water. Now the 1355 feet of hydrogen is derived entirely from the fuel, and the foot of water so formed, or rather vapour, will be equal to about 1800 cubic feet at atmospheric pressure— for a cubic foot of water converted into steam at that pressure expands about 1800 times. Hence we have an increase of more than, or nearly two-thirds over and above the oxygen forced into the fire, and equal to onefourth of the whole volume of atmospheric air necessary to supply the 659 cubic feet of oxygen gas, as a compensation for friction, &c., in forcing.

From the foregoing short description it is manifest that no more room need be occupied by a generator on this principle than what is absolutely necessary to the combustion of an adequate quantity of fuel, and the

small space of a few inches to surround the fire with water and to form a steam-chamber. The four pipes F, instead of being attached to the firechamber above the fire, should be affixed about the middle of the burning mass.

Other modifications bearing strongly on the above principle were embraced in the general plan, and some of them put in practice. One was an application of air to the fire in the manner above-described; but instead of the products of combustion being forced directly into the surrounding water of the generator through the pipes F, it passed through a flue-pipe attached to the cap for that purpose, as seen in figure 1, into a separate vessel, under a much lower pressure than the steam formed in the generator, by which the heat was absorbed, and the water thus partially heated transferred to the generator to make good the evaporation. Another mode tried was to have air forced into the close fire of a steam-boiler, having a sufficient length of flue to absorb the heat as in the usual manner, which flue terminated by descending into a cistern of water; the depth of the end of the flue below the surface being the gauge of the density of the products of combustion in the flue, which density might be increased or diminished at pleasure, as circumstances required. This method prevents the products from expanding with so great rapidity, and the heat Hence becoming latent therein.

there will be more free heat given to the surface of the flue and absorbed by the water in contact therewith. The water in which the flue terminates will absorb the remaining heat, condense the vapours, and detain all carbonacious and other ponderous matter while the gases will escape from the surface, and that nuisance, a chimney, be dispensed with.

The last modification which I shall now notice is the application of an exhausting-apparatus over the surface of the water in which the flue terminates, instead of forcing the air into the fire; by this means a partial vacuum is formed above the surface of the water equal to any required draught, and the water absorbing the

PREVENTING THE WARPING OF SMALL FILES.

heat of the flue, &c., as in the last modification, no injury to the exhausting-machine can ensue, and the chimney is also dispensed with. A drawing of this plan was made and presented to some gentlemen in 1826.

[To be concluded in our next, when we shall offer some remarks on the obvious similarity between Mr. Gilman's plans and those of Messrs. Braithwaite and Ericsson.-EDIT.]

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Sir, In No. 320 of your Magazine, I find your correspondent "C. C." wishes to be made acquainted with "the method which file-makers adopt to prevent the warping of their small files in hardening." For this reason, I send you a few hints; and should "C. C." find them useful, and make the result of his experiment known through the medium of your valuable work, he will by so doing "confer an obligation" on me; as I am of the opinion, and perfectly agree with Mr. Mackinnon, your correspondent in No. 316, wherein he states that to be master of the above art" requires experience, and cannot be taught by written directions."

First, forge your steel plates to the size required, after which they must be softened, thus:-Take a quantity of wood chips, and having heated your plates hot enough to set them on fire, let them be placed thereon, and remain there until the whole of the chips are consumed, and the plates cool. Your plates must now be filed perfectly level for cutting; and the same method must be resorted to in files which require to be re-cut. When they are cut, they should be placed in a mixture of lime and water, of moderate thickness, in which they may remain for any length of time, or till you wish to harden them; they will not rust, or take any hurt, by lying in this solution, the lime being a preventive.

When you feel inclined to harden them, they must be taken out of the mixture, and placed directly before a good fire, to dry the lime, which will fill up the cavity between the teeth, and is only used to prevent the fire from destroying the same during the

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process of hardening. You must now have in readiness a tub, containing three pailsful of spring-water, into which you may place the following ingredients:

8 oz. of sal-ammoniac, powdered;
8 oz. of aqua-fortis;

1 lb. of common salt: which water may be kept for hardening some time. You must also have at hand a wooden mallet and block, in case of your file coming in contact with a piece of coke, &c. while getting your heat, and causing the same to bend; in which case you must lay your file upon the block, and gently press the crooked part with the mallet until you have made it perfectly straight. It is farther necessary to have a flat box, containing 1 lb. of common salt, in which you must rub your file every time you take it out of the fire to ascertain your heat. Having all these requisites prepared, then blow up a good loose fire, free from gas or green coal; and when you have got a good red heat, hold your file as perpendicularly as you possibly can over the water, and sink it gradually, in the like position, into the same as far as the tang, or handle, which must not be hardened.

By this process you are likely to harden many files at the first attempt; yet sometimes you cannot prevent some from warping. If any of them should do so, they can be remedied thus: Put a quantity of grease or oil into a long flat pan, into which place the files which are warped; then heat a piece of iron red-hot, which place in a vice, and take one of the warped files out of the oil-pan, and fasten a hand-vice at each end to hold it by; then humour the same backwards and forwards, according to the warping, which will presently come straight, taking care to keep plenty of oil upon your file, which preserves the temper of the steel, and prevents the heat of the iron from softening it. This done, nothing remains to be observed but cleaning.

Place your files into a pail of warm water; then take a hard brush, on which place a little soap, and brush them till all the lime which still remains between the teeth is completely washed out; then place them directly be

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BREECH-LOADING GUN.

fore a good fire to dry, and brush them again with a dry brush. Finally, take a small quantity of the best oil, and drop a little on a soft brush, and rub them all over with the same, taking care to let the files be a little warm, which will cause the oil to spread more thinly over them. They are now in a fit state to be laid by till I wanted for use.

This, Sir, is all the information I can give your correspondent respecting this matter. But, before I con

clude, I should advise him to forge out a few pieces of steel to the dimen sions required, and let him practise hardening the same, till he is somewhat perfect; by which means he will save a quantity of files which he might otherwise spoil.

I remain, Sir,
Your most obedient servant,
R. DANIEL.

Eldon-street, Finsbury Circus,
Nov. 7, 1829.

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Sir,-To those interested in the use of fire-arms, I hope no apology is neeessary for occupying a page of your excellent Magazine with descriptions of an invention which may tend to accomplish that great desideratumthe loading at the breech. The prefixed sketches were taken from a gun which I constructed, and found to answer very well.

Before entering on a description of the different parts of the said invention, I beg leave to observe, I am far from concluding myself arrived at the ne plus ultra of breech-loading, as I confidently look forward, through the medium of your widely-circulating work, for great assistance from the liberal mechanic.

Fig. 1, represents the gun complete. Fig. 2, the barrel turned down for the purpose of loading, by pulling the guard, which opening from a latch affixed to the scroll, allows the barrel to turn on the trun

nions, as shown at A Fig. 3, the charger, having a patent breech, into which the cartridge is put, the cylinder of which fits accurately into the calibre of the barrel. For military purposes this charger can be dispensed with, when by means of a sharp edge attached to the under part of the false breech at B, the cartridge being inserted ball foremost into the lower orifice of the barrel, will have its end bitten off on closing the gun; thus exposing the powder to the fire from a touch-hole bored through the false breech, which is firmly rivetted between the cheeks of the iron stock, the butt alone of which is composed of wood. Fig. 4, the lock, wherein the usual order of the cock and mainspring has been reversed.

The many advantages of such an arrangement must be apparent to all who are habituated to the use of firearms. Security is hereby obtained from rain; the eyes are shielded from

MACHINE For pressinG BOOKS.

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MACHINE

FOR

DESCRIPTION OF A
PRESSING BOOKS BY ROLLING IN-
STEAD OF HAMMERING.

Sir,-Observing in No. 317, of your instructive miscellany, a notice of an improved book-binder's hydrostatic press, by Alfred Holden, it recalled to my recollection a press, which, in my opinion, answers the purpose better; and were it more generally used, would entirely supersede the old, laborious, and imperfect method of beating books with hammers, the blows of which, suddenly compressing the air between the leaves, create a heat, which is liable to make the printing set-off (as it is termed) on the opposite pages.

The press consists of two iron cylinders, about a foot in diameter, adjustible in the usual way by means of a screw, and put in motion by the power of one or two men applied to a cranked handle. In front sits a boy, who gathers the sheets into packets, by placing two, three, or four, upon a piece of tin plate, of the same size, and covering them with another piece of tin plate; and thus proceeding, alternating tin plates and bundles of sheets, till a sufficient quantity has been put together, which will depend upon the stiffness and thickness of the paper. The packet is then passed between the rollers, and is received by the man who turns the winch, and who has time to lay the sheets on one side and hand over the tin plates, by the time the boy has prepared a second packet. I have seen by means of this press, a minion Bible pressed ready for binding in one minute, whereas the time necessary to beat

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the same would have been twenty
minutes. But it is not merely a sav-
ing of time that is gained by the use
of the rolling-press; the paper is made
much smoother than it would have
been by beating, and the compression
is so much greater, that a rolled book
will be reduced to about five-sixths of
the thickness of the same book beat-
en so that a shelf that would hold
fifty books bound on the old plan, will
hold nearly sixty if passed through
the rolling-press. I will merely add,
that the expense of the machine is
but trifling compared with the advan-
tages derived from the work being
better finished, and the saving of
men's time in beating them.
I remain, Sir,

Your obedient servant,
BRACKSTONE.

EXTRACTS FROM MY NOTI-BOOK.
No. 3.

Optical Phenomenon.

"C." (vol. xi. page 31) will find an answer to his inquiry in the "London Encyclopedia," art. Optics. The passage is long, or I would transcribe it.

On the Infinite Divisibility of Matter.

"The fourth property of matter," says Ferguson, (" Lectures," p. 3.) "is divisibility, of which there can be no end. For since matter can never be annihilated by cutting or breaking, we can never imagine it to be cut into such small particles, but that if one of them be laid on a table, the uppermost side of it will be farther from the table than the undermost side." Our author then shows how matter is infinitely divisible in a "mathematical sense." On this passage, Dr. Brewster justly observes, "The above reasoning is merely ideal, and only shows that we can conceive extension to be infinitely divisible."

The Doctor's remark would have been more just, if he had said that the reasoning was misplaced.

In all cases of division or separation, the attraction of aggregation or cohesion is overcome: this, therefore, ought to be taken into consideration in any proposed proof of the infinite divisibility of matter; and unless this

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