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of the axis farthest from the face, the machinery to which it is proposed to impart motion is affixed.

The engine is worked by steam and water as follows. The annulus is in the first place half filled with water, either admitted cold, and heated by suffering the steam to flow into it through the pipe e, or admitted in a heated state from the boiler. On the steam valve being opened, the steam enters the hole in the mask, Fig. 4. through the pipe 1, Fig. 5. and passes thence through the hole in the face which happens to be opposite to the aperture in the mask, and enters the annulus; then rising through the water, it is stopped by the valve d, immediately above the radius by which it entered, which will then be closed. The steam resisted by the valve, acts against the surface of the water below it, and pressing it downwards, proportionably raises it on the opposite side of the annulus, until the pressure of the column of water acting against the closed valve, through the medium of the steam, is sufficient to overcome the resistance. The troke is now made to revolve, and, as it revolves, each of the holes in the face communicates in succession with the hole 7, and, by this construction, one entire hole in the face, or parts of two equal in proportion to one, is always in communication with the hole ; so that there is a continual flow of steam into the annulus, causing the water, through its medium, to exert a constant and uniform pressure on the valves as they ascend. The holes in the face, as they pass in succession from the hole 7 to the hole i are entirely closed by the space between them; and, immediately on communicating with the hole i, the steam rushes from the annulus through that hole into the condenser, or into the air; and the pressure of steam being thus removed from the valves, they will open by the gravity of the weights d, as they begin to descend, and thus allow the column of water to

remain on that side of the annulus. Thus a uniform rotatory motion is produced and maintained as long as the steam continues to flow into the annulus, and acting with a force proportionate to the difference of level in the water.

In Fig. 1. the troke is represented as revolving, and the steam flowing into the annulus, through the radius b 1; f represents the steam in the annulus between the closed valve and the depressed surface of the water; g the water raised on the opposite side of the annulus, while the remaining or darkest part of the annulus is where the valve and the upper surface of the water are relieved from pressure, the steam having discharged itself through b 6.

The steam may be admitted through a radius more or less horizontal, according as the column of water is higher or lower, by means of an inner mask, which changes its position; the closing spot of the valves may also be regulated accordingly, by means of catches acting on their levers. The troke is of cast iron, and, to prevent condensation, it is enclosed in a steam-tight case.

From this brief examination of Messrs. Masterman's engine, it will, we think, be apparent, that the troke alone performs the united function of cylinder, piston, beam, crank, and fly-wheel; thus ensuring a decided superiority over the reciprocating engine.

The advantages resulting from the use of steam engines have, in some cases, been considered as fully equipoised by the smoke and noxious effluvia which proceed from their capacious vomitories; and this, in large manufacturing towns, is indeed an evil of some importance, to obviate which a variety of contrivances have been suggested.

The first attempt at consuming smoke, appears to have been made by M. Dalesme, a French engineer, who exhibited a contrivance of this description at the Fair of St.

Germaine in 1685*. In 1785 Mr. Watt obtained a patent for the construction of an economical furnace, which not only consumed the smoke, but employed it as an useful auxiliary in increasing the heat. To understand this it will be necessary to observe, that the dense smoke which is usually discharged at the top of the chimney, is, in fact, so much good fuel, which requires but a sufficient supply of oxygen to render it fit for combustion.

Mr. Watt accomplished this in his early engines by stopping up every avenue to the chimney, except such as might be left in the interstices of the ignited fuel, and the smoke from the fresh coal was consumed by passing through the burning fuel or coke.

A variety of improvements have since been introduced, an account of which will be found in Appendix (B,) and we shall content ourselves, in the present instance, with briefly noticing those that appear best calculated to answer their intended purpose.

Mr. Roberton's plan is nearly similar to that employed by Mr. Watt. The opening through which the fuel is introduced into the furnace is shaped like a hopper, from the mouth or entrance of which it inclines downward to the place where the fire rests on the bottom grate. The fresh coals contained in the hopper answer the purpose of a fire-door, and the principal point to be attended to in the management of this furnace is, that the hopper shall be so filled with small coal as to prevent as much as possible the passage of atmospheric air by the hopper. Beneath the lower part of the hopper the furnace is provided with front bars, which serve to admit air among the fuel which is undergoing the process of coking in the lower part of the hopper, and at the same time offers a ready mode of

* Vide Transactions of the Royal Society, vol. xvi. p. 78..

forcing the ignited fuel thus deprived of its smoke upon the centre of the burning mass, where it is completely consumed, while an additional supply of fresh coal falls down the hopper to supply its place. By this arrangement, and the judicious admission of a thin stratum of fresh air, by a valve placed near the mouth of the hopper, the quantity of smoke is considerably reduced, the whole of the fuel being brought into a state of ignition before it has arrived at the middle of the burning mass, and a sufficient supply of oxygen is furnished by the air-valve for the purpose of combustion.

Sir William Congreve's invention consists in the application of chalk, or any other calcareous substance convertible into lime by means of heat, as auxiliaries to the ordinary articles of fuel. This is effected by converting the furnace into a species of lime-kiln, in which the mass of heated coal is employed not only to heat the boiler, but calcine a large quantity of the above substance; thus concentrating and keeping in action a most powerful heat in aid of the ordinary operation of the fuel.

The following is the substance of a series of experi ments and calculations, made in the Royal Laboratory at Woolwich, which serve to shew the great advantages attendant on the adoption of this method.

Thirty gallons of water were evaporated in seven hours by half a bushel of coal, weighing forty-two pounds, calcining at the same time one bushel and a half of lime. Thirty-four gallons of water were afterwards evaporated in the same time, without burning the lime, and required one bushel and a half, or 126 pounds of coal. These experiments were afterwards repeated, and the same results obtained.

It appears therefore, from these trials, that half a bushel of coal, with lime, generates very nearly the same quantity

of steam as one bushel and a half without the lime. This

however may be better illustrated by the following statement of the comparative expense.

First experiment.-Half a bushel of coal ....
One bushel and a half of chalk.

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Second experiment.—One bushel and a half of coal 1 9

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In the first experiment the lime produced by this species of burning may fairly be averaged at nine pence, so that, compared with the present mode, the saving on evaporating thirty gallons of water by means of the chalk, where a ready mode of disposing of the lime can be devised, is nearly is. 9d. or the total expense of the fuel.

Mr. Parkes employs an air-valve, somewhat similar to that of Mr. Roberton, though placed in a different part of the furnace; and either of these plans, if properly managed by the fireman, would fully answer the end for which they were intended; but unfortunately this requires a degree of mechanical skill and attention seldom found in this class of persons; and though the nuisance may be abated for a short time, or while the engine is under the immediate superintendance of the engineer, no very permanent benefit has yet been found to accrue. To remedy this, Mr. Brunton proposes to employ a mechanical apparatus completely beyond the control of the attendant, whose attention may in this case be almost entirely dispensed with. In Mr. Brunton's furnace the grate bars are made to revolve in an horizontal direction beneath the boiler, by which means the heat is uniformly distributed over the whole of its lower surface, and a regular supply of coal is furnished from a hopper above.

To effect this the axis upon which the grate turns is connected with the steam engine itself; and for a boiler of

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