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height of the valve, and is ultimately enlarged so as to prevent any danger of explosion. The piston-rod is also furnished with a number of weights, fitting loosely on a small shoulder, similar to those employed in the common hydrometer; and these may be removed or increased at pleasure.

Another advantage likely to result from the adoption of this safety-valve is, the facility with which it may be employed to regulate the fire of the steam-engine furnace to the intensity of the elastic vapour required. This may readily be effected by a register pressing on the top of the safety-piston, and connected with the apertures for the admission of air, which, by increasing or decreasing the supply of oxygen, will produce a proportionate result on the steam generated in the boiler, and consequently effect a considerable saving in the expenditure of fuel.

Another safety-valve, opening internally, has, we believe, also been added by Messrs. Boulton and Watt. This is of great utility, more particularly in large engines, as it prevents the sides of the boiler being crushed in by the sudden introduction of water, or any artificial condensation that may take place from reducing the heat of the boiler-head.

CHAPTER VI.

Savery's Engine improved by Pontifex.-Atmospheric Engine.-Single-acting Engine, by Boulton and Watt. -Murray and Wood's Engine.-High-pressure Engine. -Locomotive Engine.-Maudslay's Portable Engine. -Masterman's Rotatory Engine.—Smoke-consuming Furnaces.

THE Engine invented by Savery, and improved by Pontifex, possesses considerable advantages over the Marquis of Worcester's apparatus, and it is probable that the extreme simplicity of this engine will, when better known, bring it into more general use. With this view we have selected it as the subject of our first plate, in preference to the original engine, the principle of which has been already very fully explained. The apparatus we are about to describe, was originally erected for the City Gas Works.

Plate I. Fig. 1 and 2. represent front and side elevations of the cylinders, and connecting apparatus.

Fig. 3. A back view, with section through the cistern and buckets.

Fig. 4. and 5. Vertical and horizontal sections; the latter commencing at the dotted line a a, Fig. 1.

Fig. 6. and 7. Side and end view of the waggon boiler.

b b. Fig. 1. Two steam cylinders connected by cross tubes at cc, in each of which a vacuum is alternately formed by the condensation of elastic vapour, conducted from the boiler by the bent tube d, and admitted to the steam-cylinders by means of the sliding-valve e.

ff. Fig. 4. Two tubes perforated with small holes for the admission of steam and injection water, the latter of which is distributed by falling on the strap g.

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h. The suction-pipe proceeding to the bottom of the well, which in no case ought to exceed from twenty-eight to thirty feet in depth; so that a vacuum being formed in the copper vessels bb, the water will be raised by the pressure of the atmosphere, and passing up the tube h will take the place of the elastic vapour.

ii. Two valves placed at the upper end of the suctionpipe h, which allow of the upper passage of the water from the well, but prevent its return.

jj. Two similar valves opening into the air-vessel k, to which is attached the nozzle 1, serving to convey the water from the copper vessels to any required point.

m. The injection tube, furnished with a valve at o, and intended to convey water from the box n, to the taper tubes ff.

p. Stop-cock to regulate the supply of condensing

water.

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q. Tube passing from the bottom of the cistern n, to the injection tube m, and furnished with a stop-cock

at s.

The quantity of water in the cistern r is regulated by a floating valve t, which in Fig. 3. is represented immediately over the pipe q, so that the valve is opened whenever the water rises beyond the required depth.

uu. Two tubes communicating with the back part of the chambers n n, and the inverted vessels v v, each tube

being furnished with a valve at w to admit the water from the chamber to the buckets x x.

xx. Two buckets suspended by rods, and a chain passing over the wheel 2, which is fixed on the end of the axis 3, and supported by a bracket 4. From the other end of the axis 3 projects an arm 6, provided with a stud T.

9. Is a view of the horizontal axis turning in a stuffingbox at 10, on one end of which is fixed a pinion 11, which serves to give motion to the sliding-valve e.

To put this engine in action, the steam must be first raised to the boiling point, and the valve or cock opened, which admits it to pass from the boiler to the pipe d. One of the buckets must now be made to descend, which will open the sliding-valve e, and admit the steam into the cylinder b, 1. The atmospheric air, which will thus be expelled from the cylinder, is allowed to pass through the valvej and nozzle 1. The other bucket must then be depressed, and by its action upon the sliding-valve it will open a communication for the injection water through the pipe qq, which passing down the perforated tube ƒ will immediately condense the steam, and form a vacuum in the vessel. The whole pressure of the atmosphere being now removed from the suction pipe h, the water will rush up to restore the equilibrium, and the vessel b being filled will furnish a supply at the bent-tube 7.

Having examined the action of one-half of the apparatus, we may suppose the same effect to be produced on the opposite side. The steam will, in the first instance, be admitted by the pipe c, and a communication afterwards opened by means of the sliding-valve with the condensing water, which by reducing the steam to its original bulk will form a vacuum, and the water will again ascend as in the first vessel.

The stop-cock y must now be opened, and the bucket a first described made to descend, which will remove the sliding-valve e to its original position, and admit the steam to the upper part of the first vessel, which will depress the water, and cause it to flow through the valvej and nozzle 1, while at the same time the water will pass through the tube uu, in which the valve w is inserted beneath the inverted vessel v. The water will continue to enter the bucket æ till its increasing weight causes it to preponderate, and turn the sliding-valve e in the opposite direction.

Should there not be a sufficient supply of water in the cistern rr for the purpose of condensing the steam in the large vessels, the stop-cock p must be opened, and an additional supply of water will then be furnished from the chambers n n by the tube m, and in the event of the bucket not being depressed at the instant that the water is expelled from the chamber n of the vessel b, the steam will pass through the tube u u, and act between the under side of the fixed inverted vessel v, and the surface of the water in the moveable bucket x, the descent of the bucket being accelerated by the repellant force of the steam, so that by the alternate action of the buckets aa, the motion of the engine is rendered continuous.

It appears that each steam-vessel in the engine employed at the City Gas Works, contains about thirty-six gallons of water, which is raised about twenty-eight feet three times every two minutes; one bushel of coals, or two of coke, serving the boiler about two hours and threequarters.

The Atmospheric Steam-engine, which is next in the order of invention, is now but little employed; indeed, if we except the mining districts where it is occasionally seen connected with the pumps for raising water, this species of engine is of very rare occurrence. The great

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