PP

, the injection-pipe, of 3 or 4 inches diameter, which turns up in a curve at the lower end, and enters the cylinder bottom: it has a thin plate of iron upon the end a, with 3 or 4 adjutage holes in it, to prevent the jet of cold water of the jack-head cistern from flying up against the piston, and yet to condense the Steam each stroke, when the injection-cock is open.

c, a valve upon the upper end of the injection pipe within the cistern, which is shut when the engine is not working, to prevent any waste of the water.

f, a small pipe which branches off from the injection-pipe, and has a small cock to supply the piston with a little water to keep it air-tight.

Q, the working plug, suspended by a chain to the arch g of the working beam. It is usually a heavy piece of timber, with a slit vertically down its middle, and holes bored horizontally through it, to receive pins for the purpose of opening and shutting the injection and Steam cocks, as it ascends and descends by the motion of the working beam.

h, the handle of the steam-cock or regulator. It is fixed to the regulator by a spindle which comes up through the top of the receiver. The regulator is a circular plate of brass or cast iron, which is moved horizontally by the handle h, and opens or shuts the communication at the lower end of the pipe E within the receiver. It is represented in the plate by a circular dotted line.

ii, the spanner, which is a long rod or plate of iron for communicating motion to the handle of the regulator: to which it is fixed by means of a slit in the latter, and some pins put through to fasten it.

kl, the vibrating lever, called the Y, having the weight k at one end and two legs at the other end. It is fixed to an horizontal axis, moveable about its centre-pins or pivots mn, by means of the two shanks op fixed to the same axis, which are alternately thrown backwards and forwards by means of two pins in the working plug; one pin on the outside depressing the shank o, throws the loaded end k of the Y from the cylinder into the position represented in the plate, and causes the leg l to strike against the end of the spanner; which forcing back the handle of the regulator or steam cock, opens the communication, and permits the steam to fly into the cylinder. The piston immediately rising by the admission of the Steam, the working beam II rises; which also raises the working-plug, and another pin which goes through the slit raises the shank p, which throws the end k of the Z towards the cylinder, and, striking the end of the spanner, forces it forward, and shuts the regulator Steam-cock.

qr, the lever for opening and shutting the injection cock, called the F. It has two toes from its centre, which take between them the key of the injection cock. When the working-plug has ascended nearly to its greatest height, and shut the regulator, a pin catches the end q of the F and raises it up, which opens the injection-cock, admits a jet of cold water to fly into the cylinder, and, condensing the Steam, makes a vacuum; then the pressure of the atmosphere bringing down the piston in the cylinder, and also the plugframe, another pin fixed in it catches the end of the lever in its descent, and, by pressing it down, shuts the injection-cock, at the same time the regulator is opened to admit Steam, and so on alternately; when the regulator is shut the injection is open, and when the former is open the latter is shut. |

R, the hot-well, a small cistern made of planks, which receives all the waste water from the cylinder.

S, the sink-pit to convey away the water which is injected into the cylinder at each stroke. Its upper end is even with the inside of the cylinder bottom, its lower end has a lid or cover moveable on a hinge which serves as a valve to let out the injected water, and shuts close each stroke of the engine, to prevent the water being forced up again when the vacuum is made.

T, the feeding pipe, to supply the boiler with water from the hot-well. It has a cock to let in a large or small quantity of water as occasion requires, to make up for what is evaporated; it goes nearly down to the boiler bottom.

U, two gage cocks, the one larger than the other, to try when a proper quantity of water is in the boiler: upon opening the cocks, if one give Steam and the other water, it is right; if they both give Steam, there is too little water in the boiler; and if they both give water, there is too much.

W, a plate which is screwed on to a hole on the side of the boiler, to allow a passage into the boiler for the convenience of cleaning or repairing it.

X, the Steam-clack or puppet valve, which is a brass valve on the top of a pipe opening into the boiler, to let off the Steam when it is too strong. It is loaded with lead, at the rate of one pound to an inch square; and when the Steam is nearly strong enough to keep it open, it will do for the working of the engine.

f, the snifting valve, by which the air is discharged from the cylinder each stroke, which was admitted with the injection, and would otherwise obstruct the due operation of the engine.

tt, the cylinder-beams; which are strong joists going through the house for supporting the cylinder.

v, the cylinder cap of lead, soldered on the top of the cylinder, to prevent the water upon the piston from flashing over when it rises too high.

w, the waste-pipe, which conducts the superfluous water from the top of the cylinder to the hot-well.

xx, iron bars, called the catch-pins, fixed horizontally through each arch head, to prevent the beam descending too low in case the chain should break.

yy, two strong wooden springs, to weaken the blow given by the catch pins when the stroke is too long.

zz, two friction-wheels, on which the gudgeon or centre of the great beam is hung; they are the third or fourth part of a circle, and move a little each way as the beam vibrates. Their use is to diminish the friction of the axis, which, in so heavy a lever, would otherwise be very great.

When this engine is to be set to work, the boiler must be filled about three or four feet deep with water, and a large fire made under it; and when the Steam is found to be of a sufficient strength by the puppetclack, then by thrusting back the spanner, which opens the regulator or Steam-cock, the Steam is admitted into the cylinder, which raises the piston to the top of the cylinder, and forces out all the air at the snifting valve; then by turning the key of the injectioncock, a jet of cold water is admitted into the cylinder, which condenses the Steam and makes a vacuum; and the atmosphere then pressing upon the piston, forces it down to the lower part of the cylinder, and makes a stroke by raising the column of water at the other end of the beam. After two or three strokes are made in this manner, by a man opening and shutting the cocks to try if they be right, then the pins may be put into the pin-holes in the working plug, and the engine left to turn the cocks of itself; which it will do with greater exactness than any man can do.

There are in some engines, methods of shutting and opening the cocks different from the one above described, but perhaps none better adapted to the purpose; and as the principles on which they all act are originally the same, any difference in the mechanical construction of the small machinery will have no influence of consequence upon the total effect of the grand machine.

The furnace or fire-place should not have the bars so close as to prevent the free admission of fresh air to the fire, nor so open as to permit the coals to fall through them; for which purpose two inches or thereabouts is sufficient for the distance betwixt the bars. The size of the furnace depends upon the size of the boiler; but in every case the ash-hole ought to be capacious to admit the air, and the greater its height the better. If the flame is conducted in a flue or chimney round the outside of the boiler, or in a pipe round the inside of it, it ought to be gradually diminished from the entrance at the furnace to its egress at the chimney; and the section of the chimney at that place should not exceed the section of the flue or pipe, and should also be somewhat less at the chimney-top.

The boiler or vessel in which the water is rarefied by the force of fire, may be made of iron plates, or cast iron, or such other materials as can withstand the effects of the fire, and the elastic force of the Steam. It may be considered as consisting of two parts; the upper part which is exposed to the Steam, and the under part which is exposed to the fire. The form of the latter should be such as to receive the full force of the fire in the most advantageous manner, so that a certain quantity of fuel may have the greatest possible effect in heating and evaporating the water; which is best done by making the sides cylindrical, and the bottom a little concave, and then conducting the flame by an iron flue or pipe round the inside of the boiler beneath the surface of the water, before it reach the chimney. For, by this means, after the fire in the furnace has heated the water by its effect on the bottom, the flame heats it again by the pipe being wholly included in the water, and having every part of its surface in contact with it; which is preferable to carrying it in a flue or chimney round the outside of the boiler, as a third or a half of the surface of the flame only could be in contact with the boiler, the other being spent upon the brick-work. This cylindric lower part may be less in its diameter than the upper part, and may contain from four to six feet perpendicular height of water in it. |

The upper part of the boiler is best made hemispherical, for resisting the elasticity of the Steam; yet any other form may do, provided it be of sufficient strength for the purpose. The quick going of the engine depends much on the capaciousness of the boiler-top; for if it be too small, it requires the Steam to be heated to a great degree, to increase its elastic force so much as to work the engine. If the top is so capacious as to contain eight or ten times the quantity of Steam used each stroke, it will require no more fire to preserve its elasticity than is sufficient to keep the water in a proper state of boiling; this, therefore, is the best size for a boiler top. If the diameter of the cylinder be c, and works a six-foot stroke, and the diameter of the boiler be supposed b, then .

The effect of the injection in condensing the Steam in the cylinder, depends upon the height of the reservoir and the diameter of the adjutage. If the engine makes a 6 feet stroke, then the jackhead cistern should be 12 feet perpendicular above the bottom of the cylinder or the adjutage. The size of the adjutage may be from 1 to 2 inches in diameter; or if the cylinder be very large, it is proper to have three or four holes rather than one large one, in order that the jet may be dispersed the more effectually over the whole area of the cylinder. The injection pipe, or pipe of conduct, should be so large as to supply the injection freely with water; if the diameter of the injection pipe be called p, and the diameter of the adjutage, a, then .

For a further account of these engines, see Desaguliers's Exp. Philos. vol. 2, sect. 14, pa. 465, &c.; or for an abstract, Martin's Phil. Brit. number 461, or Nicholson's Nat. Philos. p. 83 &c. And for an account of the improvement made in the fire-engine by Mr. Payne, see Philos. Trans. number 461, or Martin's Philos. Brit. p. 87 &c.

Mr. Blakey communicated to the Royal Society, in 1752, remarks on the best proportions for Steam-engine cylinders of a given content: and Mr. Smeaton describes an engine of this kind, invented by Mr. De Moura of Portugal, being an improvement of Savery's construction, to render it capable of working itself: for both which accounts, see Philos. Trans. vol. 47 art. 29 and 72.

We are insormed in the new edit. of the Biograph. Brit. in the article Brindley, that in 1756 this gentleman, so well known for his concern in our inland navigations, undertook to erect a Steam-engine near Newcastle-under-Line, upon a new plan. The boiler of it was made with brick and stone, instead of iron plates, and the water was heated by iron flues of a peculiar construction; by which contrivances the consumption of fuel, necessary for working a Steam engine, was reduced one half. He introduced also in his engine, wooden cylinders, made in the manner of cooper's ware, instead of iron ones; the former being both cheaper and more easily managed in the shafts: and he likewise substituted wood for iron in the chains which worked at the end of the beam. He had formed designs of introducing other improvements into the con- struction of this useful engine; but was discouraged by obstacles that were thrown in his way.

Mr. Blakey, some years ago, obtained a patent for his improvement of Savery's Steam-engine, by which it is excellently adapted for raising water out of ponds, rivers, wells, &c, and for forcing it up to any height wanted for supplying houses, gardens, and other places; though it has not power sufficient to drain off the water from a deep mine. The principles of his construction are explained by Mr. Ferguson, in the Supplement to his Lectures, pa. 19; and a more particular description of it, accompanied with a drawing, is given by the patentee himself in the Gentleman's Magazine for 1769, p. 392.

Mr. Blakey, it is said, is the first person who ever thought of making use of air as an intermediate body between Steam and water; by which means the Steam is always kept from touching the water, and consequently from being condensed by it: and on this new principle he has obtained a patent. The engine may be built at a trifling expence, in comparison of the common fire-engine now in use; it will seldom need repairs, and will not consume half so much fuel. And as it has no pumps with pistons, it is clear of all their friction; and the effect is equal to the whole strength or compressive force of the Steam; which the effect of the common fire-engine never is, on account of the great friction of the pistons in their pumps.

Ever since Mr. Newcomen's invention of the Steam fire engine, the great consumption of fuel with which it is attended, has been complained of as an immense drawback upon the profits of our mines. It is a known fact, that every fire-engine of considerable size consumes to the amount of three thousand pounds worth of coals in every year. Hence many of our engineers have endeavoured, in the construction of these engines, to save fuel. For this purpose, the fire-place has been diminished, the flame has been carried round from the bottom of the boiler in a spiral direction, and conveyed through the body of the water in a tube before its arrival at the chimney; some have used a double boiler, so that fire might act in every possible point of contact; and some have built a moor-stone boiler, heated by three tubes of flame passing through it. But the most important improvements which have been made in the Steam-engine for more than thirty years past, we owe to the skill of Mr. James Watt; of which we shall give some account: premising, that the internal structure of his new engines so much resembles that of the common ones, that those who are acquainted with them will not fail to understand the mechanism of his from the following description: he has contrived to observe an uniform heat in the cylinder of his engines, by suffering no cold water to touch it, and by protecting it from the air, or other cold bodies, by a surrounding case filled with Steam, or with hot air or water, and by coating it over with substances that transmit heat slowly. He makes his vacuum to approach nearly to that of the barometer, by condensing the Steam in a separate vessel, called the condenser, which may be cooled at pleasure without cooling the cylinder, either by an injection of cold water, or by surrounding | the condenser with it, and generally by both. He extracts the injection water, and detached air, from the cylinder or condenser by pumps, which are wrought by the engine itself, or blows them out by the Steam. As the entrance of air into the cylinder would stop the operation of the engines, and as it is hardly to be expected that such enormous pistons as those of Steamengines can move up and down, and yet be absolutely tight in the common engines; a stream of water is kept always running upon the piston, which prevents the entry of the air: but this mode of securing the piston, though not hurtful in the common ones, would be highly prejudicial to the new engines. Their pisston is therefore made more accurately; and the outer cylinder, having a lid, covers it, the Steam is introduced above the piston; and when a vacuum is produced under it, acts upon it by its elasticity, as the atmosphere does upon common engines by its gravity. This way of working effectually excludes the air from the inner cylinder, and gives the advantage of adding to the power, by increasing the elasticity of the Steam.

In Mr. Watt's engines, the cylinder, the great beams, the pumps, &c, stand in their usual positions. The cylinder is smaller than usual, in proportion to the load, and is very accurately bored.

In the most complete engines, it is surrounded at a small distance, with another cylinder, furnished with a bottom and a lid. The interstice between the cylinders communicates with the boilers by a large pipe, open at both ends: so that it is always filled with Steam, and thereby maintains the inner cylinder always of the same heat with the Steam, and prevents any condensation within it, which would be more detrimental than an equal condensation in the outer one. The inner cylinder has a bottom and piston as usual: and as it does not reach up quire to the lid of the outer cylinder, the Steam in the interstice has always free access to the upper side of the piston. The lid of the outer cylinder has a hole in its middle; and the piston rod, which is truly cylindrical, moves up and down through that hole, which is kept Steam-tight by a collar of oakum screwed down upon it. At the bottom of the inner cylinder, there are two regulating valves, one of which admits the Steam to pass from the interstice into the inner cylinder below the piston, or shuts it out at pleasure: the other opens or shuts the end of a pipe, which leads to the condenser. The condenser consists of one or more pumps furnished with clacks and buckets (nearly the same as in common pumps) which are wrought by chains fastened to the great working beam of the engine. The pipe, which comes from the cylinder, is joined to the bottom of these pumps, and the whole condenser stands immersed in a cistern of cold water supplied by the engine. The place of this cistern is either within the house or under the floor, between the cylinder and the lever wall; or without the house between that wall and the engine shaft, as conveniency may require. The condenser being exhausted of air by blowing, and both the cylinders being filled with Steam, the regulating valve which admits the Steam into the inner cylinder is shut, and the other regulator which communicates with the condenser is opened, and the Steam rushes into the vacuum of the condenser with violence: but there it comes into contact with the cold sides of the pumps and pipes, and meets a jet of cold water, which was opened at the same time with the exhaustion regulator; these instantly deprive it of its heat, and reduce it to water; and the vacuum remaining perfect, more Steam continues to rush in, and be condensed until the inner cylinder be exhausted. Then the Steam which is above the piston, ceasing to be counteracted by that which was below it, acts upon the piston with its whole elasticity, and forces it to descend to the bottom of the cylinder, and so raises the buckets of the pumps which are hung to the other end of the beam. The exhaustion regulator is now shut, and the Steam one opened again, which, by letting in the Steam, allows the piston to be pulled up by the superior weight of the pump rods; and so the engine is ready for another stroke.

But the nature of Mr. Watt's improvement will be perhaps better understood from the following description of it as referred to a figure.—The cylinder or Steam vessel A, of this engine (fig. 5, pl. 27), is shut at bottom and opened at top as usual; and is included in an outer cylinder or case BB, of wood or metal, covered with materials which transmit heat slowly. This case is at a small distance from the cylinder, and close at both ends. The cover C has a hole in it, through which the piston rod E slides; and near the bottom is another hole F, by which the Steam from the boiler has always free entrance into this case or outer cylinder, and by the interstice GG between the two cylinders has access to the upper side of the piston HH. To the bottom of the inner cylinder A is joined a pipe I, with a cock or valve K, which is opened and shut when necessary, and forms a passage to another vessel L called a Condenser, made of thin metal. This vessel is immersed in a cistern M full of cold water, and it is contrived so as to expose a very great surface externally to the water, and internally to the Steam. It is also made air-tight, and has pumps N wrought by the engine, which keep it always exhausted of air and water.

Both the cylinders A and BB being filled with Steam, the passage K is opened from the inner one to the condenser L, into which the Steam violently rushes by its elasticity, because that vessel is exhausted; but as soon as it enters it, coming into contact with the cold matter of the condenser, it is reduced to water, and, the vacuum still remaining, the Steam continues to rush in till the inner cylinder A below the piston is left empty. The Steam which is above the piston, ceasing to be counteracted by that which is below it, acts upon the piston HH, and forces it to descend to the bottom of the cylinder, and so raises the bucket of the pump by means of the lever. The passage K between the inner cylinder and the condenser is then shut, and another passage O is opened, which permits the Steam to pass from the outer cylinder, or from the boiler into the inner cylinder under the piston; and then the superior weight of the bucket and pump rods pulls down the outer end of the lever or great beam, and raises the piston, which is suspended to the inner end of the same beam.

The advantages that accrue from this construction are, first, that the cylinder being surrounded with the Steam from the boiler, it is kept always uniformly as hot as the Steam itself, and is therefore incapable of destroy- | ing any part of the Steam, which should fill it, as the common engines do. Secondly, the condenser being kept always as cold as water can be procured, and colder than the point at which it boils in vacuo, the Steam is perfectly condensed, and does not oppose the descent of the piston; which is therefore forced down by the full power of the Steam from the boiler, which is somewhat greater than that of the atmosphere.

In the common fire-engines, when they are loaded to 7 pounds upon the inch, and are of a middle size, the quantity of Steam which is condensed in restoring to the cylinder the heat which it had been deprived of by the former injection of cold water, is about one full of the cylinder, besides what it really required to fill that vessel; so that twice the full of the cylinder is employed to make it raise a column of water equal to about 7 pounds for each square inch of the piston: or, to take it more simply, a cubic foot of Steam raises a cubic foot of water about 8 feet high, besides overcoming the friction of the engine, and the resistance of the water to motion.

In the improved engine, about one full and a fourth of the cylinder is required to fill it, because the Steam is one-fourth more dense than in the common engine. This engine raises a load equal to 12 pounds and a half upon the square inch of the piston; and each cubic foot of Steam of the density of the atmosphere, raises one cultic foot of water 22 feet high.

The working of these engines is more regular and steady than the common ones, and from what has been said, their other advantages seem to be very considerable.

It is said, that the savings amount at least to two thirds of the fuel, which is an important object, especially where coals are dear. The new engines will raise from twenty thousand to twenty-four thousand cubic feet of water, to the height of twenty-four feet by one hundred weight of good pit coal: and Mr. Watt has proposed to produce engines upon the same principles, though somewhat differing in construction, which will require still much less fuel, and be more convenient for the purposes of mining, than any kind of engine yet used. Mr. Watt has also contrived a kind of mill wheel, which turns round by the power of Steam exerted within it.

The improvements above recited were invented by Mr. James Watt, at Glasgow, in Scotland, in 1764: he obtained the king's letters patent for the sole use of his invention in 1768; but meeting with difficulties in the execution of a large machine, and being otherwise employed, he laid aside the undertaking till the year 1774, when, in conjunction with Mr. Boulton near Birmingham, he completed both a reciprocating and rotative or wheel engine. He then applied to parliament for a prolongation of the term of his patent, which was granted by an act passed in 1775. Since that time, Mr. Watt and Mr. Boulton have erected several engines in Staffordshire, Shropshire, and Warwickshire, and a small one at Stratford near London. They have also lately finished another at Hawkesbury colliery near Coventry, which is justly supposed to be the most powerful engine in England. It has a cylinder 58 inches in diameter, which works a pump 14 inches in diameter, 65 fathoms high, and makes regularly twelve strokes, each 8 feet long, in a minute. They have also erected several engines in Cornwall; one of which has a cylinder 30 inches in diameter, that works a pump 6 1/2 inches in diameter in two shafts, by flat rods with great friction, 300 feet distant from each other, 45 fathoms high in each shaft, equal in all to 90 fathoms, and can make 14 strokes, 8 feet long, in a minute, with a consumption of coals less than 20 bushels in 24 hours. The terms they offer to the public are, to take in lieu of all profits, one third part of the annual savings in fuel, which their engine makes when compared with a common engine of the same dimensions in the neighbourhood. The engines are built at the expence of those who use them, and Messrs. Boulton and Watt furnish such drawings, directions, and attendance, as may be necessary to enable a resident engineer to complete the machine. See the appendix to Pryce's Mineralogia, &c, 1778.

It has been said that some useful improvements have been made in the Steam engine by Mr. William Powel, who had lately the direction and care of an engine of this kind at a colliery near Swansea, in Glamorganshire.

It is hardly necessary to add, that Dr. Falck, in 1776, published an account and description of an improved Steam-engine, which, as he says, will, with the same quantity of fuel, and in an equal space of time, raise above double the quantity of water raised by any lever engine of the same dimensions; as he does not seem to have constructed even a working model of his proposed engine. The principal improvement, however, which he suggests, is to use two cylinders; into which the Steam is let alternately to ascend, by a common regulator, which always opens the communication of the Steam to one, whilst it shuts up the opening of the other: the piston rods are kept (by means of a wheel fixed to an arbour) in a continual ascending and descending motion, by which they move the common arbour, to which is affixed another wheel, moving the pump rods, in the same alternate direction as the piston rods, by which continual motion the pumps are kept in constant action.