456

Savery's Single Engine.

[Book IV. water, a fire made under it and the steam raised. One of the cocks was then opened, and the steam passing through filled the receiver by driving the air previously within it into the forcing pipe: the cock was then closed, and the steam within the receiver soon became condensed by the cold air in contact with its exterior surface, or by pouring cold water upon it; hence a vacuum was produced within, and consequently the water in which the lower end of the suction pipe was immersed was driven up by the pressure of the atmosphere so as to fill the void. When this had taken place the same cock was again opened, and the steam rushing in urged by its expansive force the contents of the receiver up the forcing pipe. In this manner water was alternately raised into and expelled from both vessels.

As a practical miner, and consequently conversant with the subject of raising water on a large scale, Savery was better qualified to carry his views into operation than a mere philosopher. His first essay in employing steam was a proof of this. "I have heard him say myself [observes Switzer] that the very first time he play'd, it was in a potter's house at Lambeth, where tho' it was a small engine, yet it [the water] forc'd its way through the roof, and struck up the tiles in a manner that surpris'd all the spectators."

Sometimes Savery employed but one receiver. No. 194 represents an engine of this kind, erected by him at Kensington. A description of it was first published by Mr. Bradley in his "New Improvements of Planting and Gardening." It is also figured and described by Switzer, who examined it and thought it "the plainest and best proportion'd of any" he had seen. Its effects were considered proportionally greater than those with two receivers. C, a spherical boiler of the capacity of forty gallons, and charged through the tunnel. B, the receiver, which held thirteen gallons. A, the suction pipe, sixteen feet long and three inches bore. D, the forc ing pipe, of the same bore and forty two feet long. A valve opening upwards was placed in A, and another at the lower part of D, at H. E, the steam pipe, an inch in diameter. G, a sliding valve or cock, furnished with a lever handle. F, a cock in the forcing pipe, to admit cold water

Chap. 8.]

Publication of the Miner's Friend.

457

to flow upon the receiver. A pipe attached to the tunnel descended into the boiler and served the purpose of a gauge cock.

The operation will be understood from the description of figure No.193. By turning the handle of G stearn is admitted into B, and as soon as the air is expelled from the latter, G is closed and F opened; the affusion of cold water (see the figure) quickly condenses the contained vapor, and hence the receiver becomes charged with water by the pressure of the atmosphere through the suction pipe A. F is then shut and G opened, when the steam issuing from the boiler displaces the water from the receiver, and having no other way to escape the liquid is driven up the pipe D into the reservoir prepared to receive it. As soon as all the water is expelled from the receiver, (which was known by applying the hand to the lower part, for it would be hot) G is shut and F again opened, when the operation is repeated as before.

"When this engine begins to work [says Switzer] you may raise four of the receivers full in one minute, which is fifty two gallons, [less the quantities drawn from F for the purposes of condensation]—and at that rate in an hour's time may be flung up 3120 gallons. The prime cost of such an engine is about fifty pound, as I myself have had it from the ingenious author's own mouth. It must be noted that this engine is but a small one, in comparison of many others of this kind that are made for coal-works; but this is sufficient for any reasonable family, and other uses required for it in watering all middling gardens."

Here is no provision made to replenish the boiler with water except through the tunnel: hence the working of the machine had to be stopped, and the steam within the boiler allowed to escape, before a fresh supply could be admitted. Under such circumstances the boilers were very liable to become injured by the fire when the water became low. They were also exposed to destruction from another cause, the force of the steam; for they had no safety-valves to regulate it, and hence the necessity of the following instructions: "When you have rais'd water enough, and you design to leave off working the engine, take away all the fire from under the boiler, and open the cock [connected to the tunnel] to let out the steam, which would otherwise, was it to remain confin'd, perhaps burst the engine."

Savery, from his profession, was aware of the want of an improved mode of draining mines. The influence of the useful arts in enriching a nation was then beginning to be understood. A stimulus was imparted to manufactures, and the demand for coal and the ores of England rapidly increased. As a necessary consequence the depth of the mines increased also; and hence proprietors became anxious to possess some device for clearing them of water, and by which the old, inefficient and excessively expensive horse-gins and buckets might be dispensed with. The cost of drainage was so great in some mines, that their produce hardly equalled the cost of working them: in one mine five hundred horses were constantly employed. Numerous novel projects had been tried and abandoned: what they were we are not informed, but as Ramseye and Worcester and probably others had proposed fire machines for the purpose, steam had probably been tried in some way or other and had failed. Having greatly improved his machine, Savery published an account of it, illustrated with engravings, in a pamphlet entitled The Miner's Friend; or a Description. of an Engine for Raising Water by Fire, with an Answer to the Objections against it. London, printed for S. Crouch, 1702. In his address he begs proprietors not to let the failure of other plans prejudice them against the trial of his. "Its power [he observes] is in a manner infinite and unlimited,

458

Savery's Double Engine.

[Book IV. and will draw you water 500 or a 1000 feet high, were any pit so deep. I dare undertake that this engine shall raise you as much water for eight-pence, as will cost you a shilling to raise the like with your old engines." The original figures in the Miner's Friend were inserted in Harris's Lexicon Technicum, in 1704, and copied into Switzer's Hydrostatics in 1729, and by Desaguliers in his Experimental Philosophy in 1744, (which works are before us) and subsequently into almost every treatise on the steam-engine. No. 195 is a reduced copy: the figure of the fireman is an addition.

A detailed description of this elegant apparatus is not necessary, since its operation will be understood from the explanation of the two preceding machines. It is substantially the same as No. 193, except that this one has two boilers, which are heated by separate furnaces, G H. The addi tional boiler G was designed merely to supply the other with hot water, and need not therefore divert the attention of the reader in realizing the working of the essential parts. The upper end of the suction pipe shown at the mouth of the pit consists of two branches, which are connected to similar branches on the lower part of the forcing pipe N. The suction valves are at B A, and the forcing ones at E F, all opening upwards.

Chap. 8.]

Its excellent features-Coupling Screws.

459

Between these valves two short curved tubes connect the bottoms of the receivers I M with the branches, as represented, and two other bent tubes, P Q, unite the top of the receivers with the boiler H. On the top of this boiler, and forming a part of it, is a stout round plate, having two openings of the same size as the bore of the tubes last mentioned. In these openings the two steam tubes P Q terminate. Between the openings, and on the under side of the plate, is a moveable disk, which by a short arm is connected to an axle and moved by the long lever shown on the top of the boiler; so that by moving this lever the disk can be made to close either opening, so as to admit or exclude steam from the receivers, and answering every purpose of a three-way cock. It is made somewhat on the plan of the one in No. 189, page 421. The face of the disk is ground smooth, so as to fit close to the under side of the plate, against which it is pressed by the steam. The perpendicular axle by which the disk is turned passes through the plate, and the opening is made tight by a stuffing box. (The plate and moveable disk are represented in the small figure at the top, one of the openings being covered by the disk and the other exposed.) A small cistern, U, is placed over the receivers, and kept supplied with cold water from the forcing pipe by means of a ball cock, viz. a cock that is opened and shut by a ball floating in the cistern. From the bottom of this cistern a short pipe, T, proceeds; and to it is connected, by a swivel joint or stuffing box, another one at right angles. This pipe furnishes water to condense the steam in the receivers, over both of which it can be moved by the rod attached to the plug of the cock as shown in the figure. The upper cistern denotes the place where the water raised by the engine is to be discharged.

A communication is made between the boilers by a siphon or bent tube, R, whose legs extend nearly to the bottom of the boilers. In the leg within the small boiler is a valve opening upwards, which permits the water of G to pass into H, but prevents any returning from the latter. When the attendant wishes to inject into H a fresh supply of water, he increases the little fire kept up under the boiler G, (which is always kept supplied with water by the pipe S,) and as soon as the liquid boils and the force of the steam exceeds that in H, the contents of G, both steam and hot water, are forced through the valve; and thus H is kept supplied without the action of the machine being stopped. The cock on the pipe S is then opened, the small boiler again charged, and the water becomes gradually heated; so that by the time it is wanted in the other boiler, a small addition to the fuel quickly raises its temperature, and it is again forced in as before.

The quantity of water in the boilers was ascertained by gauge cocks. These were inserted at the top, (see figure) and pipes soldered to them descended to different depths. The principal boiler had two of these, the other but one.

The general arrangement of this engine and the adaptation of its various parts to each other are admirable, and could hardly be improved. The obviously good workmanship-the improved form of the receivers-and the connection of these with the boilers and pipes, and the latter with each other, by coupling screws, thus securing easy access to the valves-are highly creditable to Savery and the workmen he employed. Every part was made of the best materials. The cocks, coupling screws, regulator, valves, and all the pipes immediately connected with them, were of brass; while the boilers, receivers and suction pipes were of "the best hammered copper, of sufficient thickness to sustain the force of the working engine: in short, [continues the inventor] the engine is so naturally adapted to

460 Joints melted by Steam-Origin of Savery's Engine. [Book IV.

perform what is required, that even those of the most ordinary and meanest capacity may work it for some years without injury, if not hired or employ'd by some base person on purpose to destroy it;"-that is, by inattention or design to permit steam to accumulate within the boilers till they were burst. Some device to prevent this was wanting, viz. a safety-valve or something analogous to it; and it is astonishing that he never thought of such a thing, but permitted his machine for lack of it to fall into disrepute.

The miners could not be induced to adopt it, in consequence of the danger of explosion. "Savery [says Desaguliers] made a great many experiments to bring this machine to perfection, and did erect several, which raised water very well for gentlemen's seats, but could not succeed for mines, or supplying towns where the water was to be raised very high and in great quantities; for then the steam required being boiled up to such a strength, as to be ready to tear all the vessels to pieces. I have known Captain Savery at York's Buildings make steam 8 or 10 times stronger than common air; and then its heat was so great, that it would melt common solder, and its strength so great as to blow open several of the joints of his machine; so that he was forced to be at the pains and charge to have all his joints soldered with spelter or hard solder." Ex. Philos. ii, 467.

There has been much discussion respecting the origin of this famous engine; some writers contending that it was wholly Savery's own, others that he derived it from one of Worcester's, or from the Century of Inventions. Desaguliers asserts that Savery, to conceal its origin, "bought up all the Marquis of Worcester's books that he could purchase in Paternoster Row, and elsewhere, and burn'd 'em in the presence of the gentleman his friend, who told me this." But as Savery denied being indebted to any one for it, and as he was certainly a man of great mechanical genius, it is probable that the doctor was imposed upon by his informant. It is not likely that Savery would have committed such an act in the presence of a witness, when there was not only no necessity for one, but every possible inducement for secrecy. Many years before the publication of this charge by Desaguliers (in 1744) the opinion was prevalent that the machine was not original with Savery. In 1729 Switzer remarks, "others say that the learned Marquis of Worcester, in his Century of Inventions, which book I have not seen, gave the first hint for this raising of water.” (Hydr. 325.) Dr. Hutton, in his Math. Dictionary, asserts, though on what authority we know not, that Savery knew more of Moreland's experiments than he was willing to acknowledge; and Desaguliers maintains that he invented the story of the experiment with the wine flask "to make people believe that he had not got the idea from Worcester's Century of Inventions."

In reply to the above it may be remarked, that independently of those coincidences of thought that always have and will happen to inventors, there are circumstances which strongly corroborate Savery's own account In the first place, the experiment with the wine flask was one very likely to occur in the manner he has mentioned, and to a mind like his would naturally lead to a practical application of it. His thoughts, we are told, were always employed in hydrostatics or hydraulics, or in the improvement of water-works." Then there is no evidence that he was much of a reader had he been conversant with books, he would not have proposed the propulsion of vessels with paddle-wheels as new. These occurred to him as they have done to thousands in every age when devising means to increase the speed of boats; and so it may have been with his steam ma

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