that

In 1801, Messrs. John and James Robertson, of Glasgow, obtained a patent for an improved steam-engine, the form of which differs little in construction from many other engines, except that, in place of one working cylinder, in these there are two; in this, the lesser cylinder (n) is placed on the top of the larger (m), and made fast to it. To each cylinder there is a piston fitted, which are connected together by a cylinder D: or this cylinder is so made as to have the pistons in one piece with it. This cylinder is made so that it may nearly fill the small cylinder n; and down so that the external suris, that it work may up face of the one may not rub on the internal surface of the other. The steam and conducting pipes, with the valves, are explained in the accompanying diagram and following description of the operation of the engine:

"Let the working handles, with the valves, be placed in such a manner, that steam from the boiler may have free access through the pipes and cylinders into the condensing vessel, to free the whole of the air, as in the

usual manner. When this is

done, the engine is set to work by the valves b and c being shut, and by that of a left open, and water let into the condensing vessel C, when a vacuum takes place in it by means of the condensation of the steam, and also in the under part of the large cylinder m, below its piston (there being a communication from

B

9

m

R

A

(John & Jas. Robertson's Engine. 1801)

144

ROBERTSONS ENGINE.

condensing vessel by the pipe F); at the same time the steam from the boiler has free access through the pipe A, and valve a into the small cylinder n, above its piston h, and exerts its force upon it, and presses it downwards with as much force as in the usual manner. But as it is found, from experience, that a considerable quantity escapes past the piston this piston is in part detained by the secondary piston g, and exerts its force on that part or annular section ss that is contained betwixt the cylinders m and D, and assists in forcing the whole downwards; while, at the same time, the steam which is lodged in this annular space s s, and around the cylinder D, prevents so great a quantity from escaping past the first piston, as would otherwise be the case where there is no secondary piston, and the vacuum is much more complete below the first piston, consequently there is a greater power produced from a smaller quantity of steam than with a single piston. During the time of the piston's descent, the steam valve a is shut, and the elasticity of the steam within the cylinders carries the pistons forward to near the bottom of these cylinders, when the valves b and c are opened by the handles and plug-work admitting the steam to pass from the upper sides of both pistons through the pipes B and E to the condensing vessel C, while the counter-weight at the other end of the beam, or this connected with a fly wheel raises the pistons again, when the valves b and c are shut, and that of a opened by the plug- work, when the engine makes another stroke as before. The piston rod R joins the working beam in any of the usual modes, and in other respects the engine is much the same as in common practice."

The same specification describes a most ingenious method of constructing the furnace, by which the smoke was par tially consumed, instead of being discharged as hitherto through the chimney. Messrs. Robertson have the credit of being the first who succeeded in this project. After the adoption of this plan, several manufacturers, for not using the improvement, had their works indicted as nuisances, as the smoke incommoded many neighbourhoods so much, that some manufactories were stopped on account of it.

The invention, in principle, consists in supplying the burning fuel more fully with air, having this fuel more in a body together, and a less quantity in combustion, at the same time, than what usually takes place in other furnaces, which are applied to the same uses; in supplying the fue with a portion of fresh air, admitted from an opening made for that purpose, and directed in such a manner as it may come in contact with the smoke, from the kindling coal and great heat of the furnace together; and the fuel being more fully supplied with air, and consequently a greater degree of heat taking place, and the smoke and fresh air uniting in the great heat, the smoke is inflamed, and rendered useful in adding to the heat of the furnace; besides, this portion of fresh air is so conducted as to act partly on the kindling or kindled fuel, and raising it to a greater degree of heat after it has served its purpose, by uniting with and inflaming the smoke; and therefore is employed, in some measure, usefully, even after the coal has ceased to smoke: secondly, to the above may be added, the frame of the furnace, which is so constructed that the full-kindled fuel is kept backward in the furnace, while the fresh coal lies before, and is more gradually kindled than if introduced farther among the full-kindled fuel, while the heat of the furnace is little injured or damped by the introduction of fresh coal, as is more fully described afterwards.

John & Jas. Robertson's Smoke-consuming Furnace. 1801.)

The coal is admitted into the furnace by a hopper, feeder, or mouth-piece A, made of cast iron, but which may be made of other materials, and inclined to the horizon; so that the coal in it may, in some measure, fall into the fire-place above the bars, as the fuel is consumed; in the upper part of this hopper, feeder, or mouth-piece, is a plate a, placed at a small distance, or from about threeeighths to three-fourths of an inch from the upper side of the hopper, betwixt which plate and the upper plate, or side of the hopper, a stream of air rushes downward on the fire, at an angle of 45 degrees to the horizon, which stream of air assists in consuming the smoke, as before mentioned, and more fully described hereafter. B is a section of the bars, which are, in general, a little inclined to the horizon, as in the figure, in order that the fuel may more easily fall, or be pushed backwards in the furnace; at c is an opening above the bars, and below the lower end of the hopper, which is in general fitted with a grated door or doors, which open for the more convenient cleansing of the furnace; and the grated form of the doors is also designed for admitting air into the fuel, as well as at the bars, consequently the air is more concentrated in the middle of the burning fuel, and produces a greater heat than if admitted only betwixt the bars; this grated form of the doors is very convenient for the admission of a poker or instrument for pushing backward the kindled fuel, while the fresh coal, or that which is not so well kindled, falls to supply its place. In some modifications of these furnaces, the opening below the lower end of the hopper, and above the fore-end of the bars, is left without doors at all; at this opening it is convenient, when the fire is mended, to push the coal from the foreside backward, as mentioned above, or it may be pushed backward with a hooked poker, P, by applying the hooked part of it through the furnace bars below; by either of which means the kindled coals are put backwards, while the fresh coal, or that which is not so well kindled, falls down to supply their place; that is, the coals in the situation c, are pushed towards d, while those in the situation ƒ fall down to supply the place of