GUNPOWDER ENGINE.

91

vacuum and the other piston which is depressed; and the air is at the same instant admitted beneath that which has just been impelled into its cylin

der.

Papin proposed, by this most ingenious scheme, to transmit the power of the water-wheels, driven by the Seine, to work pumps, instead of the operose and clumsy methods which then so greatly excited the admiration of the vulgar at Marli. Still this was found to be useless in practice, from the extreme difficulty of procuring and preserving a perfect vacuum in the apparatus, and also from the exceeding tediousness of the process. It is, however, due to the ingenious contriver to observe, that this idea has been considered to be one of great practical value; and an accomplished modern mechanic suggests, that the only addition wanting to his apparatus, to make it usefully efficient, is a receiver, or air chamber, near the cylinders, to be kept exhausted by the pumps; and this being of sufficient capacity the air will rush into it, and be taken away from beneath the piston the instant the cock is opened, whereas, without it, it would be drawn off more slowly by the pumps; but if the conveyance be made of large dimensions, it will effect the same end completely. Papin lessened the pipe.

The instantaneous combustion of gunpowder had been pointed out by Hautefeuille as offering a ready means of producing a power to elevate a piston; and stimulated by the thought of its being more noble and praiseworthy to show how to apply gunpowder to aid man in his labour, than to teach its application to machines used for his destruction, Papin conceived, that a speedy vacuum could also be formed by condensing its vapour; * Recueil, p. 53,

86

STEAM CYLINDER.

but notwithstanding all his ingenuity, a fifth, and sometimes a greater proportion of the air remained in the cylinder, so that instead of a piston of a given size raising, as it ought to have done, upwards of three hundred pounds weight, it seldom elevated even so much as one hundred and fifty.*

In this state his projects remained until 1695, when Papin published a collection of essays descriptive of these and some other projects.

In a letter to the Comte de Sintzendorff, who had applied to him for his advice as to the best mode of draining some mines, after enumerating these projects, he abandons them as liable to insuperable objections. But he goes on to say, that he believes it would not be difficult to make a machine which, possessing the same arrangement of parts, and acting on the same principle, would accomplish the purpose the Comte de Sintzendorff had in contemplation. For as water possesses the property of being converted by heat into vapour, which possesses the same elasticity as air, and afterwards may be so completely recondensed by cold, that no part of its elastic power shall remain ; therefore, by means of heat, and a small quantity of water, he could make that perfect vacuum, which he in vain attempted to produce by igniting gunpowder and condensing its vapour.

The scheme to which he gave the preference is very simple. A cylinder, fig. 1, made air-tight at the bottom, is fitted also with an air-tight piston, d. The stem of the piston goes through the cover of the cylinder. A lever, n, turning on a hinge, is fastened to the top, and a spring acts so as to press it into a notch in the piston rod, when Papin gives a figure of Recueil, p. 53,

Acta Eruditorum, p. 498. 1688. his gunpowder cylinder, in tab. x.

STEAM CYLINDER.

93

it comes above the cover. A small pipe, e, is inserted through the cover of the cylinder, and also through the piston, and firmly closed at the upper end.

The stopper of the small pipe being taken out, the piston is then easily moved to the bottom of the cylinder. A small quantity of water is introduced through it beneath the piston, and it is again closed. The cylinder is now placed over a fire; steam of a high temperature is quickly produced, which forces the piston to the top of the cylinder, when the lever is immediately pressed by the spring into the notch in the piston-rod, which retains it in that position. The fire being withdrawn from the bottom, the air cools the apparatus, which condenses the steam, and a vacuum is thus formed beneath the piston. The lever being then disengaged from the notch, the pressure of the atmosphere impels the piston with a great force to the bottom of the cylinder. A fresh charge of water may again be introduced by the small pipe; when the fire is applied to the cylinder the piston will ascend a second time; and after a vacuum is formed by the cooling of the cylinder, it will be impelled downwards, as before, by the pressure of the atmosphere, and this alternate motion may be continued and prolonged at pleasure.

In our ignorance of Lord Worcester's mode, this may be considered the most important and masterly attempt that had yet been made to employ the elasticity of steam as a motive power; and it cannot but he a matter of regret, that its persevering and ingenious author should abandon his pursuit at the moment he had laid the foundation of the splendid mechanism of the lever engine, and had in his grasp a brilliant reward for a life of labour.

94

HEATING CYLINDERS.

The simplicity of his experiment is not the least of its merit; and although the moving of the fire from and to the cylinder would now be reckoned as inartificial as it would be found inconvenient in practice, we should recollect that it was intended by its author as a rough experi ment only to illustrate a principle.

It is still, however, very remarkable, that the condensation was always produced by cooling the cylinder by air; artificial means of refrigeration have never yet been suggested. Decaus condensed the steam in the ball by air; Hautefeuille followed the same plan; Lord Worcester has left us no observations upon it; and we are ignorant of Sir Samuel Morland's method. Papin's claim will not therefore be to the mode of producing steam in a cylinder, and raising a piston by its elasticity, for Hautefeuille did this; and so also, we conceive, did Lord Worcester, in the same way as that now practised in high-pressure engines; but for combining the force of steam to raise the piston, and forming a vacuum under it by condensing the vapour, thus bringing the atmospheric pressure to aid the effect of his apparatus. He asserts from experience, that an ordinary fire produced as much steam in a minute as was sufficient to elevate the piston in the cylinder with a force equal to the pressure of the atmosphere; by proportioning the fire, large cylinders, in his opinion, could be heated with almost greater facility than small

ones.

The mode proposed by Papin, of withdrawing the cylinders from the fire, required that these vessels should be made as light as possible:* and the doctor set his speculation afloat, when he conceived that a cylinder might be made which *P. 55, ibid.

REVERSING FLAME.

95

should weigh not more than forty pounds, and yet be strong enough to contain a piston which would elevate a weight, equal to two thousand pounds, to a height of four feet.

Neither did it escape his penetration, that although in many situations steam could be used as a motive power, at a much smaller expense than animal labour, yet even in the most favourable case the consumption of fuel to form this vacuum must be enormous, and be attended with a great outlay. He had also observed, that this was partly occasioned by the imperfect combustion of the fuel itself, which was used in the furnace: and he proposed to diminish the waste by a different arrangement of the fire-place. In the usual construction coals are laid on a grate, over which is placed the boiler, and the air which "feeds the fire" rises through the fuel. Papin reversed this operation. He laid the coals on a grate, a, and the chimney, b, descended, and then rose in the manner of the two legs of a bent syphon; in the opposite end of which, c, was placed the steam cylinder. The portion of this syphon, which ascended, and, which contained the cylinder, was longer than that containing the grate: the coals were spread on the grate in the common manner; wood was laid on the surface of the coals, this was inflamed, and a current of air was forced downwards upon the partially ignited materials; from the difference in the length of the two legs of the syphon, the descending current thus produced was continued; the materials were completely consumed, and instead of the fuel escaping in the form of a heavy and offensive vapour, the gases emitted were nearly imperceptible.

By using this construction of furnace the economy of fuel is prodigious; the intense heat which