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A Vacuous Space in a Hot Cylinder

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A VACUOUS SPACE IN A HOT CYLINDER.

Still the important difficulty before alluded to remained to be surmounted. The vessel in which the condensation was effected — the condenser — would speedily become surcharged with the injection water, the.condensed steam, and the incondensible steam that must accumulate therein; how were these impediments to be disposed of ? The water might be alowed to escape by its own gravity, but the incondensed steam, so long as it remained within the condenser, would necessarily resist the descent of the piston in the cylinder. To remedy this capital fault, he devised the employment of a pump, (since called "the air pump') which should draw off the several contents of the condenser at each operation of the engine, and leave it totally unimpeded : it was easy to perceive that this pump might be wrought by the engine itself. Here, then, was the second great advance made in the invention.

Before we proceed, however, in the narration of the improvements upon the steam-engine, under Mr. Watt's hands, it may be proper to allude to a counter claim which has been asserted oif behalf of another individual to the merit of suggesting a separate condenser, and which has been countenanced by authorities of high respectability. Mr, Hornblower, a rival and contemporary of Watt, states in his paper on the subject, in Gregory's Mechanics, that occurred to Mr. Gainsborough, the pastor of a dissenting congregation, and brother to the painter of that name, that it would be a great improvement to condense the steam in a vessel distinct from the cylinder, where the vacuum was formed ; and he undertook a set of experiments to the principle he had established, which he did, by placing a small vessel by tile side of the cylinder, which was to receive just so much steam from the boiler as would discharge the air and condensing water in the same manner as was the practice from the cylinder itself in the Newcomenian method, that is, by the shifting valve and sinking pipe. In this manner he used no more steam than was just necessary for that particular purpose, which at the instant of discharging was entirely uncommuni cated with the main cylinder, so that the cylinder was kept constantly hot as the steam could make it. Whether he closed the cylinder as Mr. Watt does is uncertain ; but his model succeeded so well as to induce some of the Cornish adventurers to send their engineers to examine it. and their report was so favourable as to induce an intention of' adopting it. This, however, was soon after Mr. Watt had obtained his act of Parliament for the extension of his term ; and he had about the same time made proposals to the Cornish gentlemen to send his engine into that country. This necessarily brought on a competition, in which Mr. Watt succeeded ; but it was asserted by Mr. Gainsborough that the mode of condensing out of the cylinder was communicated to Mr. Watt by the officious folly of an acquaintance, who was fully informed of what Mr. Gainsborough had in hand. This circumstance, as here related, receives some confirmation by a declaration of Mr. Gainsborough, thepainter, to Mr. T. Moore, late secretary to the Society for the encouragement of the Arts, who gave the writer [Hornblower] the information ; and it is well known that Mr. Gains borough opposed the petition to parliament, through the interest of General Conway." It is needless to go into the details of this controversy, but it appears that this same Mr. T. Moore declared upon oath, in the trial of the cause golton v. Bull, in 1792, " that he never saw the principles laid down in Mr. Watt's specification either applied to the steam-engine previous to his taking

it up, or ever read of any such thing whatever." This singular discrepancy cannot now be reconciled ; but, whether Hornblower's allegation be founded in truth or in detraction, Mr. Watt's claim to originality of thought in this respect has been generally, if not universally, admitted, To resume :—The discovery thus made gave birth to other and important improvements. Having obtained so great a preventive of loss, it became s rea sonable, and almost necessary conseauence of thought, that the heat of the cylinder, now undiminished by the injection of cold water, should, if possible, be constantly maintained ; this it was impossible to effect so long as the cylinder should remain open at the top, as heretofore, because the descent of the piston being accompanied by the descent of cold air on its upper surface, a large portion of the caloric would be abstracted from the sides of the cylinder, and the steam admitted on the next ascent of the piston become prematurely con densed. Besides, the layer of water resting on the upper surface of the piston to make it air-tight, would become heated into steam on its descent by the in ternal superfices of the cylinder, and its office quickly neutralized. Mr. Watt's fertile genius immediately suggested to him the expedient of employing the elasticity of the steam from the boiler to impel the piston dome the cylinder, is p/ace of the pressure ofthe atmosphere. He therefore determined to close the top of the cylinder entirely, excepting, of course, so much of it as would allow the pas sage of the piston rod, so as effectually to prevent the ingress of cold air from above, or the escape of steam from below the piston, and thus concerting the " atmosphe• ric" engine into a machine wholly and indeed impelled by the power of steam. ' Note.—To this modification is now applied the term "low-pressure," in order to distinguish it from both the "high-pressure" and the "atmospheric" engine. ' It has been before stated that Mr. Watt's early experiments were conducted with very simple agents, using apothecaries' phi s, and similarly cheap and im perfect materials, as his time and his means permitted : favouring circumstances enabled him to carry them into business practice. Having added to his other varied pursuits that of a land-surveyor, he accidentally became acquainted in that capacity with Dr. Roebuck, an English physician, who was at that period realizing a handsome fortune from the manufacture of sulphuric acid; and being a man of capital and enterprise, Watt communicated to him the result of his labours, and an alliance was thus formed which led to a partnership speculation. In the year 1769, some time after Watt had effected his improvements in the steam-engine, a patent was applied for, and obtained in their joint names ; and extensive preparations were made to erect engines on a large scale. Roebuck, however, soon afterwards became embarrassed, in consequence of engaging upon some mining speculations, and unable to make the pecuniary advances nem, sary to prosecute the joint undertaking; and Watt was once more baffled in his efforts to carry his improvements into profitable effect. But just as he was on the point of abandoning his 'chews an overture was made to him on behalf of Mr. Matthew Bolton, at that time en engineer of eminence, large connexions, and considerable capital, to purchase Roebuck's share of the patent ; to this proposal Watt of course _gladly assented, and in 1773 a partnership between Mr. Bolton and Watt was effected.

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