THAT portion of the wonderful Soho which had been assigned to Watt for the manufacture of his exquisite mechanism, was soon found to be of incompetent dimension for the developement of the magnificent scheme which Bolton had formed, to become the sole fabricator of the condensing engine in England. A neighbouring spot was, therefore, selected, in which might be concentrated those artisans and machines that were found to be necessary for the formation of every part of the apparatus. "We are systematizing the business of engine making," says Bolton to Smeaton, we are training workmen, and making tools and machines to form the different parts with more accuracy, and at a cheaper rate than can possibly be done by the ordinary methods of working. Our workshops will be of sufficient extent to execute all the engines which are likely to be soon wanted in this country; and it will not be worth the expense for anyother engineers to erect

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APPLICATION OF CONDENSER.

similar works, for that will be like building a mill to grind a bushel of corn." The classification of labour answered his most sanguine expectation. A band of workmen and artificers, expert in the management, and familiar with the construction of the machines. was soon trained; and to every engine which Bolton erected, one of these artisans was attached, until the servants of the proprietors could be instructed in its management. And Soho became a nursery, from which engineers were sent forth to carry its improvements into every part of the country; and Bolton was soon enabled also to state," that comparing the new engines with the old, (those not of the same size but of the same power) the first cost of both was nearly the same.' But in every point relating to elegant and accurate workmanship, the comparison was immensely in favour of the Soho machines.

A philosophical friend of Watt's had given currency to the statement, that his condenser was originally suggested as an economical appendage to Newcomen's engine; but he himself contradicted the statement. From the first," he said, "I intended to operate with steam instead of the atmosphere, and my apparatus was SO structed."

con

This modification it was thought, if made on Newcomen's engine, would improve it at a very small additional cost; and the proprietors of some large and expensive machines on that peculiar construction, being anxious that the condenser should be adapted to their apparatus,with this view Watt was persuaded to make an experiment on an engine at Soho; but the results, he tells Smeaton, 66 were not such as to induce him to try it any where else." He refused, there

FORM OF CONDENSER.

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fore, to apply it to the engine at a large mine in Cornwall, because the savings of fuel were not great, in comparison to the complete machine. By adding," says he, "our condenser to engines that were not in good order, our engine would have been introduced into Cornwall, which we look upon as our richest mine, in an unfavourable view; and without such profits as would have been satisfactory to us or to the adventurers, and thus have injured our reputation."

The condenser in its first form, was composed of several thin coppper-plate pipes communicating with each other, and placed in a cistern kept constantly filled with cold water. Sometimes, instead of pipes, thin flat copper vessels were employed, and placed so as to present the greatest possible surface to the action of the cold water in which they were immersed. The steam which flowed from the cylinder into the vessels or tubes, coming into contact with the cold metallic surfaces, was condensed with great rapidity. But a very few trials showed that an extent of condensing surface, necessary to produce a perfect vacuum under the piston of a powerful engine, could only be attained by using tubular or flat vessels, altogether of preposterous magnitude.

The water also in which these condensers were often placed, formed a crust upon their surfaces which greatly diminished the power of the metal for conducting heat; and this impaired its efficacy as a medium for condensing vapour. Notwithstanding this drawback, the method was considered to be an economical one; for the air and water produced by the condensation could be extracted by a pump of a size that would require a comparatively moderate power to work it.

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JET CONDENSER.

In the end, the inconvenience of large vessels decided Watt to sacrifice a little more power than he before thought was advisable, in order to have a less cumbrous mechanism; and he returned to a discarded scheme that he had tried in the Kinneil engine, of condensing the steam by bringing it into contact with a jet of cold water, as it flowed through the eduction pipe into the cylinder. "In pursuing this idea," says Watt, "I have tried several kinds, and have at last come to one, which I am not inclined to alter. It consists of a jackhead pump, shut at the bottom with a common clack bucket, and a valve in the corner of the pump to discharge the air and water. The eduction steam-pipe which comes from the cylinder, communicates with this pump, both above and below the bucket, and has valves to prevent any thing going back from the pump to the eduction pipe. The bucket descends by its own weight, and is raised by the engine, when the great piston descends, being hung to the outer end of the great lever. The injection is made both into the upper part of this pump and into the eduction pipe, and operates beyond my ideas in point of quickness and perfection."

Becoming apprehensive that the additional weight which this pump put on the engine might have a tendency to twist the great lever, he hoped to guard against it in a large engine erected near Coventry, by using three pumps; two of them were fixed side by side, and the third placed over, in the space between them, received the hot water lifted by the two lower pumps. Less power was supposed to be expended by this arrangement, than by having only one pump from the surface of the piston which was exposed to the pressure of the atmosphere, having a much smaller area.

The practice of placing the air-pumps at the mine-end of the great lever was now also discontinued. The extraction of the air going on while the steam piston was descending, or making its working stroke, was less advantageous than placing the condenser pump on the opposite side of the axis, and drawing the air from the condenser before the descent of the piston; the vacuum beneath it by this means was perfected at the proper moment. Two condenser pumps, one made double the size of the other, were afterwards found sufficient for the largest engines, and in small machines a single pump performed the office.

The piston cylinder also underwent a great modification. The steam was made to flow into the cylinder from a pipe coming directly from the boiler, instead of being first conveyed into the space between the cylinder and its jacket. And Watt writes, that he had also laid aside the clumsy cast iron cylinder, and substituted a case of wrought iron plates, leaving an interstice about an inch and a-half all round, which extends to within six inches of the top, and three inches of the bottom: a small pipe, furnished with a cock, conducts steam from the boiler into the interstice. The effect of this casing was nearly equal to that of the outer cylinder; "but when we tried to lay aside the jacket altogether, we had no reason," says he, "to applaud our economy, for the consumption of fuel was considerably greater."

This required a new arrangement of the valves and pipes attached to the cylinder; a, the piston; b, the cylinder; d, the equilibrium pipe, and i, the equilibrium valve; f, eduction pipe and valve;, the steam pipe proceeding from the