XI.]

MODEL OF THE SEPARATE CONDENSER.

145

pump worked by the engine, to clear the condenser of both water and air at the same time.

Immediately after starting the idea of using a separate condenser, Watt proceeded to construct models to test the new plan by experiment. His first apparatus was designed to try the effect of condensing the steam and producing a vacuum in a

FIG. 29.-DIAGRAM OF WATT'S SEPARATE CONDENSER APPARATUS, 1765.

vessel detached from the cylinder. The cylinder of his model (Fig. 29) consisted of a brass syringe one and three-quarter inches in diameter, and ten inches in length. Covers of tin-plate were applied at both ends. To save apparatus, the cylinder was inverted. The piston-rod was made hollow, and fitted with a valve at its lower end, to admit of the escape of the water

L

resulting from the steam condensed in first heating the cylinder. One pipe communicated between the boiler and both ends of the cylinder; another between the top of the cylinder and the condenser. The condenser consisted of two pipes of thin tin-plate, ten or twelve inches long, and about one-sixth of an inch in diameter, standing perpendicularly, and communicating at the top with a short horizontal pipe of large diameter, which had an aperture on its upper side shut by a valve opening upwards. These pipes were joined at the bottom to another perpendicular pipe about an inch in diameter, which served for the air and water pump; and both the condensing pipes and the air pump were placed in a small cistern filled with cold

water.

"The steam-pipe was adjusted to a small boiler. When steam was produced, it was admitted into the cylinder, and soon issued through the perforation of the piston-rod, and at the valve of the condenser. When it was judged that the air was expelled, the steam-cock was shut, and the air-pump piston-rod was drawn up, which leaving the small pipes of the condenser in a state of vacuum, the steam entered them and was condensed. The piston of the cylinder immediately rose, and lifted a weight of about eighteen pounds, which was hung to the lower end of the piston-rod. The exhaustion-cock was shut, the steam was readmitted into the cylinder, and the operation was

XI.]

DIFFICULTIES AND DELAYS.

147

repeated; the quantity of steam consumed, and the weights it could raise, were observed; and, excepting the non-application of the steam case and external covering, the invention was complete, in so far as regarded the saving of steam and fuel. A large model, with an outer cylinder and wooden case, was immediately constructed, and the experiments made with it placed the advantage of the invention beyond the reach of doubt. It was found convenient afterwards to change the pipe-condenser for an empty vessel, generally of a cylindrical form, into which an injection played; and, in consequence of there being more water and air to extract, to enlarge the air. pump."

The progress of Watt's invention was retarded for several years after his important discovery of the separate condenser, by untoward circumstances of various kinds. The new engine required a much nicer adjustment of parts than was necessary in Newcomen's engine. Even in constructing models, great difficulty was experienced in obtaining cylinders of a bore sufficiently accurate, and consequently in preventing the leakage of steam past the sides of the piston. The very fertility of Watt's genius operated to some extent as a hindrance; the idea of constructing a rotary engine lured him away for a time from his first invention.

1 Muirhead's Life of Watt, 2nd ed. pp. 80-81.

Watt, moreover, was a poor man, and required to apply himself to other avocations than experimenting with steam engines, in order to earn a living for himself and family. Not being himself possessed of the necessary means to make trial of his engine on a large scale, and having besides incurred a debt of 1,000l. in the prosecution of his experiments, Watt, in 1767, entered into partnership with Dr. Roebuck, one of the founders of the ironworks which had recently been established at Carron, near Falkirk, for the manufacture of iron with mineral coal.1 The terms of the partnership were, that Roebuck was to pay the above debt and all the expense of a patent and further experiments, in consideration of which two-thirds of the property in the invention was assigned to him."

At length Watt had so far matured his engine, and got results of such a satisfactory character, as to decide him in securing the invention by a patent. In August, 1768, he proceeded to London with this object; and on the 5th of January, 1769, the memorable patent for "A new method of lessening the consumption of steam and fuel in fire engines," was obtained.

The building of a working engine near Dr. Roebuck's residence at Kinneil, some of the parts of which had been prepared several years before, was forthwith

1 The first furnace at Carron was blown in on the 1st of January. 1760. 3 No. 913.

2 Muirhead's Life of Watt, 2nd ed. p. 238.

XI.] KINNEIL ENGINE-ROEBUCK'S FAILURE. 149

begun. It was set to work early in September; and though the results of its first trial were not very decisive, chiefly owing to the inequality of the cylinder arising from defective workmanship, it served to show that a very much less quantity of steam was required to work it, as compared with the common engine. Watt estimated the saving of steam at one-half, supposing that no further improvement could be effected on the engine.1

It had been doubtful, for some time, whether the state of Dr. Roebuck's affairs would admit of his providing the funds necessary to bring forward the invention, and Watt was anxious to secure the assistance of a partner better qualified for this purpose. Overtures had already been made to Mr. Boulton, of Soho, near Birmingham, with a view to inducing him to purchase a share in the enterprise, but no agreement had been arrived at. Now, when success seemed almost within reach, further progress was arrested by the increasing pecuniary embarrassment in which Dr. Roebuck was becoming involved. Neither of the partners could render assistance to the other. Watt was forced to abandon his steam-engine experiments, and betake himself to remunerative work, in order to obtain the necessaries of life. This was the darkest hour in the history of Watt's invention. The final insolvency of Dr. Roebuck, which followed soon after, proved a turning point for the better.

1 Muirhead's Life of Watt, 2nd ed., p. 186.