In attaching the separate condenser, he first attempted surface condensation; but this not succeeding well, he substituted the jet. Watt had to find a way to prevent the filling of the condenser with water.
James Watt at first lead a pipe from the condenser to a depth greater than the height of a column of water which could be counterbalanced by the pressure of the atmosphere; subsequently he employed an air pump, which relieved the condenser of the water and air which collected in the condenser, and lessened the vacuum. He next substituted oil and tallow for the water used to lubricate the piston, keeping the steam tight and preventing the cooling of the cylinder. Another cause of refrigeration of the cylinder, and consequent waste of power in its operation, was the entrance of air, which followed the piston down the cylinder at each stroke, cooling its interior by its contact. The inventor prevented this from happening by covering the top of the cylinder.
He not only covered the top, but surrounded the whole cylinder with an external casing, or "steam jacket" that allowed the steam from the boiler to pass around the steam cylinder and press on the upper surface of the piston.
After James Watt built his larger experimental engine, he hired a room in an old deserted pottery. There he worked with mechanic Folm Gardiner. Watt had just met Doctor Roebuck, a wealthy physician, who had, with other Scotch capitalists, just founded the celebrated Carron Iron Works. James Watt frequently wrote to Roebuck describng his progress.
In August, 1765, he tried the small engine, and wrote Roebuck that he had "good success" although the machine was very imperfect. He then tells his correspondent that he was about to make the larger model. In October, 1765, he finished the large steam engine. The engine, when ready for trial, was still very imperfect. It nevertheless did good work for so crude a machine.
James Watt was now reduced to poverty, after borrowing considerable sums from friends, he finally had to seek employment in order to provide for his family. During an interval of about two years he supported himself by surveying, exploring coal fields in the neighborhood of Glasgow for the magistrates of the city. He did not, however, entirely give up his invention.
In 1767, Roebuck assumed Watt's liabilities to the amount of £1,000, and agreed to provide more capital in exchange for two thirds of Watt's patent. Another engine was built with a steam cylinder seven or eight inches in diameter, which was finished in 1768. This worked sufficiently well to induce the partners to ask for a patent, and the specifications and drawings were completed and presented in 1769.
James Watt also built and set up several Newcomen engines, partly, perhaps, to make himself thus thoroughly familiar with the practical details of engine building. Meantime, also, he prepared the plans for, and finally had built, a moderately large engine of his own new type. Its steam cylinder was 18 inches in diameter, and the stroke of piston was 5 feet. This engine was built at Kinneil, and was finished in September, 1769. It was not all satisfactory in either its construction or its operation. The condenser was a surface condenser composed of pipes somewhat like that used in his first little model, and did not prove to be satisfactorily tight. The steam piston leaked seriously, and repeated trials only served to make more evident its imperfections. He was assisted in this time of need by both Dr. Black and Dr. Roebuck; but he felt strongly the risks which he ran of involving his friends in serious losses, and became very despondent.
Writing to Dr. Black, he says: "Of all things in life, there is nothing more foolish than inventing; and probably the majority of inventors have been led to the same opinion by their own experiences."
Misfortunes never come singly; and Watt was borne down by the greatest of all misfortunes the loss of a faithful and affectionate wife while still unable to see a successful issue of his schemes. Only less disheartening than this was the loss of fortune of his steadfast friend, Dr. Roebuck, and the consequential loss of his aid. It was at about this time, in the year 1769, that negotiations were commenced which resulted in the transfer of the capitalized interest in Watt's engine to the wealthy manufacturer whose name, coupled with that of Watt, afterward became known throughout the civilized world, as the steam engine in its new form was pushed into use by his energy and business tact.