The morning following that Sunday afternoon on which the idea of the condenser had occurred to Watt he borrowed a brass syringe from a college friend, and using this as a cylinder and a tin can as a condenser tried his experiment. The scheme worked, albeit in a primitive way, and Watt saw that he was on the track of an engine that would revolutionize the labor of men. But he saw also that it would take both time and money to bring his invention to its most efficient form. His instrument-making business had prospered, he had taken in a partner, and the firm now employed sixteen workmen. About the same time he married, and rented a house outside the university grounds. Soon he was busily at work building a working model of his steam-engine. A working model was very hard to make. Watt himself was a skilful mechanician, but the men who helped him were not. The making of the cylinder and the piston gave him the chief trouble. The cylinder would leak. It took him months to devise the tools that would enable him to make a perfect-fitting cylinder, and when he had accomplished that he still found that in one way or another a certain amount of steam would escape. Yet, although imperfect, his model was already many times more powerful than the Newcomen engine he had started with. But before very long Watt found that this work was leading him into debt. He told his good friend Professor Black, who had discovered the latent heat of steam before Watt had, that he needed a partner to help him in his business of building engines. Black suggested Dr. Roebuck, who had opened the well-known Carron Iron Works near Glasgow. The two men met, and, after some negotiations, formed a partnership. Roebuck agreed to pay Watt’s debts to the sum of a thousand pounds, to provide the money for further experiments, and to obtain a patent for the steam-engine. In return for this he was to become the owner of a two-third interest in the invention. It was more difficult to secure a patent in those days than in later times, for both the courts and the public considered that the right to make use of any new invention should belong to the whole world, and not alone to one man or to a few men. Watt’s models had to be very carefully made, and his designs very accurately drawn if he was to secure any real protection, and the preparation of these took a vast amount of time. But Roebuck continued to encourage him, and on January 5, 1769, he was granted his first patent, the very same day on which another great English inventor, Arkwright, obtained a patent for his spinning-frame. This first patent covered Watt’s invention of the condenser, but not his next invention, which was the double-acting engine, or in other words, a method by which the steam should do work on the downward as well as on the upward stroke.