Acting on their advice, he resolved on making a long-promised visit to Scotland, and he set out on his tour in the autumn of 1783. He went by Newcastle, where he visited the principal coal mines, and from thence to Edinburgh, where he had some pleasant intercourse with Dr. Black and Professor Robison. It is evident from his letters that he did not take much ease during his journey, for he carried about with him his steam-engine--at least in his head. “I talked with Dr. Black and another chemical friend,” he wrote, “respecting my plan for saving alkali at such bleach-grounds as our fire-engines are used at instead of water-wheels: the Doctor did not start any objections, but, on the contrary, much approved it.” From Edinburgh he proceeded to the celebrated ironworks at Carron, a place in which he naturally felt a peculiar interest. There his friend Roebuck had started his great enterprise, and there Watt had erected his first engine. His visit there, however, was not so much for curiosity or pleasure, but for business and experiment. “During my residence in Scotland,” said he, “one month of my time was closely employed at Carron Ironworks in settling accounts, but principally in making a great number of experiments on all their iron ores, and in putting them into the train of making good bar-iron, in which I succeeded to my wishes, although they had never made a single bar of tough iron at Carron before.”[257] In the course of his journey he made a large collection of fossils for his museum, and the weight of his bags sensibly increased almost daily. On his way through Ayrshire he called on Lord Dundonald, a kindred spirit in chemical and mechanical scheming, and examined his mineral tar works. He wrote to Mr. Gilbert, the Duke of Bridgewater’s manager at Worsley, that “the tar is better for the bottoms of vessels than the vegetable tar; and the coal-oil hath many uses. Query--if such a work might not be a useful appendage to your colliery and canal.” [257] Letter to Thomas Knox, M.P.