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 globes Roebuck now substituted leaden chambers. The change effected a revolution in the manufacture of sulphuric acid, which was thus reduced to a fourth of its former cost, and was soon applied to the bleaching of linen, displacing the sour milk formerly used for that purpose. The first of the leaden chambers was erected by Roebuck and Garbett in 1746, and the modern process of manufacture is still substantially that of Roebuck (, i. 474–6; cf., Chemistry, 1895, p. 220).

Encouraged by the success of the new process, Roebuck and Garbett established in 1749 a manufactory of sulphuric acid at Prestonpans, eight miles east of Edinburgh. This proved for a time very profitable, but the firm neglected at the outset to procure a patent for their invention either in England or in Scotland, and endeavoured to reap exclusive profit from it by keeping the process a secret. The nature of the process became, however, known in England through an absconding workman, and in 1756 it was used by rivals in England, and later by others in Scotland. In 1771 Roebuck took out a patent for Scotland (cf. specification printed in the Birmingham Weekly Post, 19 May 1894), and with Garbett sought to restrain the use of the invention in Scotland by others than themselves. The court of session decided against this claim, on the ground that the process was freely used in England, and therefore could be freely used in Scotland. A petition against this decision was in 1774 dismissed by the House of Lords (Journals, xxxiv. 76, 217).

It is uncertain whether Roebuck was still in Birmingham when he turned his attention to the manufacture of iron. With the death of Dud Dudley [q. v.] the secret of smelting iron by pit-coal instead of by charcoal, a much more expensive process, had expired or become latent. The smelting of iron ore by coke made from pit-coal was probably rediscovered by Abraham Darby [q. v.] at Colebrookdale about 1734, but Roebuck was undoubtedly among the first to reintroduce the industry into Britain, and, further, to convert by the same agency cast iron into malleable iron. If the iron manufacture was comparatively unproductive in England, it was virtually non-existent in Scotland, although a country abounding in ironstone and coal. After adding a manufacture of pottery to that of sulphuric acid at Prestonpans, Roebuck appears to have thought of trying in the same district the manufacture of iron on a small scale (, p. 71). In the result there was formed for the purpose of manufacturing iron on a large scale in Scotland a company consisting of Roebuck and his three brothers, Garbett, and Messrs. Cadell & Sons of Cockenzie (, i. 478). The latter firm had already made some unsuccessful efforts to manufacture iron. Every arrangement of importance in the establishment of the company's works was due to Roebuck's insight and energy. He selected for their site a spot on the banks of the river Carron in Stirlingshire, three miles above its influx into the Firth of Forth. The Carron furnished water-power, the Forth a waterway for transport, and all around were plentiful supplies of coal, ironstone, and limestone. The first furnace was blown at Carron on 1 Jan. 1760, and during the same year the Carron works turned out fifteen hundred tons of manufactured iron, then the whole annual produce of Scotland (, Industrial Biography, p. 136). Large quantities of charcoal were used at first (, p. 84); but Roebuck's ingenuity brought the much cheaper pit-coal into play, both for smelting and refining. In 1762 he took out a patent for the conversion of any kind of cast iron into malleable iron by the ‘action of a hollow pit-coal fire’ (Specifications of Patents, 1762, No. 780). The use of pit-coal on a large scale required, however, a much more powerful blast than was needed for charcoal. Roebuck consulted Smeaton [see ], in whose published ‘Reports’ (1812, vol. i.) are to be found accounts of several of his ingenious contrivances in aid of the operations at Carron. The chief of these was his production of the powerful blast needed for the effective reduction of iron by pit-coal. The first blowing cylinders of any magnitude constructed for this purpose were erected at Carron by Smeaton about 1760 (cf., p. 83, and , Life of Smeaton, p. 61). Besides turning out quantities of articles of manufactured iron for domestic use, the Carron works became famous for their production of ordnance, supplied not only to our own army, but to the armies of continental countries. It was from being made at Carron that carronades derived their name. The first of them was cast at Carron in 1779 (, Industrial Biography, p. 137 n.) The Carron ironworks were long the largest of their kind in the United Kingdom, and are still productive and prosperous.

When the Carron works were firmly established in a career of prosperity, Roebuck, unfortunately for himself, engaged in a new enterprise which proved his ruin. Mainly to procure an improved supply of coal for the Carron works, he took a lease from the Duke of Hamilton of large coalmines and saltworks at Borrowstounness (Bo'ness) in