Innovation in 18th-century Birmingham often took the form of incremental series of small-scale improvements to existing products or processes, but also included major developments that lay at the heart of the emergence of industrial society. In 1709 the Birmingham-trained Abraham Darby I moved to Coalbrookdale in Shropshire and built the first blast furnace to successfully smelt iron ore with coke, transforming the quality, volume and scale on which it was possible to produce cast iron.  In 1732 Lewis Paul and John Wyatt invented roller spinning, the "one novel idea of the first importance" in the development of the mechanised cotton industry.  In 1741 they opened the world's first cotton mill in Birmingham's Upper Priory.  In 1746 John Roebuck invented the lead chamber process, enabling the large-scale manufacture of sulphuric acid, and in 1780 James Keir developed a process for the bulk manufacture of alkali, together marking the birth of the modern chemical industry.  In 1765 Matthew Boulton opened the Soho Manufactory, pioneering the combination and mechanisation under one roof of previously separate manufacturing activities through a system known as "rational manufacture".  As the largest manufacturing unit in Europe, this came to symbolise the emergence of the factory system.