Sir Clement Clerke and the Adoption of Coal in Metallurgy

Abstract

For many centuries charcoal or wood was the normal fuel for most metallurgical processes. Indeed one of the features that characterises the Industrial Revolution is the transition in fuel from sustainable to non-sustainable development, that is, from a fuel that regenerates of its own accord to one that is eventually exhausted. The objective of this paper is to examine that transition from organic to mineral fuel in the production of metals. It will amongst other things identify the key innovators, who were much fewer than might be supposed. 1 One of these was undoubtedly Sir Clement Clerke of Launde Abbey in Leicestershire. His role was identified in a treatise by Dr John Woodward, probably written in the 1700s. This treatise is now in the British Library, but the relevant section is printed as an Appendix to this paper with a fuller discussion of its date. 2 Woodward described Sir Clement Clerke as a ‘most excellent mineralist’ and identified him as a key innovator applying reverberatory furnaces to three industrial processes. These were ‘cupoloes for reducing lead ore with sea cole’, ‘copper reverberatory furnaces … for reducing that metal with sea-cole’, and works ‘for remelting and casting old iron with sea cole’. 3 The story to be told begins with iron, it then moves on to lead and copper and finally back to iron. Some of the story is well known, but other aspects have recently been discovered from the inadequately listed archives of the Courts of Exchequer and Chancery. All of the processes are relatively simple in terms of their chemistry, consisting of the reduction of a metal oxide to the metal by the use of carbon, or carbon monoxide, but metal ores generally contain impurities, and mineral coal, then known as pitcoal or seacoal, always does. Accordingly a successful smelting process must not only remove oxygen, but also cope with sulphur, phosphorus, and silicon. These must either be removed as a gas or as a fusible slag, and limestone has accordingly often been used as a flux so as to form a calcium silicate slag. The traditional wood fuels, such as charcoal, had the advantage of being relatively pure, but the disadvantage that when a coppice had been cut, corded, coaled, and the resultant charcoal used, it took 14 or more years until another crop of wood could be cut. Though coalmines do eventually become worked out, coal is abundant and there to be dug out as fast as it is wanted. Accordingly coal based metallurgy was a long sought after goal. 4 The reverberatory furnace was not Sir Clement Clerke’s invention, having been used for bell-founding for centuries. 5 However it does not seem to have been applied to other purposes until the latter part of the seventeenth century. The first evidence of Sir Clement’s interest in non-ferrous metallurgy comes from 1676, when he was living in Channel Row, Westminster and had a furnace in his house. That May he was proposing some metallurgical