It is said that in 1664 Sir John Winter of England made coke by burning sea coal in closed pots. But this was not followed up, and the use of charcoal and the destruction of the forests went on until 1735, when Abraham Darby of the Coalbrookdale Iron Works at Shropshire, England, commenced to treat the soft pit coal in the same way as wood is treated in producing charcoal. He proposed to burn the coal in a smouldering fire, to expel the sulphur and other impurities existing in the form of phosphorus, hydrogen and oxygen, etc. while saving the carbon. The attempt was successful, and thus _coke_ was made. It was found cheaper and superior to either coal or charcoal, and produced a quicker fire and a greater heat. This was a wonderful discovery, and was preserved as a trade secret for a long time. It was referred to as a curiosity in the _Philosophical Transactions_ in 1747. In fact it was not introduced in America until a century later, when in 1841 the soft coal abounding around Pittsburgh in Pennsylvania and in the neighbouring regions of Ohio was thus treated. Even its use then was experimental, and did not become a practical art in the United States until about 1860. With the invention of coke came also the revival of cast iron. The process of making cast steel was reinvented in England by Benjamin Huntsman of Attercliff, near Sheffield, about 1740. Between that time and 1770 he practised melting small pieces of “blistered” steel (iron bars which had been carbonised by smelting in charcoal) in closed clay crucibles.