Coke smelting made it possible for the blast furnace to develop and the iron industry took advantage of its new freedom. It was no longer necessary to choose sites that were near to woodlands and sources of iron ore: blast furnaces could be built near to the new fuel, coal, and where coal was to be found, iron ore was usually available as well. The iron trade began to expand in different parts of the country. But the blast furnace needed power. Windmills, used for centuries for grinding corn and a few other industrial processes (see Chapter 4), were of no use for ironmaking.
The wind varies in strength and sometimes it does not blow at all, and the blast furnace needs a constant and continuous amount of power. Streams and rivers suitable for driving waterwheels were scarce and often in the wrong place. Moreover, water has an unfortunate habit of drying up in the summer and freezing in the winter. Some protection against the failure of water supplies in a drought could be provided by building dams to store water and this was usually done. Against frost there was no defence at all. Forced stops when the water supply failed for any reason meant, naturally, that the furnace produced no iron. It takes several days to raise the temperature of a furnace to the working level, and also to blow it out, so there were periods beyond the actual stop when the furnace was unproductive.
It was not practicable to locate a furnace in a place where there was a good stream but no coal or iron ore and then transport the raw materials to it. There were no railways and the roads were very bad; some of them were no more than tracks. The cost of transporting tonnes of ore and coal over even a few kilometres would have been much too high. A further difficulty was that, although the blast furnace could now use coke fuel, charcoal was still needed at the finery to convert the blast furnace cast or pig iron into wrought iron. There was no point in making great quantities of cast iron if it could not be converted into the wrought product, which was still the one in greatest demand.
The iron trade needed a new source of power and a new way of making wrought iron from pig iron. Both came at about the same time. They were James Watt’s improved steam engine and Henry Cort’s wrought ironmaking process, which became known as puddling. Both were of great importance but of the two the steam engine was the greater. It had a tremendous effect on the iron industry, and it was also responsible for many changes in the life and standard of living of Britain and indeed of the whole world. It laid the foundations of the industrial towns—not just the ironmaking centres but the others as well. For steam power could operate any kind of machinery and there was a great surge of inventions which could never have succeeded without mechanical power.
The Darby works at Coalbrookdale supplied a number of cast-iron cylinders for the engine devised by Thomas Newcomen in 1712 (see p. 275). Cast iron was ideal for the purpose. It would withstand the heat of steam and it could be cast into the cylindrical form required. The Newcomen engine was used at a number of coal mines and it also found a limited use at a few ironworks, where it pumped water from the waterwheel back into the reservoir, from which it could be reused. Watt went into partnership with a Birmingham manufacturer, Matthew Boulton, in 1775, to market his improved steam engine and the first one was supplied for draining a Midland coal mine. The second went to a famous ironmaster, John Wilkinson, to blow one of his blast furnaces at Broseley, in Shropshire. Wilkinson, in fact, built the engine, by arrangement, to Watt’s design.
The association between Wilkinson, Boulton and Watt was not only of great importance to the iron trade; it was an interesting example of three remarkable men, each of whom could contribute something vital to success. Watt was purely an inventor; Boulton was a businessman; Wilkinson was both. He was a fanatic about iron. He used it for everything he possibly could, even making himself a cast iron coffin and joking about it to his friends. (He was not, in fact, buried in it, for when the time came he was too fat.) Naturally, people scoffed at him—he was called ‘Iron-mad Wilkinson’—but apart from his personal publicity stunts he did some valuable work. He invented a machine for boring cast iron cannons, but which would also bore engine cylinders to a much greater degree of accuracy than the earlier ones. For a time, Wilkinson was really the only person who could cast and bore a cylinder suitable for the Watt engine.
He went on to pioneer other iron developments including, in 1787, a wrought iron boat. Wilkinson was also associated with the building of the famous cast-iron bridge which still stands at Ironbridge in Shropshire, though he was not the actual builder of it. The credit for this, the first iron bridge in the world, goes to Abraham Darby III, the grandson of the Abraham Darby who invented coke smelting. The bridge was cast at the Coalbrookdale works in 1779.
Mineral Fuels a Requirement of Technological Advances
