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Updated: May 21, 2025
Thus one invention stimulates another; and when the steam-engine had been perfected by Watt, and enabled powerful-blowing apparatus to be worked by its agency, we shall find that the production of iron by means of pit-coal being rendered cheap and expeditious, soon became enormously increased.
They erected furnaces and works in the Forest of Dean; but, though Cromwell and his officers could fight and win battles, they could not smelt and forge iron with pit-coal. They brought one Dagney, an Italian glass-maker, from Bristol, to erect a new furnace for them, provided with sundry pots of glass-house clay; but no success attended their efforts.
In the experiments made at the laboratory of the School of Mines in Madrid it yielded four per cent. of ashes, and a heating power of 4,825 caloria; i.e., by the burning of one part by weight 4,825 parts by weight of water were heated to 1° C. Good pit-coal gives 6,000 cal.
He was studying at Baliol College, Oxford, in the year 1619, when the Earl sent for him to take charge of an iron furnace and two forges in the chase of Pensnet in Worcestershire. He was no sooner installed manager of the works, than, feeling hampered by the want of wood for fuel, his attention was directed to the employment of pit-coal as a substitute.
In another charter, given by the lord of the manor in 1305, the first allusion is made to Welsh coal, for the people among other privileges are allowed to dig "pit-coal in Ballywasta." Thus began the industry that has become the mainstay of prosperity in South Wales.
His method may be thus briefly described: the bottom of the reverberatory furnace was hollow, so as to contain the fluid metal, introduced into it by ladles; the heat being kept up by pit-coal or other fuel.
He there describes his new process as follows: "I melt pig or any kind of cast-iron in a hearth heated with pit-coal by the blast of bellows, and work the metal until it is reduced to nature, which I take out of the fire and separate to pieces; then I take the metal thus reduced to nature and expose it to the action of a hollow pit-coal fire, heated by the blast of bellows, until it is reduced to a loop, which I draw out under a common forge hammer into bar-iron."
Mushet says of the early manufacture of iron at Merthyr Tydvil that "A modification of the charcoal refinery, a hollow fire, was worked with coke as a substitute for charcoal, but the bar-iron hammered from the produce was very inferior." The pit-coal cast-iron was nevertheless found of a superior quality for castings, being more fusible and more homogeneous than charcoal-iron.
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