Originator of the Use of Coke for Iron Smelting
Little information exists about Darby’s life. He was born about 1678 near Dudley, England, and became an ironworks master at Bristol, where coke was already utilized for smelting copper. In 1708 Darby founded the Bristol Iron Company and began investigating the possibility of smelting iron with coke. He acquired an iron foundry at Coalbrookdale, near ample deposits of iron ore and good coking coal. He successfully used coke to smelt iron in 1709.
In seventeenthcentury England, technical problems limited the development of the iron industry. To smelt iron, a source of fuel is required to react with Oxygen, producing heat to melt the iron ore. Charcoal was the traditional fuel, but the scarcity of wood, from which charcoal was made, combined with an increased demand for charcoal had raised its price significantly. Attempts to increase the iron yield by increasing the size of the furnaces were unsuccessful: charcoal is too weak to support a large column of iron ore. Coal could not be used in place of charcoal because coal contains sulfur, which spoils the quality of the iron. Darby took the logical next step and replaced charcoal with coke, which contains no sulfur. (Coke is the purified residue left after coal has undergone destructive distillation, a purification process.)
Coke’s strength allowed the use of larger furnaces, increasing the rate at which iron could be smelted. Larger furnaces meant more draft and hotter fires, further improving the process. The high quality of his coke smelted iron permitted Darby to manufacture thin castings for producing pots and other cookware that were competitive with the heavy brass items then available.
Darby did not patent his coke smelting invention. He died on March 8, 1717, at Madeley Court, England.
Abraham Darby’s Legacy
Darby’s direct legacy takes the form of his son’s and grandsons’ significant contributions to the iron industry. In a broader sense, the introduction of coke to the iron smelting process was an essential step along the path toward industrialization.
Only a half dozen coke furnaces for iron smelting were built in the 50 years following Darby’s invention; by some estimates, charcoal was still cheaper to use than coke, perhaps accounting for the slow adoption of coke smelting.
However, Darby’s Coalbrookdale foundry was kept busy, particularly by THOMAS NEWCOMEN’S 1712 invention of the first practical steam engine. Newcomen engines required sixton iron cylinders, and by 1758, the coke process had produced more than 100 of them. Charcoal fueled iron smelting could not have produced such huge iron cylinders.
Darby’s eldest son, Abraham Darby, Jr., succeeded his father as head of the Coalbrookdale iron foundry. He helped it retain its prominence within the industry.
Darby’s grandson, Abraham Darby III, designed, cast, and erected one of the world’s first casti ron bridges, near Coalbrookdale, in 1779. The Coalbrookdale foundry also built, in 1802, the first high pressure steam railway locomotive, for engineer Richard Trevithick.
As charcoal prices skyrocketed in the mideighteenth century, coke rapidly became the primary fuel in iron smelting. In 1760 the enormous Carron Ironworks, the largest iron plant in Great Britain, opened in Scotland. Coalbrookdale supplied its equipment and operators. Great Britain was soon producing the cheapest and strongest iron and steel in the world. As these metals were invaluable to numerous industries, the country led the Industrial Revolution. Coke remains the predominant fuel in modern iron smelting.
Using coke for fuel in iron processing made the metal less expensive and more readily available for new products: water pipes to and from homes (replacing leaky wooden ones), machinery parts, and cast iron rails were just some of the new products the process made possible. Iron implements became widely available, which helped to improve health, safety, and efficiency at home and in the factory.
Abraham Darby – c. 1678-1717