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In the winter of 1854, after meeting Napoleon III, whose cast-iron cannons were bursting in the Crimean War, Henry Bessemer set out to make cheap steel. Steel then took skilled workers a day or more per small batch, so bridges and guns relied on brittle cast iron or soft wrought iron. His 1856 patent blew air through molten pig iron in a pear-shaped converter, burning off carbon and silicon in an exothermic reaction that kept the metal liquid and turned out up to five tons in 10 to 20 minutes.

The four ironmasters who paid him £27,000 for licenses produced steel a friend called rotten hot and rotten cold, ruined by poor timing, trapped nitrogen and sulfur. Bessemer bought the licenses back for £32,500. Robert Forester Mushet supplied the fix, burning out every impurity and then adding spiegeleisen, whose manganese cured hot shortness, but Mushet’s patent lapsed over unpaid stamp duties. Bessemer licensed the process worldwide, Andrew Carnegie built the Edgar Thomson Steelworks, and steel rails fell from $100 a ton to $18 by the 1890s.

• American William Kelly claimed English visitors stole his air-blowing method, though historians favor independent discovery.
• Göran Fredrik Göransson bought the Swedish and Norwegian rights and founded the company that became Sandvik.
• Alexander Lyman Holley brought the process to Troy, New York.
• U.S. steel output rose from about 157,000 tons a year to 26 million tons by 1910.
• Sidney Gilchrist Thomas’s limestone lining handled phosphorus-rich ore, and U.S. Bessemer production ended in 1968.