Bessemer converter introduction (1856)

The counterflow preheating innovation that made it possible to reach 1500°C using hydrocarbon combustion, by preheating incoming air with exiting combustion gases.

We've been making cast iron for thousands of years, but it wasn't until 1856 that Henry Bessemer style-melted steel. Where does steel come from before the 1850s? It either came from meteorites — which made it very valuable, fairly rare — they would take meteorites, which are iron-nickel alloys, and they'd beat them down into swords. Or they would take iron ore and reduce it in a rarefied atmosphere with a lot of carbon, and they would get carbon monoxide, taking the oxygen out of the steel as carbon dioxide, and you get sponge iron. Basically solid-state reduction, and you get this porous spongy iron. The Japanese were doing it a thousand years ago, the people in the Basques were doing it 2,000 years ago. India used to make steel, and that's where the steel sword blades came from. But it was a very laborious process — spongy iron, you ever seen pumice from lava, fifty percent air — a guy would forge it until he knocked all the air bubbles out and forged it together. To be able to make steel really didn't happen until the application of fossil fuels.