In addition to decrease cost and better availability, coke had other essential advantages over charcoal in that it was harder and made the column of materials (iron ore, fuel, slag) flowing down the blast furnace more porous and did not crush in the a lot taller furnaces of the late nineteenth century. These were operated by the flames playing on the ore and charcoal or coke mixture, decreasing the oxide to metal. Using less coal or coke meant introducing fewer impurities into the pig iron. The...