It is a porthole opening upon a sea of flame.

The heat of these flames would wither a man's body, and so they are enclosed in a shell of steel.

Through this working door I put in the charge of "pigs" that were to be boiled.

These short pieces of "mill iron" had been smelted from iron ore; they had taken the first step on their journey from wild iron to civilized iron.

There isn't much use for pig-iron in this world.