As a building material, iron was of two types: cast iron and wrought iron. Cast iron (so called because it is cast in molds) was great at compression—supporting its own weight—but not so good under tension and tended to snap like a pencil when stressed horizontally. So it made excellent pillars, but not beams. Wrought iron, in contrast, was strong enough for horizontal duty but was more complicated, time-consuming, and expensive to manufacture since it had to be repeatedly folded and stirred while it was still molten. As well as making it comparatively strong, the folding and stirring made it
...more
