7 Sir Henry Bessemer 7decoration of the time demanded great quantities of such
material, and Bessemer’s secret process soon brought him
great wealth.
He developed other inventions, notably sugarcane-
crushing machinery of advanced design, but he was soon
devoted to metallurgy. In his time there were but two
iron-based construction materials: cast iron made by the
treatment of iron ore with coke in the blast furnace and
wrought iron made from cast iron in primitive furnaces
by the laborious manual process of “puddling” (stirring
the melted iron to remove carbon and raking off the slag).
Cast iron was excellent for load-bearing purposes, such
as columns or bridge piers, and for engine parts, but for
girders and other spans, and particularly for rails, only
wrought iron was suitable. Puddling removed carbon,
which makes cast iron brittle, and produced a material
that could be rolled or forged, but only in “blooms,” or
large lumps of 100–200 pounds (45– 90 kg), and that was
full of slag. The blooms had to be laboriously forged
together by steam hammers before they could be rolled
to any useful length or shape. The only material known
as steel was made by adding carbon to pure forms of
wrought iron, also by slow and discontinuous methods;
the material was hard, would take an edge, and was used
almost entirely for cutting tools.
During the Crimean War, Bessemer invented an elon-
gated artillery shell that was rotated by the powder gases.
The French authorities with whom he was negotiating,
however, pointed out that their cast-iron cannon would
not be strong enough for this kind of shell. He thereupon
attempted to produce a stronger cast iron. In his experi-
ments he discovered that the excess oxygen in the hot
gases of his furnace appeared to have removed the carbon
from the iron pigs that were being preheated—much as
the carbon is removed in a puddling furnace—leaving a