7 The 100 Most Influential Inventors of All Time 7skin of pure iron. Bessemer then found that blowing air
through melted cast iron not only purified the iron but
also heated it further, allowing the purified iron to be easily
poured. This heating effect is caused by the reaction of
oxygen with the carbon and silicon in the iron. Utilizing
these new techniques, which later became known as the
Bessemer process, he was soon able to produce large, slag-
free ingots as workable as any wrought-iron bloom, and far
larger; he invented the tilting converter into which molten
pig iron could be poured before air was blown in from
below. Eventually, with the aid of an iron-manganese alloy,
which was developed at that time by Robert Forester
Mushet, Bessemer also found how to remove excess oxygen
from the decarburized iron.
His announcement of the process in 1856 before the
British Association for the Advancement of Science in
Cheltenham, Gloucestershire, brought many ironmasters
to his door, and many licenses were granted. Very soon,
however, it became clear that two elements harmful to
iron, phosphorus and sulfur, were not removed by the
process—or at least not by the fireclay lining of Bessemer’s
converter. It was not until about 1877 that the British
metallurgist Sidney Gilchrist Thomas developed a lining
that removed phosphorus and made possible the use of
phosphoric ores of the Continent.
Bessemer had, unknown to himself, been using
phosphorus-free iron, but the ironmasters were not so
lucky. Their iron was perfectly satisfactory for the pud-
dling process, in which phosphorus is removed because
the temperatures are lower, but it could not be used in the
Bessemer process. Bessemer was forced to call in his
licenses and find a phosphorus-free source of iron in
northwestern England; thus he was able to enter the steel
market on his own. Once the phosphorus problem was
recognized and solved, he became a licensor once again,