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In page Bessemer process:

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Basic oxygen steelmaking is essentially an improved version of the Bessemer process (decarburization by blowing oxygen as gas into the heat rather than burning the excess carbon away by adding oxygen carrying substances into the heat). The advantages of pure oxygen blast over air blast were known to Henry Bessemer,[citation needed] but 19th-century technology was not advanced enough to allow for the production of the large quantities of pure oxygen necessary to make it economical.