<P> The modern process is named after its inventor, the Englishman Henry Bessemer, who took out a patent on the process in 1856 . The process was said to be independently discovered in 1851 by the American inventor William Kelly, though there is little to back up this claim . </P> <P> The process using a basic refractory lining is known as the "basic Bessemer process" or "Gilchrist--Thomas process" after the English discoverers Percy Gilchrist and Sidney Gilchrist Thomas . </P> <P> The blowing of air through the molten pig iron introduces oxygen into the melt which results in oxidation, removing impurities found in the pig iron, such as silicon, manganese, and carbon in the form of oxides . These oxides either escape as gas or form a solid slag . The refractory lining of the converter also plays a role in the conversion--clay linings are used when there is little phosphorus in the raw material - this is known as the acid Bessemer process . When the phosphorus content is high, dolomite, or sometimes magnesite, linings are used in the alkaline Bessemer limestone process . These are also known as Gilchrist - Thomas converters, after their inventors, Percy Gilchrist and Sidney Gilchrist Thomas . In order to produce steel with desired properties, additives such as spiegeleisen (a ferromanganese alloy), can be added to the molten steel once the impurities have been removed . </P> <P> When the required steel had been formed, it was poured into ladles and then transferred into moulds while the lighter slag was left behind . The conversion process, called the "blow", was completed in approximately 20 minutes . During this period the progress of the oxidation of the impurities was judged by the appearance of the flame issuing from the mouth of the converter . The modern use of photoelectric methods of recording the characteristics of the flame greatly aided the blower in controlling final product quality . After the blow, the liquid metal was recarburized to the desired point and other alloying materials were added, depending on the desired product . </P>

How has the bessemer process changed over time