Sidney Gilchrist Thomas (1850 – 85)

Sidney Gilchrist Thomas was essentially an amateur scientist, and died young, but he was responsible for an innovation that profoundly influenced the development of steel production in many countries.

Thomas was born in London and was educated at Dulwich College, but the death in 1867 of his Welsh-born father, a civil servant, necessitated the abandonment of his ambition to become a doctor. Until 1879 he worked as a clerk at a police court. He studied chemistry in his spare time at the Birkbeck Institute (now Birkbeck College), part of the University of London, and set himself the task of discovering how steel could be produced in a Bessemer converter from pig iron made from phosphoric ores.

By 1875 he calculated that this could be done by lining a Bessemer converter with lime or magnesian limestone that would cause the oxidation of the phosphorus in the iron, producing basic slag, that proved to be useful as a fertiliser. He set out to prove his theory with the aid of his cousin, Percy Carlyle Gilchrist (1851-1935), who had studied at the Royal School of Mines, and was chemist at the Blaenavon Ironworks in South Wales. Edward Martin, the manager of the Blaenavon works, provided facilities for their experiments, but the costs were born by Thomas and Gilchrist. Once they had established the soundness of Thomas’s calculations, their discovery was announced at a meeting in March 1878 of the Iron and Steel Institute, but it attracted little attention at the time. A formal paper, ‘The Elimination of Phosphorus in the Bessemer Converter’, was prepared for the autumn meeting of the Institute but was not read until May 1879. Subsequently Thomas met E W Richards of Bolckow Vaughan, the large ironmaking concern in Cleveland, north Yorkshire, who took up the process and showed that it was effective on a large scale.

Patents were acquired in the principal industrialised countries, and by 1882 it was being used at steelworks in Belgium, France, Germany, the Hapsburg Empire and Russia. Andrew Carnegie paid a quarter of a million dollars for the right to use it in the United States and commented, ‘These two young men, Thomas and Gilchrist of Blaenavon, did more for Britain’s greatness than all the Kings and Queens together. Moses struck the rock and brought forth water. They struck the useless phosphoric ore and transformed it into steel’.

Thomas suffered from ill-health that a long sea voyage and a stay in Egypt failed to cure, and he died in Paris at the age of 35. Percy Gilchrist also suffered from ill-health, but retired early, and lived to the age of 84.