Sidney Gilchrist Thomas (16 April 1850 – 1 February 1885) was an inventor from England, famous for his work in the iron and steel industry.

Life

Thomas was born in Canonbury, London, and attended school at Dulwich College. His father, who was from Wales, worked in the government, and his mother was the daughter of Reverend James Gilchrist. After his father passed away, the family had much less money. Because of this, Thomas gave up his plan to become a doctor and instead took a job as a police court clerk, a position he held until May 1879.

During these twelve years, Thomas worked in the police court, where he learned about social challenges. In his free time, he studied chemistry and attended classes at the Birkbeck Institute, which later became Birkbeck College. One evening, George Chaloner, a chemistry teacher at the institute, said, "The man who removes phosphorus using the Bessemer converter will become rich." This comment interested Thomas, and he decided to find a way to remove phosphorus from iron made by Bessemer converters. By the end of 1875, he believed he had discovered a method. He shared his idea with his cousin, Percy Gilchrist, a chemist at Blaenavon Ironworks in Wales. Experiments confirmed their method worked. Edward Martin, the manager of Blaenavon Ironworks, allowed them to test the process on a larger scale and helped them apply for a patent. In March 1878, Thomas and Gilchrist announced their discovery at a meeting of the Iron and Steel Institute. They applied for a patent in May 1878, but it received little attention. In September, they wrote a paper about their process for the institute, but it was not presented until May 1879.

Thomas met Edward Windsor Richards, the manager of Bolckow Vaughan & Co’s works in Cleveland, Yorkshire. Richards became interested in their invention, and this led to the process being widely adopted. Patents were then filed in many countries.

The "basic process," also called the Gilchrist–Thomas process, was especially useful in Europe, where iron with high phosphorus levels was more common. In Belgium and Germany, Thomas and Gilchrist became well-known for their work, even more so than in Britain. In the United States, where phosphorus-rich iron was less common, the invention still attracted significant interest. The process produced more slag in the converter. Thomas found that this "basic slag" could be used as a fertilizer, called Thomas meal.

In 1883, Thomas and George James Snelus, who had previously discovered the process but failed to develop it, were awarded the Bessemer Gold Medal by the Iron and Steel Institute for their work on removing phosphorus from iron.

Thomas had been working very hard for many years, and his health suffered. A long trip by sea and time spent in Egypt did not help him recover. He died in Paris in 1885 and was buried in Passy.

Legacy

He was described by William Ewart Gladstone, in a 1891 review of his Memoirs, as having a "deep care for people," and he gave his money to support charitable efforts. A police court mission was funded in his honor.

In July 1960, an obelisk was built in South Wales to remember him. The Newport and District Metallurgical Society, along with the Iron and Steel Institute, created it. Money for the obelisk came from many places, showing recognition of his work by people in the United Kingdom and other countries. In 1985, the former American Society for Metals made a plaque to honor his contributions to the ironworks. The obelisk and plaque can still be seen at the ironworks.