# Dictionary of National Biography, 1885-1900/Thomas, Sidney Gilchrist

​THOMAS, SIDNEY GILCHRIST (1850–1885), metallurgist and inventor, born on 16 April 1850 at Canonbury, London, was son of William Thomas (1808–1867), a Welshman in the solicitors' department of the inland revenue office, and his wife Melicent (b. 1816), eldest daughter of the Rev. James Gilchrist, author of the ‘Intellectual Patrimony’ (1817). Thomas, who was mainly educated at Dulwich College, early manifested a strong bent towards applied science. The death of his father when Thomas was still at school and not yet seventeen led him to resolve to earn at once a livelihood for himself. For a few months he was an assistant master in an Essex school. Later in the same year (1867) he obtained a clerkship at Marlborough Street police-court, whence in the summer of 1868 he was transferred to a similar post at the Thames court, Arbour Square, Stepney. Here, at a very modest salary, he remained until 1879. Meanwhile he had, after office hours, pursued the study of applied chemistry, and the solution of one special problem became, about 1870, the real purpose of his life. This problem was the dephosphorisation of pig-iron in the Bessemer converter. A sentence used by Mr. Chaloner, teacher of chemistry at the Birkbeck Institution, in the course of a lecture which Thomas heard, seems to have imprinted itself deeply on Thomas's mind: ‘The man who eliminates phosphorus by means of the Bessemer converter will make his fortune.’
​Both the Bessemer and the Siemens-Martin processes, which were then, and still are, the most used methods of converting pig-iron into steel, laboured under the serious drawback that in neither was the phosphorus, which is a very common impurity of iron ores, removed. This was a matter of the highest practical importance; for the retained phosphorus rendered steel made by these systems from phosphoric ores brittle and worthless. Consequently only non-phosphoric ores could be used, and the great mass of British, French, German, and Belgian iron became unavailable for steel-making. If phosphoric pig-iron could be cheaply dephosphorised in the course of these processes, the cost of the production of steel would be diminished and the supply of the raw material indefinitely increased. From 1860 onwards Sir Henry Bessemer and an army of experimentalists vainly grappled with the difficulty.
Thomas devoted his whole leisure to these questions, experimentalising unceasingly in a little workshop at home, and attending systematically the laboratories of various chemical teachers. He submitted himself from time to time to the science examinations of the science and art department and of the Royal School of Mines, and he passed all the examinations qualifying him for the degree in metallurgy given by this latter institution, but was denied it because he was unable to attend the day-time lectures. Holidays from his police-court labours were mainly spent in visiting ironworks in this country and abroad. In 1873 he was offered the post of analytical chemist to a great brewery at Burton-on-Trent, but declined it from conscientious scruples about fostering, even indirectly, the use of alcohol. During 1874 and subsequent years he contributed regularly to the technical journal ‘Iron.’
Towards the end of 1875 Thomas arrived at a theoretic and provisional solution of the problem of dephosporisation. He discovered that the non-elimination of phosphorus in the Bessemer converter was dependent upon the character, from a chemical standpoint, of its lining. This lining varied in material; but it was always of silicious sort. The phosphorus in the pig-iron was rapidly oxidised during the process, or, in other words, formed phosphoric acid. This phosphoric acid, owing to the silicious character of the slag, was again reduced to phosphorus and re-entered the metal. Thomas, therefore, saw clearly the necessity of a change in the chemical constitution of the lining. A basic lining was essential, a ‘base’ being a substance which would combine with the phosphoric acid formed by the oxidising of the phosphorus. In this way the phosphorus would be hindered from re-entering the metal and would be deposited in the slag. The basic substance must be one able to endure the intense heat of the process, since the durability of the ‘lining’ was essential to that cheapness which was the main requisite of commercial success. A long series of experiments led Thomas to the selection, for the material of the new lining, of lime, or its congeners—magnesia or magnesian limestone. Thomas foresaw not only that by employing such a lining he was removing phosphorus from the pig-iron, but that in the phosphorus deposited in the basic slag he was creating a material itself of immense commercial utility.
To a cousin, Mr. Percy Gilchrist, M.R.S.M. (afterwards F.R.S.), who was chemist to large ironworks at Blaenavon, Thomas communicated the ‘basic theory,’ and Gilchrist joined him in further experiments with varying success; but ultimately the two young men established their theory. Thomas took out his first patent in November 1877. Mr. E. P. Martin, the manager of the works where Mr. Gilchrist was employed, was early in 1878 admitted into the secret, and proved most helpful. In March 1878 Thomas first publicly announced, at a meeting of the Iron and Steel Institute of Great Britain, that he had successfully dephosphorised iron in the Bessemer converter. The announcement, however, was disregarded, but the complete specification of his patent was filed in May 1878, and patent succeeded patent down to the premature death of the inventor. Thomas had meanwhile made an all-important convert in Mr. E. Windsor Richards, then manager of Messrs. Bolckow, Vaughan, & Co.'s huge ironworks in Cleveland. On 4 April 1879 most successful experiments on a large scale were carried out at that company's Middlesborough establishment. These experiments at once secured the practical commercial triumph both of the process and of the inventor. A paper, written earlier by Thomas in conjunction with Mr. Gilchrist for the Iron and Steel Institute on the ‘Elimination of Phosphorus in the Bessemer Converter,’ was read in May 1879. There the problem to be solved and its solution, now experimentally demonstrated by the ‘basic’ process, were clearly and succinctly stated. Thomas proved that he had solved the problem by substituting in the Bessemer converter a durable basic lining for the former silicious one, and he avoided ‘waste of lining by making large basic additions, so as to secure a highly basic slag at an early stage of ​the blow.’ This last branch of the solution differentiated the successful Thomas-Gilchrist process from some other attempts on somewhat similar lines. The process could also be adapted to the ‘Siemens Martin’ system. It was immediately used both in Great Britain and abroad, and it spread rapidly. In 1884 864,700 tons of ‘basic’ steel were produced in all parts of the world, and in 1889 2,274,552 tons. Moreover in this last year there were also produced, together with the steel, 700,000 tons of slag, most of which was used for land-fertilising purposes. In England and Germany alone—no figures are now accessible for other countries—the output in 1895 amounted to 2,898,476 tons. The production of basic slag in the same year may be estimated as about a third of the weight of the steel produced.
Thomas, who was possessed of great financial ability, as well as of a thorough knowledge of British and continental patent law, had early secured his inventor's rights, not only in Great Britain but also on the continent and in America. He thus secured the ‘fortune’ predicted by Mr. Chaloner. But systematic overwork had ruined his health, and serious lung trouble soon manifested itself. In May 1879 he at length resigned his junior clerkship at the Thames police-court. In the early part of 1881 Thomas paid a triumphal visit to the United States, where he was enthusiastically welcomed by the leading metallurgists and ironmasters. In 1882 he was elected a member of the council of the Iron and Steel Institute, succeeding Sir James Ramsden, and on 9 May 1883 he was voted the Bessemer gold medal by the council of the institute. But the last few years of his short life were occupied in a vain search for health. After sojourns at Ventnor and Torquay, he made in 1883 a prolonged voyage round the world, by way of the Cape, India, and Australia, returning by the United States. The winter of 1883 and the spring and early summer of 1884 were spent in Algiers. Here experiments were pursued on the utilisation of the ‘basic slag’ formed in the Thomas-Gilchrist process. New lines of research were also begun—notably an endeavour to produce a new type-writer. In the summer of 1884 Thomas came northward with his mother and sister to Paris, where he died on 1 Feb. 1885 of ‘emphysema.’ He was buried in the Passy cemetery. He was unmarried.
Thomas secured a large financial reward for his labours; but from the first he held ‘advanced’ political and social views, and had he lived he had intended to devote his fortune to the alleviation of the lives of the workers. He bequeathed this intention to his sister as a sacred trust. After a modest provision had been made for her and for his mother his money was spent on philanthropic objects.
There is a portrait of Thomas in oils by Mr. Hubert Herkomer, R.A. (executed from photographs after death), now in the possession of Mrs. Percy Thompson at Sevenoaks.
R. W. B.