Page:Dictionary of National Biography volume 56.djvu/197

 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