His next great achievement was the production of steel direct from the raw ores by means of his regenerative furnace, which the President of the Board of Trade in 1883 mentioned in the House of Commons as one of the most valuable inventions ever produced under the protection of the English patent law, and he said further that it was then being used in almost every industry in the kingdom. Siemens had spent fourteen years in perfecting this regenerative furnace, and it took him other fourteen to utilise it, and perfect it in making steel direct from the raw ores. Martin of Sireil, who made one or two additions to the Siemens steel furnace, has been termed its inventor, but this claim has no foundation. What is known, however, as the 'Siemens-Martin process' is now competing very effectively with the Bessemer process. It consists essentially in first obtaining a bath of melted pig-iron of high quality, and then adding to this pieces of wrought-iron scrap or Bessemer scrap, such as crop ends of rails, shearings of plates, &c. These, though practically non-infusible in large quantities by themselves, become dissolved or fused in such a bath if added gradually. To the bath of molten metal thus obtained spiegeleisen or ferro-manganese is added to supply the required carbon and to otherwise act as in the Bessemer converter. The result is tested by small ladle samples, and when it is of the desired quality a portion is run off, leaving sufficient bath for the continuation of the process. Siemens took out his patent for the 'open hearth' process of steel-making (the Forth Bridge is built of steel made in this way) in 1861, and four years later erected sample steel works at Birmingham. The engineer of the London and North-Western Railway adopted his system at Crewe in 1868, and the Great Western Railway works followed. In 1869 this process was being carried out on a large scale at the works of the Landore-Siemens Steel Company and elsewhere in England, as well as at various works on the Continent, including Krupp's, at Essen.