Page:Dictionary of National Biography. Sup. Vol I (1901).djvu/249

 ment this price was six shillings a yard, hut it was ultimately reduced to twopence, when he abandoned the industry.

About 1840 Bessemer turned his attention to the manufacture of bronze powder and gold paint, an industry that had been known in China and Japan for many centuries, and was very successfully imitated in Germany, where the price of the powder and paint was about 5l. 10s. a pound. After many trials and failures, and encouraged considerably by De La Rue, Bessemer succeeded in producing an article at least equal to that made in Germany, and at so cheap a rate that he was enabled to defy all competition. The manufacture of this material affords perhaps the most remarkable illustration of the successful working of a secret process. The various details were entrusted to a few relatives, by whom the works were managed for nearly forty years, until the price of the powder had fallen from 4l. to 2s. 6d. a pound, and the margin was too small to carry on the business profitably. During the first half of this time, however, Bessemer derived relatively large revenues from the industiy, and was thus enabled to find the means for developing his third great invention. It may be mentioned here that between 1849 and 1853 he was considerably interested in the processes of sugar refining, and obtained a number of patents (thirteen in all) for machinery for the purpose. No profitable results, however, attended these efforts, which were somewhat outside the range of Bessemer's special line of invention.

The commencement of the most important part of Bessemer's career dates back to the Crimean war, when the obvious imperfections in the artillery of the British army brought to the front a large number of more or less able inventors. Naturally Bessemer was among this number ; one of his early proposals was to fire elongated shot from a smooth-bore gun and obtain rotation by grooving the projectile. He received no encouragement from the British war office, but a good deal from the Emperor Napoleon, who invited him to Vincennes, where some interesting experiments proved conclusively that the material then available for gun construction was entirely too weak. To obtain a stronger material was now the object of Bessemer's most earnest investigations. His efforts were directed to the production of a combined metal by the fusion of pig or cast iron with steel in a reverbatory or cupola furnace. This was the subject of the first of the long series of patents taken out by Bessemer in connection with the manufacture of steel, which extended over a period of fifteen years from August 1854 to August 1869. The combination of cast iron and steel (a process protected by a patent dated 10 Jan. 1855) produced a metal that gave promising results, but was altogether deficient in the qualities required. Accident led Bessemer to experiment in another direction. He was melting pig iron in a reverberatory furnace, and observed some pieces exposed to the air blast on one side of the bath that remained unmelted in spite of the intense heat ; on examination these proved to be mere shells of wholly decarbonised iron, the carbon having been burnt out by the blast. This accident was at once turned to account, and a number of interesting experiments followed that formed the basis of the second Bessemer steel patent dated 17 Oct. 1855. This patent describes the use of a furnace large enough to contain a number of crucibles charged with melted pig iron, through which air under pressure or steam was blown. This was followed by another patent, dated 7 Dec. 1855, for running the melted pig iron from the blast furnace or cupola into a large tipping vessel — the Bessemer converter — the air blast being introduced through tuyeres so as to pass up through the charge. Two patents, dated 4 Jan. and 12 Feb. 1856, describe improvements in mechanical details, and on 15 March following, another specification was filed, for the addition of some recarbonising material to be added to the charge from which the carbon and impurities had been burnt out by the blast, so as to restore a given percentage of carbon, according to the quality of steel it was desired to manufacture. This completes the list of master patents that controlled the Bessemer process. There were many others, but they were of relatively minor importance. Between the middle of 1855 and the summer of 1866, when he read a famous paper at the Cheltenham meeting of the British Association for the Advancement of Science, Bessemer carried out a great number of experiments at his laboratory, Baxter House, St. Pancras, with the object of establishing his process on an industrial scale.

The problem to be solved was how to decarbonise the charge completely, and to keep it fluid by the active combustion of the impurities in the molten iron by means of an air blast. The first converter used for this process was a cylindrical chamber lined with fireclay, with a row of tuyeres near the bottom and an opening at the top for the discharge of the burning gases. The converter held ten hundredweight of molten metal, and an air blast of fifteen pounds' pressure to the square inch was used. This