Page:Dictionary of National Biography volume 39.djvu/437

 sample of ‘spiegeleisen,’ an alloy of iron and manganese, manufactured in Rhenish Prussia from a double carbonate of iron and manganese known as spathose iron-ore. Mushet immediately commenced making experiments with this metal, and, although the results were of no immediate practical value, they ultimately became of great importance in connection with the Bessemer process. He found that spiegeleisen possessed the property of restoring the quality of ‘burnt iron,’ i.e. of wrought iron which had been injured by long exposure to heat. Bessemer's celebrated process of refining iron by blowing air through it when in a molten condition was made public in a paper read before the British Association at Cheltenham in August 1856, and a sample of the refined metal fell into Mushet's hands shortly afterwards. It appeared to him to be in a condition analogous to that of ‘burnt’ wrought iron, and he found by experiment that the addition of molten spiegeleisen produced a substance which ‘was, in fact, cast steel, worth 42s. per cwt. I saw then,’ says Mushet, ‘that the Bessemer process was perfected, and that, with fair play, untold wealth would reward Mr. Bessemer and myself’ (The Bessemer-Mushet Process; or, Manufacture of Cheap Steel, 1883, p. 11). On 16 Sept. 1856 he took out three patents for improving the quality of iron, refined by blowing air through it when in a molten condition, and two other patents were entered on the 22nd of the same month; but none of the specifications contain any direct reference to Bessemer's process, the method being stated to be applicable to an abortive patent taken out by Martien in 1855. Mushet bases his claim to the invention upon his patent of 22 Sept. (No. 2219), in which he specifies ‘the addition of a triple compound or material of or containing iron, carbon, and manganese, to cast iron which has been purified and decarbonised by the action of air whilst in a molten or fluid state.’ Mushet took out several other patents for modifications of the process, but by an unfortunate accident (so he asserts) he omitted to pay the stamp duty on the patent of 1856, which became due in 1859, so that all his patent rights in this country and abroad were at once extinguished.

Much discussion has taken place as to the originality and value of Mushet's invention. There was an admitted difficulty in ascertaining with certainty when the decarbonising action of the blast of air in the Bessemer process had proceeded to the right extent, and therefore when it should be stopped. Mushet's plan was to decarbonise completely or nearly so, and then add a given proportion of carbon in the state in which it exists in molten spiegeleisen, the precise composition of which should, of course, be known. Mr. J. S. Jeans states in the ‘Engineering Review’ for 20 July 1893, p. 7, that, ‘as a matter of fact, Bessemer had actually gone so far with his experiments on manganese that he had virtually solved the problem before the Mushet patents were published,’ and this fact will, it is believed, be made clear by Sir Henry Bessemer's ‘Autobiography.’ Mushet says: ‘I by no means arrogate to myself the idea that, if I had not invented my spiegeleisen process, no one else would ever have found it out. On the other hand, I have frankly and publicly said that Mr. Bessemer would, in all probability, sooner or later have made the discovery. I, however, was fortunate enough to anticipate him’ (The Bessemer-Mushet Process, Preface). In 1876 the Bessemer Medal of the Iron and Steel Institute was awarded to Mushet, with the full approval of the founder. In making the presentation, the president, Mr. Menelaus, said that the application of spiegeleisen was one of the most elegant, as it was one of the most beautiful, processes in metallurgy, and that it was worthy of being associated with Mr. Bessemer's process. But the reticence of both parties has rendered it difficult to determine the degree of validity to be allotted to all Mushet's pretensions. In 1883 Mushet published his version of the matter, but Sir Henry Bessemer has not yet put his entire case forward. Although he paid Mushet an annuity of 300l. for some years before his death, he invariably refused to pay him royalty; and he intimated his readiness to allow Mushet and his legal advisers to see the whole process carried out, and challenged him to bring an action for infringement. This challenge Mushet declined (cf., Creators of the Age of Steel, p. 61; and , Steel, p. 78).

Between 1859 and 1861 Mushet took out about twenty patents for the manufacture of alloys of iron and steel with titanium, tungsten, and chromium. A summary of these patents is given in Percy's ‘Iron and Steel,’ pp. 165, 188, 194. His experiments with tungsten alloys led to the invention about 1870 of what is known as ‘special steel,’ which possesses the remarkable quality of self-hardening. It is forged at a low red heat, and allowed to cool gradually, acquiring a degree of hardness which renders it of great value for engineers' tools, for which it is now very largely used (Engineering, April 1870, pp. 223, 236;, Steel, p. 532). The precise mode of preparation is a secret, but, from an analysis by Gruner (Bulletin de