The Bessemer process has another peculiar and romantic feature in its history in that it has been twice invented. When he took out United States patents in 1856 Bessemer was confronted at once by a priority of claim to invention by William Kelly. The contention was sustained in the United States courts and Kelly was granted a patent. It is now not doubted that while the two men independently and separately discovered the principle, Kelly was ahead of Bessemer some eight or nine years in his dis covery. Kelly was in the iron business in Eddy ville, Ky., in 1846, refining iron in an old fashioned refinery, to make kettles used in the manufacture of sugar. He was an inventive genius, but a poor business man. An inspiration came to him one day while watching the progress of his refinery, on noticing that at a certain place where the blast of air happened to play on the molten iron direct without the intervention of any fuel, it became white hot and boiled violently. He immediately realized the revolutionary nature of his discovery and his knowledge of metallurgy easily furnished him with the explanation, namely, that the car bon content of the iron was acting as fuel, and by its combustion increasing the temperature of the iron. It was later discovered that the lar gest addition of heat arose from the oxidation of the silicon content, and that where less than one per cent of silicon exists in the iron the Besse mer process fails. On speaking of his hopes he was met with derision, but proceeded to make a public demonstration which convinced all who saw it. But, as with nearly all important dis coveries, there was a hard bat* ahead of Kelly. There is always a prejudice against revolutionary discoveries, and Kelly's customers refused to accept iron refined by the new method even though it passed the customary tests. His financial backing was also withdrawn, but Kelly could not be extinguished. How he persevered with his process when experiment after experiment failed, how he worked secretly in the forest, and finally got permission. from the Cambria Iron Works to erect a converter (the eighth he had constructed) in their works, and how after a disastrous commencement suc cess was finally achieved, are familiar stories. Kelly was recognized as the inventor of the Bessemer process, and while Bessemer's patents were refused renewal, Kelly's were renewed. He died in 1888.
The Bessemer Process To-Day.— In mod ern American practice the pig iron is sometimes used direct in a fluid condition from the blast furnace and sometimes remelted in cupolas. Rapid working is the object aimed at so as to avoid loss of heat by radiation, and permit of the use of lower silicon in the pig iron. To day but little more than 1 per cent of silicon is permitted in the charge and the blow is made in from 9 to 12 minutes. With a larger pro portion of silicon the blow is unduly pro longed. Even with this comparatively low content of silicon the blows are sometimes too hot and steel scrap has to be added in the con verter during the blow to cool it off. In place of scrap a jet of steam is sometimes turned on. As regards the capacity of the converter any thing less than 10 tons is considered a small converter and the usual amount treated at one time is from 10 to 20 tons. Two types of the Bessemer process are in use, known respec tively as the acid process and the basic process.
The difference lies in the character of the lining with which the converter is fitted. In the first named type this lining is of acid material, chiefly silica (held together with fire-clay) ; and in the second type it is of basic quality, generally calcined dolomite, held together with a small proportion of tar. In the latter case a percentage of lime is added to the charge before the blowing begins — the purpose being the formation with the silica of a basic slag which does not attack the lining.
In the acid process the sulphur and phos phorus elements of the iron are not removed, the acid slag refusing to dissolve them. It is imperative, therefore, that iron selected for the acid process should contain less than .10 per cent of phosphorus and less than .08 per cent of sulphur in order to yield a grade of Bes semer steel acceptable to the market. In the basic process the oxidized silicon is readily ab sorbed by the basic slag, and hence is more quickly removed than it is in the acid process. The carbon ingredient is next eliminated; and following that condition the phosphorus and a part of the sulphur are absorbed by the basic lime slag. The basic process is most largely in use in regions where the phosphorus con tent of the iron is large—particularly in Ger many and Great Britain. In the United States the acid process prevails almost universally. The lining generally consists of brick, sand or stone and the walls are lined to a thickness of about one foot. The bottom section of the converter containing the tuyeres is separate from the main section and is about 26 inches thick on account of the great amount of corro sion that takes place there and each vessel has a number of extra bottoms so that they can be quickly changed when burned out. The diameter of the tuyeres is about half an inch. The pressure of blast varies from 30 to 10 pounds, the former being used at the com mencement of the blow and the latter being the lowest it would ever be safe to reduce it to, and this only when the blow is particularly hot or the projections of slag excessive. Sufficient air must always be kept on to support the iron and prevent it running into the tuyeres and wind box. The converters are rotated to suit the exigencies of blowing, and receiving or pouring the metal, by means of a pinion at tached to the trunnion, and a hydraulically driven rack. The illustrations to this article give a good idea of the development of the converter from the earliest type.
The Clapp-Griffiths Bessemer.—This proc ess, which is now practically obsolete, was one of the earlist types of Baby Bessemer con verters. Its capacity was from two to three tons. A stationary side-blown converter was used, having a slag spout at one side from which the slag poured during the boil. The converter was in two sections, being jointed on a line above the tuyeres and the bottom section was handled and put in place on a car which could be lifted by a hydraulic ram. The only original feature of the converter was the slag spout, and the benefit derived from its use was always problematical. It was claimed that the steel made in this converter, even though high in phosphorus, was vastly superior to that made in ordinary converters. This claim was of course not substantiated.