Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/353

IKON 337 difficulties in the way of regulating the degree of carbonization, the cost, and the impurity of the resulting steel (unless excessively pure ores were used) rendered the process practically a failure. Fig. 55 indicates the apparatus used by Blair for the production of spongy iron. A is the reducing chamber into which the ore is placed along with about 5 per cent, of lime, which is found to accelerate the reduction considerably, so that a charge can be worked off in about a fifth of the time that would otherwise be requisite. Through this chamber a current of carbon oxide and nitrogen is led, Fig. 55. produced in the gas generator B ; ore and fuel are supplied from time to time through the respective hoppers g. g. The escaping gases pass away through the flue deh, a valve/ being applied so that part of the gas can be passed back again through the producer so as to keep the action from going on too quickly. From time to timetho reduced metal is withdrawn by the slide n from the cooling-box kk, which is surrounded by a water jacket to facilitate the cooling of the spongy iron. Siemens has attempted to apply a modification of the spongy iron process to the manufacture of steel, the spongy metal from a mixture of ore and carbonaceous matter heated in a revolving furnace being dropped into a bath of melted pig metal ; this method, however, was found to give unsatisfactory results, first because the spongy iron would not readily dissolve in the molten pig but floated on its surface, and secondly because sulphur was taken up by it from the gases during its reduction ; accordingly the precipitation method described below was adopted in its place. Dupuy has recently proposed a direct process worked as follows: the ore to be reduced is mixed with carbon, and the mixture placed in an annular vertical cylinder of sheet iron some 3 feet high, the outer diameter of the cylinder being about 20 inches, and the inner diameter 7 or 8 inches ; a number of these masses are arranged on the coke floor of a reverberatory furnace ; after heating for some hours the reduced metal and the sheet iron coatings cake together so that the masses can be removed and hammered and squeezed to muck bar, cut up, piled, and reheated and rolled into plates, bars, &c. ; or they may be fused down on the open hearth into steel. It is claimed that by this treatment the metal takes up not more than one-fourth of the phosphorus contained in the ore instead of practi cally the whole as when smelted in the blast furnace ; thus the ore of the Republic Mine of the Lake Superior district and the metal made from it by Dupuy s process gave the following numbers (Dupuy, Journal Franklin Institute, Deeember 1877 ; see Iron, vol. x. p. 803) : Ore. Dupuy s Metal made therefrom. Iron , 68-48 99-704 0-Q53 O OIG Carbon 042 Silicon 01 Sulphur 03 > Slag 185 100-000 Phosphorus per 100 of iron 0-076 001G The inventor considers that the phosphorus compounds do not become largely reduced in the process owing to the incomplete fusion of the metal during the reduction, the phosphates remaining blended with the cinder ; as he states that the process works much better when alkalies, in quantity and kind determined by analysis of the ore, are added to the mixture before reduction, presumably the non-reduction of phosphorus is due to the basic " nature of the cinder. 31. Siemens Precipitation Process. About the most successful of the methods for producing iron or steel direct from the ore at one operation is that designated by Siemens the "precipitation process" (Chem. Soc. Journal, 1873, p. 661) ; although it is doubtful whether this can yet be said to have completely emerged from the conditions of experi mental trial as to the best conditions for competing with other methods in regard of cheapness of production, yet its practical success is demonstrated by its having been worked commercially not only in England but also in America. The principle of the process is essentially the fusion by means of an intensely heated " regenerative " furnace of the ore to be reduced with a suitable flux (lime, aluminous ore, &c.), and the reaction upon the fused substance of heated anthracite or hard coke forming the covering of a lower bed in the furnace (fig. 56), on to which the fused ore FIG. 56. Cascade Furnace Longitudinal Section, is allowed to flow from the upper bed. Under these cir cumstances the solid carbon precipitates iron from the fluid in the same way that iron precipitates copper from copper sulphate solution (saving that in the latter case no gases are evolved as complementary products) ; the iron agglu tinates together into a pasty ball immersed in a fluid bath of cinder ; when the operation is sufficiently advanced the ball is removed and shingled into blooms or made into steel by dropping it into a mass of fused pig iron, in which it rapidly dissolves. The cjnder thus produced ontains much iron, usually at least 15 per cent,, and sometimes upwards of 40 per cent. In an improved form of process, the double bed is dispensed with and a rotary furnace substituted (figs. 57,58), much resembling Siemens s puddling furnace, save that the combustion chamber is rotative ; the ore and flux are introduced and melted ; small coal of the size of nuts is then shovelled in, when a rapid evolution of carbon oxide results, so that it is un necessary to introduce more than a little gas from the gas regenerative heater, but mainly only heated air to burn the evolved carbon oxide ; when the reduction is nearly com plete, the fluid cinder is drawn off and the spongy metal balled by quick rotation for a short time. In this way, according to Siemens, a ton of iron may be reduced with XIII. 43