936 



IRON 



and partly in the state of fine dust or greillade, which principally goes into the slag ; 

 while in the latter the whole of the ore is powdered and clayed in alternate layers with 

 the fuel. The Stuck-Ofen is larger than the open fire, and the operation is continued for 

 several hours ; the lump of reduced iron being removed by breaking away the breast 

 of the furnace, instead of pulling it out from the top. The common Indian method of 

 making iron is conducted in a furnace of this class, but of very small dimensions ; 

 not more than 5 or 6 feet high, instead of 15 or 20 feet, as is used in Europe. In 

 the Chenot and similar processes the reduction is effected in fire-clay retorts, with 

 the production of spongy masses of iron ; while in the last, or Siemens' process, 

 which is of recent introduction, the ore is melted in a cylindrical vessel, with a refrac- 

 tory lining, and reduced by churning it up with carbonaceous matter ; lime, or other 

 fluxes, being previously introduced to combine with the silica, and prevent unnecessary 

 loss of iron by scorification. 



In the Catalan, or French method, the ore previously roasted in a kiln is afterwards 

 strongly torrefied in the forge before the smelting begins ; operations which follow in 

 immediate succession. Ores treated in this way should be very fusible and very 

 rich ; such as black oxide of iron, haematites, and certain spathose iron ores. From 

 100 parts of ore, 50 of metallic iron have been procured, but the average product 

 is 35. The furnaces employed are rectangular hearths, figs. 1212 and 1213, the 

 water-blowing machine being employed to give the blast. There are three varie- 

 ties of this forge : the Catalan, the Navarrese, and the Biscayan. The dimensions 

 of the first, the one most generally employed, aro as follow : 21 inches long, in 

 the direction pf, fig. 1213 ; 18$ inches broad, at the bottom of the hearth or creuset, 



1212 



1213 



in the line A B ; and 17 inches deep, fig. 1212, The tuyere, q p, is placed 9J inches 

 above the bottom, so that its axis is directed towards the opposite side, about 2 inches 

 above the bottom. But it must be moveable, as its inclination needs to be changed, 

 according to the stage of the operation, or the quantity of the ores. It is often raised 

 or lowered with pellets of clay ; and even with a graduated circle, for the workmen 

 make a great mystery of this matter. The hearth is lined with a layer of brasque 

 (loam and charcoal-dust worked together), and the ore, after being roasted, is sifted ; 

 the small powder being set aside to be used in the course of the operation. The 

 ore is piled up on the side opposite to the blast in a sharp saddle ridge, and it 

 occupies one-third of the furnace. In the remaining space of two-thirds the char- 

 coal is put. To solidify the small ore on tho hearth, it is covered with moist cinders 

 mixed with clay. 



The fire is urged with moderation during tho first two hours, the workman being 

 continually employed in pressing down more charcoal as the former supply burns 

 away, so as to keep the space full, and prevent the ore from crumbling down. By a 

 blast so tempered at the beginning the ore gets well calcined, and partially reduced 

 in the way of cementation. But after two hours, the full force of the air is given ; 

 at which period the fusion ought to commence. It is easy to see whether tho torre- 

 faction be sufficiently advanced by the aspect of the flame, as well as of the ore, which 

 becomes spongy or cavernous ; and tho workman now completes the fusion, by de- 

 taching the pieces of ore from the bottom, and placing them in front of tho tuyere. 

 When the fine siftings are afterwards thrown upon tho top, they must be watered, 

 to prevent their being blown away, and to keep them evenly spread over tho whole 

 surface of the light fuel. They increase tho quantity of tho products, and pivo a 

 proper fusibility to the scoriae. When tho scoriae are viscid, tho quantity of siftings 

 must be diminished; but if thin, they must bo increased. The excess of S!;ILT is 

 allowed to run off by tho chio or floss-hole. Tho process lasts from five to six hours, 

 after which the pasty mass is taken out, and placed under a hammer to be cut into 

 lumps, which are afterwards forged into bars. 



Each mass presents a mixed variety of iron and steel, in proportions which may bo 



