IRON 



943 



of the slags shows a variable percentage of iron, amounting rarely to less than 15 

 per cent., but reading occasionally up to 40 per cent. 



A form of rotating furnace, represented in fig.^ 1217 in longitudinal section, and in 

 an end elevation in jig. 1216, has been found to give very successful results in practice. 

 It consists of a cylindrical chamber of wrought iron mounted upon friction-rollers, and 

 capable of receiving motion at different speeds from pairs of spur-wheels driven by a 

 steam-engine. The arrangements for forcing, which are those of the usual regenera- 

 tive gas-furnace, are placed at one end of the cylinder, while the other is closed by a 

 working door with a stopper-hole like that of an ordinary reverberatory furnace, as 



1216 



seen in fig. 1216. The slags are received into a waggon, which runs upon a railway, 

 in a pit below the cylinder. The lining or fettling of the cylinder is formed of a 

 bauxite or aluminous iron ore, which is ground up with a little graphite, and strongly 

 heated. The iron of the ore is thus reduced to the metallic state ; and the alumina, 

 from the intense and long-continued heating, is converted into a dense substance 

 resembling emery, which is capable of resisting abrasion by the materials of the 

 charge, as well as being unaffected chemically. 



The rotative furnace is worked as follows : 



The ore to be smelted is broken up into fragments, riot exceeding the size of peas or 

 beans ; to it is added lime or other fluxing material in such proportion that thegangue 

 contained in the ore and flux combines with only a little protoxide of iron into basic 

 and fluid slag. If the ore is haematite, or contains silica, it is preferable to add alumina 

 in the shape of aluminous iron ore ; manganiferous iron ore may also be added with 

 advantage. A charge of say 20 cwts. of ore is put into the furnace when fully heated 

 while it is slowly revolving. In about 40 minutes this charge of ore and fluxing 

 material will have been heated to a bright redness, and from this time from 5 cwts. to 

 6 cwts. of small coal of uniform size (not larger than nuts) are added to the charge, 

 whilst the rotative velocity is increased in order to accelerate the mixture of coal and 

 ore. A rapid reaction is the result ; the peroxide of iron being reduced to magnetic 

 oxide begins to fuse, and at the same time metallic iron is precipitated by each piece 

 of carbon, while the fluxing materials form a fluid slag with the siliceous gangue of the 

 ore, The slow rotative action is again resorted to, whereby the mass is turned over 



