IRON 



953 



charge is withdrawn through six passages, i, and air serving to oxidise the sulphur in 

 the hot ore also gains access through these apertures. The openings, I, m, serve for 

 introducing bars for working the ores when necessary ; 0, o, are sight-holes; and, n t 

 is the chimney, furnished with a damper for regulating the draught. 



1228 



1229 



The diameter of the shaft varies in different 

 kilns from 6 to 10 feet, and the number of pas- 

 sages for withdrawing the roasted ore may vary 

 from 5 to 10. The following figures have been 

 given by Westman as representing the quantities 

 of ore roasted in 24 hours with kilns of various 



With 



5 passages for drawing 

 the charge ," . 

 6 

 8 

 10 



22 to 30 tons. 

 28 36 

 35 48 

 45 60 , 



The temperature in Westman's kiln can be governed 

 by regulating the admission of air and gas, and if 

 necessary by addition of solid fuel. When the 

 kiln is at a proper working temperature, it exhibits 

 a red heat in the neighbourhood of the discharge 

 passages, i ; the ore sinters in front of the gas- 

 openings, k ; is in a pasty condition in the 

 neighbourhood of the holes, I ; in an almost pasty state, but having the edges sharp, 

 at m, and the temperature gradually diminishes in the upper part of the furnace. If 

 the ores are very sulphurous, they are roasted twice. After the first roasting the ore 

 is broken up, weathered by exposure to the air, and again roasted at a higher tempera- 

 ture. It is said that by the perfect method of roasting in this kiln, it is possible to 

 produce good pig-iron 'in the blast-furnace from Swedish ores containing too much 

 sulphur to be otherwise smelted. 



Flux. The flux that is used .in the blast-furnace is limestone, either in the state of 

 carbonate as it comes from the quarry, or calcined in kilns, by which it is deprived of 

 water and carbonic acid. The lowest bed of the coal-formation usually rests on 

 limestone, and in the coal-formation itself are found not only the ore and its most 

 appropriate fuel, but the pebbly grits which afford the blocks of refractory stone neces- 

 sary for building those parts of an iron furnace that are required to endure the utmost 

 extremity of heat, as well as those seams of refractory clay, of which the fire-bricks 

 are composed, with which the middle and upper parts of the furnace are lined. In 

 Styria where the spathic ores contain large quantities of protoxide bases, such as lime, 

 magnesia and manganese, siliceous and aluminous fluxes are sometimes required in 

 the form of quartzose schists and clay-slate. Very siliceous haematites are beneficially 

 fluxed by the addition of coal-measure shale, in addition to the limestone, or preferably 

 by the aluminous brown haematite found in the basalt of Antrim. Titaniferous iron 

 ores also require the use of aluminous fluxes, such as Labrador felspar or even ordinary 

 brick in addition to limestone. 



The composition of the limestone to be used in smelting operations is of consider- 

 able importance ; where calcareous ores are used, the presence of silicic acid in the 

 limestone is advantageous ; if clay ores are the main material from which iron is 



