124 president's address — section b. 



from the introduction of carbonaceous fuel is, of course, the ideal ; 

 but even the best existing practice still finds necessary the application 

 either of a hot blast, with or without coke, or of about 1 per cent, to 

 1^ per cent, of coke (figured on the weight of furnace charge) when 

 cold blast is used. One reason is that under present conditions of 

 furnace height there is too great a loss of heat at the furnace top — 

 not so much through the non-combustion of the volatile portion of the 

 sulphur as because the low columns used allow the gases to escape 

 with too high a temperature. Wholly against a prevailing notion, the 

 low column of the converter vessel should not be imitated. It is only 

 an incidental feature of that vessel. Compliance with the true Besse- 

 mer principle first of all requires complete absorption of the oxygen 

 blown in, therefore adequate height of column. The gases should leave 

 the furnace free from uncombined oxygen, and the charge should be 

 kept as high as at all compatible with the ready descent of the stock. 

 The height of the stock line is consequently a function of the air-supply, 

 and, to prevent waste of heat on the one hand and to achieve a proper 

 transmission of the heat of the ascending gases to the descending 

 masses on the other, it should be kept at as high an elevation as is 

 conformable with the annoying peculiarity of iron pyrites to agglome- 

 rate under the influence of a low heat, thus impeding the descent of the 

 charge. Pyrrhotite ores and mattes, when re-treated for concentration 

 purposes, are free from this drawback, and can be run with cold tops. 

 Pyritic ore furnaces usually exhibit the combustion of the subb'med 

 sulphur a little distance above the stock line, where the gases come 

 into contact with the atmosphere ; but this spurious " over-fire " is 

 not disconcerting, or a real waste of heat. The latter arises when the 

 gases and sulphur vapors, as they issue out of the top of charge, are 

 too hot. 



The inner working of the pyrite furnace differs essentially from 

 that of the ordinary coke-fed furnace treating partially oxidised material 

 into matte. In the first place there is, or should be, no oxidising action 

 anywhere except in the slag- forming zone itself. This is situated at a 

 somewhat higher level than in the coke-fed furnace, especially when a 

 cold blast is employed, and in it the oxidation of the special compound 

 of iron and sulphur which arrives at this point, and the scorification 

 of the iron, take place simultaneously. Below it there is no special 

 •chemical action and no further generation of heat, and above it there 

 is none of the latter, but a decided progressive disintegrating alteration 

 in the composition of the molten sulphide itself. The pyrites, after 

 losing its volatile sulphur atom a few feet below the top of charge, and 

 being thereby transformed into a compound very similar to magnetic 

 pyrites, is fused by the heat of the escaping neutral gases— which, in 

 this region, are solely composed of nitrogen, sulphurous acid, and 

 carbonic acid (out of limestone and coke) — long prior to reaching any 

 great depth. Subsequently, while coursing down the furnace to lower 

 depths, it suffers a further desulphurisation, without oxidation, simply 

 under the influence of the gradually rising temperature. A roasting 

 action does not take place anywhere. The particular combination of 

 iron and sulphur which finally reaches the actual zone of simultaneous 



1 



