holes or “tuyeres” near the bottom or “hearth,” and through the melting away, by the heat thus generated, both of the iron itself which has been deoxidized in its descent, and of the other minerals of the ore, called the “gangue,” which unite with the lime of the limestone and the ash of the fuel to form a complex molten silicate called the “cinder” or “slag.”
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| Fig. 7.—Section of Duquesne Blast Furnace. | |
GG, Flanges on the ore bucket; |
P, Cinder notch; |
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| Fig. 8.—Lower Part of the Blast Furnace. |
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* The ore and lime actually exist here in powder. They are
shown in lump form because of the difficulty of presenting to the
eye their powdered state.
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| Fig. 9.—Method of transferring charge from bucket to main charging bell, without permitting escape of furnace gas (lettering as in fig. 7). |
Interpenetrating this descending column of solid ore, limestone and coke, there is an upward rushing column of hot gases, the atmospheric nitrogen of the blast from the tuyeres, and the carbonic oxide from the combustion of the coke by that blast. The upward ascent of the column of gases is as swift as the descent of the solid charge is slow. The former occupies but a very few seconds, the latter from 12 to 15 hours.
