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METALLURGY OF CAST IRON.
never seen a furnace. The tapping-hole K is generally made at an angle somewhat as shown. After the metal has run out all it will by force of gravity, the blast pressure is increased above the ordinary to drive or siphon it out, as called by some, to about the level shown at the dotted line O.
With the weight of stock bearing down on the molten mass in a crucible and blast pressure of 10 pounds or more to the square inch, it seems reasonable to expect the results described. We know the weight of stock and pressure of blast exerts such a driving-out influence, from the fact that when about two-thirds of the pig beds are poured, the metal will often almost stop running, at which point the blast pressure being increased a fourth more metal will often be forced out, and the more acute the angle of the notch, so as to carry its opening lower into the crucible, the more metal to a depth of about 15 inches below the level of the bottom of the iron trough can be siphoned out in tapping a furnace. A .question which suggests itself here is the reason for having such a body of metal below the level of a notch-hole. The great depth sometimes attained is not really desired, but is erased by the liquid mass burning out the bottom brick-work.
When "blowing-in" a new furnace, the bottom bed ofir interior lined with fire brick, the same as is done with the " down-comer " which carries the dead gas from the top of the furnace down to the combustion chamber of the hot blast stoves to protect them and prevent loss of heat.gathers on the combustion chambers for a distance of about twenty feet in height, and on the bottom of the stoves, which have openings as at K and H for getting at or cleaning out the stove, or, if shut off, for repairs.d checkered brickres, etc. It may also beency :|,