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Io6                       METALLURGY   OF   CAST   IRON.
the molten metal from the main runner to the sow.
At Fig. 31 are shown what are called '' runner staples, '' which are used to support the *' cutters,'' as seen at Nos. i, 2, 3, 4, 5, and 6, Figs. 24 and 28, also in the perspective view of the main runner seen in Fig. 34. As each pig bed fills up, the cutters stop the now of metal, permitting it to flow into the adjoining bed as above described. When half of the beds are about poured off, slag then commences to come out with the iron at the notch-hole. To prevent the slag from passing down the runner to the pig beds, a " skimmer plate, " seen at I, Fig. 24, is knocked down to about the depth shown and then some sand is thrown against it on the side at K. By ramming this sand, the opening below the lower edge of the skimmer plate I and the bottom of the runner can be decreased at will, so that only iron may pass beyond the skimmer plate and its flow may be regulated. The slag is let run out at the " slag runner" shown at the dotted lines K, Fig. 24. The slag running out of the tap-hole at every cast is considerable; often for every ten tons of iron there may be two tons of slag.
After the pigs are cast they must be broken. This constitutes the most laborious work about a furnace. Before starting to break the pigs, which is not done until they have solidified sufficiently to not " bleed," sand to a depth of about % inch is thrown over their surface. Two or three men wearing wooden soles about 1% inches thick attached to their shoes, now start at the first poured bed with pointed ij^-inch bars about six feet long. By inserting the point of the bar between the pigs at the end furthest from the i * sow,'' they are readily broken loose from thean opening to admitt it struckat the regular notch.    It is often surprising how rapidly, as about 75 per cent of the heat generated from the solid fuel is utilized. This is attained where one ton of coke will produce one ton of iron; and Sir........................    2,720     "