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96                      METALLURGY   OF   CAST   IRON.
held at the mouth of the notch, can, if there is not too great a force, often almost stop the escape of metal. This stopper is made by rolling a i^-inch rod in a stream of slag as the furnace is being flushed out. Shotild the metal force itself out too fast at any time during a tap, the blast is slackened or stopped, until the metal has flowed off all it will of its own gravity, when the blast is again put on, and the ^increased pressure then drives out the metal and slag as above described. This end achieved, the blast-is then completely shut off and the notch stopped.
The process of stopping the notch by hand is proceeded with as rapidly as possible, in order to prevent loss of time in making iron. The first thing done is to throw a sheet-iron plate across the top of the iron trough; which, covered over with sand, protects the men from the heat of the trough, and permits them to come directly over their work. The notch at this stage greatly resembles a crater that has died down after vomiting its lava. Lumps of dross and fuel will be found sticking to its sides, which have been greatly increased in area from the effects of the "blow." A bar is used to loosen this debris, and then an iron scoop pulls it out of the notch-hole. After this debris has been removed as well as the inflowing slag will permit, the bar is again used to push down into the crucible any lumps which may be sticking to the sides of the notch, and a bar of the same shape as Fig. 21, only made of round iron, is now used to press down into the crucible the dross and slag which endeavor to rise to fill the notch-hole. This done, the bar is hastily removed, and men standing with two shovelfuls of clay toss it into the notch-hole, the clay is then quickly at 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     "