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94                       METALLURGY   OF   CAST   IRON.
to empty the furnace in a few minutes. Men have been struck by such outbursts and almost buried alive in a pool of metal before assistance could be rendered.
The process for handktapping, when all is working well with a notch of a furnace, is first to take an iron bar and prick into the stopping clay, starting a hole as seen at the entrance K, Fig. 18, the "keeper" being careful to give it the shape and angle desired. As the clay is loosened, a ^-inch rod, having a flat lifter about i)4 inches square on its end, as seen in Fig. 21, below, is used to pull the loose clay up out of the hole,
which    is   generally made about 4 inches in  diameter   at   the FIG-20-                          top,   tapering   down
6/0.   ________4         to 2)4  inches at the
         bottom.     Picking by FIG- 21.                           hand bars and lifting
u'0__________*]   out the loosened clay
is continued until the FIG 22                           solid  clay  shows by
its red heat that its
thickness preventing the metal bursting out is not over 3 inches; then a steel bar of about i^ inches diameter having a sharp point is placed as shown in Fig. 18, the upper end resting on a piece of pig metal thrown across the top of the iron trough, as seen at T. A sledge is now used at the end F, the bar in the meantime having its point guided by hand so as to cut around the edge of the hole. This is continued until metal commences to ooze out slightly, when the bar is driven through the started body of the clay into the metal seeking to force itself out. The bar is thenso as to prevent its being tapped, is that illustrated by the hydrogen blow-pipe at A, Fig. 19, page 93. As used in this case,ch oftener than when it can be tapped 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     "