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580                       METALLURGY   OF   CAST   IRON.            .                                  V
the necessary dimensions. It will be noted that the bottom of the mould is conical, as seen at I. This is to present a sloping surface to the dropping iron and help to avoid its cutting the bottom of the mould.                   j
These bars  could be moulded  flat  and poured on             '
their ends by arranging the flask in such a manner that pouring gates and basins can be provided on top. The extra labor of carrying out this method, in a            j
measure counterbalances the  making of the core C.         .
The only advantage of moulding flat lies in the greater         >
certainty of obtaining bars free from swells when made by inexperienced moulders.
The sand should not be any damper than to mould well and stand the .wash of the iron without cutting',             ,
blowing,  or scabbing.     It should be rammed evenly             )
to avoid swells,   and poured by dropping the metal             1
from the top through gates or from the ladle direct             '!
into the open mould.    If the sand will not stand pour-          **s jb
ing   from   the  top,  then  pour  frenn   the  bottom   by             I
means of whirl gates.    If there are more than four bars to be poured from the same ladle of iron, where it would take more than two minutes' time in pouring,  they should be gated  so  that the one pouring        "      > basin can fill all the gates at about the same time, thus insuring all bars in a set having the same temperature              -of pouring.    After the bars are cast they should remain              I in their moulds undisturbed until cool.                                                1
i.    Unless furnace iron or subsequent annealing is specified, all gray iron castings are understood to be of in general practice, especially in making comparison <>i; the widest ranges in grades.temper '' or damp-              ,| |