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518                 METALLURGY OF CAST IRON.
bars. The reason for the recess seen in the end of the flask at E, Fig. 123, is to prevent the metal rising above that height at the close of pouring, and thus not give the metal a chance to form a " fin " between the top joint of the,flask or over the top of its ends at H and thus still the more positively insure the casting's own weight pulling the contraction downward instead of the contraction pulling the whole body of the .casting upward from the bottom of the mould, a factor which has been the cause of pulling the neck off from rolls or causing checks or total separation of parts in other kinds of castings. The cross bar in the flask is formed, as seen at R, Fig. 123, for the purpose of fitting over the runner where it connects with the whirl-gate's basin, to assist the same end just mentioned in compelling the contraction to follow a natural tendency, and noj: lifting the whole weight of a casting upward, as previously explained. At R R and O O, Fig. 122, are seen male and female pins and holes, which are arranged as shown so as to insure these two sections of the patterns coming together at true points, to make it impossible for the action of the rammer to distort them in any way.
j| In making the "whirl-gates" seen at T, Fig. 122, the operator must so proportion them that the runner joined to the basin A, Fig. 122, can carry the iron to the inlet of the " whirl-gates " as fast as they can deliver the metal to the mould, the idea being that as soon as the pouring is commenced, with either of the three standards, the upright runners are so proportioned that the pouring basin N can be kept full of iron, to prevent any dirt passing down the runner through the " whirl-gates " to the mould. Owing to the smallestsld ask such, after having              I''