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4to MKTAi.i.rkov or rAsr IKOX.
held in a wooden box, and the lower a chill or iron mould made in halves and held together by a rin<£ T, the whole resting on a bottom block U and the metal being" poured in at O. Now it will readily be seen that a casting made in such a mould would have one-half wholly chilled or body hardened, and. the other of
Pit;, "%7,-- M«.'I'U' l \ I li <
a softer <»r ])i«»n.'ci»iij]ih't»« Mj-,ty mi,\tin<<-, \\ i»irh if hvlil in a bath <»!' niulfi'ii ir»»u «>r sit-i-! \\-nnIfl b«- a \t ry pro., notmced i<*st to assist, in showing \vhi-t lu'r Iiani or »snft grades etc., of iron, when charged into a cupola or air'before it has solidified, and, which by. reason of its head pressure incased within the body of the shell, that has contracted from its chill or outer support, must be heavily strained to retain its enclosed body of still lluid metal. \Ye can see by the chill and sand contraction tests, herein recorded, how a very slight difference in the dampness of sands or nature of a mould can affect the contraction of castings or test bars, and shows us the necessity of having uniform conditions in nii-ulds and temper <>f sands in order to obtain a true e< »u i pa rat ivc record <>f contraction tests. More mi this subject is found on pai;es 454, .|<>y and 511.