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AI'l'KXmx   To  rHAl'TKK   LIV.       CONTRACTION,   KTC.    415
ways than one. Take the ease of the chiircoa.1 iron heats Xos. 5 and 6, which will illustrate the <4"reat difficulties the makers of chill rolls, etc., are confronted with. .Here we find that the chilled part of the casting will have as much attain contraction as the body of the casting" that is not chilled. It is no wonder that chill roll makers experience much trouble with the checking and cracking of the surfaces of chill rolls due to the excessive contraction of the chilled parts, which must leave or pull away from the chill mold supposed to support its enclosed body of liquid metal Ion*;'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< Ľu i pa rat ivc record <>f contraction tests. More mi this subject is found on pai;es 454, .|<>y and 511.
Comparative fusion tests by immersion were con-dueted at tin1 same time that the shrinkage and contraction tests wen* made. This was done chieily to test which of thr chilled or sand cast, ends of one bar would melt first of thr various metals used. The device the author designed for these tests is shown in Fi<.(s. Sy and KS, thr former figure, shows a three-quarter-iurh rod in the hands of a moulder bein^ held over a ladle that, holds in its end a casting made in the mould .seen at Fi#. HH, The upper half S was all y;reen sand3 per cent, of sulphur            I