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STRKTCHIXr,    CAST   IRON,    KTC.                     421
ii\^ to the one having a greater time than the other to change the combined carbon to graphite, a quality the author noted in a paper before the Foundry-men's Association at Philadelphia. Sec Chapter LIX., pai4*e 45.|. "I"his Chapter also presents analyses of one-half inch and one inch square as well as one imd one-eighth inch round test bars poured from the same ladle at the same time, showing that the graphite was much less in the one-half inch than in the one and one-eighth inch test bars, and on this account contraction was much less in the larger than the smaller bars.
The formation of graphite may be compared to the raising of bread. The longer time #iven for the yeast to act, the greater the bulk of the dovish obtained, caused by the expansion of the wheat's molecules. This is similar to the cooling of liquid iron to a solidified cold state. The longer the period for cooling, the greater the expansion of the molecules and ^rain of the iron, which is defined chemically by our having' higher graphite in slow than in fast cooling ; this is also assisted by the heaviest parts of a casting1 or that last to solidify often containing silicon to have its percentage higher than will be found in the lightest poll ion or those first to solidify, (Expansion is also a quality affecting contraction which should be considered in connection with graphite. For ciTccts of expansion, sec Chapter LIV.)
We ran take the worst kinds of sera]) iron, and by pouring them into such heavy bodies, as anvil blocks, for example, obtain iron that presents a lar^e, open "Drained fracture, often of excellent texture, proper for beinif readily machined; whereas, were the same iron poured into a casting under three incheswhen thought to vary from any given standard.                                                          J  I