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468                      METALLURGY   OF   CAST   IRON.
fluidity of metal, to afford any fair knowledge of the true relative differences in strength of cast iron. The half-inch bars from gun metal and the half-inch bars from heavy machinery practically show each to be of the same strength, where the one and one-eighth round bars indicate what we would nat-urally expect, namely, that the gun metal is materially stronger than the heavy machinery iron. Then again, the half-inch bars would indicate that the heavy machinery iron was very much stronger than the roll irons. The strength of the half-inch bars for light machinery, 454 pounds, indicates such iron to be stronger than gun metal, chill roll, car wheel or heavy machinery iron, while the one and one-eighth inch round bars show the light machinery to be but 1,931 pounds, as compared with 3,686 pounds for gun metal, 2,980 pounds for chill roll, 2,553 pounds for car wheel and 2,657 pounds for heavy machinery. The half-inch bars show a breaking load of 160 pounds for stove plate and 167 pounds for sash weight or " white iron," indicating that the latter is the stronger iron, while our one and one-eighth inch round bars show a strength of 1,798 pounds for stove plate, and only 1,406 pounds for sash weight iron, thus thoroughly demonstrating that one inch square area bars will fairly record the true relative degrees of strength of cast iron, whereas the half-inch square bar gives us absolutely little knowledge or indication of any difference in strength between one mixture and another, or any irons used in the different specialties of iron founding. A fact that further demonstrates the impracticability of using small test bars is that the tensile strength of the Table 96 records a uniformity in degrees of strength. R. A. Robertson's gun metal report,ich is characteristic ofA few of these bars were pulled for the tensile strength.hat recording the strongest mixture, seen in Table 89; the