4^4 METALLURGY OF CAST IRON.
1' temper'' of sands, as commonly used in ordinary foundry practice, can cause a radical difference in the percentage of combined carbon, in the same size and form of small castings or test bars from the same mixture of iron, poured out of the same ladle. The determinations Nos. i, 2, and 3 also indicate the necessity of adopting, for physical tests, the size and form of test bar least liable to irregularities in the combined carbon composing its shell or outer body, caused by varying conditions in the '' temper *' of sands and fluidity of metals, etc. As degrees in the strength of iron can be affected by the •" temper" of sand and fluidity of metal at the moment it is poured, so can contraction records be likewise affected, making them deceptive. Experiments which I have conducted to discover if the same conditions which give erratic results in strength records would not do likewise in contraction, have only the more confirmed me in the advocacy of bars over one square inch in area, wherever one desires to be wholly or partially guided by physical tests.
To learn whether differences in the temper of sands could cause changes in the length of contraction in small bars of the same size, cast in the same mould with the same iron, out of the same ladle, and at the same moment, I took three patterns % inch square and 12 inches long, and cast two of them between yokes and a third bar in a divided chill to form two sides and bottom of the mould, the fourth side being formed by the sand of the cope. The two bars cast between yokes had drier sand for one than for the other. The dampest sand was not so damp but that a sound casting could be produced, and the two sands differed no more than can.......... .48 •39 •52 .58 •30 •53