EFFECTS   OF   VARIATIONS   IN   MANGANESE.	243
the physical properties of the casting", something which is entirely different from the changes due to the silicon and sulphur of irons coming from any one mixture of ores, flux, and fuel. A good test demonstrating this point is found in heat No. 6, which has 2.47 silicon in Foundry pig when remelted. Here we find that an increase from .97 to 2.26 — a difference of over 1.25 per cent. — of manganese in. pieces of the same pig does not cause a chill in the ends of the square bars, when tested as at E, Fig. 55, and has only a difference of .on in the contraction. By increasing the manganese still higher until we have 3.71 —nearly 3 per cent, of an increase — we then obtain a chill of only .062 in the ends of the bars, as at E, Fig. 55, and a difference of only .021 in the contraction over that found in the test bars free of the ferro-manganese mixture. Then again, the hardness tests, column 7, show a difference of but .065 and .143 in the depth of the drilled holes, as at P, Figs. 54 and 55, with the two variations in manganese. Still further, the structure, column 8, of the gray body exhibits no difference to the eye. Another point shown by this heat comes from the manganese placed, on the molten metal in the ladle. Here we find that an increase of .19 in the percentage of manganese has made no difference in the contraction and a variation of but .033 in the depth in the hardness test. This shows that the addition of manganese in the ladle tends to slightly increase the hardness, which is contrary to what we have generally been led to believe by writers in the past. We are not confined to this one test to modify views of the past on this point, as the same result is also shown in heats Nos. 4, 5, and 6, However, when we get to low silicon irons, as to.