MOULDING AND CASTING PIG IRON, ETC. 109
28. By making1 a comparison in the depth of the opening P with M and N, Fig. 25, it will be seen that the opening at P could not deliver any metal unless the iron was raised in the runner to its level, and the chances are, in the general working, that the iron in the main runner might never reach the bottom of the opening* at P. But to compel it to do so, a stopper composed of slag, chilled on the end of a one-inch iron rod, as seen at S, Figs. 25 and 27, is placed in the main runner to impede the flow of the metal. This action raises the height of the" metal in the runner so as to make it flow out at P, and the moment the stopper S is lifted, the metal is lowered below the level of this outlet, and hence instantly ceases to flow into any mould which may be run by such a plan. This last method governs well the actions of the main runner in filling' moulds; but there is still another point to guard against where two or more castings are poured from such a branch runner, and this is the tendency of one mould to fill before another, and hence produce casting's thicker or thinner than might be desired. To regulate this point, a portion of the edge of the mould is cut away to the thickness desired, as seen at B in the plan view, Fig. 27, and also in the section A-B, Fig-. 26. Such moulds being generally raised above the level of the floor, it can be readily conceived that any overflow at the points B will be received at a lower level than that of the castings, hence the difficulty, witli good metal, of obtaining such castings thicker than they might be desired. It may be well to state that outlets, such as at P, should be made well up towards the upper end of the main runner, so that when the stopper S is lifted the metal will have a good chance to is often surprising how rapidly, as about 75 per cent of the heat generated from the solid fuel is utilized. This is attained where one ton of coke will produce one ton of iron; and Sir........................ 2,720 "