222 METALLURGY OF CAST IRON.
con, sulphur, phosphorus and manganese exist in the two castings, and still have the combined carbon much higher in one than in the other. (See pages 167 and 168.) Concerning the principles involved in the strength of cast iron, we find the most lamentable ignorance exists. Some understand that there is such a thing as soft and strong grades of iron, but when you have the latter practice ignored and the first exacted until the product approaches lead, it is time to stop and see whither we are drifting. The machine builder, ignoring strength but finding his castings growing softer, has encouraged the foundryman in giving such .soft castings, until to-day many of our machines might as well almost be made of so much .glass. Such practice injures the reputation of cast iron and encourages its being replaced by steel, etc. It is not to disparage the founder that the author writes of this subject, but if possible to awaken thought and action toward a movement by the builders of machinery for the exercise of some reason and the attainment of knowledge as to where to draw the line at wanting softness at the sacrifice of strength. Before the founder knew so much about silicon, and had good luck in mixtures, his castings would generally show a rich, dark, open fracture, making a strong, soft casting, instead of being found, as to-day with many, in a close, silvery-grained grade, making a soft, rotten, leaden casting.
In using silvery or silicon pig to any extent in mixture there is a very fine line to be drawn in the use of just enough to attain the happy medium approaching strength and softness. Some would rather take their chances of being over the line than under it, and many have gone over the line so far as to have castings so weak as to break of their own accord. oxide in the so-The philosophical explanation of this extraordinary effect i my opinion, to be found in the fact that the f erro-manganesu .ğR. C. Hindiey, M. Hoskins, Harvard College, Havemeyer University, Henry Hiels Chemical Co., Isabella Furnace, Iron Gate Furnace, Iroquois Iron Co., Illinois Steel Co., Jefferson Iron Co., Kittan-ning Iron & Steel Co., C. A. Kelly Plow Co., Lebanon Furnace, Longdale Iron Co., Lackawanna Iron & Steel Co., Logan Iron........................ 16,720 " t-