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^y0                     METALLURGY   OF   CAST    IRON.
This Chapter presents facts which should greatly aid in settling all disputes as to the value of the round over the square bar for recording the best natural strength of cast iron, and that we should not use a bar less than of one square inch area. * The tests exhibited are all of sound fracture, and in all bars but those for sash weight iron could be machined as described on page 300. For tests of larger round bars than one and one-eighth inch diameter, and a discussion on the utility of test bars, see pages 533, 536, 577 and 579.
Previous to this series ol tests, etc., being first published, the author had no knowledge of any person thinking to advance information on the physical properties of cast iron, working other than in one "grade," and drawing conclusions from this as being applicable to anything that might come under the head of cast iron, which is a broad term and means any "grade" that the metalloids, silicon, sulphur, phosphorus and manganese when combined with metallic or "pure iron,'' make workable for conversion into castings. While it is true the quality of '' grades '' being in cast iron was not recognized as it should be by experimenters, etc., making or reporting physical tests, the author is pleased to note that this work has "caused cognizance being taken of this, as such a course places all in a position to arrive at correct conclusions to the sooner fathom any phenomena that may puzzle or make mysterious the workings of cast iron. It would be well to study Chapter XX. in connection with this paragraph.
A study of the cuts seen in Figs. 95 and 102 will show how the metal is best permitted to have its
*The American Foundrymen's Association adopted resolutions  that test bars smaller than ij^-incn diameter were not recognized, see pages 573, 577............^.15° <(