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<^J2 MKTALLUKUV OF I'AST IKON.
However, if any one should cut a 4*4 -inch square bar of gray iron into i-inch square sections, they would find that any one of the sections would then stand a much less transverse or tensile load than bars of the same area that had been cast i inch square of the same iron.
It was a current impression that a large body of cast iron is weaker in'strength per square inch, than small ones of the same grade or cast. We find by a study of Tables 115 to 126 that this is true only in. the case of tensile strains. This is the first time that the author knows of attention being called to this fact, and now that such is publicly done herein it will result, no doubt, in changing many practices that have been followed, based on the supposition that in the same iron large bodies were weaker in strength per square inch than small ones.
The difference between the strength of finished and unfinished bars, as shown by the A. P. A. tests, demonstrates that where the same thickness of iron is removed in finishing test bars, finished bars are less erratic in recording strength tests than unfinished bars, and that as a rule finished bars are weaker than unfinished ones of the same iron. A finished bar that will prove stronger than an unfinished one would generally be due to the outer snrfaee hodv holding tin-combined carbon higher than was best for strength in that grade of iron. This generalIv oeetirs onlv in bars that give a great strength in an unfinished as \\vll as finished state. To show the difference bet went unliir ishccl and finished bars, to make an approximate e<»m parison, seven tests, A, H, (\ (», II, I, and | «f thr 1.70 diameter unfinished bars and seven u.'st.si»f theof which are fully explained on page 555.SlolrlciiKc .i! : •,» l'fjii]-.y!v,iu;.i M.ii!« ,«!.'.. <•*'•, t«.Mii«! i v, I'it l:,l.ui>;, P,i,ll. The chilland j^reen sand showedast on end, us such will tfive truer results than the [J4™inch round bar in general practice, especially in making comparison <>i; the widest ranges in grades.temper '' or damp- ,| |