Iron in Ancient India c7.s2: Tensile Strength of Indian Iron
Iron in Ancient India c7.s2
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Tensile Strength of Indian Iron
c7.s2.1
Mr. Monomohon Ganguli of the Public Works Department, whose recent work on " Orissa and her Remains " is an excellent publication on the subject, sent a very small piece of wrought iron from an iron beam at Bhubaneswar to the Civil Engineering College, Sibpur, where Prof. Sarat Kumar Dutt tested its tensile strength in the Testing laboratory of the College. Prof. Dutt got a small piece made of it of cross-section ·27" X ·415" and after testing it observed " this broke at 1·6 tons. The breaking strength accordingly comes to about 14·3 tons per square inch . . . . unfortunately the sample was not without flaws and the test piece broke at one of these flaws . . . . If it had been possible to obtain a decent sample of the iron, I believe, a strength of 20 tons per square inch could be easily attained," the accepted tensile stress of pure wrought iron having an average of 25 tons per square inch. "The assurance of Prof. Dutt that a decent sample of this iron could easily show a strength of 20 tons per square inch reflects great credit on the Orissan matallurgists of a bye-gone age, for the average tensile strength of wrought iron was 23 tons per square inch in England only 36 years ago."¹
c7.s2.2
¹ Monomohon Ganguli's "Orissa and her Remains", p. 263.
c7.s2.3
Prof. Dutt's experiments are, however, not very conclusive. Fortunately we have before ourselves the experiments of Sir Robert Hadfield on the tensile strength of Ceylonese iron, which are quite conclusive. Sir Robert found that the breaking load in the case of the iron nail was 21 tons per square inch, the chisel 26 tons, and bill-hook as high as 29 tons per square inch, being higher than the figure for wrought iron. This no doubt is owing to the considerable percentage of phosphorus present, which stiffens or hardens iron.
c7.s2.4
Hadfield has also determined the Fremont shock test, the Brinell ball test for hardness, as well as scleroscope hardness of the specimens of Ceylonese iron. His conclusions are summarized thus: "The Fremont shock tests show fair results on the specimen taken from the chisel, namely 17 kilogrammes, with 85° bend. The other specimens, however, show much lower figures, namely the nail (1 kilogramme by only 1° bend) and the bill-hook (7 kilogrammes by 35° bend). The hardness by the Brinell method varied from 117 to 166, one result from the nail showing 209; but this is abnormal, and cannot be accepted as representative. The scleroscope tests varied from 25 to 44, and as a comparison it may be mentioned that water-quenched carbon steel by this latter method shows 100 and ordinary wrought iron about 20."