. Journal. ystalline condition from oue or otherof the causes mentioned above. The molecular alteration indicated by the appearance ofthe fracture has a considerable influence on the mechanicalproperties of the iron. The alteration from the fibrous tothe crystalline state is generally accompanied by a diminu-tion in tensile strength, while the elastic limit is but slightlyaltered and the elongation is decreased. Although a redheat appears to be necessary to bring about the changesrecorded above, yet considerable alterations in the me-chanical properties of iron and steel take place at lowertem
. Journal. ystalline condition from oue or otherof the causes mentioned above. The molecular alteration indicated by the appearance ofthe fracture has a considerable influence on the mechanicalproperties of the iron. The alteration from the fibrous tothe crystalline state is generally accompanied by a diminu-tion in tensile strength, while the elastic limit is but slightlyaltered and the elongation is decreased. Although a redheat appears to be necessary to bring about the changesrecorded above, yet considerable alterations in the me-chanical properties of iron and steel take place at lowertemperatures, as has been shown by A. le Chatelier (GenieCivil, 147, 107 ; cf. this Journal, 1889, 710). In all casesin his experiments the tensile strength decreased from atemperature of 15° C. up to 8o° C. above which it rose againand attained a maximum at 250°—3u0 C. These resultsare shown more clearly iu the diagram below. * (To convert kilos, per sq. mm. into tons ner sq. in. 0-636*.) ?. Degrees 25 50 75 100 25 50 75 200 25 50 75 300 25 50 75 400 25 50 75 520 25 50 350 THE JOURNAL OF THE SOCIETY OF CHEMICAL INDUSTRY. [April 30, 1892, \ difference is observed according to the speed withwhich the test is made, the (lotted lines uniformly followinga different course from the continuous Hues which representthe figures obtained by the slower test*. The elastic limitappears to decrease in proportion as the temperature is increased. The diminution is very slight at first, hutbeyond 300 C. it becomes extremely rapid and difficult tomeasure. The effect upon the elongation is shown bythe diagram below. ,w° 1 ^ - ^ \- 5 1 a. n r Vfi> Swedis h iron 5>\\ \l-1^ ? 1 . v 01 \ 11 Dap 50 00 25 50 75 200 25 50 ~>5 300 25 50 75 59 75 500 25 So (t is noticeable that if a test piece be heated to a mod. , cij., 100° <.. and then slightly stretched, itwill he found to give a higher tensile strength when testedafterwards at the ordinary temperature than o
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