L 373 J 



XXXVIII. On the Temperature Coefficient of Young* s Modulus 

 for Electrically Heated Iron Wire. By E. P. Harrison, 

 Ph.D., F.R.S.B., Professor of Physics, Presidency College. 

 Calcutta, and Sujit K. Chakravarti, M.Sc, Bengal 

 Government Research Scholar *. 



OF recent years several observers t of the effect of tem- 

 perature on Young's Modulus claim that for loads 

 below a certain magnitude the modulus for metal wires 

 reaches a maximum in the neighbourhood of 100° C. 



The circumstances in which this peculiarity is said to 

 occur are somewhat restricted ; the total load must be rela- 

 tively small, and heating must be effected by the direct 

 passage of an electric current. When other methods of 

 heating are employed, such as vapour-baths or the radiation 

 from a surrounding helix conveying a current, no maximum 

 is observed, the coefficient of elasticity decreasing uniformly 

 as the temperature rises. ShakespearJ alone appears to have 

 noticed an increase in the modulus during ordinary heating 

 (steam), but he found that the effect ceased after several 

 heatings and coolings, whereby the wire was reduced to a 

 condition in which it behaved normally and possessed a 

 negative temperature coefficient of elasticit}-. One of the 

 present writers §, in a series of experiments recently pub- 

 lished, failed to detect any sign of a maximum in Young's 

 modulus for nickel during electric heating ; but the research 

 being more particularly concerned with values of the elas- 

 ticity near the Curie point at 400°, did not afford very strong 

 evidence either for or against the existence of a maximum 

 below 100°. Consequently the experiments described below 

 were undertaken as an additional attempt to settle what 

 appears to be a somewhat doubtful issue. 



Present Experiments. 



It was decided to use iron wire, electrically heated, and 

 to carry out two separate tests, one on a portion of wire 

 annealed at 400° C, and the other on an unannealed portion 

 straightened by stretching when cold. Both portions were 

 taken from the same hank of wire. 



The apparatus and method used for finding the modulus 



* Communicated by Prof. A. W. Porter, F.R.S. 



f Noyes, Physical Review, vol. ii. & vol. iii. (1895), vol. iii. (1896). 

 H. Walker, Proc. R. S. Edinburgh, vol. xxvii. Part 4, No. 34 (1907) : 

 vol. xxviii. Part 8, No. 40 (1908) ; vol. xxxi. Part 1, No. 10 (1911;. 



J Shakespear, Phil. Mag. vol. xlvii. (1899). 



§ Harrison, Proc. Phys. Soc. London, vol. xxvii. Dec. 15 (1914). 



