Temperature Changes Accompanying the Adiabatic Compression of Steel

r I ^HE formulae of Clapeyron, which apply to reversible transformations•*• of a body whose state is a function of two independent variables, lead to the conclusion that all substances which expand when heated will experience a rise in temperature when mechanically compressed, and vice versa.It was first shown by Lord Kelvin 1 that, as a result of the second law of thermodynamics, the rise in temperature Ad produced in a rod or wire by an increase AF in the stretching force should be expressed by the equation where r and p are the radius and density, respectively, of the wire, a is its thermal coefficient of expansion, s is its specific heat, 6 is the absolute temperature and J is the mechanical equivalent of heat.Joule 2 first attempted a verification of this equation by measuring the temperature changes produced by suddenly stretching or compressing various liquids, metals, wood, rubber, etc.Although in a general way Joule's observations agree with the theory, there is an average discrepancy between theory and experiment amounting to about 15 per cent.Later Edlund, 3 experimenting with metal wires, showed that the relative temperature changes in different metals may be accurately predicted by Thomson's formula, but failed to prove the absolute accuracy of the formula.In the case of steel, for instance, the apparent temperature increase was only 63 per cent, of that predicted by the formula.By using a greatly improved method of measuring small temperature changes in wires and by taking into account the effect of possible variations in the thermal coefficient of expansion of the wire at different tensions, 4 Haga 5 succeeded in verifying Thomson's formula within 2.54