EXPERIMENTAL RESEARCHES ON DRAWN STEEL. 
31 
Temperature Coefficient of Young’s Modulus, 
5. In determining the temperature coefficient of Young’s modulus the same 
apjDaratus as before was used, with the addition of a brass tube in which slots were 
cut, so that the upper ends of the supports could project into the interior of it. This 
tube enclosed the steel wire, and another slot of smallest allowable size was cut at 
the centre of the tube to permit the passage of the suspension for the pan and 
weights. The slots near the ends were made steam-tight, but, necessarily, this could 
not be done for the central one, as the suspension wire which passed througli had to 
hang freely. One end of the tube was in connection with a boiler, and this produced 
a supjjly of steam which could pass freely along the tube and escape at the other 
end. No special arrangement, liowever, was made for the cooling of the tube, the 
steam was simply shut off and the tube and its contents allowed to grow cold 
gradually. A thermometer projected into the tube, with the bulb nearly at the 
centre, and the temperature of the steel was taken to be the reading of the 
thermometer. 
The apparatus thus set up was at first intended for rapid tests, to ascertain 
whether the sign of the coefficient changed at any stage, and less attention was paid 
to its magnitude, but later on it became possible to obtain numerical results which 
are worth recording. In some earlier experiments the metliod was tried of observing 
the position of the fiducial mark at air temperature, then at steam temperature, and 
again at air temperature, from which data the coefficient could easily have been 
deduced. But it was found much better to follow the plan of loading and unloading 
as already described for determining the modulus, carrying out the observations 
firstly at air temperature, secondly at steam temperature, again at air temperature, 
and so on alternately, and calculating the coefficient, y, from the observed depressions, 
Dq and D/, thus : 
y — 
By adopting this method, corrections for expansion of supports, etc., were eliminated. 
The formula assumes that the change in Young’s modulus is linear and that there are 
no hysteresis-like effects, but these assumptions are, no doubt, not quite justifiable, 
although probably not far from the truth. 
With rise of temperature the modulus was found to decrease, but on cooling it 
it was very seldom that it returned exactly to its original value, although, after a 
repetition of the experiments, the modulus was found to change from one to another 
of two nearly constant values ; thus there is a permanent change before a cyclic state 
is established, Here is an example ;— 
