55 " " 72 " "
62 " " 60 " bent
44 " " 68 " broke
60 " bent 40 " "
--- ---
Average, 58-1/3 Average, 59-5/6

"I did not notice any perceptible difference in the perfection of
elasticity in the two sets of needles. The result, as far as it goes,
is in favor of the cold metal.

"3d. The above are doubtless decisive of the question at issue. But
as it might be alleged that the violence to which a railway wheel is
subjected is more akin to a blow than a steady pull; and as, moreover,
the pretended brittleness is attributed more to cast iron than any
other description of the metal, I have made yet another kind of
experiment. I got a quantity of cast iron garden nails, an inch and
a quarter long and 1/8 in. thick in the middle. These I weighed,
and selected such as were nearly of the same weight. I then arranged
matters so that by removing a prop I could cause the blunt edge of a
steel chisel weighted to 4lb. 2oz., to fall from a given height upon
the middle of the nail as it was supported from each end, 1-1/16 in.
asunder. In order to secure the absolute fairness of the trials, the
nails were taken at random, and an experiment with a cold nail was
always alternated with one at the ordinary temperature. The nails to
be cooled were placed in a mixture of salt and snow, from which they
were removed and struck with the hammer in less than 5"."

The collective result of the experiments, the details of which need
not be given, was that 21 cold nails broke and 20 warm ones.

Dr. Joule adds, "The experiments of Lavoisier and Laplace, of Smeaton,
of Dulong and Petit, and of Troughton, conspire in giving a less
expansion by heat to steel than iron, especially if the former be in
an untempered state; but this, would in certain limits have the effect
of strengthening rather than of weakening an iron wheel with a tire of
steel.

"The general conclusion is this: Frost does _not_ make either iron
(cast or wrought), or steel, brittle.

Mr. Spence, in his experiments, decided on having some lengths of
cast iron made of a uniform thickness of 1/2 in. square, from the same
metal and the same mould.

He writes:--"Two of the four castings I got seemed to be good ones,
and I got the surface taken off, and made them as regular a thickness
as was practicable.

"I then fixed two knife-edged wed