of too brittle a nature, more resembling chisel steel. It was broken
again under a falling weight of 10 cwt. with a 10 ft. drop = 12½ tons.

The mild steel now used was first tried in 1880. It possessed tensile
strength of 24 to 25 tons per square inch. It was then considered
advisable not to exceed this, and err rather on the safe side. This
shaft has been in use eight years, and no sign of any flaw has been
observed. Since then the tensile strength of mild steel has gradually
been increased by Messrs. Vickers, the steel still retaining the
elasticity and toughness to endure fatigue. This has only been arrived
at by improvements in the manufacture and more powerful and better
adapted hammers to forge it down from the large ingots to the size
required. The amount of work they are now able to subject the steel to
renders it more fit to sustain the fatigue such as that to be endured
by a crank shaft. These ingots of steel can be cast up to 100 tons
weight, and require powerful machines to deal with them. For shafts
say of 20 inches diameter, the diameter of the ingot would be about 52
inches. This allows sufficient work to be put on the couplings, as
well as the shaft. To make solid crank shafts of this material, say of
19 inches diameter, the ingot would weigh 42 tons, the forging, when
completed, 17 tons, and the finished shaft 11¾ tons; so that you see
there is 25 tons wasted before any machining is done, and 5¼ tons
between the forging and finished shaft. This makes it very expensive
for solid shafts of large size, and it is found better to make what is
termed a _built shaft_; the cranks are a little heavier, and engine
framings necessarily a little wider, a matter comparatively of little
moment. I give you a rough drawing of the hydraulic hammer, or
strictly speaking a _press_, used by Messrs. Vickers in forging down
the ingots in shafts, guns, or other large work. This hammer can give
a squeeze of 3,000 tons. The steel seems to yield under it like tough