the greatest strains, and though you _may not_ have a hot bearing,
they often extend until the shaft becomes unseaworthy.

[Diagrams shown illustrated the various forms of flaws.] These flaws
were not observable when the shafts were new, although carefully
inspected. They gradually increased under strain, came to the outside,
and were detected. Considerable loss fell upon the owners of these
vessels, who were in no way to blame; nor could they recover any money
from the makers of the shafts, who were alone to blame. I am pleased
to state, and some of the members here present know, that considerable
improvement has been effected in the use of better material than iron
for crank shafts, by the introduction of a special mild steel, by
Messrs. Vickers, Sons & Co., of Sheffield, and that instead of having
to record the old familiar defects found in iron shafts, I can safely
say no flaws have been observed, when new or during eight years
running, and there are now twenty-two shafts of this mild steel in the
company's service.

I may here state that steel was used for crank shafts in this service
in 1863, as then manufactured in Prussia by Messrs. Krupp, and
generally known as _Krupp's steel_, the tensile strength of which was
about 40 tons per square inch, and though free from flaws, it was
unable to stand the fatigue, and broke, giving little warning. It was
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 = 121/2 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