rsion. This
process constitutes the annealing after tempering.

The manufacture of steel-armor plates is a specialty of Le Creusot,
which is engaged in an active competition with the manufacturers of
compound armor. Plates up to 60 centimeters in thickness and 3 meters
wide are forged here; they are tempered after forging, but what
subsequent treatment they receive was not explained.

The tempering pit for the plates consists of an excavation of
convenient size, in the center of which is placed a tank containing
180 tons of oil. At the four corners of the pit are furnaces in which
the plates are raised to a proper temperature. When sufficiently
heated, a plate is seized by a walking crane and immersed in the oil.

Hoops for cannon are manufactured here in large quantities. They are
cut from solid ingots, and those for guns up to 24 centimeters are
rolled like railway tires; those for larger calibers are forged on a
mandrel. Jackets of large size are also manufactured; these are made
from solid ingots, which, after being forged, are bored out.

At Le Creusot a remarkable test of hoops was witnessed, which
exemplifies not only the excellence of the manufacture of the steel
but also the exacting character of the French requirements. The hoops
for naval guns are made with the interior surface slightly conical.
When forged, turned, and brought under a hammer, a standard mandrel of
steel, conically shaped to suit the form of the cone in the hoop, but
of a slightly increased diameter, is introduced, the smaller end
of the mandrel being able to enter the larger end of the hoop. The
mandrel is then forced in by the hammer until its lower edge has
passed through the hoop. The blows are then made to operate on the
upper edge, detaching it from the mandrel. Careful measurements are
taken of the diameter of the hoop before and after this test, and it
is required that the measurement subsequent to the operation shall
show that the hoop has partially, but not entirely, returned to the
diameter that it had before the entrance of the mandrel. This would
show that there is left to the metal a small margin within its elastic
limit. A system of manufacture which can comply with such a refinement
of exactitude must be very precise.

Perhaps the most striking feature at Le Creusot is the forge, where is
assembled an array of steam hammers not equaled in the world, viz.:

One 100 ton hammer with a fall of 5 meters.
One 40 ton hamme