ough the rolls, bent,
planed, fitted, tempered, and annealed to reduce internal strains.

[Illustration: Fig. 8.]

In heating the compound plates for rolling, the plate is placed in the
furnace with the steel face down, so that the iron part gets well
heated and the steel does not become too hot. Great care must be taken
not to overheat the plate, and in working, many passes are given the
plate with small closings of the rolls. The steel part of a compound
plate is usually about one third of the full thickness of the plate.

Forged steel armor, tempered in oil, is fabricated at Le Creusot,
France, by Schneider & Co., using open-hearth steel, and forging under
the 100 ton hammer. The ingots are cast, with twenty-five per cent.
sinking head and are cubical in form. The porter bar is attached to a
lug on one side of the ingot. By means of a crane with a curved jib
which gives springiness under the hammer, the ingot is thrust into the
heating furnace. On arriving at a good forging heat it is swung around
to the 100 ton hammer, under which it is worked down to the required
shape. A seventy-five ton ingot requires about eight reheatings before
being reduced to shape. Having been reduced to shape, the plate is
carefully annealed, then raised to a high tempering heat, and the face
tempered in oil. It is reannealed to take out the internal strains,
care being taken not to reduce the face hardness more than necessary.
The Schneider process of tempering is based upon the utilization of
the absorption of heat caused by the fusing or melting of a solid
substance, and of the fact that so long as a solid is melting or
dissolving in a liquid substance, the liquid cannot get appreciably
hotter, except locally around the heating surface. The body to be
hardened is plunged at the requisite temperature into a bath
containing the solid melting body, or is kept under pressure in the
solid material of low melting point until the required extraction of
heat has taken place, more solid material being added if necessary as
that originally present melts and dissolves.

Nickel steel armor is made in a similar manner to the steel plates,
the material used in casting the ingot being an alloy of nickel and
steel containing between three and four per cent. of nickel.

The Harvey process of making armor consists in taking an all-steel
plate and carbonizing the face. This carbonizing process is very
similar to the cementation process of producing s