ammer or under the rolls, in the ordinary manner of making plates,
and has been exhaustively studied and experimented with--more so than
any other form of armor.

[Illustration: Fig. 2.]

Chilled cast iron armor is manufactured by Gruson, in Germany, and is
used in sea coast defense forts of Europe.

In 1867 several compound plates were made by Chas. Cammell & Co., of
Sheffield, England, and were tested at Shoeburyness, in England, and
at Tegel, in Russia. These plates were made by welding slabs of steel
to iron; but the difficulties were so great that the idea was
abandoned for the time.

[Illustration: Fig. 3.]

[Illustration: FIG. 4.]

Compound armor, as now manufactured, is of two types: Wilson's patent,
a backing of rolled iron, faced with Bessemer steel; Ellis' patent, a
backing of rolled iron, faced with a plate of hard rolled steel,
cemented with a layer of Bessemer steel. Both these kinds are
manufactured in England and France in sizes up to fifty tons weight.
The Wilson process is used at the works of Messrs. Cammell & Co., of
Sheffield, England, and the Ellis process at the Atlas Works of Sir
John Brown & Co., of the same place. These are the two leading
manufacturers of compound plate.

[Illustration: Fig. 5.]

The method employed by Wilson in making compound plate is to first
make a good wrought iron plate. To the surface of this and along each
side of the length of the plate are fixed two small channel irons, as
shown in Fig. 5. The plate is then raised to a welding heat in a gas
furnace, and transferred to an iron flask or mould. Wedges are driven
in between the back of the plate and the side of the mould, thus
forcing the channel irons up snug against the opposite side of the
mould. Moulding sand is then packed around the back and sides of the
plate (see Fig. 6). The mould is lowered in a vertical position into a
pit. Molten steel, manufactured by either the Siemens-Martin or
Bessemer process, is then poured in through a trough that forms
several streams, and forms the hard face of the plate. The molten
steel as it runs down cleans the face of the wrought iron plate,
scoring it in places, and, being of much higher temperature, the
excessive heat carbonates the iron to a depth of one-eighth to
three-sixteenths of an inch, forming a zone of mild steel between the
hard steel and soft iron. The mould is placed in a vertical position
to insure closeness of structure and the forcing of gases out of