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 the
steel. After solidifying, the whole plate is pressed, and passed
through the rolls to obtain thorough welding. It is then bent, planed,
fitted, tempered, and annealed to remove internal strains.

[Illustration: Fig. 6.]