rison, Fox and Deighton types
are made from plates originally rolled of a uniform thickness, made
into a cylindrical form with a welded longitudinal joint and then
corrugated, the only difference between them being in the shapes of
the corrugations. In the other three types the plates from which the
furnaces are made are rolled with ribs or thickened portions at
distances of 9 in. These furnaces are stronger to resist collapse than
plain furnaces of the same thickness, and accommodate themselves more
readily to changes of temperature.

[Illustration: FIG. 5.--Vertical Boiler with Water-tubes (the "Tyne,"
by Messrs Clarke, Chapman & Co.).]

There are two distinct types of connexion between the furnaces and the
combustion chambers. In one, shown in fig. 8, the furnace is flanged
at the crown portion for riveting to the tube plate, and the lower
part of the furnace is riveted to the "wrapper" or side plate of the
combustion chamber. In the other type, shown in fig. 7, and known
generally as the "Gourlay back end," the end of the furnace is
contracted into an oval conical form, and is then flanged outwards
round the whole of its circumference. The tube plate is made to extend
to the bottom of the combustion chamber, and the furnace is riveted to
the tube plate. The advantage of the Gourlay back end is that in case
of accident to the furnace it can be removed from the boiler and be
replaced by one of the same design without disturbing the end plates,
which is not possible with the other design. The Gourlay back end,
however, is not so stiff as the other, and more longitudinal stays are
required in the boiler.

[Illustration: FIG. 6.--Vertical Boiler with internal combustion
chamber (the "Victoria," by Messrs Clarke, Chapman & Co.).]

[Illustration: FIG. 7.--Single-ended Marine Boiler.]

The flat sides and backs of the combustion chambers are stayed either
to one another or to the shell of the boiler by numerous screw stays
which are screwed through the two plates they connect, and which are
nearly always fitted with nuts inside the combustion chambers. The
tops of the chambers are usually stayed by strong girders resting upon
the tube plates and chamber back plates. In a few cases, however, they
are stayed by vertical stays attached to T bars riveted to the boiler
shell. A few boilers are made in which the chamber tops are
strengthened by heavy tr