rtion of the length of the boiler, and
thus compel the products of combustion to pass in a definite course
amongst all the tubes. In the Blechynden and White-Foster boilers
there are also three chambers connected by bent tubes, the curvature
being so arranged that in the former boiler any of the tubes can be
taken out of the boiler through small doors provided in the upper part
of the steam-chest, and in the White-Foster boiler they can be taken
out through the manhole in the end of the steam-chest.

Reed.

In the Reed boiler the tubes are longer and more curved than in the
Normand boiler, and there are no "water-walls," the products of
combustion passing from the fire-grate amongst all the tubes direct to
the chimney. The special feature of the boiler is that each tube,
instead of being expanded into the tube plate, is fitted at each end
with specially designed screw and nut connexions to enable them to be
quickly taken out and replaced if necessary. At their lower ends the
tubes are reduced in diameter to enable smaller chambers to be used
than would otherwise be necessary. Provision is made for access to the
lower tube ends by means of numerous doors in the water-chambers.
Access to the top ends is obtained in the steam-chest.

Thornycroft.

Messrs John I. Thornycroft & Co. make two forms of express boiler. One
called the Thornycroft boiler consists of three chambers connected by
tubes which are straight for the major portion of their length but
bent at each end to enable them to enter the steam- and water-chambers
normally. The outer rows of tubes form "water-walls" at their lower
parts, but permit the passage of the gases between them at their upper
ends. Similarly the inner rows form "water-walls" at their upper
parts, but are open at the lower ends. The products of combustion are
thus compelled to pass over the whole of the heating surfaces. The
fire-rows of tubes in this boiler are made 1-3/8 in. outside diameter
and the remainder are made 1-3/8 in. diameter. Large outside
circulating pipes are provided at the front end of the boiler.

Thornycroft-Schulz.

In the other type of boiler, known as the Thornycroft-Schulz boiler
(fig. 20), there are four chambers, and the fire-grate is arranged in
two separate portions. The two outermost rows of tubes on each side
are arranged to form water-walls at their lower part, and permit