rum, and support A, by means of strips passed between the G and H tubes,
in its correct position relatively to B and C. The E tubes can now be
pushed into B and C and silver-soldered. The supports may then be removed,
and the a and H tubes be got into position and secured. Drum D then demands
attention. The connecting tubes, KK, should be silver-soldered in, as the
boiler, if properly made, can be worked at pressures up to 100 lbs. per
square inch.

The casing is of 1/20-inch sheet iron, and in five parts. The back end must
be holed to allow A, B, and C to project 1 inch, and have a furnace-door
opening, and an airway at the bottom, 5 inches wide and 1 inch deep, cut in
it. The airway may be provided with a flap, to assist in damping down the
fire if too much steam is being raised. In the front end make an inspection
opening to facilitate cleaning the tubes and removing cinders, etc.

The side plates, m m, are bent as shown in Fig. 86, and bolted to a
semicircular top plate, n, bent to a radius of 6 inches. A slot, 1-1/2
inches wide and 11-1/2 inches long, must be cut in the top, n, to allow it
to be passed over drum D; and there must also be a 3 or 3-1/2 inch hole for
the chimney. A plate, p, covers in D. A little plate, o, is slipped over
the slot in n, and asbestos is packed in all round D. The interior of the
end, side, and the top plates should be lined with sheet asbestos held on
by large tin washers and screw bolts. To protect the asbestos, movable iron
sheets may be interposed on the furnace side. These are replaced easily if
burnt away. The pieces m m are bent out at the bottom, and screwed down to
a base-plate extending the whole length of the boiler.

The fire-bars fill the rectangle formed by the tubes B, El, and E2. A plate
extends from the top of E2 to the front plate of the casing, to prevent the
furnace draught being "short circuited."

Boiler Fittings.

[Illustration: FIG. 89.-Safety valve.]

Safety Valves.--The best all-round type is that shown in Fig. 89. There
is no danger of the setting being accidentally altered, as is very possible
with a lever and sliding weight. The valve should be set by the steam
gauge. Screw it down, and raise steam to the point at which you wish the
safety valve to act, and then slacken off the regulating nuts until steam
issues freely. The lock nuts under the cross-bar should then be tightened
up. In the case of a boiler with a large heating surface, which makes steam