d on
wooden base.]

Assembling.--The order of assembling is:--Rivet in the bottom; put the
steam-pipe in place; rivet in the top; insert the flue, and screw collar y
to the top; expand the bottom of the flue by hammering so that it cannot be
withdrawn; insert the stays and screw them up tight; silver-solder both
ends of the flue, the bottom ends of the stays, and the joint between
bottom and barrel. The water-tubes are then inserted and silver-soldered,
and one finishes by soft-soldering the boiler top to the barrel and fixing
in the seatings for the water and steam gauges, safety-valve, mud-hole,
filler, and pump-if the last is fitted.

The furnace is lined with a strip of stout sheet iron, 7 inches wide and
19-1/4 inches long, bent round the barrel, which it overlaps for an inch
and a half. Several screws hold lining and barrel together. To promote
efficiency, the furnace and boiler is jacketed with asbestos--or
fire-clay round the furnace--secured by a thin outer cover. The enclosing
is a somewhat troublesome business, but results in much better steaming
power, especially in cold weather. Air-holes must be cut round the bottom
of the lining to give good ventilation.

A boiler of this size will keep a 1 by 1-1/2 inch cylinder well supplied
with steam at from 30 to 40 lbs. per square inch.

A Horizontal Boiler.

[Illustration: FIG. 82.--Longitudinal section of large water-tube
boiler.]

The boiler illustrated by Fig. 81 is designed for heating with a large
paraffin or petrol blow-lamp. It has considerably greater water capacity,
heating surface--the furnace being entirely enclosed--and water surface
than the boiler just described. The last at high-water level is about 60,
and at low-water level 70, square inches.

The vertical section (Fig. 82) shows 1/16-inch barrel, 13 inches long over
all and 12 inches long between the end plates, and 6 inches in diameter.
The furnace flue is 2-1/2 inches across outside, and contains eleven
1/2-inch cross tubes, set as indicated by the end view (Fig. 83), and 3/4
inch apart, centre to centre. This arrangement gives a total heating
surface of about 140 square inches. If somewhat smaller tubes are used and
doubled (see Fig. 84), or even trebled, the heating surface may be
increased to 180-200 square inches. With a powerful blow-lamp this boiler
raises a lot of steam.

Tubing the Furnace Flue.--Before any of the holes are made, the lines on
which the centres lie must be sco