ide of
the flue closely, made up of a 9-inch and a 4-inch part. The last slips
into the end of the flue; the first may contain a coil for superheating the
steam.

A Multitubular Boiler.

[Illustration: FIG. 86.--Cross section of multitubular boiler.]

Figs. 86 and 87 are respectively end and side elevations of a multitubular
boiler having over 600 square inches of heating surface--most of it
contributed by the tubes--and intended for firing with solid fuel.

The boiler has a main water-drum, A, 5 inches in diameter and 18 inches
long, and two smaller water-drums, B and C, 2-1/2 by 18 inches, connected
by two series of tubes, G and H, each set comprising 20 tubes. The H tubes
are not exposed to the fire so directly as the G tubes, but as they enter
the main drum at a higher point, the circulation is improved by uniting A
to B and C at both ends by large 1-inch drawn tubes, F. In addition, B and
C are connected by three 3/4-inch cross tubes, E, which prevent the small
drums spreading, and further equalize the water supply. A 1-1/2-inch drum,
D, is placed on the top of A to collect the steam at a good distance from
the water.

Materials.--In addition to 1-1/2 feet of 5 by 3/32 inch solid-drawn
tubing for the main, and 3 feet of 2-1/2 by 1/16 inch tubing for the lower
drums, the boiler proper requires 22-1/2 feet of 1/2-inch tubing, 19
inches of 3/4-inch tubing, 2-1/4 feet of 1-inch tubing, 1 foot of
1-1/2-inch tubing, and ends of suitable size for the four drums.

[Illustration: FIG. 87.--Longitudinal section of multitubular boiler.]

CONSTRUCTION.

[Illustration: FIG. 88.-Two arrangements for tube holes in multi tubular
boiler.]

The centres for the water-tubes, G and H, should be laid out, in accordance
with Fig. 88, on the tops of B and C and the lower part of A, along lines
scribed in the manner explained on p. 207. Tubes H must be bent to a
template to get them all of the same shape and length, and all the tubes be
prepared before any are put in place. If the tubes are set 7/8 inch apart,
centre to centre, instead of 1-1/4 inches, the heating surface will be
greatly increased and the furnace casing better protected.

Assembling.--When all necessary holes have been made and are of the
correct size, begin by riveting and silver-soldering in the ends of the
drums. Next fix the cross tubes, E, taking care that they and B and C form
rectangles. Then slip the F, G, and H tubes half an inch into the main
d