red from end to end of the flue on the
outside. The positions of these lines are quickly found as follows:--Cut
out a strip of paper exactly as long as the circumference of the tube, and
plot the centre lines on it. The paper is then applied to the tube again,
and poppet marks made with a centre punch opposite to or through the marks
on the paper. Drive a wire-nail through a piece of square wood and sharpen
the point. Lay the flue on a flat surface, apply the end of the nail to one
of the poppet marks, and draw it along the flue, which must be held quite
firmly. When all the lines have been scored, the centring of the water
tubes is a very easy matter.

[Illustration: FIG. 83.-End of horizontal boiler, showing position of holes
for stays and fittings.]

The two holes for any one tube should be bored independently, with a drill
somewhat smaller than the tube, and be opened to a good fit with a reamer
or broach passed through both holes to ensure their sides being in line.
Taper the tubes--2-7/8 inches long each--slightly at one end, and make
one of the holes a bit smaller than the other. The tapered end is passed
first through the larger hole and driven home in the other, but not so
violently as to distort the flue. If the tubes are made fast in this way,
the subsequent silver-soldering will be all the easier.

[Illustration: FIG. 84.--Doubled cross tubes In horizontal boiler flue.]

The Steam Dome.--The large holes--2 inches in diameter--required for
the steam dome render it necessary to strengthen the barrel at this point.
Cut out a circular plate of metal 4 inches across, make a central hole of
the size of the steam dome, and bend the plate to the curve of the inside
of the barrel. Tin the contact faces of the barrel and "patch" and draw
them together with screws or rivets spaced as shown in Fig. 85, and sweat
solder into the joint. To make it impossible for the steam dome to blowout,
let it extend half an inch through the barrel, and pass a piece of 1/4-inch
brass rod through it in contact with the barrel. The joint is secured with
hard solder. Solder the top of the dome in 1/8 inch below the end of the
tube, and burr the end over. The joint should be run again afterwards to
ensure its being tight.

[Illustration: FIG. 85.--Showing how to mark out strengthening patch
round steam dome hole.]

The positions of stays and gauges is shown in Fig. 83.

Chimney.--This should be an elbow of iron piping fitting the ins