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.
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