In Figs. 96 (a) and 96 (b) are shown two forms of fire-tube kettles (a and
b) and two of water-tube (c and d). For use over a spirit or Swedish
petroleum stove the first two types are most convenient; the third will
work well on a stove or an open fire; and the last proves very efficient on
an open fire. One may take it that, as a general rule, areas of heating
surface being equal, the water-tube kettle will boil more quickly than the
fire-tube.
Fire-tube Kettles.
The tubing of Figs. 96 (a) and 96 (b) presents a little difficulty in each
case. The straight tube is the more difficult to insert, owing to the
elliptical shape of the ends; whereas the bent tube requires only circular
holes, but must be shaped on a template.
The tubing used for (a) should have at least 5/8-inch internal diameter,
for (b) 1/2 inch, and be of thin copper. Hot gases will not pass willingly
through tubes much smaller than this, in the absence of induced or forced
draught.
For convenience in fitting, the tubes should run at an angle of 45 degrees
to the bottom and side of the kettle, as this gives the same bevel at each
end.
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