The tubes of c and d, which require bending
to somewhat sharp curves, may be of 3/8-inch internal diameter. In the last
two cases the direction of the water travel is shown. The up-flow end,
which projects farther through the bottom than the down-flow, is nearer the
centre, where, if a gas stove is used, the heat is more intense than at the
circumference of the bottom. (Note.-If type c is for use on a three-support
stove, increase the number of tubes to 9, equally spaced, 40 degrees apart,
so that the kettle may be adjusted easily.)
The copper tubing should be annealed or softened by heating to a dull red
and plunging in cold water. Cut a wooden template of the exact outline of
the inside line of the shape that the tube is to assume, and secure this
firmly to a board. Fill the tube with melted resin, to prevent, as much as
possible, "buckling" or flattening on the curves. The tube must be kept up
to the template by a stop of hard wood, at the end at which bending
commences. Don't cut the tube into lengths before bending, as short pieces
are more difficult to handle. When a piece sufficient for a tube has been
bent, cut it oft, and remove the resin by heating.
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