h.

Whether the plunge bath be placed in a separate chamber, in the
lavatorium, or partly in the frigidarium, its construction will remain
essentially the same. If not in shape and size, in other respects it is
a small swimming bath. The weight and pressure of the water must be
remembered. A good foundation must be prepared for the bath, with a
thick layer of concrete passing well under the side walls and covering
the whole floor. The side walls should be built of concrete and lined
with white glazed bricks. In certain soils, the excavation for the bath
may be puddled with advantage, but if properly constructed, this should
be unnecessary. The bottom of the bath need not be flat, as the most
economical method of constructing a plunge bath is to make its deepest
part about two-thirds of its length from the end at which the bather
enters. This may be about 4 ft. 6 in. in depth from bottom to
water-line. From this point the floor will slope towards either end,
gradually towards the entering end, and more rapidly towards the exit.
At either end, where the depth of water should be about 3 ft, must be
provided steps for ascent and descent. If the bath be not more than 6
ft. wide, these should occupy the whole width, and be of marble or slabs
of some cheaper material on brick bearers, or they may be built solid.
A coping of marble, stone, or purpose-made bricks must be placed on the
side walls; and, if the bath be in the cooling room, this may
advantageously be raised several inches to protect from splashing. On
the coping may be required metal standards and a neat hand-railing. A
water-supply pipe and screw-down tap, an overflow and a waste-pipe will
be needed, all of which I have more particularly specified hereinafter.

The plunge bath is at times a source of two difficulties--it may leak,
and it may be below the level of drain. The first evil is the result of
an error in design, or of bad workmanship; the latter is unavoidable.
The following method of constructing a plunge bath has been adopted with
perfect success:--On the bed of concrete prepared for its floor, erect
side walls of concrete, and on the floors and walls thus formed spread
two distinct layers of asphalt, covering all and running up to the
underside of coping. Against the sides build half-brick walls in cement,
with glazed face, and lay the floor with glazed bricks flat. The general
principles of this construction I show in the accompanying illustration.