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cooling recover completely their proper shape and dimensions,
and the distortion never becomes cumulative. This
arrangement of cast-iron waste-pipes for hot water is the
best and most permanent at present known, and their
only drawback is that iron pipes corrode inside more
rapidly than do lead pipes. But where soapy water or
other organic matter passes, this corrosion is not rapid.
With rain-water, corrosion is much more rapid.
8. These three sets of drainage-pipes, being all
open full-bore to the sky above the roof and to
the external air in the basement, there yet remains
one more costly provision—i.e., that of trapping every
bath, basin, and sink - waste so that its contents
shall instantly run off, while no reflux of air nor
of liquid can pass back from the main waste into
the chamber to which the basin, bath, or sink belongs.
This object is secured by a syphon-trap of lead or gunmetal,
which is affixed to the waste of each basin, bath,
or sink. But a difficulty here crops up. When numerous
traps are connected successively to one long vertical mainwaste,
it is found that the rush of water down the mainwaste
when a bath or large basin is suddenly emptied, will
pull the water out of the other traps on the same stack-pipe,
and so leave these traps open to carry foul air from the main
waste-pipe into the chamber to which the basin, etc., may
belong. In a large building this would be a fatal defect.
This reflux current of air would bring with it the smell
of the rancid and decomposing soap which lines the main
wastes. With the water-closet traps, where a series of successive
floors of closets are served by the same soil-pipe,
a similar reflux would be not only offensive, but
dangerous. The difficulty has to be overcome by providing
every trap in the building with an anti-syphonage airpipe.
This anti-syphonage pipe is a leaden pipe ranging
from 1½ to three inches in diameter, and connected with
the pipe which discharges the trap into the main waste.
This air-pipe prevents the water being sucked out of the
the trap to which it belongs, and so ensures the trap