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is thus made up with easy, telescope-like joints, and these
joints give play for a small to and fro sliding movement
under the influence of heat and cold—the upper pipe
never being rammed down solidly on to the shoulder of
the pipe below. These pipes, being wholly of pure
lead, are unpuckered by the rigid bands of solder
with which soil-pipes are jointed; they therefore expand
and contract freely and uniformly all over, and they
never tear. They also escape the corroding action of the
galvanic current which is set up wherever dissimilar metals
come into contact Pipes thus put together endure for hundreds
of years, as do the old cast lead water-cisterns that
used to be constructed without solder. But when we come
to the arms which connect the closet-pans with the
vertical part of the soil-pipe, new and altogether
different elements of weakness come in. The trap beneath
the closet-pan is liable to be stopped up by cloths
which careless servants drop in, by entire newspapers
which slovenly people put down, and by various objects
which children and malicious persons throw down.
If the closet be disused for a few weeks, the water
dries out of the trap and the trap becomes a
channel for laying on a stream of soil-pipe air
into the room to which the closet belongs. Then the
perforations which so frequently conduct soil-pipe air into
houses are always found in the upper segment of the more
or less horizontal soil-pipe arm. As I have already
stated (page 16), these perforations in the aerial half
of this pipe are generally produced by the corrosive
vapours of disinfectants, such as chloride of lime, which
ignorant housewives industriously put down the closets.
It therefore seems that to insist upon putting the vertical
part of the soil-pipe outside the building, while the more
vulnerable closet syphon and sloping arm of the
soil-pipe are left inside, is an illusory provision. It also
seems clear that the endurance of the vertical part of the
soil-pipe is lessened by putting it outside the building, while
the countervailing advantage is very questionable