pipe, and lead pipe having all been used. The last-named
pipe is now too expensive for use in any great lengths. Hollow wooden
pipes are employed occasionally, but, except in unusual localities, they
also are more expensive than other forms, and are short lived on
account of their tendency to decay. Cast-iron pipe, commonly used for
municipal water-supplies, is not made in small sizes and may be excluded
from the possibilities for an individual house. There remains only tile
and wrought-iron pipe. Under certain conditions, the use of tile pipe is
to be recommended, since it may be installed even in large sizes at a
comparatively low cost, the objection to it being that it is very
difficult to make the joints water-tight, and practically impossible
when the pressure is greater than ten feet. It is more difficult to make
joints in a pipe line of small diameter water-tight than in a pipe line
of larger diameter, because the space for the cement in the former is so
small. The writer has tried both four-inch and six-inch pipe, and while
the four-inch line can be laid with tight joints, it requires much more
careful and conscientious effort on the part of the workman than with
six-inch pipe. The joints must be thoroughly filled with cement, not
very wet, so that it can be rammed or packed with a thin stick into
every part of the joint. Merely plastering the cement over the surface
of the joint will always result in a leaking joint.

It often happens that a water-supply coming from a distance of a mile or
so runs at first nearly level, so that, except for surface pollution,
the water might be carried in an open ditch. An open ditch is, however,
far better replaced by vitrified tile, six inches in diameter, which
entirely prevents surface pollution, and which costs only about ten
cents a running foot. When the slope of the ground exceeds the natural
fall of the water, so that a pressure inside the pipe is created, iron
pipe must be used. If vitrified pipe is used, the joints must be made
with the greatest care, and every precaution taken to prevent leakage.
Figure 42 shows a section of a joint in tile pipe.

[Illustration: FIG. 42.--A joint in tile pipe.]

In using iron pipe large enough to furnish the amount of water required,
due regard must be paid to friction in the pipe. In flowing through a
pipe of small size, water loses a great deal of head by friction. This
friction between the sides of the pipe and the water, which m