ed resistance of curves. The weight of
the pipe should not be supported upon the sockets (see Figure 3), partly
as a question of strength, and partly because any irregularity of form
or thickness of the socket would change the inclination of the sewer.
The bottom of the trench being brought exactly to the required grade,
let there be dug out a depression greater than the projection of the
socket, the pipe resting upon its finished bottom for its whole length.
(See Figure 4.) Too much care cannot be given to the thorough filling
with cement of the space between the socket and the pipe inserted into
it; the whole circle being well flushed and wiped, so that there may be
no possibility of leakage.

[Illustration: FIG. 3 PIPES RESTING ON THEIR SHOULDERS.]

[Illustration: FIG. 4. PIPES RESTING ON THEIR FULL LENGTH.]

The objection to leakage is twofold: sewage matters escaping into the
soil might contaminate wells and springs; and it would also rob the flow
through the pipes of water needed to carry forward the more solid
contents. The continued efficiency of these small drains for carrying
away the solid or semi-solid outflow of the house is dependent very
largely upon the presence of sufficient water to create a scouring
current. While eight-inch pipes are admissible as a safeguard against
imperfect laying, they are liable to the grave objection, that, where
the service to be performed is greatly less than their capacity, the
stream flowing through them will not be sufficiently concentrated to
carry forward the more solid parts of the sewage. Up to the limit of
their capacity, six-inch pipes properly laid are greatly to be
preferred, as insuring a deeper stream which will more generally attain
the velocity of three feet per second, needed to move the heavier
constituents of the sewage. The difference in cost between six-inch and
eight-inch pipes will be sufficient to cover any extra cost of the most
careful workmanship. However much attention may be given to the
cementing of the joints, it will be impossible to prevent the running
into the pipes of a certain amount of mortar; and the workman should
have a swab or a disk of India rubber of the exact size of the bore of
the pipe, with a short handle attached to its middle, to draw forward as
each joint is finished, and so scrape away any excess of mortar before
it hardens.

Wherever it is, or may probably become, necessary to attach a
house-drain or land-drain, there sho