r
_Copper_ pipes must be made by means of "wiped" solder joints. A wiped
joint is made by solder being poured on two ends of the two pipes, the
solder being worked about the joint, shaped into an oval lump, and
wiped around with a cloth, giving the joint a bulbous form.

All connections between _Lead Pipes_ and _Iron Pipes_ are made by
means of brass ferrules. Lead cannot be soldered to iron, so a brass
fitting or ferrule is used; it is jointed to the lead pipe by a wiped
joint, and to the iron pipe by an ordinary lead-calked joint.

_Putty_, _Cement_, and _Slip_ joints should not be tolerated on any
pipes.

[Illustration: FIG. 18.]

=Traps.=--We have seen that a trap is a bend in a pipe so constructed
as to hold a quantity of water sufficient to interpose a barrier
between the sewer and the fixture. There are many and various kinds of
traps, some depending on water alone as their "seal," others employing
mechanical means, such as balls, valves, lips, also mercury, etc., to
assist in the disconnection between the house and sewer ends of the
pipe system.

The value of a trap depends: (1) on the depth of its water seal; (2)
on the strengths and permanency of the seal; (3) on the diameter and
uniformity of the trap; (4) on its simplicity; (5) on its
accessibility; and (6) on its self-cleansing character.

The depth of a trap should be about three inches for water-closet
traps, and about two inches for sink and other traps.

Traps must not be larger in diameter than the pipe to which they are
attached.

The simpler the trap, the better it is.

Traps should be provided with cleanout screw openings, caps, etc., to
facilitate cleaning.

The shapes of traps vary, and the number of the various kinds of traps
manufactured is very great.

Traps are named according to their use: gully, grease, sediment,
intercepting, etc.; according to their shape: D, P, S, V, bell,
bottle, pot, globe, etc.; and according to the name of their
inventor: Buchan, Cottam, Dodd, Antill, Renk, Hellyer, Croydon, and
others too numerous to mention.

The S trap is the best for sink waste pipes; the running trap is the
best on house drains.

[Illustration: FIG. 19.

FORMS OF TRAPS.]

[Illustration: FIG. 20.

FORMS OF TRAPS.]

=Loss of Seal by Traps.=--The seals of traps are not always secure,
and the causes of unsealing of traps are as follows:

(1) _Evaporation._--If a fixture in a house is not used for a long
time, the water cons