20 "
7 " " 20 " " " 27 "
8 " " 25 " " " 33-1/2 "

The light-weight pipe, though extensively used by plumbers, is
generally prohibited by most municipalities, as it is not strong
enough for the purpose, and it is difficult to make a gas-tight joint
with these pipes without breaking them.

Cast-iron pipes are made in lengths of five feet each, with an
enlargement on one end of the pipe, called the "hub" or "socket," into
which the other, or "spigot," end is fitted. All cast-iron pipe must
be straight, sound, cylindrical and smooth, free from sand holes,
cracks, and other defects, and of a uniform thickness.

The thickness of cast-iron pipes should be as follows:

2-inch pipe, 5/16 inches thick
3 " " " " "
4 " " 3/8 " "
5 " " 7/16 " "
6 " " 1/2 " "

Cast-iron pipes are sometimes coated by dipping into hot tar, or by
some other process. Tar coating is, however, not allowed in New York,
because it conceals the sand holes and other flaws in the pipes.

=Joints and Connections.=--To facilitate connections of cast-iron
pipes, short and convenient forms and fittings are cast. Some of these
connections are named according to their shape, such as L, T, Y, etc.

[Illustration: FIG. 16.

DIFFERENT FORMS AND FITTINGS.]

_Iron Pipe_ is joined to _Iron Pipe_ by lead-calked joints. These
joints are made as follows: the spigot end of one pipe is inserted
into the enlarged end, or the "hub," of the next pipe. The space
between the spigot and hub is half filled with oakum or dry hemp. The
remaining space is filled with hot molten lead, which, on cooling, is
well rammed and calked in by special tools made for the purpose. To
make a good, gas-tight, lead-calked joint, experience and skill are
necessary. The ring of lead joining the two lengths of pipe must be
from 1 to 2 inches deep, and from 1/2 to 3/4 of an inch thick; 12
ounces of lead must be used at each joint for each inch in the
diameter of the pipe. Iron pipes are sometimes connected by means of
so-called rust joints. Instead of lead, the space between the socket
and spigot is filled in with an iron cement consisting of 98 parts of
cast-iron borings, 1 part of flowers of sulphur, and 1 part of sal
ammoniac.

[Illustration: FIG. 17.]

All connections between _Lead Pipes_ and between _Lead_ and _Brass_ o