172 GREENHOUSE CONSTRUCTION AND HEATING. 
ends have to be joined, a ‘‘loose collar” (A), or double 
socket (B), as in Fig. 112, is employed. A cast-iron pipe 
is easily cut by nicking it all round with the corner of a 
flat or triangular file, going a full din. deep. Then with 
a cold chisel and hammer go all round in the nick, 
striking smartly but not too heavily, and it will presently 
crack off at the “nick.” Pipes of the best quality cut 
more easily than common or cheap ones, which are 
usually made of very hard and imperfectly smelted metal. 
A tool known as a pipe-cutter is used by fitters, and 
saves a great deal of time and labour. It consists of 
five or six hard steel discs or wheels, with cutting edges, 
carried in a kind of short steel chain, with double links, 
and a handle and thumb-screw to tighten it up. The 
chain and wheels are passed round the pipe, hitched 
and tightened up and then worked round several times 
by means of the lever, tightening up the wheels occasionally 
so as to keep them cutting. When a good deep cut has 
been made the cutter is taken off, and a few taps with 
the hammer and chisel causes the pipe to drop apart. 
Socket-pipes, as shown in Fig. 111, are usually employed 
for heating, especially by nurserymen and market-growers 
generally, though. in some cases the ‘‘ expansion-joint ” 
and other kinds of piping (to be described presently), are 
used, but chiefly in small or amateur’s houses. The joints 
of socket-pipes may be made in several ways, the old- 
fashioned method being to pack each joint well with 
rope-yarn and a mixture of red and white lead, with a 
little oil, letting the whole ‘‘set”’ well before using. But 
this is a far too slow and troublesome process for the 
present day, while such joints are also very apt to leak, 
