d handling of cast-iron pipes of large
diameter, a care which must be unfailing from the time of casting
until they are jointed in their final position in the ground. They are
cast vertically, socket downwards, so that the densest metal may be at
the weakest part, and it is advisable to allow an extra head of metal
of about 12 in., which is subsequently cut off in a lathe. An
inspector representing the purchaser watches every detail of the
manufacture, and if, after being measured in every part and weighed,
they are found satisfactory they are proved with internal fluid
pressure, oil being preferable to water for this purpose. While under
pressure, they are rapped from end to end with a hand hammer of about
5 lb. in weight, in order to discover defects. The wrought-iron rings
are then, if required, shrunk on to the sockets, and the pipes, after
being made hot in a stove, are dipped vertically in a composition of
pitch and oil, in order to preserve them from corrosion. All these
operations are performed under cover. A record should be kept of the
history of the pipe from the time it is cast to the time it is laid
and jointed in the ground, giving the date, number, diameter, length,
thickness, and proof pressure, with the name of the pipe-jointer whose
work closes the record. Such a history sometimes enables the cause
(which is often very obscure) of a burst in a pipe to be ascertained,
the position of every pipe being recorded.

Cast-iron pipes, even when dipped in the composition referred to,
suffer considerably from corrosion caused by the water, especially
soft water, flowing through them. One pipe may be found in as good a
condition as when made, while the next may be covered with nodules of
rust. The effect of the rust is twofold; it reduces the area of the
pipe, and also, in consequence of the resistance offered by the rough
surface, retards the velocity of the water. These two results,
expecially the latter, may seriously diminish the capability of
discharge, and they should always be allowed for in deciding the
diameter. Automatic scrapers are sometimes used with good results, but
it is better to be independent of them as long as possible. In one
case the discharge of pipes, 40 in. in diameter, was found after a
period of about twelve years to have diminished at the rate of about
1% per year; in another case, where the water was soft and where t