water should be close-grained, hard, white metal. In such metal
the small quantity of contained carbon is chemically combined
with the iron, but in the darker or mottled metals it is
mechanically combined, and such iron soon becomes soft, like
plumbago, under the influence of sea water. Hard white iron has
been proved to resist sea water for forty years without
deterioration, whether it is continually under water or
alternately wet and dry.

Several types of sea outfalls are shown in Figs. 25 to 31.[1]
In the example shown in Fig. 25 a solid rock bed occurred a
short distance below the sand, which was excavated so as to
allow the outfall to be constructed on the rock. Anchor bolts
with clevis heads were fixed into the rock, and then, after a
portion of the concrete was laid, iron bands, passing around
the cast iron pipes, were fastened to the anchors. This
construction would not be suitable below low-water mark. Fig.
26 represents the Aberdeen sea outfall, consisting of cast iron
pipes 7 ft in diameter, which are embedded in a heavy concrete
breakwater 24 ft in width, except at the extreme end, where it
is 30 ft wide. The 4 in wrought iron rods are only used to the
last few pipes, which were in 6 ft lengths instead of 9 ft, as
were the remainder. Fig. 27 shows an inexpensive method of
carrying small pipes, the slotted holes in the head of the pile
allowing the pipes to be laid in a straight line, even if the
pile is not driven quite true, and if the level of the latter
is not correct it can be adjusted by inserting a packing piece
between the cradle and the head.

Great Crosby outfall sewer into the Mersey is illustrated in