nce the beginning of the 20th century considerable advance has been
made in the use of Priestman grabs, not only for dredging and
excavating (for which work they were originally designed), but also in
discharging bulk cargo. The first quadruple dredger used by the
Liverpool Docks Board had grabs of a capacity of 30 cub. ft., but
subsequently second and third quadruple dredgers were put to work in
the Liverpool Docks, with grabs having a capacity of 70 and 100 cub.
ft. respectively. In discharging coal at Southampton, Havre, Erith,
as well as at the coaling station at Purfleet on the Thames, grabs
having a capacity of about 80 cub. ft. are in constant use. Perhaps
the most difficult kind of bulk cargo to lift is "Narvick" iron ore,
which sets into a semi-solid body in the holds of the vessels, and for
this purpose one of the largest grabs, having about 150 cub. ft.
capacity and weighing about 8 tons, has been adopted. This grab was
designed as a result of experiments extending over a long period in
lifting iron ore. It is fitted with long, forged, interlocked steel
teeth for penetrating the compact material, which is very costly to
remove by hand labour. The Priestman grab is made to work with either
one or two chains or wire ropes. Grabs worked with two chains or ropes
have many advantages, and are therefore adopted for large
undertakings.

Wild's single chain half-tine grab works entirely with a single chain,
and has been found very useful in excavating the cylinders in Castries
harbour. Upon experimenting with an ordinary grab a rather curious
condition of things was observed with respect to sinking. On
penetrating the soil to a certain depth the ground was found as it
were nested, and nothing would induce the grab to sink lower. Sir W.
Matthews suggested that a further set of external tines might possibly
get over this difficulty. A new grab having been made with this
modification, and also with a large increase of weight--all the parts
being of steel--it descended to any required depth with ease, the
outside tines loosening the ground effectually whilst the inside
bucket or tines picked up the material.

_Miscellaneous Appliances._--There are several machines or appliances
which perhaps can hardly be called dredgers, although they are used for
cleansing and deepening rivers and harbours.

Kingfoot's dredger, used for cleansing the river Stour, consi