546 DOCK ENGINEERING.
below the top of the cylinder. There are two other angle-iron rings, one
at the top and the other at the bottoni of the cylinder, and between these
three rings of tee-iron.
The roof-plating is about £ inch thick, and the side-plating ranges from
| inch thick at the top to ^ inch at the bottom. The tanks are set on a
bed of sand and stand their full height above the ground.
A venthole is provided at the apex of the roof, with a screw-down
cover, and there are manholes, with covers bolted on, in the roof and also
in the bottom side-plates.
The wrought-iron settling tank is 36 feet in diameter and 5 feet deep.
It is open at the top, and contained within a brick house octagonal in plan.
There are also large barrelling sheds and a cooperage.
Eig. 564. —Buoy with Anchorage.
Ordinary Russian petroleum weighs 8^ Ibs. per gallon, American petro-
leum 8 Ibs. per gallon. Petroleum increases in bulk 1 in 200 with an
increase in temperature of 10° F.
Moorings may be classified as water moorings and quay moorings.
The former class, the object of which is to afford means of berthing
ships while discharging cargoes into lighters in mid-stream or in creeks,
includes anchored buoys and piled stagings. The buoys (fig. 564) are secured
by chains to screw piles or to heavy blocks of masonry bedded in the ground.
The stagings (figs. 565 and 566) consist of clusters of piles suitably braced
and stiffened.