[Illustration:  CROSS-SECTION OF POWER HOUSE]

Water for condensing purposes is drawn from the river and discharged into it through two monolithic concrete tunnels parallel to the axis of the building.  The intake conduit has an oval interior, 10 x 8-1/2 feet in size, and a rectangular exterior cross-section; the outflow tunnel has a horseshoe-shape cross-section and is built on top of the intake tunnel.  These tunnels were built throughout in open trench, which, at the shore end, was excavated in solid rock.  At the river end the excavation was, at some places, almost entirely through the fill and mud and was made in a cofferdam composed chiefly of sheet piles.  As it was impossible to drive these piles across the old timber crib which formed the old dock front, the latter was cut through by a pneumatic caisson of wooden-stave construction, which formed part of one side of the cofferdam.  At the river end of the cofferdam the rock was so deep that the concrete could not be carried down to its surface, and the tunnel section was built on a foundation of piles driven to the rock and cut off by a steam saw 19-1/2 feet below mean hightide.  This section of the tunnel was built in a 65 x 48-foot floating caisson 24 feet deep.  The concrete was rammed in it around the moulds and the sides were braced as it sunk.  After the tunnel sections were completed, the caisson was sunk, by water ballast, to a bearing on the pile foundation.

Adjacent to the condensing water conduits is the 10 x 15-foot rectangular concrete tunnel, through which the underground coal conveyor is installed between the shore end of the pier and the power house.

[Sidenote:  Steel Work]

The steel structure of the power house is independent of the walls, the latter being self-supporting and used as bearing walls only for a few of the beams in the first floor.  Although structurally a single building, in arrangement it is essentially two, lying side by side and separated by a brick division wall.

There are 58 transverse and 9 longitudinal rows of main columns, the longitudinal spacing being 18 feet and 36 feet for different rows, with special bracing in the boiler house to accommodate the arrangement of boilers.  The columns are mainly of box section, made up of rolled or built channels and cover plates.  They are supported by cast-iron bases, resting on the granite capstones of the concrete foundation piers.

Both the boiler house and the engine house have five tiers of floor framing below the flat portion of the roof, the three upper tiers of the engine house forming galleries on each side of the operating room, which is clear for the full height of the building.

The boiler house floors are, in general, framed with transverse plate girders and longitudinal rolled beams, arranged to suit the particular requirements of the imposed loads of the boilers, economizers, coal, etc., while the engine-room floors and pipe and switchboard galleries are in general framed with longitudinal plate girders and transverse beams.