CAISSONS. 255 



Loop-bolts are fixed to the corners of the caisson for attach- 

 ing tackle for hauling it into and out of its berth. 



A 2-inch brass cock is fixed near the bottom of the inside 

 face of the caisson to run off the bilge water into the graving 

 dock, and a hand-pump is provided to pump out any water in 

 the event of the caisson springing a leak while out of its berth. 

 The sinking valves are conical spindle- valves of gun-metal, with 

 spindles carried up to the roadway deck; the cast-iron inlet 

 pipes pass by bends through the water-tight deck and are 

 secured to the outside skin, the mouths being protected by brass 

 rose-heacls. There are three sluices through the air-chamber for 

 filling the dock with water ; the valves are three feet in diameter, 

 of cast-iron, faced on both sides with gun-metal, and enclosed in 

 cast-iron cases with gun-metal faces, and connected with the sides 

 of the caisson by cast-iron pipes 3 feet in diameter, supported by 

 the floor-plates. The spindles are of gun-metal, passing up 

 through the water-tight deck in gun-metal stuffing-boxes, and 

 continued up to the roadway deck by wr ought-iron rods worked 

 by wheels and screws provided with indicators. 



Iron Floating Caisson at the Lime -kiln Dock. 1 This caisson, 

 shown by Figs. 252, 253, 254, designed by Mr. W. R. Kinipple, 

 is of a box form of unusual plan, being like the two leaves 

 of an ordinary dock gate, and is divided into an upper and 

 lower compartment by a water-tight deck, these compartments 

 being subdivided by two water-tight bulkheads. 



The outer plating is of wrought iron, the three lowest strakes 

 being J inch in thickness ; the three above are ^ inch, and 

 the two top strakes f inch in thickness in alternate inside and 

 outside strakes, with single-riveted lap-joints and vertical butt- 

 joints with cover-straps. The upper edge of the top strake 

 is finished off with an angle-iron, to which is bolted a timber 

 handrail. 



The plating of the bottom is 1 inch in thickness and stiffened 

 by angle-irons forming the floor beams. The plating of the 

 water-tight deck is f^ inch in thickness, having butt-joints and 

 cover-straps, and connected to the skin plating and framing by 

 angle -irons 3 inches by 3 inches by f inch. The side frames are 

 formed of single angle-irons spaced 2 feet apart, and divided into 

 two pieces by the water-tight deck. The angle-iron cross-beams 

 are also of the same size, screwed to the side frames with lugs. 

 1 M.r.l.C.E., vol. Ixv. p. 341. 



