212 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



end walls are formed of brickwork with rectangular voids rilled 

 with concrete, and having a freestone string-course on each 

 side for the hauling-chain path. The floor is brick in cement, 

 with granite stones and cast-iron blocks alternately for carrying 

 the rails on which the caisson travels. 



The covering of the chamber consists of Lindsay's steel- 

 trough decking, the troughs of which are filled in with concrete, 

 with, in addition, a layer of concrete 4 inches thick over the 

 whole surface, which is causewayed over to form part of the 

 ordinary roadway. 



The dock is emptied by the main pumping engines of the 



<jo FEET 



FIG. 200. 



adjacent dock through a culvert at the head 5 feet 6 inches in 

 diameter. 



The engines are placed underground in roomy houses, the 

 walls of which were lined with white glazed bricks ; the roofs 

 being formed by rolled beams and concrete, with prismatic 

 lenses inserted for admitting light by day. 



The proportions used for making the concrete were, for the 

 cylinders, 5 parts of gravel and sand to 1 part of Portland 

 cement. For the floor and sides of the dock, G parts of stone 

 and sand to 1 part of Portland cement. For the covering of the 

 caisson chamber, 8 parts of stone and sand to 1 part of Portland 

 cement, and for filling the concrete cylinders, C J parts of stone 



