Proceedings.]AND DOCKYARD AT GIBRALTAR.
27about a cubic yard, and levelled by divers. I n order to avoid loss m. Reed. of cement, the skips, which were of the " Stothert and Pitt " type, were closed at the top and bottom, with doors at the bottom, which were opened automatically to discharge the concrete. The top doors were added at Gibraltar, and were also opened automatically when the concrete was deposited, so as to allow the water to follow the concrete quietly down when the latter was being discharged. They were very successful, and concrete in the dock dam deposited by them and afterwards bared was found to be very solid and as good as concrete deposited in the dry. The Author referred in the Paper t o the small dry-dock constructed by the contractors for the use of their vessels. That dock, which was 250 feet long, with 46 feet width of entrance and 11 feet of water over the sill, cost only $8,000, including the dredging of an entrancechannel, the gates and equipment.It was founded on good shale and only 1 foot of concrete was put on the bottom. The sides were lined with a veneer of rubble masonry. The contractors had about seventy dredgers, tugs and barges, which were accommodated in the dock from time to time, and the local steamers used it as well. He believed the Admiralty were using it at the present day. The gates were simple in design and of very cheap construction, consisting only of balks of pitch-pine laid one on another with vertical bolts. They varied in size from 14 inches by 14 inches at the bottom to 1 2 inches by 6 inches at the top, and the gates cost 1 IS. 6d. per square foot erected complete, which he thought cheap for dock-gates for a 46-foot entrance. All the wharf-walls were constructed of small blocks as explained in the Paper. The blocks, which numbered about 120,000, were all set in the wet, .The design had been very successful, and no difficulty was found in bringing them up to good lines and levels. It was essential that they should be made accurately, both as to size and squareness. Great care was taken with the block-moulds, which were of wood, and the blocks were made 5 inch less than the dimensions on the drawings to allow of inequalities in jointing. The blocks were set by Spanish clivers, who soon got into the habit of setting them fairly quickly. Fig. 15 illustrated the method in which the concreteblock floor of the docks was made.The blocks were divided into 16-foot lengths, and each block was made one day's work. The shutters were put up to a certain height, and the work was then stepped in to the lines shown on the sections. It would be observed thnt the lines were radial. The A4dmiralty had really got a concealed arch in the Boor, as would be seen from the diagram. A 2-inch bed of cement mortar was put in under the granite floor, and it
DISCUSSION ON TIIE N E W ITAILDOUX-WORKS [Minutes ofwas specified that all joints between the concrete were to be rendered in neat cement. I n spite of that, it was found after the work was completed that water came through and sli...