2.22 REPORT— 1876. 



25 lb., so as to secure liomogeneity and a smootli surface. Twelve hours after 

 filling the moulds the division-plates are veithdrawn, and two days thereafter the 

 moulds are removed from the sides of the rings ; and in a period varying from nine 

 days in dry hot weather to three weeks in rainy weather, the rings are ready for 

 removal and building. The content of one ring complete is lOj cubic yards and 

 the weight 18 tons ; the heaviest portion weighs about 6 tons. 



The shoes are of cast-iron, 2 feet deep, of the same external shape as the bottom 

 of the cylinder, of 1-inch metal, with a bevelled inner shelf on which the corbelled 

 ring of tlie cylinder rests, and to which it is secured with a malleable iron ring or 

 washer, 5 inches by ^ inch thick, held down by Ij-inch bolts. The shoes of the 

 ordinary triune cylinders weigh about 4| tons each, and, for convenience in handling, 

 are made in six parts. 



In the construction of the cylinder substructure, a trench is made in the line of 

 the foundation (the bottom being about low-water level), of the necessary width, 

 and slopes of about 1| horizontal to 1 perpendicular, over vrhieh, or alongside, is 

 erected the necessary staging to carry tlie travelling cranes and digging apparatus. 

 The shoes are placed on the bottom of the trench in proper line and position ; the 

 concrete rings are then built up in rings of tliree and four pieces alternately, 

 pointed in cement, and the digging out of the sand or gravel &c. within the 

 cylinder-wells is commenced. Special diggers or excavators have been designed 

 for this purpose. 



A load of from 300 to 400 tons of cast-iron weights is generally required during 

 the sinking of each triune group of cylinders, to assist in sinking it to the proper 

 depth, which is 48 feet 7 inclies from the cope-level of the quay to the bottom of 

 the shoe. The average rate of sinking is about 12 inches per hour in good working 

 sand ; however, as much as 3 feet per hour has been attained. 



When each group of cylinders is sunk to the proper depth, the wells are filled 

 to the top with Portland-cement concrete, lowered to its place carefully. 



To effectually close up the apertures formed by the joining of each two gi'oups 

 of cylinders, a timber chock-pile, 2o feet long by 9 inches square, is driven behind, 

 anglewise, so that a sharp corner may bear hard against each of the cylinders. 



The foundation for the swing-bridge consists of twelve concrete cylinders, each 

 9 feet in external diameter, 29 feet in depth by 23 inches thick, formed in rings, 

 and resting on cast-iron shoes, as described for the quay-wall foundations. After 

 the cylinders were sunk, they and the interstices between them were cleaned out 

 and filled to the top with concrete, chock -piles being driven -where required. On 

 the cylinder-foundation thus formed, a stepped ashlar pier, 16 feet square at the 

 bottom and 10 feet square at the top, by 7 feet high, is erected, with a block of gra- 

 nite 7 feet square by 3 feet G inches deep, on which the centre lifting-press of the 

 bridge rests. This pier is surrounded by concrete rubble, the whole forming a 

 mass of masonry 36 feet 6 inches by 32 feet G inches by 10 feet 6 inches high. 



The foundations for the hydraulic rams, capstans, and side walls of the bridge-pit 

 are formed on single concrete cylinders placed apart and spanned between by brick 

 arches. The cartoons showed the details of the foundations. 



The first of the ground acquired for the docks was bought in 1845, at 6s. 6d. per 

 square yard, and the last in 1872, at 35s. 



The total cost of the docks, when fully equipped, will approach £1,500,000. 



Improved Safety-Apparatus for Mine- Hoists and Warehouse- Lifts. 

 By Thomas Dobson. 



This apparatus, for checking the downward movement of the cage, or hoist-box, 

 in case of the breaking of the suspending-rope or gear, consists of a mechanical 

 arrangement of levers, which expand through the intervention of a spring acting 

 upon the inner end of such levers through a sliding-sleeve, and so " strutting out," 

 as it were, against the guides, or by gripping the guide-ropes, where ropes are em- 

 ployed instead of upright timbers. 



