Engineering Wonders of the World
Volume III

GREAT BRITISH DAMS AND AQUEDUCTS. 185 or the pipe is of unusually large diameter, steel is used. According to the duty which it may have to do, a 48-inch cast Cast-iron . . Pipes pipe—about the limit diameter for this type—varies in thick- ness from 1 inch, to inches. A pipe is cast socket end downwards, so that the densest metal may be at the part liable to fracture during the caulking of the lead at the joint. Bars are cast at the same time as a pipe and numbered similarly, and subjected to certain standard weight tests. If the bars do not come up to requirements, the pipe to which they refer is rejected. If the pipe passes this test, and also those for dimension, uni- formity of thickness, ability to withstand a pressure considerably greater than it will have to bear in the aqueduct, soundness (made by inspection and by rapping it with a hammer), and weight, it is heated and dipped bodily into an anti-corrosive preparation. When this coating has dried, the pipe is ready for laying. Full records are kept of every pipe for reference purposes. The commonest form of cast pipe has a socket at one end and a spigot at the other. A spigot has an external diameter somewhat smaller than the internal diameter of a socket, so that when a spigot MakinS‘ the j . , , j. Joints, is inserted into the socket of the next pipe an annular space shall be left between the two for yarn packing and for lead, which is run in, allowed to cool, and caulked, or compressed, with a special tool. The socket is recessed inside so that the lead may resist any 'force tending to draw the two CULVERT IN THE CAREG-DDU SUBMERGED DAM, ELAN RIVER ; DOWNSTREAM FACE. {Photo, by courtesy of Messrs. J. Mansergh and Sons.)