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CRA1STES.

3000 pieces, shaped like the lid of a box, 15 inehes by 12inches wide, with a 3-inch deep rim all round, were requiredto be made of 1-inch steel plate, and this was easily effectedin two heats by a couple of strokes of a 14-ineh ram.” Healso described that, in erecting the great 1700 feet spans ofthat bridge, the massive girders were put together at a lowlevel, and were hoisted as high as the top of St. Paul’s Cathedral , by hydraulic power. Continuous girders, nearly one-third of a mile in length, were similarly raised, together withthe necessary sheds, cranes, appliances, and workmen, the'whole weight on the platforms being in some instances morethan 1000 tons.

In the excavation of the foundations of the Forth Bridge 'hydraulic appliances of a novel kind were used. The hugewrought iron Caissons (70 feet in diameter and 70 feet high)for the foundations had to be sunk through tenacious boulderclay, which was excavated by hydraulic spades. Hydraulicrams worked in the hollow handles, which were thrust againstthe roof, and by turning a tap the spade was forced into theclay, with a pressure of three tons. These hydraulic spadeswere employed in an electrically lighted diving-bell 70 feet indiameter, 7 feet high, and 90 feet below the sea.

GRAUES.

In all the designs for hydraulic cranes, the principle employedis that of using the direct thrust of a ram or piston through ashort stroke, and multiplying the stroke by carrying the liftingchain over a series of sheaves. In general, the cylinders andmachinery are placed horizontally in a charnber Underground.In some cases the lifting cylinder is placed vertically, and ismade to form part of the pillar of the crane, as is shown by Plate22, fig. 1, which represents a Goods Station Crane for a loftygoods shed, the pillar being carried by top and bottom bearings.The lifting cylinder is placed in the pillar of the crane, to