Compressed Air Work And Diving 1909

90 COMPRESSED AIR WORK. economical to import their own. They had seen a goocl deal of use, and as the sliding doors were not quite air-tight, for a time at low pressures it was found an advantage to connect up high-pressure air, as it was available, in order to equalise the pressure inside the bucket chamber when a bucket was being sent in, instead of using the low-pressure air from the working chamber. Except for this they were quite satisfactory and worked quickly. They were, however, a little dangerous, as there was no interlocking arrangement to prevent both doors being openecl at once. The two caissons on the Long Island side were stink by compressed air. Those on the Manhattan side were stink in the open, and were carried clown to a clepth of 40 ft., where they were made to rest on a ledge of rock 5 ft. wide all round. The skafts were then sunk the remaining 40 ft. without any support to the sides, and the shields were built in them in the open. It was also intended. to clo this on the Long Island side, but the rock proved too rotten, so the caissons had to be taken clown the whole way. On the Long Island side com- pressed air was used for sinking, and also when the plugs were cut out. After the caissons had been sunk, a water-tight concrete floor was put in, and the air pressure taken off. The shields were then built, and the ceiling of the working chamber put back at a higher level above the shields. The compressed air was then put on again, and the shields starteel after the pings had been cut out. The caissons, after having been put together in situ, were pitched in the following manner. Brackets were boltecl to the outside skin in pairs. Jacks under each alternate bracket then took the weight, and lowered the other brackets 011 to packings. The jacks were