The Montgomery advertiser., 1908-04-05

cal steam consumption.
 On the Long Island side. on account of supplying air for the headings at East Avenue and the more porous na- ture of the overlaying sand and gravel in the river. 1t was found necessary. to provided for the Manhattan tunnels. by two additional compressors electrical ly driven, powerrbeing supplied by the Lond Island Railroad power house, each compressor. requiring a TOO horse power. motor to drive It. This brings the total maximum capacity of the Long Island City power house for air pressure up to 53.75o cubic feet of free air per minute.e
 How Doctors Treat Victims of the
 Bends.
 When the purpose of tho great air compressors had thus been explained by Mir. Moir and the other engineers, the men were escorted to the doctor. There are two, physicians on duty at each end of the tunnels with an elab- crate equipment for treating injuries. The regulations require that such stan be maintained and two hospital air locks" for the treatment of men with the bends" the tunnel workers strange malady.
 Start Made Through the Tunnel.
 The party then went down In lift to the entrance to the under water sec- ton. right at the water edge. Before going under the river they walked about 1000 feet to the east, under Long Island City. up through the long, curving tunnel. This tunnel was prac- of its length. and men were bus.ly en- gagged in lining the few remaining iron segments that were uncovered, with two feet of solid concrete.
 The four tubes, through which the heaviest trains of the Pennsylvania system will pass. are of an outside di- amter of 23 feet. The 2-foot lining of concrete reduces the inside diameter to 1g feet, but there is still abundant headway for the tops of the cars and room on each side of the tracks for conduits of vitritied brick carrying cables for electric light and power. These conduits are built like long benches. and would form convenient sidewalk for passengers in the event of the trans becoming stalled in the tunnel.
 The party then retraced It's steps to the rivers edge. and entered the cais- son of Tunnels A and B. From each caisson a pair of tunnels has been driven under the river. to similar calls sons on the opposite side. The total length from ca.sson to caisson under the river is. about 1000 feet. The to- tai cast iron lining, used is about l0O.- 900 tons consisting of eleven segments to the ring, each ring weighing about eleven and one-half tons- About 1 800, 900 bolts of 1 1-2 inches diameter were used to fasten the segments to- gether. In the, under river sections, the concrete lining is not yet in place. and the party examined with interest the admirable precision with which every part of the, tube fitted together.
 The party then proceeded about 500 feet from shore fin tunneI"A" until the first air lock was reached. They all entered at once into the air chamber. which looked like hugh boiler. and the ar pressure was gradually brought up to about fifteen pounds. Only one man admitted great discomfort, but he was encouraged by MT. Lapp and Mir. Moir to keep up. and soon he became used to the situation. From this point on the air pressure Is maintained in order to prevent leaks through the lining, which has not all been caulked.
 As the party proceeded they walked in single file along rude gangway half way up the side of the tunnel, which was lighted by incandescent lights. This gangway Is a precaution- ary measure for the escape of the work men if water should flood the tunnel. Every few hundred feet great air. tight iron bulkhead extends from the roof of the tunnel down halfway like great half-moon. If water should rush in. the space between any two of these bulkheads in the upper half of the tube would remain filled with air on the principle of a diving bell. and the men could rush out through this space along the gangway. At each end bulkhead they would be obliged to dive under. through the water. but would instantly emerge .on the other side in the air again.
 It was not thought best by the men in charge of the party to go all the way through to the Manhattan shore, as the air locks would have to be negotiated on that end, and all the land City. So after proceeding about 1000 feet more toward Manhattan, the party descended lader into chamber below the tube. This Is called the "sun1p." and Is a drainage chamber in which powerful electric pumps will be installed to pump out what little seepage may leak into the tubes, and to pump out the water of condensation which gathers on the walls. No leaks are expected, but, these pumps are another measure of precaution due to the foresight of the Pennsylvania engineers. The party passed through the stump and up into tunnel, "B." where they watched the men placing the few remaining seg- ments in place and cutting apart the shields which had here fully performed their service.
 Mechanism and Method of Using the
 Shields.
 The engineers here explained the mechanism and method of using the shields. When the shafts at the river edge had been sunk the shields were lowered in sections to the bottom and built on timber cradles on the align ment of the tunnels. They are twen- ty-three feet, six and one-half inches outside diameter by eighteen feet long. and weigh 315 tons each. They are fitted with twenty-seven hydraulic jacks, nine inches in diameter, and with a water pressure of 5000 pounds per square inch. They are each cap able of eXerting a total push of 5000 tons
 On the back of the shield are two hydraulic erectors for building the cast iron tunnel lining, segment by segment. The operation in full rock face, which was the first class of material met by the shields from both sides of the river. was to drive a rough heading in advance of the shield.