The following morning, at the turn of the tide, the caisson was shifted into position inside the new basin, the whole operation taking little more than an hour. As the crowded ferries churned in and out of the slip next door, young men were seen climbing to the tops of the cabins for a better look.
For the next several weeks additional courses of timber were built on the roof, each course at right angles to the other, with spaces left between the timbers, which were filled in with concrete to add weight and to help preserve the wood. Additional sections for the water shafts, air locks, and supply shafts were also installed as the roof grew in size. And on May 10, Roebling, Colonel Paine, and Francis Collingwood made the first inspection below. The temporary air compartment put in for the launching was removed, two doorways were cut through each of the interior walls, and any loose rock or mud under the edges was shoved out. A few men complained of trouble breathing the heavy air and apparently there was a sharp change in temperature inside the air lock every time the pressure changed, about which something would have to be done. The heat was up over 100 degrees. But otherwise everything was going as expected.
In his report to the directors of the Bridge Company, signed June 12, Roebling wrote:
For three weeks past a gang of forty men have been at work in the caisson for eight hours every day, under the charge of Mr. Young, principally in leveling off and removing boulders which happened to lie under the frames and the edges. A deposit of dock mud, from two to three feet deep, has made this work exceptionally unpleasant. The dredges, which are now beginning to work, will remove it in short time. The removal of large stones from under the shoe, some of them 100 cubic feet, is a matter requiring considerable skill and perseverance.
During all this time the caisson was rising with every high tide, then resting on the bottom again at low tide, which, of course, meant that work within could be carried on only during the low-tide time of day, when the chambers were comparatively free from water.
As more timber courses were added on top and the over-all height of the caisson was increased by a full ten feet, its center of gravity was raised considerably, causing a condition of “unstable equilibrium”—that is, the caisson would no longer rise uniformly with the rise of the tide. One end would come up ahead of the other and this would cause what was known as a blowout, a phenomenon of imposing appearance, as Roebling said, and the subject of much excited talk in Brooklyn.
As the tide was rising, and the downward weight of the caisson was being overcome by the increased tension of the air inside, along with the buoyancy of the river outside, one end of the caisson would suddenly tip up six inches or more. For an instant the tension of the air inside exceeded the head of water outside, and there would be a huge rush of air from beneath the shoe, carrying with it a column of water weighing hundreds of tons to a height of maybe sixty feet. Fish would fall all over the top of the caisson and the men working there would scramble to gather them up.
For the men inside the caisson such occurrences were quite terrifying at first, but of little serious consequence. There would be a terrific roaring noise and a sudden blast of air, both of which were decidedly unsettling, but after it had happened two or three times the men grew accustomed to it and the loss of a few hundred tons of air from a volume so large (163,000 cubic feet) was nothing to worry about especially.
Seen from the shore or the ferry, however, the sudden appearance of a waterspout on the East River was a spectacle that would be talked about for years by all who saw it.
It took three courses of stone and most of June before the vast wooden box was bobbing up and down no longer and was grounded on the bottom to stay. The first stone to be placed on top, the cornerstone as it were, was a block of blue limestone from the Kingston quarry, three feet by eight, weighing 5,800 pounds. There was no particular ceremony that went with it and so far as is known nothing was carved on it.
A stoneyard, as it was called, had been established downriver, below the Atlantic Docks, near Red Hook, and four huge scows had been especially built to bring the stone up to the site. McNulty had been put in charge of laying the first courses and the work had gone much slower than normal since portable derricks had to be used to move massive blocks, weighing anywhere from two thousand to three thousand pounds apiece. But once the caisson was righted down, three permanent derricks were mounted directly on top of it. They had great wooden masts fifty feet high, like the masts of a ship, and booms that were capable of swinging to any point on the deck.
By now, too, six big air compressors, built by the Burleigh Rock Drill Company, of Fitchburg, Massachusetts, were in operation inside a long shed nearby in the yard. Each had a twenty-horsepower steam engine driving two single-acting air cylinders of fourteen-inch stroke and fifteen-inch diameter. Each engine had its own boiler and they were all so connected that the stopping or breaking down of one boiler or engine would not affect the others. All piping and connections were in good order and working properly. (A ten-inch main took the compressed air underground some 150 feet to the caisson, where two six-inch rubber hoses carried the air down the supply shafts to the work chambers.) Thomas Douglas, a mason who had done the finest stonework in Prospect Park, had been put in charge of the labor outside the caisson, while the foreman inside was a strapping man named Charles Young.
To date everything had gone exactly as planned. There had been no serious interruptions. Material had arrived on time. All necessary machinery had been purchased and installed. Proper offices had by now been established for the Bridge Company in the Union Building on Fulton Street, which was only a short walk from the Fulton Ferry. Everyone involved was to be congratulated, wrote General Superintendent William Kingsley in his own first official report.
The great caisson could now begin its descent.
9
Down in the Caisson
We have no precedent just like this bridge.
—WASHINGTON ROEBLING
IN ALL the thousands of years men had been building things, no one had ever attempted to sink into the earth so large a structure as the Brooklyn caisson and there were not very many places where the job would have been more difficult than the Brooklyn side of the East River.
Roebling and his assistants thought they had learned quite a lot about the ground they had to penetrate while dredging the site, but as he commented with his usual dispassion, “The material now became sufficiently exposed to enable us to arrive at the conclusion that it was of a very formidable nature, and could only be removed by slow, tedious, and persistent efforts.” Compared to this everything before had been child’s play. Now that which had looked so reasonable on paper was turning out to be quite a different matter in practice. Indeed, so bad was the first month of excavation inside the caisson, so painfully slow and discouraging, that it began to look as though the whole idea for the foundations had been a terrible mistake, that they would have to give up and try again some other way or some other place.
There was never any public awareness of such feelings, which was just as well. There was, for that matter, very little real awareness on the part of the public of what actually went on inside the caisson, the work being entirely concealed.
The best over-all view of the site was still from the deck of the ferry. So every day thousands of people on their way to and from New York got a splendid, close-up look at the three towering boom derricks swinging blocks of limestone into place and at the squads of men swarming about the masonry work or through the adjacent yards, every last man appearing to know just what was expected of him. There were half a dozen different steam engines sending up columns of black smoke and everywhere a bewildering clutter of tackle, hand tools, nail kegs, and tar barrels, stacks of lumber and great heaps of coal, sand, and stone. How anything orderly or rational might emerge from such seeming chaos was something for ordinary men to ponder in dismay.
Still, seen from above, the work did not appear all that different from other big construction projects. The activity a
round the gigantic new Post Office being built in New York, for example, was every bit as confusing and impressive to watch. All this was lit by the same light of day and the men appeared no different from other mortals, breathing the same good air. But down in the caisson, everyone had heard, things were different. That was the part of the work that had the most fascination and of course the fact that it was hidden away where no one could see it, except for a relative few, made the fascination that much greater.
The newspapers sent reporters down soon enough. By July better than two hundred workers were going down every day and naturally they had their own stories to tell. So as a result a picture began to emerge, of a strange and terrifying nether world at Brooklyn’s doorstep, entered only by men of superhuman courage, or by fools, and as sometimes happens with ideas that grow in the imagination, it was not so very far from the truth.
Probably the most vivid description was one given by E. F. Farrington, Roebling’s master mechanic, a plain, blunt, practical man ordinarily. There would be rumors later about who actually was doing Farrington’s writing for him, or at least dressing up his literary style, but there is no doubting the authenticity of the image.
Inside the caisson everything wore an unreal, weird appearance. There was a confused sensation in the head, like “the rush of many waters.” The pulse was at first accelerated, then sometimes fell below the normal rate. The voice sounded faint unnatural, and it became a great effort to speak. What with the flaming lights, the deep shadows, the confusing noise of hammers, drills, and chains, the half-naked forms flitting about, with here and there a Sisyphus rolling his stone, one might, if of a poetic temperament, get a realizing sense of Dante’s inferno. One thing to me was noticeable—time passed quickly in the caisson.
Even the air lock was an unnerving experience for most men the first time they went down. For some it was also an extremely painful experience. The little iron room was abundantly lighted by daylight through glass set in the ironwork overhead. But once the attendant had secured the hatch with a few turns of a windlass, the common sensation was that of being enclosed in an iron coffin. Then a brass valve was opened. “An unearthly and deafening screech, as from a steam whistle, is the immediate result,” wrote one man, “and we instinctively stop our ears with our fingers to defend them from the terrible sound. As the sound diminished we are sensible of an oppressive fullness about the head, not unaccompanied with pain, somewhat such as might be expected were our heads about to explode.” (For many the sensation did not pass and they were said to be “caught in the lock.”) Then the sound stopped altogether, the floor hatch fell open by itself, and the attendant pointed to an iron ladder leading into the caisson. The immediate wish of most men at this point, whether they showed it or not, was to get back out into the open air just as fast as humanly possible. But once the ladder had been negotiated and three or four minutes had passed, most men also found they felt reasonably steady.
The initial view of the caisson interior was generally something of a shock, once the eyes had adjusted to the light. The six big chambers looked something like vast cellars from which a flood had only recently receded. Every post and partition, every outside wall, and the entire ceiling were covered with a slimy skim of mud. Every man in the place wore rubber boots and got about on planks laid from one section to another and between the planks the muck and water were sometimes a foot deep or more. Most days the work force would be concentrated in a few locations, leaving some of the huge chambers as dark and silent as subterranean caves.
Where there was light it came from calcium lamps, limelights as they were also called, which threw steaming, blue-white, luminous jets into the corners where the men worked, or from squat sperm candles that blazed like torches at the end of iron rods planted alongside the plank walkways. “The subject of illuminating a caisson in a satisfactory manner is rather a difficult problem to solve,” Roebling remarked in his report to the directors of the Bridge Company. At first the candles had burned with such vigor in the compressed air and sent up such clouds of smoke that the air had become intolerable. This had been overcome somewhat by reducing the size of the wick and of the candle and by mixing alum with the tallow and drenching the wicks in vinegar. Even so Roebling worried about the quantities of floating carbon the men were breathing into their lungs.
Kerosene lamps had to be ruled out from the start. They smoked even worse than candles, and with fire a constant hazard in such a charged atmosphere, Roebling did not want the risk of spilled oil. So he had hit upon the idea of limelights, of the kind ordinarily used for stage lighting or nighttime political rallies. He had the gas—a combination of compressed oxygen and coal gas—piped into the caisson, put burners in every chamber, and found two lamps per chamber would do the job. One small explosion had singed the beard off an attendant, but other than that the system had worked most satisfactorily. Ordinary street gas would have been about five times less expensive, but when that had been tried, the heat inside the caisson had built up to the point where no one was able to take it.
The air as it was, besides being heavy and dank, was uncomfortably warm. On the way from the compressors it passed through a cooling spray of water. Even so, winter or summer, regardless of the time of day or the weather outside, the temperature inside stayed at 80 degrees or more and the air was so saturated with water that under the best conditions the chambers seemed continuously shrouded in mist. Visitors who did not have to exert themselves in any way soon found they were wringing-wet with perspiration.
Most of the people who visited the caisson—newspapermen, local politicians, an artist from Harper’s Weekly, editors from some of the professional journals—came out with their clothes thoroughly mud spattered and quite relieved to have the experience behind them. Many of them also expressed open amazement that men could actually work in such a place day after day.
The first load of rock and mud was hauled out of the caisson by clamshell dredge buckets on July 5. Most of the effort inside was spent removing the sharp-edged boulders that threatened to damage the frames and shoe as the caisson began to come down on them with crushing force. Boulders under the water shafts were the most serious initial problem, for if the caisson were to settle suddenly, the shafts might be blocked shut or badly damaged. And there was no way to get the boulders out of there except to chip away laboriously hour by hour, by hand, with long steel bars and sledge hammers.
In the middle chambers the ground was nearly all traprock, packed like gravel and joined by what Roebling described as a natural cement made of decomposed fragments of green serpentine rock. Every boulder was coated with this unyielding substance, upon which a steel-pointed pick had virtually no effect. Only by driving in steel-pointed crowbars with heavy sledges were the men able to make the slightest headway.
In chambers No. 1 and 2, those nearest the ferry slip, there was clay and gravel between the rocks, which made the going easier, while in Nos. 5 and 6, those at the upstream end of the caisson, there was a gummy blue clay that extended down forty feet, just as indicated by earlier soundings. This made the digging there relatively easy, of course, but it also meant that the caisson would have to go down at least forty feet—or beyond the clay. As Roebling said, no better foundation could have been wished for than what they were finding in chambers No. 3 and 4, but only if it had extended all over. And with the nature of the material so vastly irregular from one chamber to the other, lowering the caisson uniformly seemed practically an impossibility.
Roebling kept careful track of the rock uncovered. Nine-tenths of it, he found, was of Hudson River Palisades origin, transported, like all of Long Island, millions of years before by the glaciers. This traprock, as it was commonly called, was basalt, an igneous rock, like granite, and nearly as hard. As the men dug into the caisson floor, the traprock emerged in chunks the size of paving blocks or in monstrous boulders, but when a shovel or pick first struck one of them, with a sharp metallic clink, there was no telling which size it would tur
n out to be.
Boulders of quartz and gneiss occurred here and there, but rarely. Two big boulders of red sandstone were also found. But a collection made by Roebling of all the different varieties of smaller rocks uncovered, most of which had been worn down to pebble size, presented a complete series of the rocks to be found for a hundred miles to the north and northeast of Brooklyn.
The idea of driving the cutting edge of the caisson through such material by building weight overhead had to be abandoned at the start. The pressure needed to do that would crush the cast-iron shoe and smash the bearing frames. So the cutting edge would simply not cut. Instead, every boulder, every rock of any size, had to be removed before the shoe or frames began bearing down on them. And all such work had to be done by probing underwater since there were trenches along the inside edge of the shoe, clear around, and these were nearly always brimful of water that seeped in from the outside. (This water flowed in turn into cross trenches at the foot of the frames, which supplied the big pools under the water shafts.)
Just finding the boulders under the shoe, let alone removing them, was an unbelievably tough and disagreeable task. The full perimeter of the cutting edge was 540 feet. This added to the five frames, each 102 feet long, brought the caisson’s full bearing surface to 1,050 lineal feet, or a distance greater than the length of three football fields, every inch of which had to be probed beneath with a steel sounding bar twice daily with each shift. Whenever a new shift came down, the work accomplished in the preceding eight hours had to be carefully explained; and since most of the trouble spots discovered would be underwater, there was no way simply to point them out—the information had to be written down or memorized. “Moreover,” as Roebling wrote, “a settling of the caisson of six inches or a foot would bring to light an entirely fresh crop of boulders in new positions, and very often half without and half within the caisson.”
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