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10 . THE BROOKLYN BRIDGE.
ward—the two piers were ‘completed at about the same time.
The cast abutment pier was also carried down to the bed-rock,
eight feet lower than the cast channel pier, or 136 feet below
high-water mark. The pneumatic caisson was, of course, used
here also. . Do ape |
- Some striking differences, however, will be observed between
the plans of Roebling and Eads. The latter at first proposed
to sink a simple curb of plate iron through the bed-sand of the
river down to the rock. It would be in effect a huge tub of
an elliptical form, open at both ends, and large enough to en-
close not only the pier, but a floating coffer-dam of wood, with-
in which the pier should be built.’ Its office was not'to be to
exclude the water, but only the sand, from its interior. After
pumping out the sand to the bed-rock, the latter was to be lev-
elled off with a stratum of, conerete (by means of the diving-
bell or of submarine armor), and then the coffer-dam, a sort of
wooden tank, would be placed within the iron curb, the pier
would be built on its bottom, and would gradually sink, as its
weight increased, to- the bed prepared for it, the sides of the
coffer-dam or tank being, of course, built up as the pier was
built, so as to continue to exclude the water, and case ‘the
structure downward. ey
' Before the time arrived for carrying out this plan Captain
Eads visited Europe, and became convinced that the pneumatic
method as there employed, with recent improvements, would
be more economical. ‘The pneumatic caisson as used at St.
Louis eventually was built of plate iron instead of timber, as at
New York. The sides were three-quarters of an inch thick,
and the top one-half of an inch. The roof was strengthened
with thirteen iron girders across the top at intervals of five and
a half feet, each girder being five feet high, and the spaces
between them being filled with masonry. Beneath the roof
were built two massive girders of timber in the opposite diree-
tion to the iron girders above, or lengthwise of the caisson,
extending from the roof to within two fect of the lower edges
of the sides. These girders rested on the sand, and formed
the support of the whole structure while the excavation pro-
ceeded; assisted by a course of heavy timber around the sides.
The sides, projecting downward beyond the supporting girders
two feet, formed a cutting edge, facilitating the descent of the
caisson through the sand. The sides were continued up above
the roof by riveting on additional plates as fast as sunk in the
progress of the pier.
The greatest difficulty and the most interesting subject from
a humane point of view connected with all this deep submarine:
building, both at St. Louis and New York—in cither case un-
precedented in its extreme depth—is the effect of the intensely
compressed air on the health and lives of the men employed
in the caisson. These .two. experiences combined, with,.the
valuable. observations made and, expedients devised by, the
medical advisers of the respective companies, have contributed
greatly to the safety of such operations in,the future... While
everything possible under’ the circumstances appears to, have
been done for the safety of the workmen in both: cases, theré
is, nevertheless, a. sad expense of human life to charge to the
construction account of these magnificent works. This, in fact,
is apt to be the case with, great works, through the many
disastrous ‘accidents which are liable to attend the handling of
immense forces, whether expansive, explosive, or. gravitating,
as steam, compressed air, gunpowder, nitroglycerine, or even
masses of building material. | : . na
.: The visitor to the caisson of the Brooklyn pier looked down
first through an oval “man-hole” in the iron’ roof of the -air-
lock or air-tight chamber at the top of the great iron tube or
shaft leading down through the, masonry of .the pier to. the
submarine excavation below it. . Letting himself down through
this hole by. a steep iron ladder into the air-lock, he found
himself in an iron can or jar of large size, sufficient for a dozen
men to stand in erect, and faintly lighted through a thick glass
bull’s-eye ‘in. the top.. Under his feet was an iron trap-door,
and over his head’a sinilar door, so that the whole party, were
hermetically sealed, like meats for preservation, _ Immediately
‘a faucet in the floor was opened, and.the compressed. air, from
the caisson far below rushed hissing and roaring into the “ can.”
After a half-minute. of this, the compression of the common air
before in the- chamber develops an. oppressive. heat, like. that
of an oven, while the increasing density of the air‘ begins to
be painfully felt in pressure upon the organs of- respiration,
and particularly in the ears... Directions have been given to
the visitor to relieve the pressure in the ears by swallowing,
which he tries with good effect. He finds it easier to become ..°
accustomed to the pressure than to the excessive and increas-,
ing heat, which apparently. threatens. him with suffocation or.
fainting in much less:time than the shortest visit to the caisson
will require.. But, as soon as the pressure becomes equalized
with that of the caisson, the temperature begins to return to
equilibrium also, and the distress and apprehension ‘of roasting
is-soon and agreeably relieved. by the cool air found in.the
caisson. One visitor, who made nothing of the: pressure, was
so much overcome by the heat and the mistaken apprehension
that it would have to be endured throughout the visit, that he
insisted on being let out before the air-lock was filled. He
was afterward not a little chagrined to learn that he had really
gone through the whole of his sufferings, and had only missed
the gratification of the curiosity for which he had taken so
much trouble. In locking out, the reverse process, or rarefac-
tion of the air, causes a preternatural degree of cold in the air-
lock. Both the heat and the cold, however, were obviated in
the air-locks to the New York caisson by artificial means,
_ But to the majority of persons the disturbing’ effects, sensi-
ble and constitutional, of the pressure are the most serious
and to some they are fatal. - Therefore, while Eads: reports
that not one instance of illness.was known to have occurred
among hundreds of visitors to his caissons, including many
ladies, it is nevertheless wise to. take personal examination and
advice from a physician experienced in “caisson disease” be-
fore exposing one’s self to the effects of powerfully compressed
air. Especially should the managers of such works be scrupu-
lous to subject all candidates for employment in.the caisson
to strict examination, and admit no man who is, in’ medical _
judgment, ill prepared to withstand the effects of the situation.
It might be salutary to insist on such ‘a requirement in the
charter of any company likely to, prosecute work-in compressed
air. The cases of disease among the caisson. laborers treated
by Dr. Andrew If. Smith, surgeon to the New York Bridge
1 yo ' . : : ,
‘Company, were one hundred and ten in number, of which
three were fatal. , +
Frorn the data collected by Dr. Smith in his investieations
with reference to the treatment of his caisson patients, it ap-
pears that the discoveries of Torricelli, in 1648, which led to
his invention of the barometer, and the farther elucidation by
Pascal, five years later, of the principles of atmospheric. press-
ure, immediately gave rise to extensive medical speculation and
experiment upon the effects of widely varying pressures upon
animal life. In 1664 Dr, Hanshaw, an English physician, pro-
posed to treat diseases by artificially increasing or diminishing
the normal-atmospheric, pressure on.the patient. In 1783 the
Academy of Sciences of Haarlem offered a prize for the: best
apparatus for experimenting on the vital and: physiological ef-
fects of compressed air., The. diving-bell had. been in use from
the beginning of the sixteenth century, but the first medical
observations of value in that connection were made by a dis-
tinguished Russian physician named Hamel, who availed him-
self of an opportunity for personal experiment in a divine-bell
employed in some engincering work: near Dublin in 1890
Compressed air was tried soon after as a remedial awent by
Jarnod, who published the results of his experiments in 1835
From this time the pneumatic treatment began to be a system
—the “compressed-air baths” of Europe became and continue
to be highly successful, particularly in, pulmonary diseases and
dyspepsia, So an
Compressed air asa remedy and compressed air as a cause
of discase differ greatly in intensity or degree, the extra press-
ure employed for the former purpose being only about. cight
or ten pounds to the Square inch, whereas submarine opera-
tions, such as those under review, require a pressure. of from
tothe square ial aaonding fe the eet teats exe
uare inch, according to the height of water to be over-