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_ experiments,
12 THE BROOKLYN BRIDGE,
come. The effects, immediate and secondary, are in the latter
case, therefore, as painful as in the former they are agreeable.
The first application of compressed .air in engineering was
made in 1839 by M. Triger (a native of the country which has
given birth, but not development, to so many leading ideas in
this line), for the purpose of sinking a shaft through a deep
stratum of quicksand permeated by the water of the Loire, to
a bed of coal which nobody before had been able to get at.
The medical apparatus already in use served for preliminary
An iron tube with air-lock exactly like that run-
ning vertically through the masonry of the Brooklyn Bridge
pier was sunk through the quicksand successfully, and the coal
was reached.
M. Triger noticed that persons in the compressed-air cham-
ber all spoke through the nose, making it in one respect an ad-
vantagcous “institute” for learning the language of the coun-
try. It does not seem as if this circumstance had attracted the
attention of any of the popular professors of French in our in-
genious and enterprising nation.. He also noted the impor-
tant fact that under the pressure nobody could whistle: no
more, he might have added, than the king could around an
Englishman’s cottage. The abortive exertions of a brass band
in such an atmosphere, or rather in so many atmospheres,
might be ludicrous to sce, if there were any occasion for intro-
ducing a band into the caisson. It is difficult to send enough
extra pressure of air through the organs to overcome the pre-
vailing pressure and make a noise. The voice sounds faint
and weak. Perhaps it is partly for this reason that hearing
seems to be impaired, while it is evident also that the pressure
on the tympanum must dull its vibrations. But a laborer, who
had been deafened for seven years by the cannonading at the
siege of Antwerp, not only heard, but heard more distinctly
than any of his comrades. It was much easier to ascend in
this than in ordinary air, of course, and probably with a little
ingenuity men might be enabled to fly in it. At least, a light
air-chamber might be made to run up and down in the com-
pressed air as an clevator, to carry the men to and from their
work. The effort of climbing a great height in common air,
after leaving the caisson through an air-lock at the bottom of
the shaft, is set down by Dr. Smith as a very serious aggrava-
tion of the evils of caisson labor. Eads had his air-locks at
the top of the shaft, or.else had an elevator run by stcam to
carry the men up and down. ‘The writer’s patent pneumatic
elevator (for which a caveat-is hereby issued) will save both
troubles. The method of getting in front of the balloon is
not yet fully developed, but meanwhile the men may be al-
lowed to get on top of it, and find their way in and out by the
usual air-lock at the upper end of the shaft.
After Triger’s experiment a number of mining operations
were successfully performed in compressed air. The first appli-
cation of compressed air in sinking picrs below water was in the
construction of the railway bridge over the Medway, between
Rochester and Chatham, in 1850. A system of iron’ tubes,
cast three and one-half fect in diameter, served the purpose for
which a single caisson is now employed, and the piers were’
borne upon them down to their submarine bed. Eight or nine
years later, a number of bridges were built with the aid of this
method at Lyons, Macon, and other places. The bridge over
the Rhine at Strasburg, at about the same time, was an exten-
sive work, in which fourteen caissons were employed, each about
cightcen by twenty-five fect, and going to an extreme depth of
perhaps forty-five fect. In 1863 a bridge at Argentenil was
founded on piers sunk by the aid of compressed air. In near-
ly all cases of caisson-building medical observations have been
taken and reports or memoirs published. Lastly come the
works at New York and St. Louis, which dwarf all preceding
operations of the kind to insignificance. :
Many curious effects of working in compressed air have been
observed besides those already mentioned. For example, ex-
-citement of the pulse on entering, followed by depression in
the caisson of, say, fifteen beats to the minute, and a rebound
on emerging just as many beats above the natural standard the
volume of the pulse diminished; these effects, however, vary-
ing widely in kind and degree in different individuals; black
expectoration and blackening of the contents of the body gen- ,
erally with soot from the lights which burned away as many :
times. faster as the pressure was multiplied; cumbrous and -
difficult motion of the tongue in speaking ; excessive perspira- °
tion, apparently, which proves, however, to be surface condensa-_
tion; impaired appetite, and in some cases emaciation; also
the opposite; itching of the skin; bleeding at the nose; a re-
markable cure of advanced consumption; the pitch of sounds
is raised, so that the deep roar of a powder-blast is changed to
a sharp report like that of a pistol, and a bass voice becomes a
shrill treble; the frequency of respiration is reduced ; its depth
was increased, under a pressure of thirty-three pounds, in the
proportion of nearly two to one.
The severer effects are neuralgic pains, sometimes of the
most excruciating character, pain at the stomach, and vomiting,
and, above all, paralysis. The chief condition back of these
sensible symptoms appears to be blood congestion, especially
to the brain and spinal cord. The laws of congestion by com-
pressed air, deduced. by Dr. Smith, are (1) that the blood will
be pressed to the centres at the expense of the surface, as
shown by the pallor characteristic of the caisson disease: (2)
that the blood will be pressed ont of the softer tissues into the
more ‘firm and compact organs: (3) that structures within
closed bony cavities (as the brain and spinal cord and marrow
-of the bones) tend to become engorged with blood by its par-
tial expulsion from parts not thus protected. .
But the painful consequences of this unequal distribution of
blood under pressure are experienced only on letting the press-
ure suddenly off. None of the blood-vessels ean suddenly re-
sume their natural activity under natural conditions. All are
relaxed in tone and contractility, whether by the slackening or
the distension previous, and so on the release of the pressure
the blood flows languidly back from the. engorged vessels, and
the lately compressed vessels, though re-opened, carry it lan-
guidly onward, the effete blood clogs the capillaries, and while
everything is out of order the worst effects are felt from the
morbid action of the nervous centres which have suffered most.
change from blood. pressure and its sudden removal, owing.
to their bony incasements. IIence the excruciating neuralgic.
pains and sometimes fatal paralysis. It is curious but obvious
also that immediate relief from the sufferings is obtained by
re-entering the pressure, and the best preventive and cure, at
once, is to remove the pressure so gradually that the system
‘shall have time to accommodate itself to the change. It is im-
possible to allow time. enough for this in locking ont, but the
bad effect may be greatly mitigated by making the release of
pressure as slow’as consistently may be; so much so, in fact,
as to prevent serious consequences in almost if not all cases of
persons well adapted to the work. Dr. Smith. proposes that
‘the hospital preparations for future caisson work should include
compressed air baths, or air chambers so arranged that patients
may be run into them horizontally on a wheeled couch, and
_may lie there in’a pressure at first suited to relieve the symp-
toms, but which shall be diminished at such exceedingly slow
rate as shall make the transition to the ordinary atmospheric
pressures quite imperceptible. He also suggests that the com-
mon experience of neuralgic pains and other symptoms at the
approach of a storm may be due, not to the dampness to which
it is commonly attributed, but to the sudden diminution of ba-
rometric pressure, analogous to the change from caisson press-
ure to that of the ordinary atmosphere, and though slight, in-
deed, severely affecting extremely sensitive nerves.
The poisonous effects of the great amount of. carbonic acid
evolved by respiration and combustion in the caisson were coun-
teracted at New York by supplying a considerable excess of
compressed air, which escaped under the sides of the caisson
‘making the deep to boil like a pot” around the sides of the
descending pier. The soot. from the lights was removed by
placing funnels over them connected with small tubes opening
into the atmosphere, with, of course, a powerful current out.
ward, carrying off the impurities thoroughly. a
_ The action of the compressed air upon fire in the wood-work
of the Brooklyn caisson was curiously intense. A few fibres
of the timber were charred by contact with the flame of a la-