Year: 1870




Democrat gives the following
graphic description of how Colo
mel Eads is sinking the great iron
caissons for the piers to the bridge
across the Mississippi at that city:


Two immense piers are to be
constructed in the river, of solid
stone masonry. These piers, to
be substantial, must rest on the
solid rock that lies fifty, sixty or
Il hundred feet under the sand,
under the water Of the rushing
river. The question was, how to
get down all these feet through
water and sand, to tind the rock
to lay. the solid foundation. One
way would have been to build
Golfer dams, and pump out the
water, dig out the sand, and lay
the piers in the empty space. But
this was impracticable, if not inn
possible, and MIR. Eads' science
and wisdom selected anotherplan,
which, though not original with
him, has been greatly improved
on by him, and applied more SEN
sibly and effectively than it was
ever done before. This plan was
to build within a caisson, till the
rock was reached and the pier
completed, and to make this COM
! prehensible to every child it shall
be illustrated very simply.


ILLUSTRATION. OF THE SINKING
| CAISSON.


| Did you ever hold a goblet bot
tom side up, and press it down
into q vessel Of water? If you
have you know the water does
not enter into the empty tumbler,
but the air in it keeps the water
out, and as you sink it and press
it down it drives the water UP the
sides of the vessel. Now suppose
instead Of the goblet you hold all
inverted metallic vessel in the
same way, the same facts would
! the inside of it. If the bottom of
this inverted vessel were fiat, you
could put a brick on it, and an
other, and another, until you have
weighed enough to sink it to the
bottom of the water, when you
have a pier of bricks. Now this
| is exactly what Colonel Eads has
done in building the eastern pier
Of the bridge. But his inverted
"plan'' is of the size he wishes the
bottom Of the pier to be, and is
forty. fifty, or sixty feet across,
as the case may be. OF course
this immense ssiron dish,'' bottom
| side UP, was held in position on
the water by machinery. He then
| laid solid courses Of stone masonry
on the ''dish'' or sscaisson, and as
he built, the weight pressed it
hasreached the bottom of the river,
and even six feet into the sand,
and the pier is forty Or fifty feet
high. But it has yet to sink fifty
or sixty feet further to meet solid
rock, and the sand cannot be dis
placed as the water was, but must
be removed by artificial means,
and this is what is] being success
fully done now. Of course, as
the sand is dug away from under
| the sides of the caisson it will
sink just as fast. To dig this
away men must get into the cup
turned dish'' or "caisson," or s'air-
chamber under the pier, and
work there. We will explain how
this is done.


| ENTERING THE AIR-CHANIBER.


Everyone will understand that
the air in the chamber must be
very much condensed, and that
most essential requisite is that
it must be kept SO, and not allow
ed to escape. If a direct opening
were made to it anywhere, the
escape of air would cause the
water and sand to wash in from
underneath, the vacuum would
beinstantlyf filled, and there would
be the end of sinking the
caisson and pier. Colonel Eads
has arranged a very simple and
perfect way Of entering this cham
Der, which is now six or eight feet
lower than the bottom of the riv-
er, and yesterday we went down
into it and saw the men at work.