San Antonio daily light. [volume] (San Antonio, Tex.) 1886-1907, 1893-12-21

| ing a previously arranged period
no train was dispatched be-
fore reliable Information was re-
ceived that the track was clear
Each working gang was covered
| by electric lights or torches
While the maintenance OF travel
impeded the work, the available
track was an advantage in facili.
tating the handling of material,
and the continuous down grades
from both ends of the long tunnel
were used for gravity tracks. The
original cost of the st. Gothard
Railway was $4S,O00.00O Of which
$12, 100000 were spent for the
great tunnel, so the expenditure Of
100000 for double tracking APP
pears quite reasonable.
Electric forging is now pretty
we'll known to people interested
in mechanical matters, but some
recent improvements in the pEo-
cess may not be so familiar. AS
now carried out the plant re-
quired comprises an alternating
current dynamo and a transformer.
The dynamo gives a current OF
high voltage and small amperage,
the function of the transformer be-
ing to transform the current into
one Of large volumns and low
voltage. The reason for this is APP
parent on considering the heating
effect of two common balls shot
against a metal plate. A little one
shot at a high velocity will go
through the plate without heating
it very much, but larger one
fired at a lower velocity will be
stopped by the plate, which be-
comes considerably heated in so
doing. Velocity in the balls cor
responds to voltage in the current
and amperage to weight, conse-
quently for electric welding it is
desirable to use many amperes at
a low voltage in order to get the
desired heating properties. But as
the bar to be welded becomes hot
ter the voltage necessary to drive
the current through it increases,
and it becomes requisite to use a
current Of greater intensity. To
be satisfactory this adjustment Of
the voltage to the temperature of
the heated bar must be automatic,
and after some years spent in eX-
perimenting with a large number
of devices it has been found that
good method lies in a special way
Of winding the wires on the dyna-
mo, which make it give out just
the right kind Of a current for the
work.
A bridge is now in course Of
erection across the Missouri River,
between East Omaha and Council
Bluffs, which will be remarkable
when completed as possessing the
longest span in the world-52O
feet-being Is feet longer than the
the swing span of the bridge over
the Thames River, in Connecticut.
The structure has been designed
by Prof. J. A. L. Waddell, Of Kan
sas City. The construction Of the
pier Of this swing span was COM
pleted few months ago and pre-
scented many features Of interest
to engineers. From a long article
in Engineering News it appears
that the work was begun by sink
ing a steel caisson for foundation
such as A. p. Boiler started work
on the swing span Of large bridge
in New York City a year ago.
The outer shell of the casson
is 40 feet in diameter and the
inner 20 feet, the latter spreading
out at the base to join the former
and thus give a cutting edge. Both
shells are made of half-inch steel,
| reinforced at the lower edge, where
they meet, by two bands of inch
| steel, one inside and the other out
| side. The two shells were kept in
their proper relative positions by
braces running between them, OF
which there were twenty in all
made of half-inch plates. The
caisson proper is l6 feet high. Above
this the two steel cylinders extend
to a height of 100 feet, making q
total OF lie feet from the cutting
edge to the top of the cylinder
Above the caisson the plates are re
duced in thickness to three-eighthE
of an inch, and are braced by bars
and rods rather than the heavier
and more costly plates required il
the lower part. The friction Of thu
earth against such long cylinde
is very great, and to reduce it ;
number of pipes run down tn
whole length of the caission ant
shell. These open at the bottom o
the caission and at intervals Of i
feet above. SO that by forcing waite