The Middlebury register. [volume] (Middlebury, Vt.) 1850-1882, 1859-04-13

shafts at the same time, by as many gangs
Of workmen, This method, by providing
for great number of opera tors to execute
the work shortens its completion, and the
short run Of each gang in the tunnel ad-
mits of easy ventilation. Under high
mounta in, this system Of tunneling is i'm.
possible, because shafts cannot be sunk !;
therefore tunnel in such a situation can
only be bored from two points at once;
the termini a. each side,--On the Pied
mont Railroad, now being constructed
through the Alps, long tunnel of several
miles is required between Modane and
Bardoneche. 1t will pass 5000 feet be.
low the summit, and, of course, the sink
ing of shafts was impracticable in such
case, BY the common methods Of tun.
neling, it has been calculated that it would
require thirty.siz years to complete the
operations: and it was also held to be i'm
possible, by known means, to ventilato the
tunnel when it had attained to a great
depth, owing principally to the great
amount of blasting required, which would
vitiate the atmosphere.
Unless some new means wero devised
to overcome such difficulties, the execu-
ton of this great tunnel could and would
not have been undertaken. BY the inge-
nuity of three Sandman engineers, Messrs.,
Sommeiiler, Grattone, and Grandis, pro-,
vision was made for surmounting all these
obstacles. On the mountain, adjacent to,
the line, there was large stream of water
on fall of sizty.fve feet. This they ap.
piled to operate hydraulic motor, which
condenses air in o reservoir to the pressure
OF 90 lbs. on the square inch this is
conducted in an extension tube into the
tunnel, where it first operates machinery
which drives the drills. then ii escapes and
supplies the miners with fresh air, thus
performing two duties, namely, drilling
and ventilating. By this machinery
eighteen holes arc bored in the same space
required for six miners in drilling, and
each bole is bored in one.twelfth Of the
time taken up by hard labor. When it is
taken into consideration that three.iourths
of the time in tunneling is occupied in.
boring, the immense saving Of time by
these arrangements is obvious. With
such original application of condensed air
to tunneling it is calculated that this sub.
Alpine tunnel will now be completed at a
greatly reduced cost in six years--a very
great difference from thirty.six, by the
ordinary means Of boring.
In this tunnel some peculiar phenomena
of temperature are witnessed. The com.
mon heat of the air, at such depth, is
over 100 deg. Fab, too hot for the miners
to work comfortably, but this is modified
to pleasant temperature 10 degrees
Fah.-by the condensed air which is fed
into the machines. By the refrigerating
effects of the expansion, when the com.
pressed air at SO lbs. pressure escapes, it
absorbs heat from the surrounding air and
thus cools it down. This power of ab.
sorbing heat BY expansion is so great that
water placed close to the escape air valves
is CONCEALED into ice. A sufficient supply
of fresh air secured for the ventilation of
this tunnel at its greatest depth. No less
than IA, 800 cubic yards of six atmospheres
pressure can be furnished every twenty.
four hours. The progress now making in
excavating this tunnel from both sides is
nineteen feet per day. When completed
il will be one of the wonders Of the world.
The use of condensed air as motive
and ventilating power for tunneling power
should arrest the attention of engineers in
every part Of the world. On all noun.
tains where deep and long tunnels are to
be cut, there are usually high waterfalls,
which can be applied to drive a simple
turbine wheel, capable Of condensing air
in reservoir by working pumps, and this
air can be made to operate drilling ina.
chimes, and also to ventilate the tunnel las
in the ore described. The same use of
water power and condensed air is appli.
cable for mines in billy regions. To our
miners in the mountains of California and
those engineers who must at some future
day tunnel through the Rocky Mountains
in constructing Pacific railroad, the
foregoing information should be treasured
up and carried into practice when the ia.
vorable opportunities are presented. We
live in an age of wonders, and the boy