CURIOSITIES OF VENTILATION.
The only air-shaft on the Comstock lode worthy of the name, is that of
the Belcher Mining Company. In many situations air-shafts do not seem to
be required, connections with the main working shafts of other mines
serving the same purpose. In some places along the lode are old
shafts—sunk in the early days—with which connection has been made, and
these often do very good service as air-shafts. The air-shaft of the
Belcher Company is sunk at a point about 100 yards to the northward of
their main hoisting-works.
The size of the excavation made in the rock is 8×14 feet. This, when
timbered up, gives two compartments, each 6×6 in size. Where the rock is
hard and perfectly solid the shaft is cribbed with timbers 6×12 inches
in size; but where it is soft and inclined to swell, it is timbered in
sets; timbers 12 inches square being used. All of this work is done in
the most substantial manner possible. From the surface to the 1000-foot
level the shaft is carried down vertically, but from this point it is on
an incline corresponding to the dip of the ledge, which is about 36
degrees, and to the east. The portion of the shaft which is carried down
on an incline was kept in the west country rock lying back of the ledge.
The object in keeping in this rock was to avoid ground that would be
liable to swell and then crush in the sides of the shaft.
This shaft is of the same size and is constructed after the same plan as
that destroyed by fire, October 30, 1874, by which accident a large
number of men were badly burned, and some lost their lives. It extends
down to the lowest levels of the mine and will be continued downward as
new levels are opened. In excavating the shaft, work was begun at the
same time on the surface and down at the 850-foot level of the mine—the
men below digging upward while those above were sinking.
The shaft is “downcast,” that is, the air from the surface of the earth
is drawn or sucked down into it and finds its way out through the main
working shaft and other shafts connecting with the mine by means of
drifts. The first shaft was also a “downcast,” but when on fire, the
draught was changed, and a column of flame darted upward from its mouth
a hundred feet into the air, with a roar that could be heard at the
distance of a mile or more. Had not the shaft caved and filled up with
rock after the timbers were burned out of it, it would always have
remained an “upcast;” at least, so say all the old miners.
Here it may not be out of place to speak of some of the curiosities of
ventilation.
The Yellow-Jacket shaft, previous to the great fire in that mine some
years ago, had a strong draught downward; the fire changed the draught,
and it has ever since remained an “upcast.” This is a curious freak of
nature which all old miners have observed. When once the change in the
draught takes place it is permanent. A curious thing in ventilation—and
it is a nut for the scientists to crack—is that everywhere along the
Comstock lode the tendency of all currents of air is to the southward—in
the same direction that the ore chimneys tend. Here certainly is at work
another mysterious force of nature. This tendency of the air-currents to
move southward has never been overcome, except in one or two instances,
and these exceptional cases will presently be mentioned. There are some
queer courses taken by currents of air when once they have descended
beneath the surface of the earth, which none of our scientific men have
attempted to explain. The commonly accepted theory is that when two
shafts are connected by means of a drift, the draught or ascending
current of air will be through the higher shaft—the longer branch of the
siphon—but exactly the reverse is seen if the short shaft happens to
stand to the southward of the long one.
The air will even go down a shaft and crawl out through a tunnel when
that tunnel runs in a southerly direction! When the Union tunnel
connected with the old Ophir mine the air did not draw through the
tunnel and pass up and out through the main shaft, but came out of the
mouth of the tunnel. When the old Best and Belcher works connected with
the Gould and Curry tunnel, the same thing was seen—the air went down
the shaft and passed out at the mouth of the tunnel. About the next
connection of the kind made on the lead was between the Crown Point and
Belcher, at the depth of 160 feet; and the current of air went down the
higher shaft, moved southward, and came out at the Belcher. Next the
Yellow-Jacket and the Crown Point connected, and the draught was
southward to the Crown Point. The Alpha and the Imperial next connected,
and the draught went south to the Jacket. When the Gould and Curry and
the Savage connected, the draught went south to the Savage. When
connection was made between the Ophir and the Consolidated Virginia, the
air went south to the Consolidated. The only places I know of on the
lead where the air moves to the northward are between the Gould and
Curry and the Consolidated Virginia, and between the Hale and Norcross
and the Savage, and here it probably would not move north but for strong
inducements.
The latest instance of this tendency of currents of air to move
southward in mines is seen in the Overman mine. When that mine was
connected with the Belcher, the draught was southward, out through the
Overman shaft, though it stands much lower than any of the shafts
connected with the Belcher mine.
From the facts given, it will be seen that there are some curious things
connected with the ventilation of mines, and that it is not altogether
impossible that Sutro’s big tunnel may draw backwards, when completed.
A great deal of machinery is now beginning to be used on the lower
levels of the principal mines on the Comstock. Some years ago
steam-engines were set up in the lower levels of some of the leading
mines, with boilers, furnaces, and all, just as on the surface. This
would not do. The heat of the furnaces, boilers, and steam, added to the
heat of the mine, could not be endured by the engineers and others whose
duty it was to “stand watches” about the machinery.
A few years since an engine was set up on the 1000-foot level of the
Gould and Curry mine, and steam was conducted to it from boilers
situated on the surface. When this engine was started up there was a
popping of champagne corks away down there in the bowels of the earth,
and a good time was had drinking to the success of the experiment. But
it was not a success after all—it wouldn’t do. The ground began
swelling, the timbers were crushed and twisted, the engine bed could not
be kept level three days at a time—it was like a boat in a rough sea,
now on this end, and now on that—and the experiment was a failure.
The latest attempt to use steam machinery underground was at the Ophir
mine. A boiler and engine were set up on the 1465-foot level, near the
main shaft, up which was extended a sheet-iron smoke-stack reaching to
the surface. This engine was used in sinking a winze (situated 365 feet
to the eastward) to the 1700-foot level, and also in doing some work on
the level last named. The furnace and boiler heated up the level to such
a degree that it was “killing” to the men. The boiler still stands where
it was set up, but is now used as a reservoir for compressed air.
The introduction of engines and machinery to be run by means of
compressed air, was a grand forward stride in the science of mining.
In the Consolidated Virginia and California mines are to be seen at work
a number of small engines that are run by compressed air, furnished by
two powerful compressors that are constantly in operation on the
surface. The air is carried down the main shaft in a large iron pipe,
and from this smaller pipes branch off in all directions, and are
carried along the roofs of the drifts and cross-cuts, as we see
gas-pipes running through buildings in the upper-world.
Thus is the compressed air carried down into all parts of the mine where
work is being done. In places we see small engines at work at the top of
winzes, where they do all the hoisting, and effect a great saving of
both money and muscle. At other points, in passing along a drift, we
suddenly come upon a small chamber constructed on one side, and sitting
in this we see a “cunning” little engine, industriously at work at
running a blower (a machine such as we see in foundries for furnishing a
blast to the cupola, where metal is melted), which blower is sending a
stream of fresh air through a pipe to men working in some far-away,
heated cross-cut or upraise.
There are quite a number of these little engines and blowers in various
parts of the mine, and instead of heating they greatly assist in cooling
those parts of the mine in which they are used.
As the drifts and cross-cuts are advanced, the air-pipes are carried
along their roofs or sides, and are in readiness for use in running the
Burleigh drills, by means of which the holes are drilled in the face of
the drift where the rock requires to be blasted. The air-pipes being in
place in all the cross-cuts and drifts, the Burleigh drill may be moved
about from place to place as required, and thus a single drill can be
used in several different drifts during the day. When a sufficient
number of holes for blasting have been made in one drift, the drill is
placed upon its carriage and is moved along the car-track to another,
where connection is made with the air-pipe, and it is hammering away
again with but little loss of time.
In the Ophir mine a small engine, situated at the winze mentioned above
as being 365 feet east of the main shaft, does all the hoisting from the
1700-foot level, and in a more satisfactory manner in every respect than
the same work was formerly done by the old steam-engine. On the
1150-foot level of the Consolidated Virginia mine a winze was sunk to
the depth of 140 feet, with one of these little air-engines, and it
could have been sunk to any depth required, but for an influx of water
which was too strong to be contended with in that remote part of the
mine at that time.
Each year more and more machinery will be run in the mines of the
Comstock, by means of compressed air. It is exactly what is needed, as
all the air exhausted in the lower levels of a mine is beneficial and is
so much ventilation and so much food gained for the lungs of the miners.
Compressors, and machinery to be worked by them, are being ordered by
all of the leading mines, and are already considered indispensable
appliances in modern mining.