CONCERNING VENTILATION.
Although something has already been said of the ventilation of mines and
of subterranean water, I shall now devote a chapter or two to these
matters, else they may not be thoroughly understood.
The proper ventilation of a mine is a matter of the first importance.
Without ventilation no mine can be worked. Without ventilation the whole
mine, even to the mouth of the shaft, would be filled with stagnant and
foul air, in which men could not live for half a minute. No mine can be
worked unless air from the surface of the earth is introduced into it.
It is even impossible to sink a straight shaft to the depth of one
hundred and fifty or two hundred feet—all the circumstances being the
most favorable possible—without carrying fresh air down to the men
working in its bottom. When mining was first begun on the Comstock,
wind-sails were used to carry air down into the shafts. This is a
contrivance of cotton-cloth, and is a cross between a sail and a bag.
The mouth of the baggy sail is turned to the wind, and when it fills,
air is forced down a tube that leads from its lower end. Sometimes air
was forced into a shaft by means of a common blacksmith’s bellows—slow
and hard work. When water and a proper amount of fall can be obtained, a
water-blast is sometimes used. In this the water falling through a tube
carries down with it and forces into the shaft or mine a certain amount
of air.
At the present time, however, the only manner in which air is forced
into mines is by means of rotary blowers or fans—precisely the same as
those used at the foundries for furnishing a blast to the cupolas in
which iron is melted. At all of the mines along the Comstock these
blowers are seen in operation. The best, cheapest, and most thorough
means of ventilation is by making connection with the shaft of an
adjoining mine. The moment such connection is made, the air from the
surface goes down one shaft and comes up the other. In passing to the
shaft through which it again rises to the surface, the air, of course,
takes the most direct route, yet a great volume of pure air is
introduced into the two mines. By means of doors fitted to the
connecting drifts between the two mines, the air thus introduced may be
distributed pretty evenly through the principal levels, as it can be
made to circulate at a considerable distance from what would be its
direct and natural route.
In all mines, however, there are always drifts, cross-cuts, winzes, and
upraises in remote places to which it is impossible to convey the air
circulating in the body of the mine. To provide a supply of air at these
points the blowers are used. They send a column of air down into the
mine through a large iron pipe, and on the several levels are smaller
pipes which convey it to where it is required. In many of the mines
there are small blowers on the lower-levels that are run by engines
driven by compressed air. These are very useful in furnishing a supply
of air in out-of-the-way places.
It is not only necessary to furnish pure air for the miners to breathe,
but fresh air is required in great volume to cool off the rock and keep
down the heat in the drifts and cross-cuts of the lower-levels. As the
shafts and inclines increase in depth there is a constant and
corresponding increase of heat in the rocks into which the works are
advanced. At the depth of from 1,500 to 2,000 feet the rock is so hot
that it is painful to the naked hand. In many places, from crevices in
the rock, or from holes drilled into it, streams of boiling water gush
out. In these places the thermometer often shows a temperature of from
one hundred and twenty to one hundred and thirty degrees. It is as hot
as in the hottest Turkish bath. In these places men could not live but
for the supply of cool air that is pumped into the drift or other place
in which they are at work; even then the temperature often remains as
high as one hundred and ten degrees. The rock in a newly opened level
retains its heat for months, however much air may be brought into the
mine. Nearly all the leading mines on the Comstock are down to where the
rock is exceedingly hot. The Crown Point and Belcher Companies are down
1,700 feet; Yellow-Jacket, 1,740; Bullion, 1,700; Imperial-Empire,
2,100; Gould & Curry, Best & Belcher, Consolidated Virginia, and Ophir,
each 1,700; while the Savage Company are down nearly 2,300, and the Hale
& Norcross, about 2,200. In the two mines last named they find it
fearfully hot. As the Savage Company have started up machinery capable
of sinking to the depth of 4,000 feet, they will presently be in danger
of dropping into the great central fires of the earth.
As depth is attained it is found necessary to increase the size and
capacity of the blowers used and the main pipes through which the air is
forced into the mines have now been increased to about two feet in
diameter, whereas the diameter of those first used was only about six
inches. With a small pipe the air backs up on the blower and there is a
waste of power. The pipe should be so large that there is no longer any
perceptible back-pressure—so large that all the air blown into it finds
an abundance of room in which to advance without encountering the
resistance of its own elasticity. The pipes should be enlarged until the
air goes through without any rebounding.
It is a question in many minds whether the miners of Nevada have gone
the right way about the ventilation of their mines; whether instead of
forcing air into the lower-levels they should not pump the foul and
heated air out, when pure air would rush down and fill the vacuum thus
created. In the mines of Germany they practice this plan of pumping out
the foul air. In Nevada, however, it is not likely that it would answer
so good a purpose as the plan of pumping in fresh air. By blowing in air
as is now practiced there is always more or less good air at the face of
a drift about the end of the pipe, but by the pumping-out plan the air
surrounding the end of the pipe would be sucked into it, and that which
would reach the men would be such as flowed a long distance in contact
with the heated rock forming the walls of the cross-cut or drift.
American miners work so fast that the rock does not have much time in
which to cool behind them. Therefore the better plan for them seems to
be the reverse of that practiced in the Old World.
It remains to be seen what effect the Sutro Tunnel will have in creating
a circulation of air in the lower-levels of the mines when it shall have
been completed. This tunnel, about which so much has been said in
Congress and elsewhere, starts at the edge of the valley of the Carson
River, in a southeasterly direction from Virginia City, and is intended
to tap the Comstock lode at the depth of 200 feet. Its total length will
be 20,145 feet. Work was commenced on it in October, 1859, and it has
now been extended a distance of between nine and ten thousand feet.
About 1,100 feet of the tunnel, from the mouth in, has been made of full
size, twelve by sixteen feet; the remainder, what is called the header,
is six by seven feet in size.
There are along the line of the tunnel, which runs under several
mountains of considerable size, four shafts. These were designed to be
sunk down to the level of the tunnel, when work on the tunnel might be
prosecuted in two directions from the bottom. Shaft No. 1 is located at
a distance of 4,915 feet from the mouth of the tunnel; shaft No. 2,
9,065 feet from the mouth of the tunnel; No. 3, 13,545 feet from the
mouth of the tunnel; and shaft No. 4, 17,695 feet from the same point,
and 2,450 feet from the point where the tunnel will intersect the
Comstock lode. Shafts Nos. 1 and 2 are down to the level of the tunnel
and work has been done through them. Shaft No. 1 is 523 feet, and shaft
No. 2, 1,041 feet in depth. Shafts Nos. 3 and 4 are not yet down to the
level of the tunnel, the “header” of which is progressing between shafts
Nos. 2 and 3. When the tunnel shall have been completed, there will be a
connection between the Comstock lode and shaft No. 4 through which there
will be a circulation of air. This shaft (No. 4) will be 1,485 feet in
depth, and when the connection is made the air will either pass down it,
along the tunnel a distance of 2,450 feet and out through the mines at
the point of intersection, or will pass down through the mines and out
through the shaft. Which way the draught will be, no man can say, as the
course of currents of air underground is governed by laws not yet well
understood. Whichever way the draught may be, however, there will be a
great improvement in the circulation of the air in the lower-levels of
the adjacent mines, to the depth of 2,000 feet.
However diligently work may be prosecuted on the Sutro Tunnel, it must
be some years yet before it can be completed to the point of
intersection with the Comstock lode. Meantime there is being sunk at the
distance of about 2,000 feet east of the lode, and about 450 or 500 feet
west of shaft No. 4 of the Sutro Tunnel, a shaft which will be the
largest and most perfect in every respect ever sunk in that country.
This shaft is being sunk by a combination of three leading mining
companies—the Chollar-Potosi, Savage, and Hale & Norcross. It will be
ten by thirty feet in size, divided into four compartments by stout
plank partitions, and the machinery placed over it will be of a capacity
to sink it to the depth of one mile.
Rapid progress is being made in the sinking of this great shaft. At
proper intervals drifts will be run from it to the Comstock lode. The
first drift will probably be run at the depth of 2,000 feet, and it will
reach the lode long before the completion of the Sutro Tunnel, and as
regards ventilation, will do all that could be expected of the tunnel.
As two or three of the leading mines are already working at a depth of
nearly 2,500 feet, the big shaft must be looked to for ventilation
everywhere below the depth of 2,000 feet; therefore below this depth
drifts will doubtless be run between the lode and the shaft at frequent
intervals.
Owing to the lead dipping to the east at an angle of from thirty to
fifty degrees, the distance necessary to be run to connect the lode and
shaft will constantly decrease until at a certain depth the shaft itself
will cut the lead, after which time the drift to reach and ventilate the
vein must be run to the eastward. A branch-track connects this shaft
with the main Virginia and Truckee Railroad.