Year: 1874

When an upcast or air-shaft il sunk into
mine, the first thing prepared by the
manager is the erection Of huge wooden
box, thirty or forty feet in height, over the
top Of the shaft, with the object Of assisting
the ventilating current of air. Now, it
may startle great many people who pro-
fess to know something of ventilation to
state that such structure, instead of as
sistlng, only retards the force of the circu-
latlng stream of air at the very time of the
year when weak current is prevalent
that is, where artificial force is used t.
move air. In summer, when the air of the
mine is cooler and consequently denser
than the atmosphere above ground, the
higher opening is the natural "downcast,
and any addition to the height of this
shaft simply creates a stronger force of air
dOIcnl1ards, which force has 70 be overcome
by artificial power to make it an upcast at
all. And this is equally true Of the fur
mace. Instead Of being placed at the bot
tom Of the higher opening in summer, it
should invariably be at the lower, to assist
the natural forces. A mine would be bet
ter ventilated all the year round if the
furnace were always at the bottom of the
lowest opening. In winter it need not be
in use at all, and would be OF no use at al
in winter at the lower opening. as its heat
could not overcome the natural forces un-
less there were a very strong fire in constant
operation.


In deep mines, however, such as those
of England and Belgium, where the natu-
raj heat of the strata is greater at all sea
sons of the year than the summer heat
above ground, the higher opening is always
the upcsst, and any increased height Of
column in the erection of a wooden or
other artificial structure over the upcast is
Of service. the higher the better, as it adds
to the difference Of density Of the two col
umns, and consequently increases the force
of the current.


Shallow mines are more difficult Of ven
tilation than deep mines, while mines
which are comparatively new-that is,
where the excavations are yet of a limited
area-are more easily ventilated than
mines whose workings extend far under
ground.


The power Of a furnace increases in pro
portion to the depth of the air-shaft (pro-
vided the furnace is placed to assist the
natural forcesl, the power increasing in
proportion to the ratio Of depth but the
air, in its passage along long and sinuous
galleries, is obstructed by the friction or
resistance Of the sides, top and bottom of
the air-ways


1t is generally supposed that drift mines
need less attention as to ventilation than
shafts. This is true only when drifts are
opened in the 1anks of hills having high
covers, in which deep air-shafts are sunk.
because the difference of height of the
two openings increases the difference of
density of the air ; but if the two openings
are on or near the same level there can be
no circulation in the spring and fall-those
seasons when the mine air and that above
ground approach each other in density
Drift mines have frequently three and four
openings, which are claimed TO make the
ventilation more perfect. Now, it happens
that this is very frequently positive re-
tarding Of the air currents, as the shorter
routes steai from the longer ones, and, if
the circulation be languid, stop their move
ment altogether.


Unless mine managers and colliery pro
prietors learn and act on these facts we
will never have good air in mines Eng
lish ideas are of no practical value in this
country, because the physical conditions
are essentially different. Four years
hence we will all understand this subject
better.