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passed direct into the returns, each panel of gob
having its own over-cast.
(h) The initial velocity, at the point of distribution
to working places, should be sufficient
to allow some scaling without leaving any place
in the district dangerously deficient in air.
Where safety lamps are used, the knowledge
that the Clanny lamp, bonneted as commonly done
in Pennsylvania, is not safe at fifteen feet per
second in an explosive atmosphere, should enter
into a mine foreman's calculations on splitting.
(i) In working roads and return airways, air
should circulate over any cribbing, and when lag­
ging is used, air should invariably oe scaled over
it.
DISCUSSION.
MR. SAMUEL DIESCHER, Mem. Eng. So. W. Pa —
What gains are there from employing fans instead
of the furnace?
MR. F. Z. SCHELLENBERG, Mem. Eng. So. W. Pa.—
I understand with shallow working the fan is
certainly the best. In deep working the furnace
is efficient and in such great mines it is yet doing
the work. There are the benefits of the underground
heat and ot the heated column, but even
there the fan is economical, it is contended. In
Belgium, on mines a thousand meters deep, the
fan is used. The furnace uses more coal and
there is the danger from firing the strata.
MR. SAMUEL DIESCHER—Is it not possible to
direct the air better with a fan than with furnaces?
Is it not of more positive action than the furnace?
THE COAL TRADE BULLETIN. 33
Fan With liuibal Chimney and Shutter.
MR. WILLIAM CLIFFORD—You have better control
of the air with a fan than with a furnace because
you can more quickly increase, or diminish, the
speed and consequently the volume of air circulating,
and with the fan it is generally possible
to increase the ventilating pressure beyond the
capacity of a furnace of large size even in the
deepest shaft mines.
MR. SAMUEL DIESCHER—If we have a mechanical
device by which we can oring air to a certain
pressure, we can direct the air through flues or
tubes to any point we desire, as long as we have
the power. With a furnace the energy impelling
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the air currents cannot well be as high as with
the emplo> ment of mechanical means, in which
case we can give the air almost any velocity,
whereas the efficiency of a furnace depends on the
height of the stack, or flue, and the difference of
temperatures between the air in the mine and that
in the stack.
MR. F. Z. SCHELLENIIERG—Is not this nigh water
gauge concomitant with a restricted air passage?
MR. WILLIAM CLIFFORD—Yes, that is what makes
the high water gauge.
MR. SAMUEL DIESCHER—Supposing we have a
long flue through which we drive air. In order
that we can deliver a certain quantity of air at
the far end, we make a very wide flue and apply
the necessary pressure to overcome the friction,
whereas with the furnace, the friction may be so
great as to consume nearly all the energy produced
by the furnace because the furnace acts by
suction.
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