deg. this trough, laid
on the foot-wall, gives a sufficiently smooth surface for the ore
to run upon. When the dip is flat, the trough, if hung from plugs
in the hanging-wall, may be swung backward and forward. The use of
this "bumping-trough" saves much shoveling. For handling filling
or ore in flat runs it deserves wider adoption. It is, of course,
inapplicable in passes as a "bumping-trough," but can be fixed to
give smooth surface. In flat mines it permits a wider interval
between levels and therefore saves development work. The life of
this contrivance is short when used in open stopes, owing to the
dangers of bombardment from blasting.

In dips steeper than 50 deg. much of the shoveling into passes can be
saved by rill-stoping, as described on page 100. Where flat-backed
stopes are used in wide ore-bodies with filling, temporary tracks
laid on the filling to the ore-passes are useful, for they permit
wider intervals between passes.

In that underground engineer's paradise, the Witwatersrand, where
the stopes require neither timber nor filling, the long, moderately
pitched openings lend themselves particularly to the swinging iron
troughs, and even endless wire ropes have been found advantageous
in certain cases.

Where the roof is heavy and close support is required, and where
the deposits are very irregular in shape and dip, there is little
hope of mechanical assistance in stope transport.

CHAPTER XIII.

Mechanical Equipment. (_Continued_).

DRAINAGE: CONTROLLING FACTORS; VOLUME AND HEAD OF WATER; FLEXIBILITY;
RELIABILITY; POWER CONDITIONS; MECHANICAL EFFICIENCY; CAPITAL OUTLAY.
SYSTEMS OF DRAINAGE,--STEAM PUMPS, COMPRESSED-AIR PUMPS, ELECTRICAL
PUMPS, ROD-DRIVEN PUMPS, BAILING; COMPARATIVE VALUE OF VARIOUS
SYSTEMS.

With the exception of drainage tunnels--more fully described in
Chapter VIII--all drainage must be mechanical. As the bulk of mine
water usually lies near the surface, saving in pumping can sometimes
be effected by leaving a complete pillar of ore under some of the
upper levels. In many deposits, however, the ore has too many channels
to render this of much avail.

There are six factors which enter into a determination of mechanical
drainage systems for metal mines:--

1. Volume and head of water.
2. Flexibility to fluctuation in volume and head.
3. Reliability.
4. Capital cost.
5. The general power conditions.
6. Mechanical efficiency.

In the drainage appliance