ecedence
over all others on account of their combined moderate capital outlay,
great flexibility, and reasonable efficiency.

In late years, direct-coupled, electric-driven centrifugal pumps
have entered the mining field, but their efficiency, despite makers'
claims, is low. While they show comparatively good results on low
lifts the slip increases with the lift. In heads over 200 feet
their efficiency is probably not 30% of the power delivered to the
electrical generator. Their chief attractions are small capital
cost and the compact size which admits of easy installation.

ROD-DRIVEN PUMPS.--Pumps of the Cornish type in vertical shafts,
if operated to full load and if driven by modern engines, have
an efficiency much higher than any other sort of installation,
and records of 85 to 90% are not unusual. The highest efficiency
in these pumps yet obtained has been by driving the pump with rope
transmission from a high-speed triple expansion engine, and in
this plant an actual consumption of only 17 pounds of steam per
horse-power hour for actual water lifted has been accomplished.

To provide, however, for increase of flow and change of horizon,
rod-driven pumps must be so overpowered at the earlier stage of
the mine that they operate with great loss. Of all pumping systems
they are the most expensive to provide. They have no place in crooked
openings and only work in inclines with many disadvantages.

In general their lack of flexibility is fast putting them out of
the metal miner's purview. Where the pumping depth and volume of
water are approximately known, as is often the case in coal mines,
this, the father of all pumps, still holds its own.

HYDRAULIC PUMPS.--Hydraulic pumps, in which a column of water is
used as the transmission fluid from a surface pump to a corresponding
pump underground has had some adoption in coal mines, but little
in metal mines. They have a certain amount of flexibility but low
efficiency, and are not likely to have much field against electrical
pumps.

BAILING.--Bailing deserves to be mentioned among drainage methods,
for under certain conditions it is a most useful system, and at
all times a mine should be equipped with tanks against accident
to the pumps. Where the amount of water is limited,--up to, say,
50,000 gallons daily,--and where the ore output of the mine permits
the use of the winding-engine for part of the time on water haulage,
there is in the method an almost total sa