have a less average
duty, averaging from 15 to 25 feet per shift.

[Footnote *: Over the year 1907 in twenty-eight mines compiled
from Alaska to Australia, an average of 23.5 feet was drilled per
eight-hour shift by machines larger than three-inch cylinder.]

MACHINE _vs_. HAND-DRILLING.--The advantages of hand-drilling over
machine-drilling lie, first, in the total saving of power, the
absence of capital cost, repairs, depreciation, etc., on power,
compresser and drill plant; second, the time required for setting
up machine-drills does not warrant frequent blasts, so that a number
of holes on one radius are a necessity, and therefore machine-holes
generally cannot be pointed to such advantage as hand-holes. Hand-holes
can be set to any angle, and by thus frequent blasting yield greater
tonnage per foot of hole. Third, a large number of comparative
statistics from American, South African, and Australian mines show
a saving of about 25% in explosives for the same tonnage or foot
of advance by hand-holes over medium and heavy drill-holes.

The duty of a skilled white man, single-handed, in rock such as
is usually met below the zone of oxidation, is from 5 to 7 feet
per shift, depending on the rock and the man. Two men hand-drilling
will therefore do from 1/4 to 2/3 of the same footage of holes
that can be done by two men with a heavy machine-drill, and two
men hand-drilling will do from 1/5 to 1/2 the footage of two men
with two light drills.

The saving in labor of from 75 to 33% by machine-drilling may or
may not be made up by the other costs involved in machine-work.
The comparative value of machine- and hand-drilling is not subject
to sweeping generalization. A large amount of data from various
parts of the world, with skilled white men, shows machine-work
to cost from half as much per ton or foot advanced as hand-work
to 25% more than handwork, depending on the situation, type of
drill, etc. In a general way hand-work can more nearly compete
with heavy machines than light ones. The situations where hand-work
can compete with even light machines are in very narrow stopes where
drills cannot be pointed to advantage, and where the increased
working space necessary for machine drills results in breaking more
waste. Further, hand-drilling can often compete with machine-work
in wide stopes where long columns or platforms must be used and
therefore there is much delay in taking down, reerection, etc.

Many other fac