l,
mine shops can be easily overdone.

A number of machines are now in use for sharpening drills.
Machine-sharpening is much cheaper than hand-work, although the drills
thus sharpened are rather less efficient owing to the difficulty of
tempering them to the same nicety; however, the net results are
in favor of the machines.

IMPROVEMENT IN EQUIPMENT.

Not only is every mine a progressive industry until the bottom
gives out, but the technology of the industry is always progressing,
so that the manager is almost daily confronted with improvements
which could be made in his equipment that would result in decreasing
expenses or increasing metal recovery. There is one test to the
advisability of such alterations: How long will it take to recover
the capital outlay from the savings effected? and over and above
this recovery of capital there must be some very considerable gain.
The life of mines is at least secured over the period exposed in
the ore-reserves, and if the proposed alteration will show its
recovery and profit in that period, then it is certainly justified.
If it takes longer than this on the average speculative ore-deposit,
it is a gamble on finding further ore. As a matter of practical
policy it will be found that an improvement in equipment which
requires more than three or four years to redeem itself out of
saving, is usually a mechanical or metallurgical refinement the
indulgence in which is very doubtful.

CHAPTER XV.

Ratio of Output to the Mine.

DETERMINATION OF THE POSSIBLE MAXIMUM; LIMITING FACTORS; COST OF
EQUIPMENT; LIFE OF THE MINE; MECHANICAL INEFFICIENCY OF PATCHWORK
PLANT; OVERPRODUCTION OF BASE METAL; SECURITY OF INVESTMENT.

The output obtainable from a given mine is obviously dependent
not only on the size of the deposit, but also on the equipment
provided,--in which equipment means the whole working appliances,
surface and underground.

A rough and ready idea of output possibilities of inclined deposits
can be secured by calculating the tonnage available per foot of
depth from the horizontal cross-section of the ore-bodies exposed
and assuming an annual depth of exhaustion, or in horizontal deposits
from an assumption of a given area of exhaustion. Few mines, at the
time of initial equipment, are developed to an extent from which
their possibilities in production are evident, for wise finance
usually leads to the erection of some equipment and production before
development