centage of recovery
which will yield the most remunerative result, if any. This limit to
profitable recovery regulates the amount of metal which should be
lost, and the amount of metal which consequently must be deducted
from the gross value before the real net value of the ore can be
calculated. Here, as everywhere else in mining, a compromise has to
be made with nature, and we take what we can get--profitably. For
instance, a copper ore may be smelted and a 99% recovery obtained.
Under certain conditions this might be done at a loss, while the
same ore might be concentrated before smelting and yield a profit
with a 70% recovery. An additional 20% might be obtained by roasting
and leaching the residues from concentration, but this would probably
result in an expenditure far greater than the value of the 20%
recovered. If the ore is not already under treatment on the mine,
or exactly similar ore is not under treatment elsewhere, with known
results, the method must be determined experimentally, either by
the examining engineer or by a special metallurgist.

Where partially treated products, such as concentrates, are to be
sold, not only will there be further losses, but deductions will
be made by the smelter for deleterious metals and other charges.
All of these factors must be found out,--and a few sample smelting
returns from a similar ore are useful.

To cover the whole field of metallurgy and discuss what might apply,
and how it might apply, under a hundred supposititious conditions
would be too great a digression from the subject in hand. It is
enough to call attention here to the fact that the residues from
every treatment carry some metal, and that this loss has to be
deducted from the gross value of the ore in any calculations of
net values.

PRICE OF METALS.

Unfortunately for the mining engineer, not only has he to weigh
the amount of risk inherent in calculations involved in the mine
itself, but also that due to fluctuations in the value of metals.
If the ore is shipped to custom works, he has to contemplate also
variations in freights and smelting charges. Gold from the mine
valuer's point of view has no fluctuations. It alone among the
earth's products gives no concern as to the market price. The price
to be taken for all other metals has to be decided before the mine
can be valued. This introduces a further speculation and, as in
all calculations of probabilities, amounts to an estimate of the
amount