s a basis, and subtractions and additions made for more
unfavorable or favorable effect of the differences in the above
items, a fairly close result can be approximated.

Mine examinations are very often inspired by the belief that extended
operations or new metallurgical applications to the mine will expand
the profits. In such cases the paramount questions are the reduction
of costs by better plant, larger outputs, new processes, or alteration
of metallurgical basis and better methods. If every item of previous
expenditure be gone over and considered, together with the equipment,
and method by which it was obtained, the possible savings can be
fairly well deduced, and justification for any particular line
of action determined. One view of this subject will be further
discussed under "Ratio of Output to the Mine." The conditions which
govern the working costs are on every mine so special to itself,
that no amount of advice is very useful. Volumes of advice have
been published on the subject, but in the main their burden is
not to underestimate.

In considering the working costs of base-metal mines, much depends
upon the opportunity for treatment in customs works, smelters,
etc. Such treatment means a saving of a large portion of equipment
cost, and therefore of the capital to be invested and subsequently
recovered. The economics of home treatment must be weighed against
the sum which would need to be set aside for redemption of the
plant, and unless there is a very distinct advantage to be had by
the former, no risks should be taken. More engineers go wrong by
the erection of treatment works where other treatment facilities
are available, than do so by continued shipping. There are many
mines where the cost of equipment could never be returned, and
which would be valueless unless the ore could be shipped. Another
phase of foreign treatment arises from the necessity or advantage
of a mixture of ores,--the opportunity of such mixtures often gives
the public smelter an advantage in treatment with which treatment
on the mine could never compete.

Fluctuation in the price of base metals is a factor so much to be
taken into consideration, that it is desirable in estimating mine
values to reduce the working costs to a basis of a "per unit" of
finished metal. This method has the great advantage of indicating
so simply the involved risks of changing prices that whoso runs
may read. Where one metal predominates over the othe