Evening star. [volume] (Washington, D.C.) 1854-1972, 1895-11-26
HOW ORES ARE TESTED.
Various Stages of the Process and the
Results Reached.


Helena Dispatch to the Boston Transcript.
To the uninitiated but observant stranger
who wanders up and down in the labyrinth
of shafts and tunnels. diggings and dumps
of genuine mining camp, perhaps there is
no subject more full of interest than the
process by which a hump of brown ore,
which, to his inexperienced eye, looks not
in the least attractive, is made to yield its
share of silver and gold; or the means
and methods by which the mining man at
his side so confidently assures him that a
ton of that ore will go 80 33 ounces in sill
yer and s17.55 in gold.
Even the eastern mining expert, or gradu-
ate from some mining school, will wonder
how, in the log cabin or pine shanty, desti-
tute Of all the elaborate paraphernalia to
which he has been accustomed, these re-
suits are SO readily and accurately OBJ
tanned.
AS general rule the majority Of the
Ores except those containing the precious
metals. for purposes of purchase and sale
| are valued according to the cost of mining
and shipping. SO that, except for metallur-
gical purposes 1t Is unnecessary to seek to
determine with much accuracy the con-
tents and value of such ores
In the case of ores rich in the precious
metals. however, it Is entirely different, as
In their purchase and sale, both parties
the buyer as well as the seller want to as
certain accurately and to a certainty the
value of the entire lot. The methods by
which this knowledge is obtained are so
simple as to be easily understood and prac-
tiecd by many a man who does not know
the technical symbols of the metals he Is
determining. or could not give a scientific
exposition of the process; but nevertheless
IN mis- line, he Is an accurate and successful
aSSayer
When quantity of ore Is to be sampled
for assaying 1t is first broken by an ordin-
airy rock crusher into pieces the size Of an
wi inI, II to
tack into he car. but in such a manner
that every fifth shovelful Is thrown aside by
itself; the remaining four-fifths being final
ly taken away. This fifth portion. known
as the sample" is then reduced to a much
greater degree of fineness by means of Cor
nish rolls. 1t is then piled on the floor in
cone nattened out. and divided into four
equal portions; and two opposite quarters
are then removed. The remaining Quarters
are again thoroughly mixed, and again
piled in cone. fattened and ouartered.
thls operation being repeated until the sam
pie Is reduced to 100 pounds. 1t is then
weighed repeatedly, for the purpose of de-
termining the amount of moisture contained
In the ore which in some ores, especially
b nose Sc OF .ne concentrates, is SO considera-
Die as to make very appreciable difference
in the weight. The moisture is then ex-
PEELED, and the ore is crushed to such a de-
gree of fineness that it can be passed
through sieve containing 100 holes to the
linear inch, The sample is next put I'D in
small glass bottles, which are sealed with
sealing wax. and then stamped, for the
purpose of preventing the possibility of
their being opened or tempered with with
out detection.
The above is the process of sampling used
among the mines. and the sample is now
ready to be assayed, but only a small, por-
ton of 1t will be used for that purpose and
the quantity generally taken is what is
known as an assay ton." which weighs
2a.166 millgrams, or little more than $50
grains troy weight. This definite amount
| Is taken, partly as a matter of convenience
and also because the assayer wishes toJas-
certain as quickly as possible, how many
ounces of the precious metals to the ton
are contained in this ore. The method used
depends upon the following principle: The
avordupois grams ton of 1000 pounds con-
tains y. lt6 ounces troy weight: hence. when
~. 16G milligrams of the unassayed ore are
taken, the weights of the resulting but
ton of gold or silver, in the milligrams
| represents an ounce. without any further
calculation, the number of troy ounces of
gold or silver in the avoirdupois ton of the
ore.
This method was invented in the Column
bia School of Mines, in New York city, and
Is in general use throughout the world
wherever there is assaying to be done.