Greene County herald. (Leakesville, Miss.) 1898-current, 1899-06-22
THE FIRE TEST OF ORES.
HOW ASSAYERS GET THE VALUE OF
MlNERAL-BEARlNC ROCK.

Usually Pulverized Until They Be
come pulp - Delicate Mechanism of
the Button BaIance-Flux and Crucible.
The process of ascertaining the
value of piece of mineral bearing
rock Is interesting. The ore is first
pulverized in a crusher or mortar. 1t
is then quartered or split until sam
pie is obtained small enough for CON
venient handling. A "split' is series
of troughs alternating with a series of
Sits equal in number and size to the
troughs. Half of the sample is re-
tanned in the troughs every time the
ore is passed through the split This
process is repeated until the quantity
is sufficiently reduced. The sample
thus obtained is spread upon chuck
ng-board," metal plate fastened on
a firm foundation. 1t is then reduced
to powder by rolling it with ''mul
ler," which is a heavy iron sledge
with smooth convex surface. The
sample is usually pulverized until it
will pass through a sixty mesh, or
sometimes through an eighty mesh
seive In this condition the ore Is
called pulp.
The assayer uses weights which are
proportional to the commercial
weights, an assay ton, consisting of
80. 166 grams, representing n ton of
ore. The result of the assay is
weighed in milligrams. If an assay
ton of the pulp is used, each milli-
gram in the resultrepresents an ounce
of the precious metal to the ton.
Usually half an assay ton of the pulp
is used, and the result is then multi
piled by two to get the number of
ounces to the ton.
A half assay ton of the pulp is
weighed carefully on the pulp scales
and put into crucible, together with
fux. The fux consists OF carbonate
of soda, borax and litharge, or protox-
ide of lead. Sometimes flour is added.
The proportions of the ingredients in
the tiux vary according to the nature
of the ore. Some heavy lead or geleua
ores require very little litharge. Other
res which contain little or no lead
require lithayge III larger quantities.
The pulp and the flux are thoroughly
mixed and covered with salt or boraX
Borax makes a clearer fu1, but has no
other advantage over the common
salt. If there is an excess of sulphur
in the ore, iron nails are added. The
crucible is then placed in the furnace,
which has been heated to white heat
to receive it.
The furnace contains fireclay oven
called a mut1ie, which is made with an
opening at the back to permit the
fumes from the crucibles to escape
Usually half an hour or forty minutes
/ is required to reduce the contents of
the crucibles to volatile state. When
the action in the crucibre has ceased
the contents are poured into a metal
mould and allowed to cool. The Stag
is then broken off and lead button is
found at the bottom of the mould
| This lead button contains all the gold
and silver in the ore. To separate
the gold and silver from the lead the
button is placed in a cupel, a small
dish made of bone ash, and replaced
in the muffle. The lead is melted and
part of it passes off in fumes, while
part of it is absorbed, together with
any copper or other substances which
may be in the button, by the bone
ash, leaving a small silver button in
tho cupel. If the ore is known to
contain much silver, the lead button
is placed in the cupel just as it is
taken from the Stag, but if there is
very little silver in the ore, a known
quantity of pure silver is added, so
that there may be a heavy excess OF
silver in the button obtained in the
cupel This is necessary in order that
the button may be parted with acid.
The silver button is weighed on the
button balance and is then parted by
immersing it in nitric acid. The acid
dissolves the silver and leaves the gold
in the form of fine black dust. The
The gold is washed and dried and the
cup is placed in the muilie and heated
to red heat, which anneals the gold,
bringing it into a compact mass and
giving it its true color. The gold is
transferred to the tray on the button
balance and weighed. The weight OF
the gold is deducted from the weight
of the silver button, giving the weight
of silver.
The button balance is an exceedingly
delicate piece of mechanism. 1t is
kept in a glass case aud the weighing
is done with the case closed in order
that the air currents in the room may
not affect the beam. The balance is
so delicate that the vibrations caused
by person walking across the room
near them will affect the result. A
strand of maidenhair will turn the bal
ance as if it were Il young mans head.
The gold and silver are weighed to
milligrams and even to hundredths of
milligram. The weights and the
buttons are placed on the balance with
small pincers in order that the hands
may not come in contact with the
parts of the scales, for the tempera-
ture of the hand is sufficient to de-
, stroy the accuracy.
If the gold obtained in the assay
I. I Il.