The Forrest City times. [volume] (Forrest City, Ark.) 1871-1919, 1899-04-07
THE FIRE TEST FOR ORES.
now the Assayers Determine the
Value of samples Submitted
from New Mines

Oh piece OF mineral bearing rock is
interesting. The ore is first pulverized
IN a crusher or mortar. 1t is then
3uartered or split until n sample is
obtained small enough for convenient
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 a "buck-
ing board" metal plate fastened on
firm foundation. 1t is then reduced to
powder by rolling it with muller"
which is heavy sledge with smooth
convex surface. The sample is usually
pulverized until it will pass through
50-mesh, or sometimes even an S0-mesh
sieve. In this condition the ore is
called pulp.
The assayer uses weights which are
proportioned to the commercial
weights, an assay ton, consisting of 30
166 grams, representing a ton of ore.
The result of the assay is weighed in
milligrams. If an assay ton of the pulp
is used, each milligram in the result
represents an ounce of the precious
metal to the ton. Usually half an assay
ton of the pulp is used, and the result
is then multiplied 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 a
aux. The fiux consists of car Donate of
soda, borax and litharge, or protoxide
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 galeno ores
| require very little litharge. Other ores
which contain little or no lead require
litharge in larger quantities. The pulp
and the flux are thoroughly mixed and
| covered with salt or borax. Borax
| makes clearer flux, but has no other
advantage over the common salt. II
ore. Some heavy lead or galena ores
iron nails are added. The crucibie is
then placed in the furnace, which has
been heated to white heat to receive it.
The furnace contains fireclay oven
called a muffie, which is made with an
opening at the back to permit the
fumes from the crucibles to escape
Usually half an hour or 40 minutes is
required to reduce the contents of the
| crucible to volatile state. When the
action in the crucible has ceased the
contents are poured into a metal mold
and allowed to cool. The Stag is then
broken off and a lead buttonis found at
the bottom of the mold. This lead but.
ton contains all the gold and silver in
the ore. To separate the gold and sill.
yer from the lead the button is placed
in cupel, small dish made of bone.
ash, and replaced in the muffie. The
lead is melted and part of it passes of
in fumes, while part of it is absorbed.
together with any copper or other sub.
! stances which may be in the button, by
the bone-ash. leaving small silver but.
ton in the 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 oil
pure silver is added, so that there may
be heavy excess of silver in the button
obtained in the cupel. This is neces-
sary in order that the button may be
parted with acid.
The silver button is weighed on the
button balance and is then parted BY
irnmersing it in nitric acid. The acid
| dissolves the silver and leaves the gold
| in the form of fine black dust The
| parting is done in an annealing cup
The gold is washed and dried and the
cup is placed in the muffie and heated
to a red heat, which anneals the gold
| bringing it into a compact mass and
| giving il its true gold color. The gold
is transferred to the tray on the button
balance and weighed. The weight oi
the gold is deducted from the weight Of
the silver button, giving the weight OF
| the silver.
The button balance is an exceedingly
delicate piece of mechanism. 1t is kept
In a glass case, and the weighing il
done with the case closed, in order tina,
the air currents in the room may not
affect the beam. The balance is so deli
cate that the vibrations caused by g
person walking across the room neal
them will affect the result. A strand oil
maiden hair will turn the balance as il
IL were a young mans head. The gold
and silver are weighed to milligrams
and even 10 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, fol
the temperature of the hand is suff
cient TO destroy the accuracy.
III the gold obtained in the assay just
described weighs 100 milligrams, the
ore carries 200 ounces of gold to the
ton, which is good enough for any or.
binary mine.-Denyer Times.
Not n Classic.
The Guards band was playing out
on the Windsor castle terrace. during
dejeuner recently. and the queen was
so much struck by one pretty march