The Banner-Democrat. [volume] (Lake Providence, East Carroll Parish, La.) 1892-current, 1899-07-01
THE FIRE TEST OF ORES,
HOW AsSAYERS GET THE VALUE OF
MlNERAL-BEARINc ROCK.

-Usually Pulverized Until They Be-
come "Pulp" - Delicate Mechanism OF
the Button Balance-Flux and Crucible.
The process of ascertaining the
value of . piece Of mineral-bearing
rsck is interesting. The ore is first
pulverized in crusher or mortar. 1t
is then quartered or split until a sam 4
pie is obtained small enough for con-
venient handling. A "split" 10 . series
of troughs alternating with 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 buck
ing-board," metal plate fastened on
a firm foundation. It is then reduced
to powder by rolling it with a ''mul-
ler." which is heavy iron sledge
with . smooth convex surface. The
sample is usually pulverized until 1t
will pass through a sixty mesh, or
sometimes through an eighty mesh
seiye. In this condition the ore Is
called pulp.
The assayer uses weights which are
proportional to the commercial
weights, an assay ton, consisting OF
%. 1875 grams. representing q ton OF
! ore. The result of the assay is
weighed in milligrams. If an assay
ton of the pulp is used, each MILL
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 a crucible, together with
a fiux. The fux consists of carbonate
of soda, borax and litharge, or protox-
ide of lead. Sometimes -four is added.
The proportions of the ingredients in
the fux vary according to the nature
of the ore. Some heavy lead or galena
ores REQUIRE very little litharge. Other
ores which contain little or no lead
REQUIRE litharge in larger quantities.
The pulp and the fux are thoroughly
mixed and covered with salt or borax.
Borax makes clearer fux. but has nc
other advantage over the common
salt. If there is an excess OF sulphur
in the ore, iron nails are added. The
! crucibls is then placed in the furnace
which has been heated to white hea'
, to receive it.
The furnace contains fireclay over
called muff1e, which is made with al
! opening at the back to permit TIT
fumes from the crucibles to escape
, Usually half an hour or forty minute
, is required to reduce tho contents o
{ the crucibles to volatile state. Whel
the action in the crucible has ceased
I the contents are poured into meta
. mould and allowed to cool. The sla,
Q is then broken off and lead button
found at the bottom of the mould
3 This lead button contains all the gol'
and silver in the ore. 10 separat
Q the gold and silver from the lead tn
button is placed in a cupel. SINAI
dish made of bone ash, and replace
Q in the muffle. The lead is melted an
part of it passes off in fumes, Will
part of it is absorbed, together wit
); any copper or other substances whic
o may be in the button, by the bon
n ash, leaving a small silver button
r tho cupel. If the ore is known
II contain much silver, the lead butte
10 is placed in the cupel just as it
/, taken from the Stag, but If there
v very little silver in the ore, q know
quantity of pure silver is added,
W that there may be heavy excess
TO silver in the button obtained in II
eff cupel. This is necessary in order tn
70 the button may be parted with acid.
of The silver button is weighed on Il
IN button balance and is then parted
r, immersing it in nitric acid. The &C
as dissolves the silver and leaves the 60
to in the form of fine black dust. II
OF parting is done in an annealing Gu
,h The gold is washed and dried and &
h. cup is placed in the muffie and heat
%. to a red heat, which anneals the gol
e. bringing it into compact mass 81
Oh giving it its true color. The gold
or transferred to the tray on the butt
balance and weighed. The weight
RS the gold is deducted from the weig
lr. of the silver button, giving the welg
ne of silver.
re- The button balance is an exceeding
Is, delicate piece of mechanism. 1t
90 90 kept in a glass case and the weigh
'ie is done with the case closed in ORD
that the air currents in the room m
not affect the beam. The balance
SO delicate that the vibrations caus
10. by a person walking across the ro'
nat near them will affect the result.
I'VE strand of maidenhair will turn the b
in ance as if it were young mans bet
ion The gold and silver are weighed
in millierams and even to hundredths
ere milligram. The weights and
re, buttons are placed on the balance W
act small pincers in order that the har
ned NAV not come in contact with
, to parts of the scales, for the tempe
un- ture of the hand is sufficient to
any stroy the accuracy.
tch If the gold obtained in the as'
&C. Just described weighs 100 milligral
.rly the ore carries 200 ounces OF gold
ugh ton, which is good enough for any
avv opv ordinary mine