The Birmingham age-herald., 1913-02-02

teria1. These furnaces are usual. op-
Grated by gas or oil and are built of the
very finest grade of fire brick and fire
clay. The plumbago crucible which is
used is composed of graphite Cthe same
material that comprises the center OF
your lead penciD, a little fire clay and
a little sand. In the manufacture OF
these crucibles great care must be taken
TO form a uniform mixture of the compo-
nent parts, SO that when heated no por-
ton of the vessel will expand more than
any other portion. Unequalled expansion
would cause cracking.
Placed in Moulds
The crucbles are fashioned in mouds
and dried, or burned in kins after a
fashion similar to dishes or bricks. They
are made In all sizes from those having
the capacity of an after dinner coffee
cup to immense sizes holding over twelve
gallons. Before melting gold in one of
these crueibles it is necessary that it be
very carefully annealed. which means
that the last possible traces of moisture
must be expelled by slowly increasing
the temperature for several days. This
is done by placing the crucibles I'm a
steam-heated oven, where the process is
carried forward until it is deemed that
the vessel is in suitable shape to be
placed in the fire. Covers and stirrcrs
are lfldut Dl the same nldIefldi as the
erucible. The latter are used to stir the
gold in the crucible after it is melted.
Covers and stirrers pass through the
same annealing process as the crucibles,
although it is not necessary to take so
much care with them.
Gold coming direct from a mine is
never pure. 1t may contain various
base metals, the nature of which depends
upon the process hy which the gold was
won from it's matrix. Gold from stamp
mills contain some iron. very likely some
copper and often some quick silver.
From cyanide mills the billion nearly
always contains zinc, as this metal is
made use of in the process. The zinc,
to. may also have contained impurities,
some of which will very likely oe In
the resulting bullion Copper has some
of the characteristics of gold. both ply
scal and chemical, 20 that if copper is
contained in the original ore some of it
will be very likely contained in the bull
lion. Silver is always associated with
gold In the ores of the latter The
amounts may vary greatly. but it may be
stated that silver is always present in
gold ores
The problem of the melter who handles
the deposits at the assay office is to
make from the deposit bar of bullion
which will be homogeneous, or in other
words, a perfect mixture from top to
bottom and from end to end of the gold
and other metals. In order to do this he
places in the crucible with the deposit
a stated amount of fiux, varying with
the size and composition of the deposit.
The virture of this fiux is to remove a
certain portion of the base metals and
likewise to form motion mass over the
top of the bullion which will prevent
volatization of the precious metals. 1t
is lighter in specific gravity than the
metal and rises to the surface of the
melt. For clean bullion the fiux is com
posed usually of borax Perhaps some
little soda will be added. For bars which
contain or 10 per cent or more OF
the base metals the fux will be com
prised more largely of soda. This is
just the ordinary soda which the house
wife uses in collaboration with sour milk
| 10 make biscuits or other dainties. Nj
ter is also used ON bars containing large
amounts of impurities
Heat Applied
Having placed the deposit in the criic;-
BILE in the furnace. with the necessary
fiuxes the heat is applied and the metal
and flux melted in thirty to forty-hve
minutes. The melter puts on immense
pair of asbestos mitts to protect his
hands from the intense heat and re-
moves the cover of the furnace. the COW
er or the crucible. and taking the stirrel
IN pair of iorn tongs. he carefully stirs
the entire contents of the crucible. The
stirrer was placed in the furnace at the
/ time the crueible and charge We're all
mitted, and is of the same temperature
as the other contents. On very dirty OF
impure bars the stirring may be done
two or three times. the furnace being
/ closed in order that the heat may be
brought IN tbn
each stirring. The moulds into which
the gold is poured are made of iron and
full stock OF the various sizes are
Kept on hand so that no matter what the
size OF the deposit a bar will be turned
out with width suproximately twice
its depth and length about twice the
width Into this receptacle the neltet
pours the contents of the crucible. 'rhe
metal sinks to the bottom. and the Stag
as the fiuS IS known after il has passed
through the process, rises to the top.
After the metal and Stag have solidined
the mold IS overturned, the Stag separated
from the bar, the bar cleaned anc
weighed. In order that the deposito,
may receive pay for every bit of gold
which properly belongs to him, the in
side of the crucible is scraped clear
and the Stag treated by. being crushed
10 powder and panned in a miner gold
it''i- = ~ ~ pbifti III the nciief. Iflcli
II Will be seen, is to add the proper flax
TO see that the furnace produces the high
neat which is necessary in order to sue
eessfully melt the charge, to have his
efueihles in such shape that they viii
not brake In the furnace when subjected
TO the high heat and 10 dextero,isiy pour
the hullion into the mould and recover
the values from the Stag.
The weight of the granules which have
been recovered from the Stag is added
10 the weight of the bar, and this
amount is the weight of the bullion. fol
which the depositor is paid. IT is ther
the assayer's business to determine th'
proportions of gold. silver and base met
ais IN the bar. These proportions are re-
ported IN thousandths, lie obtains a
sample by means of a special clippins
machine designed for the purpose
Chemical Process
\ complicated chemical process L
necessary to determine the fineness O