, 1889-10-17
HOW ASSAYING is DONE
What the Assay Ton" Is, and
How the Ore and Fluxes
Are Used.
The Lead Button and Process of
Cupellation-Nothing Left but
Silver and Gold.
From the Helena 10

From the Helena 10 II
James Buskctt, who hul bought
out the assay business Of Hand
was found III his office yr,u ny with
furnaces going merrily, engaged in as.
saying several specimens of ore. Iio
had them pounded up almost as fine as
flour and was weighing out amounts of
each. When asked by an inquisitive
visitor what weight he took, MIR. bus
kett said an assay ton" generally, and
was 30, 106 milligrammes. The weight
Is taken for convenience In calculating
results. There are 8,l6G ounces in Il
ton, and so when 30 1866 milligrammcs
of ore are taken the weight in milli-
Grammes of the button OF gold or silver
resulting from the assay will represent
without further calculation the number
of ounces of gold or silver in a ton of the
ore. This method is distinctively an
American one, having been invented at
the Columbia School of Mines in New
York city, and is already In use gener-
ally all over the world where assaying
Is done. Sometimes when the orc to be
assayed Is very base and requires q
quantity of huxes which would too
nearly fill the cruciblc less than an as
say ton of II Is taken, when possible IA
half or II tenth or some other simple
fraction.
When the orc is weighed II is placed
on u piece of thin oil cloth or glazed
paper and the lluxes added. These vary
in kind and quantity with the quality Of
the ore. Carbonate of soda is used sim
ply as a fluX to render liquid the fused
mass and thus facilitate the action of
the chemicals. When the ore contains
much sulphur it is either roasted before
being tluxcd or II considerable amount
Of metallic iron is put In the. charge.
forms "a flisible sulphide of iron which
enters into tho Stag. If the ore is not
known to contain u sufficient quantity
of lead, lead Is added to the charge.
This is done because it Is desirable to
collect the gold and silver in button of
metallic lead. The lead Is generally
charged in the form of oxide OF lead,
called litharge, In II fine powder. This
IL dono because 1t admits of complete
and thorough mixture of the lead all
through the charge, which would not he
the case If metallic lead were used. In
order to change the oxide of lead to
metallic lead, and also to reduce the
gold and silver compounds in the ores to
o metallic state. what is called "reduc-
ing agent" is used. This is simply a
chemical or chemical compound which
has an affinity for oxygen and other elc-
ments, so that when, in II state of fusion,
IL comes in contact with other sub
stances it takes the oxygen and other
elements from them.
When the orc is placed on the glazed
paper and the above described huXes and
reagents added, the whole Is thoroughly
mixed so that each particle of ore shall
be separated by particles of Auxes and
reagents. Then the charge is placed in
n clay crucible and fused in the fur
mace. Tho oxide of lead reduced by the
sends through the charge like fine
rain, gathering as IL goes through, the
silver and gold, which have also been re-
duced to II metallic state, and collecting
in the bottom as button. If too much
of the reducing agent has been added
too much of the oxide of lead will be
changed to metallic lead and the lead
button Will be too large. Sometimes the
ore itself contains compounds which act
rs reducing agents and in this case not
only is no reducing agent added to the
charge, but 1t is sometimes replaced by
an ''oxidiaing agent" This Is simply a
compound which contains an excess of
oxygen and which will consequently,
when fused, give up oxygen to other
compounds which have an affinity for
II. Sometimes again the amount of
lead reduced to a metallic state is ktoo
small and the reducing button Is also
too small. This can be caused by too
small amount of the reducing agent in
the charge, or by the presence in the ore
of substances which have an excess of
oxygen, in combining with which the re-
dncing agent is wasted and fails to act
on the oxide of lead. A lead button
which is too small is Objectionable, for
the reason that IL may not have gathered
all the gold or silver disseminated through
the charge, and one which is too large is
equally objectionable because it wastes
time in the subsequent operations.
After the lead button of the proper
size is obtained 1t Is placed in u "Cupcl."
This is small, shallow cup made of
bone ash. 1t is ofthe size TO hold the lead
button, which should be about as big as
an ordinary chestnut. The oupeI is
placed in clay muflie heated to bright
redness, and after the cupcl is hot, the
button is dropped into it with pair of
tongs. The lead begins to oSidize, that
Is To combine with the oxygen of the air,
and the oxide is volatilizcd in fumes and
also absorbed by the porous bone ash of
which the cupcl is made. Silver and
gold do not oxidize except at much
greater heat than the lead Is subjected
to. AS the lead continues 10 oXidiac the
button grows smaller and smaller until
at last nothing IL lett but the silver and
gold. At this point the cupel is with
drawn from the furnace. When cool
tho small remaining button, composed
now of only gold and silver, is weighed.
The weight gives the amount of both
gold and silver combined which the ,ore
contains. The button after being weighed
is mashed out fiat and placed in glass
or porcelain cup and treated with nitric
acid. This dissolves the silver but leaves
the gold, which after being washed and
fused is weighed. This gives the amount
of gold in the ore and the weight of gold,
subtractcd from the weight of the gold
and silver combined, gives the amount
of silver in the ore.
Such, III brief is the general process Of
assaying for gold and silver. AS will be
seen from the description given, 1t Is full
of all sorts of problems and fine points
concerning the amounts and kinds Of
fuxes and reagents to be used, and re-
quircs the utmost care and skill at every
stage In order to obtain good results.
Mr.. Buskett says that there Is also q
"wct way" Chat Is without tho use of
iire) for determining the amount of sill
yer in an ore, but that the assay by fire
is generally preferred.
THE IRON KING.
The Richest Known Iron Deposit of
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