Bennington semi-weekly banner. (Bennington, Vt.) 1894-1902, 1894-08-31
METALS AT TIRE HINT
HOW BULLION is CLEANSEO WITH
FIRE AND BOILING ACID.

Ity oI "a A1ar a. Dess. .li..e0 " Assay i4ls.
Cheese Cakes of Silver.
1--WE do not buy bullion in small guam
titles at the mint, nothing less than 500
worth of gold or silver at time, and then
we do not pay for it until It has been as
sayed," said j. Robley Dunglisom, regis
trar of deposits at the Philadelphia mint.
eff you bring us 500 worth of metal that
| you suppose to be gold, we weigh 1t and
| give you a receipt for it, and three days
after you can call and receive the money for
whatever gold we find in iG. No matter If
the lot contains only 81 worth of gold, we
will receipt for the weight and extract the
| gold for you and pay you for It, But you
lose all the base metal, because in the re-
| filming everything but the gold and silver
Is destroyed-that is, it is practically de-
stroyed, because our work is with gold
and silver only, and we do not make any
effort to save the base metals. 1t could
easily be done, but it would not pay for
the time and trouble. We could separate
not only the gold and silver, but the cop
per also, and the lead, and whatever else is
present.
when you take quantity of old gold
to the mint to sell, your metal is not mixed
with any other metal. Each lot is kept
separate until it has been assayed. Your
| gold is put into an iron box with two
locks, and when its turn comes the box is
taken To the melting room, where 1t Is
| opened by two men, each of whom has q
key to one of the locks. The metal is put
into u crucible, with little borax to pre-
vent its sticking. Tho crucible is put in
TO furnace, and when the metal is melt
| ed 1t is nodded into bar. That bar con-
tains all the metal in your lot, whether 1t
be gold or brass, and it is the assayers
business to find out how much gold 1t con-
tains. While it is in the crucible it Is
stirred constantly and thoroughly, so that
all its metals may be distributed equally
throughout the bar.
when the bar is returned to the weigh
ing room, the assaycr chips from it a tiny
piece that must weigh just half gram,
or ~ grains troy. The bar and sample
are numbered to correspond, and the bar
is locked up in the iron box again. But
the chip is taken to the assaying room,
where it is put through one of the most
delicate mechanical processes in the world.
| No danger of visitors following the chip to
/ working with scales that will weigh the
thirteen -hundredth of grain cannot be
talking to visitors.
You are not familiar with the bone ash
| cup, suppose, that we call the cupel? To
tho uniformed that is one of the won
ders of the mint 1t is simply a little
shallow cup made of bone ashes moistened
and pressed, but it does some wonderful
u 4, l. Nt,N
melted in It, except gold and silver. That
sounds IL little doubtful, but il is fact
that can readily he accounted fOGon scien-
tific principles. You melt a lump of
mingled gold and copper in this little
cupel, and every particle Of the copper dis
| appears leaving the gold alone in the
bottom of the cup. That is the first step
| in assaying gold taking no account of o
| dozen minor operations that merely lead
up to it,
This melting in the cupel does not
| give pure gold, however, for gold is often
alleged with silver. After the tiny but
ton that remains in the cup has cooled
sufficiently it is tlattencd with hammer
and run between rollers till 1t comes out
little spiral that we call a cornet. This
is put in little vessel like q thimble with
slit in the bottom and is boiled in nitric
acid The acid dissolves the silver, which
runs ont through the slit, hut it cannot
dissolve the gold The tiny chip that re-
mains in is pure gold.
you see tho reason for this process
now, l suppose The sample weighed ~
grains at the beginning. If the pure gold
taken from it weighs half rs much, then
the sample was onn-half gold, and conse-
quently the bar is one half gold. What
ever proportion the weight of the gold
bears to n half gram, that is the proportion
Of gold In the har.
"The refining of silver is an entirely
different process. Our visitors never tire
of seeing silver disappear in the big tank
There stands big tank of boiling water
apparently, and we'drop In Jumps Of sill
vor, and they disappear in a second. But
we take good care to get them back again
1t is not boiling water in the tank, but
boiling nitric acid, which is colorless and
looks precisely like so much water. We
take the metal that is supposed to be sill
yer, or to contain silver, and cut 1t into
small pieces and throw them into the tank,
and in the twinkling Of an eye they are
gone, and nothing is to be seen but the
! clear boiling liuuid OF course the silver
is not gone, for even boiling nitric acid
cannot destroy silver or any other metal.
1t merely changes its properties and con-
vGrts the silver into nitrate of silver, which
is colorless fluid like tho acid. All the
base metal that may be mingled with it is
destroyed, practically, for it is converted
into other nitrates, which are thrown
away. We might rescue the base metals
by several simple processes, but we have
nothing to do with them. Our business Is
u recover the liQuefed silver.
The liquid is drawn from the tank into
large tubs, and little salt water is poured
into them. Immediately "a whitish sedi-
ment begins to form and fall To the bottom
to preciptate as we call it. This is the
silver again, but in another form. The salt
has. converted it into chloride Of silver.
The sediment looks like slaked lime and
feels Just like soft cheese. After 1t has
all settled we pour off the acid. and the
tubs are half full of chloride of silver.
You can make this experiment for your
self by dropping silver coin into some
boiling nitric acid. but advise you not
to, for boiling nitric acid Is dangerous
stuff to handle
The deposit is put in q hydraulic press
and pressed into round cakes that look very
much like huge cheeses. These cakes arc
then treated with spelter, or zinc, which
turns thom into metallic silver again.
When gold and silver are massed together,