We propose to speak of some silver bars ... and silver nitrate ... by Mark Twain

Territorial Enterprise, February 17-22, 1863

SILVER BARS - HOW ASSAYED

We propose to speak of some silver bars which
we have been looking at, and to talk science
a little, also, in this article, if we find
that what we learned in the latter line
yesterday has not escaped our memory. The
bars we allude to were at the banking house
of Paxton Thornburgh, and were five in
number; they were the concentrated result of
portions of two eight-day runs of the Hoosier
State Mill, on Potosi rock. The first of the
bricks bore the following inscription, which
is poetry stripped of flowers and flummery,
and reduced to plain common sense: "No. 857;
Potosi Gold and Silver Mining Company; Theall
& Co., assayers; 688.48 ounces, gold, 020
fine, silver, 962 fine; gold $572.13, silver
$1,229.47." Bars No. 836 and No. 858 bore
about the same inscription, save that their
values differed, of course, the one being
worth $1,800, and the other a fraction under
$1,300. The two largest bars were still in
the workshop, and had not yet been assayed;
one of them weighed nearly a hundred pounds
and 1 was worth about $3,000, and the other,
which contained over 900 ounces, was worth in
the neighborhood of $2,000. The weight of the
whole five bars may be set down in round
numbers at 300 pounds, and their value, at
say, $10,000. Those are about the correct
figures. We are very well pleased with the
Hoosier State mill and the Potosi mine - we
think of buying them. From the contemplation
of this result of two weeks' mill and mining
labor, we walked through the assaying rooms,
in the rear of the banking house, with Mr.
Theall, and examined the scientific
operations there, with a critical eye. We
absorbed much obtuse learning, and we propose
to give to the ignorant the benefit of it.
After the amalgam has been retorted at the
mill, it is brought here and broken up and
put into a crucible (along with a little
borax,) of the capacity of an ordinary plug
hat; this vessel is composed of some kind of
pottery which stands heat like a salamander;
the crucible is placed in a brick furnace; in
the midst of a charcoal fire as hot as the
one which the three Scriptural Hebrew
children were assayed in; when the mass
becomes melted, it is well stirred, in order
to get the metals thoroughly mixed, after
which it is poured into an iron brick mould;
such of the base metals as were not burned
up, remain in the crucible in the form of a
"sing." The next operation is the assaying of
the brick. A small chip is cut from each end
of it and weighed; each of these is enveloped
in lead and placed in a little shallow cup
made of bone ashes, called a cupel, and put
in a small stone-ware oven, enclosed in a
sort of parlor stove furnace, where it is
cooked like a lost sinner; the lead becomes
oxydized and is entirely absorbed by the
pores of the cupel - any other base metals
that may still linger in the precious stew,
meet the same fate, or go up the chimney. The
gold and silver come from the cupel in the
shape of a little button, and in a state of
perfect purity; this is weighed once more,
and what it has lost by the cooking process,
determines the amount of base metal that was
in it, and shows exactly what proportion of
it the bar contains - the lost weight was
base metal you understand, and was burned up
or absorbed by the cupel. The scales used in
this service are of such extremely delicate
construction that they have to be shut up in
a glass case, since a breath of air is
sufficient to throw them off their balance -
so sensitive are they, indeed, that they are
even affected by the particles of dust which
find their way through the joinings of the
case and settle on them. They will figure the
weight of a piece of metal down to the
thousandth part of a grain, with stunning
accuracy. You might weigh a musquito here,
and then pull one of his legs off, and weigh
him again, and the scales would detect the
difference. The smallest weight used - the
one which represents the thousandth part of a
grain - is composed of aluminum, which is the
metallic base of common clay, and is the
lightest metal known to science. It looks
like an imperceptible atom clipped from the
invisible corner of a piece of paper whittled
down to an impossible degree of sharpness -
as it were - and they handle it with pincers
like a hair pin. But with an excuse for this
interesting digression, we will return to the
silver button again. After the weighing,
melting and re-weighing of it has shown the
amount of base metal contained in the brick,
the next thing to be done is to separate the
silver and gold in it, in order to find out
the exact proportions of these in the bar.
The button is placed in a mattrass filled
with nitric acid, (an elongated glass bottle
or tube, shaped something like a bell
clapper) which is half buried in a box of hot
sand - they called it a sand bath - on top of
the little cupel furnace, where all the
silver is boiled out of said button and held
in solution, (when in this condition it is
chemically termed "nitrate of silver.") This
process leaves a small pinch of gold dust in
the bottom of the mattrass which is perfectly
pure; its weight will show the proportion of
pure gold in the bar, of course. The silver
in solution is then precipitated with
muriatic acid (or something of that kind - we
are not able to swear that this was the drug
mentioned to us, although we feel very
certain that it was,) and restored to metal
again. Its weight, by the musquito scales,
will show the proportion of silver contained
in the brick, you know. Now just here, our
memory is altogether at fault. We cannot
recollect what in the world it is they do
with the "dry cups." We asked a good many
questions about them - asking questions is
our regular business - but we have forgotten
the answers. It is all owing to lager beer.
We are inclined to think, though, that after
the silver has been precipitated, they cook
it a while in those little chalky-looking
"dry cups," in order to turn it from fine
silver dust to a solid button again for the
sake of convenient handling - but we cannot
begin to recollect anything about it. We said
they made a separate assay of the chips cut
from each end of a bar; now if these chips do
not agree - if they make different statements
as to the proportions of the various metals
contained in the bar, it is pretty good proof
that the mixing was not thorough, and the
brick has to be melted over again; this
occurrence is rare, however. This is all the
science we know. What we do not know is
reserved for private conversation, and will
be liberally inflicted upon any body who will
come here to the office and submit to it.
After the bar has been assayed, it is stamped
as described in the beginning of this
dissertation, and then it is ready for the
mint. Science is a very pleasant subject to
dilate upon, and we consider that we are as
able to dilate upon it as any man that walks
- but if we have been guilty of carelessness
in any part of this article, so that our
method of assaying as set forth herein may
chance to differ from Mr. Theall's, we would
advise that gentleman to stick to his own
plan nevertheless, and not go to following
ours - his is as good as any known to
science. If we have struck anything new in
our method, however, we shall be happy to
hear of it, so that we can take steps to
secure to ourself the benefits accruing
therefrom.

[reprinted in The Works of Mark Twain; Early
Tales & Sketches, Vol. 1 1851-1864, (Univ. of
California Press, 1979), pp. 211-14.]
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