The Alaska citizen., 1913-01-27

pies Wnen you take II in to be as
sayed9 The Citizen has asked me
TO tell in brief outlines. and in the
language of the ordinary miner.
First, the sample is rough-crushed
whether by machinery or by hand
This crushed ore is then thoroughly
mixed, and then a sample is so TAX
en-. whether by means of patent
sampler or by the old process of
hand quartering. as to be a fair
average of the whole. (No part of
the assay is more important than the
thoroughness of this first mixing.)
The portion thus selected as the
average in values is next pulverized
till It will all pass through a forty
to eighty-mesh screen. according to
the nature of the ore. II coarse gold
is present. which will not pass
through the screen. it is all care
fully screened out and proportioned
to the weight of the entire sample.
and counted in, by proper calcula.
| ton, in the final result
I The portion that has passed the
screen is then thoroughly mixed
again-if possible even more thor.
oughly than beforehand from this
/ pulverized mixture a definite weight.
called an assay ton. is weighed out
on scale considerably more SEN
sitive than a jewelers. diamond
scales. This assay ton of ore is
then thoroughly mixed with proper
fluxes and reducing agents and with
small quantity of litharge, put into
4 fire-clav crucibie. and heated in
the crucible furnace. at tempera
ture of from fifteen hundred TO two
| thousand degrees. according to the
demands of the particular ore, from
half to quarters OF an hour.
Zone of the most frequent mistakes
of assayers is, in the effort to
economiZe on time and gasoline. not
leaving the crucible in the fire long
enough. and so leaving part OF the
values In the slag)
This crucible process frees the
| gold from the gangue. and at the
same time frees metallic lead from
the litharge. which absorbs the pre-
cious metals. and straightway starts
on journey to the bottom of the
! crucible, carrying all the values with
it. OF course, in the case of Ger
/ tain ores the process is not so sim.
ple. and the problem of fluxes and
reducing agents is one to be solved
only from long technical education
and experience
When the charge In the crunihle
has been Cooked" long enough Il
is turned out into irr-molds
carrying the precious metals promnt-
w sinks to the bottom. leaving the
other materials OF the charge float.
ing above II as a Stag.
When this Stag has sufficiently
cooled the cone-shaped button" of
lead and precious metals is knocked
loose from it, hammered into
shape that will best suit the mechan-
ical requirements of the operations
vet to come. cleansed from the last
traces of Stag. and put into a small
cylinder of compressed bone-ash.
with a basin-shaped depression on
the upper side. and this bone-ash
cylinder called a "cupel." is then
put into different furnace. called
the muffle furnace, and again heat.
ed
When the lead button has melted.
air is admitted to the arch-shaped
muffie carrying the cupels: and as
the air passes over the hot molten
lead the metallic lead is returned to
an oxide OF lead. Part of this hot
oxide of lead passes off in the
draueht as vaper, and part Is absorb
ed by the cupel. TIL finally only
small bead" of precious metal df
the sample carries values at alb is
left behind.
When this bead has been cooled it
is weighed, on a balance sensitive
to less than millionth part of
pound. Nearly all assayers run two
ASSAYS at the same time from the
same ore; and SO, if the wo beads
obtained at this stage do not check
against each other in weight II is
nroof that something is wrong with
the work. and the assay must be
made again from the start
After the weight OF the bead Is
noted, sufficient quantity Of silver
Is added to guarantee that there
will be something like three times
as much silver as gold. and this .
silver and the bead are melted to
gether, using chemically pure lead