other chemical rubbish to assist digestion; if they were crisp to the
touch and would retain a dint, they were freighted with all the silver
and gold they could seize and hold, and consequently the pan needed a
fresh charge of quicksilver. When there was nothing else to do, one
could always “screen tailings.” That is to say, he could shovel up the
dried sand that had washed down to the ravine through the troughs and
dash it against an upright wire screen to free it from pebbles and
prepare it for working over.
The process of amalgamation differed in the various mills, and this
included changes in style of pans and other machinery, and a great
diversity of opinion existed as to the best in use, but none of the
methods employed, involved the principle of milling ore without
“screening the tailings.” Of all recreations in the world, screening
tailings on a hot day, with a long-handled shovel, is the most
undesirable.
At the end of the week the machinery was stopped and we “cleaned up.”
That is to say, we got the pulp out of the pans and batteries, and washed
the mud patiently away till nothing was left but the long accumulating
mass of quicksilver, with its imprisoned treasures. This we made into
heavy, compact snow-balls, and piled them up in a bright, luxurious heap
for inspection. Making these snow-balls cost me a fine gold ring–that
and ignorance together; for the quicksilver invaded the ring with the
same facility with which water saturates a sponge–separated its
particles and the ring crumbled to pieces.
We put our pile of quicksilver balls into an iron retort that had a pipe
leading from it to a pail of water, and then applied a roasting heat.
The quicksilver turned to vapor, escaped through the pipe into the pail,
and the water turned it into good wholesome quicksilver again.
Quicksilver is very costly, and they never waste it. On opening the
retort, there was our week’s work–a lump of pure white, frosty looking
silver, twice as large as a man’s head. Perhaps a fifth of the mass was
gold, but the color of it did not show–would not have shown if two
thirds of it had been gold. We melted it up and made a solid brick of it
by pouring it into an iron brick-mould.
By such a tedious and laborious process were silver bricks obtained.
This mill was but one of many others in operation at the time. The first
one in Nevada was built at Egan Canyon and was a small insignificant
affair and compared most unfavorably with some of the immense
establishments afterwards located at Virginia City and elsewhere.
From our bricks a little corner was chipped off for the “fire-assay”–a
method used to determine the proportions of gold, silver and base metals
in the mass. This is an interesting process. The chip is hammered out
as thin as paper and weighed on scales so fine and sensitive that if you
weigh a two-inch scrap of paper on them and then write your name on the
paper with a course, soft pencil and weigh it again, the scales will take
marked notice of the addition.
Then a little lead (also weighed) is rolled up with the flake of silver
and the two are melted at a great heat in a small vessel called a cupel,
made by compressing bone ashes into a cup-shape in a steel mold. The
base metals oxydize and are absorbed with the lead into the pores of the
cupel. A button or globule of perfectly pure gold and silver is left
behind, and by weighing it and noting the loss, the assayer knows the
proportion of base metal the brick contains. He has to separate the gold
from the silver now. The button is hammered out flat and thin, put in
the furnace and kept some time at a red heat; after cooling it off it is
rolled up like a quill and heated in a glass vessel containing nitric
acid; the acid dissolves the silver and leaves the gold pure and ready to
be weighed on its own merits. Then salt water is poured into the vessel