pon the mark. This eats away the alloy
and leaves only the gold.

Gold is a wonderful metal. It is of beautiful color; it can be
hammered so thin that the light will shine through it; few acids
affect it, and the oxygen which eats away iron does not harm it. Pure
gold is spoken of as being "twenty-four carats fine," from _carat_, an
old weight equal to one twenty-fourth of an ounce troy. Watchcases
are from eight to eighteen carats fine; chains are seldom more than
fourteen; and the gold coins of the United States are about eleven
parts of gold and one of copper. Coins wear in passing from one person
to another, and that is why the edges are milled, so that it may be
more easily seen when they have become too light to be used as coins.
When such pieces come into the hands of the Government, they must be
recoined.

VI

THE STORY OF A SILVER MINE

A man who goes out in search of a mine is called a "prospector." The
best prospector is a man who has learned to keep his eyes open and to
recognize the signs of gold and silver and other metals. A faithful
friend goes with him, a donkey or mule which carries his bacon and
beans, blankets, saucepan, and a few tools, such as a pan, pick,
shovel, hammer, and axe. Sometimes the prospector also takes with him
a magnifying glass and a little acid to test specimens, but usually he
trusts to his eyes alone.

When these few things have been brought together, the prospector and
the donkey set out. They wander over the hills and down into the
canyons. If a rock is stained red, the prospector examines it to see
whether it contains iron; if it is green, he looks for copper. In the
canyons and along the creeks he often tests the gravel for traces of
some valuable metal. If he finds any of these traces along the stream,
he follows them on the bank until they stop; then he carefully
examines the bank of the stream or the nearest hillside. If he
continues to find bits of metal, they will lead him to a vein of ore,
from which they have been broken by the wind, rain, and frost.

Generally a prospector is looking for some one special metal, and in
his search he often overlooks some other metal; for instance,
thousands of the gold-seekers who rushed to California in 1849 hurried
through Nevada on their way. If they had only known what was under
their feet, they would have taken their picks and shovels and begun to
dig, instead of trying to get out of the region as soon as might be.