is found in combination with one metal or
another, and is known as "rebellious" or "refractory" gold. Such gold
may sometimes be set free by heat, and sometimes by chemicals. One way
is by the use of chlorine gas, and the story of it sounds almost like
"The house that Jack built." It might run somewhat like this: This is
the salt that furnishes the chlorine. This is the chlorine gas that
unites with the gold. This is the chloride that is formed when the
chlorine gas unites with the gold. This is the water that washes from
the tank the chloride that is formed when the chlorine gas unites with
the gold. This is the sulphate of iron that unites with the chlorine
gas of the chloride that the water washes from the tank that is formed
when the chlorine gas unites with the gold--and leaves the gold free.

Another method is by the use of cyanide. More than a century ago a
chemist discovered that if gold was put into water containing a little
cyanide, the gold would dissolve, while quartz and any metals that
might be united with the gold would settle in the tank. The water in
which the gold is dissolved is now run into boxes full of shavings of
zinc and is "precipitated" upon them; that is, the tiny particles of
gold in the water fall upon the zinc and cling to it. Zinc melts more
easily than gold, so if this gilded zinc is put into a furnace, the
zinc melts and the gold is set free.

Very often gold is found combined with lead or copper. It must then be
melted or smelted in great furnaces. The metal is heavier than the
rock and settles to the bottom of the furnace. It is then drawn off
and the gold is separated from the other metals, usually by
electricity.

Sometimes large pieces of gold called "nuggets" are found by miners.
The largest one known was found in Australia. It weighed 190 pounds
and was worth $42,000. Sometimes spongy lumps of gold are found; but
as a general thing gold comes from the little specks scattered through
veins in rock, and much work has to be done before it can be made into
coins or jewelry. It is too soft for such uses unless some alloy,
usually copper or silver, is mixed with it to make it harder.
Sometimes it is desirable to know how much alloy has been added. The
jeweler then makes a line with the article on a peculiar kind of black
stone called a "touchstone," and by the color of the golden mark he
can tell fairly well how nearly pure the article is. To be more
accurate, he pours nitric acid u