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Page 43
By this time the boys were much interested.
"But what makes it do so, grandpa?" they asked.
"Quicksilver is very sensitive to heat and cold. If the weather is
warm, or if the room it is in is warm, it expands--swells out--and so
rises in the glass tube, as you have seen. The least coolness in the
air will cause it to contract, or draw itself into a smaller space;
then, of course, it sinks in the tube.
"The barometer is another instrument in which quicksilver is used. It
is intended to measure the weight of the air, therefore the quicksilver
in it must be exposed to the pressure of the air. Common barometers
have it inclosed in a small leather bag at the back of the instrument.
This we do not see, but only the tube which is connected with it. When
the weather is pleasant, the air, contrary to the general idea, being
heavier, presses against this little bag and the quicksilver rises in
the tube. When the atmosphere is damp, the pressure being less, the
metal sinks."
"Grandpa," said Harry, "when you think of it, isn't quicksilver a funny
word?"
"Yes; it was so named by people who lived many hundreds of years ago.
They called it _living silver_ also. It is the only metal found in a
liquid state; and so many strange changes did it pass through under
their experiments, that it seemed to them really a living thing. If
they tried to pick it up, it would slip out of their fingers. When
thoroughly shaken, it became a fine powder. They boasted that it had
the faculty of swallowing any other metal, while powerful heat caused
it to disappear entirely. It is now known among metals as mercury. Can
you tell me, Fred, some of the metals?"
"Oh yes, sir! There are gold, silver, iron, lead and copper."
"That is right. But, you know, all these are hard; some of them can be
chipped with a knife, but they cannot be dipped up in pails, unless
they have first been melted. Yet mercury can be frozen so hard that it
may be hammered out like lead, and sometimes it takes the form of
square crystals. Yet it can be made to boil, and then sends off a
colorless vapor."
"Grandpa." said Fred, who had scarcely listened to the last words, "if
mercury can be dipped up in pails, it must be very easy to get it. I
read somewhere that gold and silver are so mixed in with the rock that
it takes a great deal of time and money to separate them."
"That is true; but mercury is not always obtained easily. It forms part
of a soft, red rock called cinnabar, composed of mercury and sulphur.
The cinnabar is crushed and exposed to heat, when the metal, in the
form of vapor, passes into a vessel suited to the purpose, where it is
cooled. Then, being reduced to its liquid state, it is pure and fit for
use. When men working in the mines heat the rocks, the quicksilver will
sometimes roll out in drops as large as a pigeon's egg, and fall on the
ground in millions of sparkling globules. Think how very beautiful it
must be, the dark red rock glittering on every side with the living
silver, while every crack and crevice is filled with it!
"Visitors to the mines of Idria are shown an experiment that I think
would interest you boys. In large iron kettles filled with mercury are
placed huge stones, and these stones do not sink."
"Why, grandpa! how can that be?"
"Did you ever see wood floating on water?"
"Yes, sir, but that is different."
"But the principle is the same; can you tell me why?"
Both the boys looked puzzled.
"It is only because the wood does not weigh so much as water; neither
are the stones as heavy as mercury, therefore they cannot sink."
"I wish we could go into the mines. Can't you take us, sometime,
grandpa?" said Harry.
"That is asking rather too much, my child, for quicksilver is not a
common metal. There are in the world only four important localities
from which it is obtained. These are California, Peru, Austria, and
Almaden in Spain. The mines nearest us are in California. I think I
shall never go as far as that, but I hope you both may before you reach
my age.
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