into vast volumes of uncontrollable gas that
will rend the heart out of a mountain in order to expand.

Gunpowder was first used in 1350; so the old Romans knew nothing of its
power. They flung javelins a few rods by the strength of the arm; we
throw great iron shells, starting with an initial velocity of fifteen
hundred feet a second and going ten miles. The air pressure against
the front of a fifteen-inch shell going at that speed is 2,865 pounds.
That ton and a half of resistance of gas in front must be much more
than overcome by gas behind.

But the least use of explosives is in war; not over ten per cent is so
used. The Mont Cenis tunnel took enough for 200,000,000 musket
cartridges. As much as 2,000 kegs have been fired at once in
California to loosen up gravel for mining, and 23 tons were exploded at
once under Hell Gate, at New York.

How strong is this gas? As strong as you please. Steam is sometimes
worked at a pressure of 400 pounds to the inch, but not usually over
100 pounds. It would be no use to turn steam into a hole drilled in
rock. The ordinary pressure of exploded gas is 80,000 pounds to the
square inch. It can be made many times more forceful. It works as
well in water, under the sea, or makes earthquakes in oil wells 2,000
feet deep, as under mountains.

The wildest imagination of Scheherezade never dreamed in _Arabian
Nights_ of genii that had a tithe of the power of these real forces.
Her genii shut up in bottles had to wait centuries for some fisherman
to let them out.

NATURAL AFFECTION OF METALS

"Sacra fames auri." The hunger for gold, which in men is called
accursed, in metals is justly called sacred.

In all the water of the sea there is gold--about 400 tons in a cubic
mile--in very much of the soil, some in all Philadelphia clay, in the
Pactolian sands of every river where Midas has bathed, and in many
rocks of the earth. But it is so fine and so mixed with other
substances that in many cases it cannot be seen. Look at the ore from
a mine that is giving its owners millions of dollars. Not a speck of
gold can be seen. How can it be secured? Set a trap for it. Put down
something that has an affinity--voracious appetite, unslakable thirst,
metallic affection--for gold, and they will come together.

We have heard of potable gold--"_potabile aurum_." There are metals to
which all gold is drinkable. Mercury is one of them. Cut transverse
channels, or nail littl