How Balloons Are Made
: STORIES FROM PHYSICS
: Fables For Children, Stories For Children, Natural Science Stori
If you take a blown-up bladder under water and let go of it, it will fly
up to the surface of the water and will swim on it. Just so, when water
is boiled in a pot, it becomes light at the bottom, over the fire,--it
is turned into a gas; and when a little of that water-gas is collected
it goes up as a bubble. First comes up one bubble, then another, and
when the whole water is heated, the bubbles come up without stopping.
Then the water boils.
Just as the bubbles leap to the surface, full of vapoury water, because
they are lighter than water, just so will a bladder which is filled with
hydrogen, or with hot air, rise, because hot air is lighter than cold
air, and hydrogen is lighter than any other gases.
Balloons are made with hydrogen or with hot air. With hydrogen they are
made as follows: They make a large bladder, attach it by ropes to posts,
and fill it with hydrogen. The moment the ropes are untied, the balloon
flies up in the air, and keeps flying up until it gets beyond the air
which is heavier than hydrogen. When it gets up into the light air, it
begins to swim in it like a bladder on the surface of the water.
With hot air balloons are made like this: They make a large empty ball,
with a neck below, like an upturned pitcher, and to the mouth of it they
attach a bunch of cotton, and that cotton is soaked with spirits, and
lighted. The fire heats the air in the balloon, and makes it lighter
than the cold air, and the balloon is drawn upward, like the bladder in
the water. And the balloon will fly up until it comes to the air which
is lighter than the hot air in the balloon.
Nearly one hundred years ago two Frenchmen, the brothers Montgolfier,
invented the air balloons. They made a balloon of canvas and paper and
filled it with hot air,--the balloon flew. Then they made another, a
larger balloon, and tied under the balloon a sheep, a cock, and a duck,
and let it off. The balloon rose and came down safely. Then they
attached a little basket under the balloon, and a man seated himself in
it. The balloon flew so high that it disappeared from view; it flew
away, and came down safely. Then they thought of filling a balloon with
hydrogen, and began to fly higher and faster.
In order to fly with a balloon, they attach a basket under the balloon,
and in this basket two, three, and even eight persons are seated, and
they take with them food and drink.
In order to rise and come down as one pleases, there is a valve in the
balloon, and the man who is flying with it can pull a rope and open or
close the valve. If the balloon rises too high, and the man who is
flying wants to come down, he opens the valve,--the gas escapes, the
balloon is compressed, and begins to come down. Then there are always
bags with sand in the balloon. When a bag with sand is thrown out, the
balloon gets lighter, and it flies up. If the one who is flying wants to
get down, but sees that it is not what he wants below him,--either a
river or a forest,--he throws out the sand from the bags, and the
balloon grows lighter and rises again.