This Week's Experiment - #211 Egg in a Bottle
The experiment for this week is another classic, but a very
misunderstood one. You will even find that many books of science experiments
get this one wrong. You will need:
a hard boiled egg
a wine carafe or bottle with a neck that is just a little too small for the
egg to fit through
a piece of paper
matches or a lighter
Warning: This experiment uses fire, so be careful and follow all safety
procedures. Never do fire experiments when you are alone, even if you are an
adult. If you are not an adult, then at least one of the people with you
should be an adult. Think through the experiment before you try it, to be
sure that everything you do is safe.
For this experiment, we are going to put a hard boiled egg into the bottle.
First, you need a hard boiled egg. Let it cool and carefully remove the
shell. Be sure not to damage the egg, as this will keep the experiment from
working properly. If you accidentally tear your hard boiled egg, put it in a
bowl and chop it with a little mayonnaise or salad dressing. It makes a nice
snack while you are boiling another egg.
Once you get the egg peeled, then you have to put it in the bottle. Gently
place it on the top of the bottle. Not much happens. It just sits there.
If you tried to push the egg into the bottle with your fingers, the egg would
tear. We want the egg to be whole when it is inside the bottle. How are we
going to do it?
We will start by removing the egg from the top of the bottle. CAREFULLY hold
a piece of paper about one inch wide and three inches long. While you are
holding one end, use the match to light the other end. As soon as it is
burning, drop it into the bottle and quickly place the egg on top. Watch
carefully what happens.
The paper burns for a second or two. As the fire goes out, the egg begins to
move downwards into the bottle. It squeezes through the neck and drops into
the bottle. How did that happen?
Most books will tell you that the paper burned up the oxygen, lowering the
air pressure inside the bottle, and that the greater air pressure on the
outside of the bottle pushed the egg inside. They get the part about the air
pressure right, but the lowered pressure in the bottle is not due to burning
up the oxygen.
When you burn paper in oxygen, the carbon in the paper combines with oxygen
in the air to form a new gas called carbon dioxide. This gas takes up about
as much space as the oxygen, so the burned oxygen is replaced with carbon
dioxide and the pressure in the bottle stays the same.
But if the egg was pushed into the bottle by air pressure, what lowered the
pressure in the bottle? The answer is temperature. While the paper was
burning, it heated the air in the bottle. The heated air expanded and pushed
out past the egg. If you put the egg on the bottle quickly and watch
carefully, you may be able to see the egg shake as the air rushes out past
it. As the flame begins to die down, the air inside the bottle cools. As it
cools, the pressure in the bottle is decreased. The egg acts as a cork,
sealing the top of the bottle to keep air from coming in to balance the
pressure. Instead, the higher outside pressure pushes the egg into the
bottle.
Now, how do we get the egg out of the bottle? One way is to turn the bottle
upside down, with the egg resting in the neck of the bottle. Put your mouth
against the mouth of the bottle and blow as hard as you can. This increases
the pressure inside the bottle. Quickly move the bottle away from your mouth
and the egg should pop out. Rinse off the carbon from the burned paper and
your egg is now ready for snack time.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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