Activity: Egg in a Bottle

On SCOPE’s Fire Science episode, you saw Mac use fire to suck an egg into a bottle. Here’s how he did it:

CAUTION: This activity involves fire. You must have an adult present, plus water and other safety equipment the adult or you feel is needed. Make sure no flammable items are in the experiment area.

What you need
A hardboiled egg (cooked for 15-20 minutes) that has been allowed to cool
A glass bottle or jar. The opening at the top should be a couple of millimetres smaller than the egg.
Some newspaper
Matches or lighter
A sink to do the activity on
An adult helper

What to do
1. Peel the shell from your egg.
2. Place the bottle in the sink or on the ground outside in a safe place.
3. Take a small piece of newspaper (say 10cm x 10cm) and squash it into a strip that will easily fit into the bottle.
4. Have an adult light the paper and drop it into the bottle.
5. Immediately place the egg on top of the bottle. Watch what happens.

What's happening?
You should find the fire goes out, and then the egg gets slowly sucked down into the bottle.

There are a couple of things going on here. First of all, the fire needs oxygen from the air to burn. When you put the egg on the top of the bottle, you sealed the fire off from the oxygen outside. Once the oxygen inside the bottle was used up, the fire goes out.

The egg was sucked into the bottle because of how air reacts to changes in temperature. When air gets hotter it tries to expand, i.e. to spread the air molecules out over a larger volume. When air is cooled, it tries to contract.

In this experiment, the fire heated the air in the bottle. As the air got warmer, it expanded until it overflowed from the bottle. You may have noticed a little bit of air leaking out around the egg when you first put it on. Once the fire went out, the hot air left in the bottle cools down and contracts, so air tries to move back into the bottle to fill the space. As the egg was blocking the neck of the bottle, the air pressure in the bottle became lower than outside, and the air outside pushed in the egg.

Some people might tell you that this activity works because the fire uses up the oxygen in the air and the egg gets sucked in to take its place. However, this is not correct. As the fire burns, the oxygen in the air combines with carbon in the paper to make carbon dioxide. So although the oxygen is used up, it is replaced with an equal volume of carbon dioxide.

Getting the egg out of the bottle is not as easy. The easiest way is to cut the egg up with a knife.

Captions:
1. The neck of the bottle should be smaller than the egg to allow the egg to squash through. You might need to try a few different bottles or jars.
2. Have an adult light the paper and drop it into the bottle.
3. Immediately place the egg on top of the bottle. Watch what happens.
4. This bottle is now ready for de-egging