Fill a tall glass with a cup and a half of water. Place an egg in the glass. Add salt, one teaspoon at a time, testing the egg between each addition. The egg will begin to float, and eventually will float all the way to the top.
Saltwater is more dense than pure water.
You can also examine this experiment as an example of the importance of avoiding variables in experiments. We know that it was the addition of salt that changed the way the egg acted because we did not vary anything else in the experiment except the salt. The egg, the glass and the water all stayed the same. The importance of the impact of variables on experiments increases with how complicated the experiment is, but "you should always reduce the number of experimental variables that are not a necessary part of the experiment..because the effects on the experiment are not always predictable." -Exploring Creation with General Science, by Dr. Jay Wile
source: Exploring Creation with General Science, by Dr. Jay Wile