Eggs float in salt water because salt water has a higher density than fresh water. Density is defined as the amount of matter, in this case salt, in a given amount or medium. The more matter, the denser it is.
The salt water egg experiment is one of the easiest ways to demonstrate how density works. The components of this experiment are two raw eggs, table salt, two containers deep enough for an egg and tap water.
First, each container should be filled almost to the top with tap water. Add 6 tablespoons of salt in one container stir until completely dissolved, and then place one egg in each container. The egg in the salt water will sink while the one in the container with only tap water will float.
In this experiment, the egg sinks in plain water because the egg is denser than the water. It pushes the water particles out of the way and sinks to the bottom of the container. In the other container, the salt ions and the water ions have bonded together, which makes the water more dense than the egg. These new particles essentially hold the egg up in the water, causing it to float.