- Eggs, particularly fresh ones, will sink when placed in a bowl of water. This is because the density of the egg inside the shell is greater than the density of the water outside the shell. A popular, yet simple, experiment demonstrating how density affects eggs floating involves mixing salt into a volume of water. The dissolved salt particles increase the density of the water so that it is greater than the density of the egg. So, when placed in salty water the egg should float. If it does not, more salt is necessary.
- Salt increases the density of water, which makes eggs float, but can other substances do the same thing when added to water? The answer is "yes." Sugar also increases the density of water and make eggs more buoyant. Experiments using other substances like honey or vinegar can teach useful lessons on which types of molecules increase the density of water.
- Using the same concept as the floating eggs, but on a longer time scale, a rising egg experiment can teach the same concept in an interesting way. By placing a pile of dry salt into a container, and slowly pouring water onto it until the container is filled, the salt will not immediately dissolve. Over a series of several days, the salt will slowly dissolve and create a salt gradient which is concentrated at the bottom and dilute at the top. As the salt continues to dissolve, the height of the water that is denser than the egg rises, bringing the egg along with it.
- Egg quality can also be determined by placing an egg in a bowl of water. The fresher the egg, the more quickly it will drop to the bottom of a bowl. If you try this, be sure to have something soft on the bottom of the bowl, lest the egg cracks when it lands. Rotten, old or spoiled eggs tend to float in the water column.
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