One of the most reliable test of knowing whether an egg is fresh or stale is, to drop it in a glass of water. If it sinks, it is fresh, on the other hand if it floats, then it is an old egg which needs to be discarded. Old eggs have more gases filled in them, which aid in buoyancy. The reason is, as the egg begins to stale, air enters through its shell and gets trapped inside. The older the egg, the greater is the gas cell. Thus, an old egg can easily float in water. But, did you know, that you can make a fresh egg float in water as well. So, how to do it? Let us find out..
How to Make an Egg Float in a Glass of Water
Why do some objects float on water, while others sink? To answer this question, we will have to understand the concept of density. Density is defined as the amount of the material per unit size. Mathematically, it is expressed as,
Density = Mass/Volume
If you consider the density of water as standard, then all the objects that have density lower than water will float, whereas those with higher density than water will sink to bottom. Generally, any object when immersed in a liquid displaces some amount of liquid. If the amount of liquid displaced is equal to the density of the object then it floats, if it is greater, then naturally, it sinks.
Egg has a density higher than water. Therefore, it sinks in water (except when it is stale.) From the above explanation, we can deduce that, to make an egg float in water we have to make the density of egg equal to the amount of water it is likely to displace. The question is how to accomplish this? Since, it is not possible to lower the density of an egg, we are left with only one option and that is, increase the density of the water. Although, the task sounds pretty complex, it is basically a very simple science experiment and the vital ingredient required for this project is easily available in your kitchen itself. Common salt! Yes, that is the only ingredient you will require to make your eggs float in water.
Fill half a glass of water with tap water and add a tablespoon of common salt in it. Stir the water, so that salt dissolves in it completely. Drop the egg and watch the reaction. The egg jerks a little, spins and then, voila it floats! You sure must be wondering how a tablespoon of common salt could make the egg float. The explanation is very simple. The molecules of common salt (NaCl) are very large as compared to the molecules of water. Thus, adding common salt to water increases the total number of molecules in your water solution, thereby increasing its density. However, to make the egg successfully float on the top of the glass, you need to add adequate amount of salt.
If you want to demonstrate the relation between amount of salt and buoyancy of egg, you can try adding a small spoonful of salt. Since, in this case, the density of water is neither too high to float the egg, nor it is too low to submerge it completely, your egg will float midway through the glass. Alternatively, you may also try adding a tablespoon of salt and then not stirring it. Drop the egg in the glass, and watch it sink until it is halfway through the glass. As the density of water begins to increase at the bottom due to salt, the egg will float right in the middle of the glass. This is an interesting experiment for kids' science projects.
The science, behind making an egg float is very simple. This is a great experiment for kids as it demonstrates the effects of density in exciting ways.