Re: Is a chicken egg's shell harder when raw or hard boiled?

Dear Ed,

As you know, chicken eggshells are made up of calcium carbonate, which is a calcium salt which does not dissolve in water. However, at high temperatures, some of it may dissolve, or perhaps even react with some other substances which are also dissolved in the water which you use to boil your egg.

There's more to an eggshell than just a plain old shell. It consists of many layers, each of which can be affected differently by boiling. This page gives a pretty good diagram of the overall structure of a chicken egg. The internal parts of the shell can be denatured by heating as they consist largely of proteins. You can read more on eggs here.

If you do an experiment on this, you must be careful not to mistake the overall hardness of the egg for the hardness of the eggshell. When the egg is boiled, the white and yolk are denatured and become hardened, hence the name 'hard boiled'. Thus, the egg would be firmer, and less likely to break and have stuff ooze out when hit. But then it would be that the inside of the egg, the hardened white and yolk, which is supporting the shell.

You could separate the shell from the rest of the egg and boil it alone. With your parents' help, you could take four (or more eggs), and crack them neatly. Keep the whites and yolks and make an omelette with them later. Take the shells and trim them with scissors so that they are all about the same size and shape. Boil two of them, and keep the other two 'raw'. Then you could see which is harder by stacking weights on them and see how much weight it takes to break them. Of course, this would be quite messy, so ask your parents first!

This would make a pretty cool science fair project.

Keep up your interest in science!

Thiam Hock "Egghead" Tan