Osmosis: An Experiment

Did you know you can remove the outer shell of an egg, leaving a membrane which is tough enough to hold? It is also permeable, thereby letting air and water through.

We did this experiment sometime ago, and it was interesting. Thought I'd post some pics for your intellectual edification—or whatever.

Here we go.

Step One: Take an egg, and drop it in vinegar. The vinegar will interact with the calcium in the outer shell, dissolving it and leaving a membrane. We used apple cider vinegar because we didn't have any of the other stuff.

See the bubbles? Maybe not. Well, trust me, they are there! The shell bubbles off over the course of a day, and soon, you have a shell-less egg. Edmund has it here in his right hand, and an untampered-with egg in his left.

We did this to two eggs, then measured them carefully.
The larger of the two, we put into a thick sugar-syrup. The smaller, we put into water. Eggs are mostly water. If the membrane allows for osmosis, the larger egg should shrink as the water inside it escapes into the syrup, trying to bring the two into a state of equilibrium, until as much water exists inside the egg as outside it (in the syrup). The pores in the membrane are too small to allow the sugar to get inside the egg.

The smaller egg should remain unchanged, as the water in the glass and the water in the egg are pretty much the same amounts.

Here we see day one. They look about the same. The water is on the left and the syrup on the right.

Now here is day two. You can see the egg in the syrup, this time on the left, looks wrinkly and shrunken, while the egg in water on the right, looks normal.

The larger egg shrunk by about a centimeter, but I didn't get a picture of the measurement. You'll just have to trust me on this. Then we stuck it back in water and it reconstituted itself. It was fun to watch the water come out of the egg and form a halo around the it, between the egg and the syrup.

Then we threw it out on the compost heap. An ignoble demise for such a useful educational tool, don't you think?