We'll learn a little bit about how gases are diffused. Remember that in another activity, we opened a bottle of perfume in the classroom, and each student raised his/her hand when first noticing the aroma of the perfume. The perfume was gradually diffusing throughout the room, without being blown by air currents.

Now, we'll do a different kind of diffusion. Put a spoonful of cologne in a jar. Inflate a balloon, secure it with a rubber band and push it inside the top of the jar just enough to seal it.

After twenty-four hours, remove the balloon and take off the rubber band. Sniff the air as it escapes from the balloon. Does it smell like the cologne?

Of course it does. But how on earth did that happen? After all, the cologne was in the jar, and the balloon was sealed by the rubber band.

It appears as though the cologne moved as a gas through the air in the jar, and through the balloon without the aid of wind currents.

This type of movement is called diffusion.

Does this also tell us that balloons are really not completely air-tight? When we inflate a balloon, then leave it until morning, the balloon is smaller because some of the air escaped. It was diffused right through the walls of the balloon!