Close all of the doors and windows in your classroom. Everyone sit perfectly still. You need a clock with seconds that everyone in the class can see. Set it to zero.

The teacher now starts the clock and immediately sprays some toilet freshener directly up to the ceiling (not sideways) for 3 seconds (watch the clock).

Keep watching the clock. When you can smell the freshener, write down what the clock says.

After everyone can smell the freshener, make a map of all the places where you have been sitting. Write the time against each place. That will give you a map of the way the scent gas mixed in the air. Your teacher can show you how to draw lines of equal time across your map.

Find out if the gas spreads out evenly, or faster to begin with and more slowly after that.