An experiment is conducted with carbon dioxide, a colourless, odourless, heavy and invisible gas. Carbon dioxide can blow candles out, unlike oxygen. We also see how carbon dioxide gas can cast a shadow.

This clip is from:
Science Clips, Gases around Us
First broadcast:
11 October 2007

This clip could be used to ask the question "Why are the candles blown out?" The same experiment can be done with an empty bottle, asking whether or not it is empty. Then discuss how to find out by putting the bottle into water.