Soap Bubbles
Soap bubbles are difficult to examine because of their fragility and short life. However, because they are very light, soap bubbles will float on a gas that is only slightly denser than the air that fills them. Such a gas is carbon dioxide. When soap bubbles settle into a container of carbon dioxide, the bubbles float on the carbon dioxide and can be examined closely.
To read more click here to download Dr Hal's fact sheet on Soap Bubbles (900kb pdf file)