1. Limewater is used to test for carbon dioxide in air exhaled through a drinking straw.
2. Gases from combustion of a lighter are collected by covering the flame with an infusion bottle.
After adding limewater the bottle is stoppered and shaked.
In both cases the liquid becomes milky.
3. A piece of steel wool is wetted, transferred into an ampoule full of air. The ampoule is closed by a stopper that was pierced by a pipette tip from downside before. The bottle is turned upside down and dipped into a second ampoule full of coloured water.
As a control dry steel wool is kept under the same conditions.
The volume of air is reduced and coloured water rises only if the steel wool is wet.