Take a round bottom flask which is filled with air and closed with a one holed rubber cork. A narrow capillary tube is passed through the cork and the flask is supported on a tripod in an inverted position as shown in the figure, so that the end of the capillary tube is underwater. Now, heat the flask gently with a spirit lamp. You will observe bubbles coming out from the capillary tube. This shows that gases expand on heating.
Concept: Graphs Showing Variation of Volume and Density of Water with Temperature in the 0 to 10°C Range