What happens if you cover a lit candle in a water basin with a glass? The glass becomes foggy on the inside and the flame fades and eventually goes out. Then the water level in the glass rises.

The burning candle produces carbon dioxide and water in the form of water vapor. The glass becomes foggy due to this water. The flame goes out, of course, from a lack of enough oxygen in the glass.

And why does the water level rise? The air is heated while the glass moves downwards. It expands and escapes before the glass touches the water. If the air in the glass cools down and its volume decreases, a negative pressure is created inside the glass. The water is pressed into the glass by the greater external air pressure.

This video is part of:

• Chemistry Advent Calendar 2016,
  ChemViews Mag. 2016.
  DOI: 10.1002/chemv.201600101