A contribution to elucidate the main causes of the rise of water in an inverted glass over the flame of a candle.

Abstract

The rising of water inside an inverted vessel that contains a burning candle is a typical recreational experiment whose result is well known. Water ascends due to a pressure reduction inside the vessel, but the contribution of different (physical and chemical) processes to this explanation is still under debate. In this work we present a quantitative detailed discussion of the main processes involved in this experiment, concluding that the major contribution to the pressure decreasing causing the rise of the water level in the inverted vessel is due to the hot air escaping from its interior (~ 20% pressure reduction), whereas the consumption of oxygen in the chemical reaction has only a minor role (7% as a maximum). This result is practically independent of the vessel volume, the ambient temperature and, for practical purposes, the type of paraffin with which the candle is made.