In our experiments we can make the candle flame to last up to 30 s, and three
phases can be easily observed: first there is a phase of complete combustion, then there is a
phase of incomplete combustion characterized by the presence of black smoke and finally
there is a phase where only a hot white wax steam is evaporated by the artificial wick. We
repeated our experiments stopping in any of the mentioned phases, with some experiments
lasting for more than 60 s. In all of these experiments we obtain a final gas volume nearly
of the same magnitude as the initial air volume. Because the first two phases require a
different balance of the elements in the chemical reaction, our results show that the
observed transitory change in volume is only a consequence of the thermal expansion and
contraction of the gas volume. The final negligible change in volume was observed by
Lavoisier in his closed volume experiments (Lavoisier 1777) and has been also reported in
an experiment where a piece of paper was burned inside a rigid closed combustion
chamber (Vitz 2000).