Light a candle, let it burn for a while, and blow it out again. White smoke rises from the wick. If you hold a burning match in the smoke, a jet of flame shoots down to the wick, and it re lights. After the flame is blown out the stearin is still so hot that it continues to evaporate and produce a vapour. But as this is combustible, it can be re lighted at once by a naked flame. The experiment shows that solid substances first become gaseous at the surface before they will burn in a supply of oxygen.