Because the melted wax in the process of candle burning will soon become solid when it meets water and freeze around the flame. However, when the flame is below the water surface, the water will quickly bring the heat added to the wax pipe, so the wax pipe can protect the flame from burning all the time.

Water plays a key cooling role, so that the candle near water will not melt due to the burning of the wick, so that the water is separated from the outside by the unburned wax layer, and the candle in the middle will not continue to burn until it burns to the bottom of the cup.

Extended data candle burning refers to the violent oxidation reaction between paraffin wax and oxygen. Paraffin is a very stable alkane. When burning now, paraffin molecules are split into carbon atoms and hydrogen atoms, and oxygen is also split into oxygen atoms, and then oxygen atoms are combined with carbon atoms and hydrogen atoms respectively. Candle burning is the embodiment of this process.

The line in the middle of the candle is called wick, which plays the role of absorbing liquid wax oil. When the candle was first produced, there was solid wax oil on the wick. When you light a candle with fire, the solid wax oil is heated, first melted and then vaporized, and then the wax oil vapor is ignited with fire, so the candle is lit.

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Baidu encyclopedia-candle