Day 22 - – Chemical History of a Candle – The Flame and the Wick
“Shall we educate ourselves in what is known, and then casting away all we have acquired, turn to ignorance for aid to guide us among the unknown?”
― Michael Faraday, British Scientist early 1800
Here goes today’s science lecture: The flame has three regions where different chemical and physical phenomena occur. Combustion, the chemical reaction that produces carbon dioxide and water, occurs in the blue outer edge of the flame. Here the vaporized wax burns completely. This region, which is the hottest part of the flame, is not uniform: the blue is concentrated at the base of the flame, and decreases toward the top of the flame, where it is only a thin layer at the flame’s edge.
Combustion also occurs in the grayish-yellow section of the flame that surrounds the tip of the wick. Here the flame vaporizes the molten wax. The liquefied wax cools the flame and so this is the section of the flame with the lowest temperature. The wax here undergoes incomplete combustion. Incomplete combustion happens when there is not enough oxygen to combine with carbon: air, which supplies the oxygen, cannot travel easily into the flame. Because the combustion is incomplete some of the carbon from the wax remains in the flame. This darkens the flame creating the grayish cast near the wick. These heated, solid carbon particles, glow. As they rise in the flame they create a bright yellow region. This brightest part of the flame has a temperature between that of the hot blue region and the cooler grayish-yellow region. The glowing of the carbon particles is called incandescence. This phenomena occurs whenever a solid is heated enough to emit light. This incandescence is a physical change, unlike combustion in other parts of the flame, which is a chemical change. (source: Bill Hammack & Don DeCoste: Michael Faraday – Chemical History of a Candle)
