Flame
Flame, a brightly burning mixture of gases. In an ordinary flame, the gas of a fuel combines with oxygen in the air, and light and heat are produced. When a candle is lighted, the heat of the match flame melts the fat in the wax, paraffin, or tallow that surrounds the wick. The liquid fat—which is the candle's fuel—passes up the wick, is changed into gas by heat, and produces a flame. The flame consists of three cone-shaped areas:
- The area of no combustion. This is a colorless region around the wick, made up of air and gas too cool to burn.
- The area of partial combustion. This is a cone of yellowish-white light that surrounds the area of no combustion. Here the fuel gas breaks down into hydrogen and carbon monoxide, which begin to combine with oxygen to form water and carbon dioxide. Particles of carbon, freed by these reactions, become so hot that they glow.
- The area of complete combustion. This is an outer, invisible cone in which the union of hydrogen and carbon monoxide with oxygen is completed. Heat, instead of light, is produced in this region because there is enough oxygen to combine with all the hydrogen and carbon.
The heat of a flame can be increased by increasing the supply of oxygen and thus the size of the area of complete combustion. This principle is used in the Bunsen burner.