Chopped wood and Logs putting on the fire, Fraserburgh, Aberdeenshire, Scotland, UK When the volatile gases are hot enough about 500 degrees F 260 degrees C for wood, the compound molecules break apart, and the atoms recombine with the oxygen to form water, carbon dioxide and other products. In other words, they burn. The carbon in the char combines with oxygen as well, and this is a much slower reaction. That is why charcoal in a BBQ can stay hot for a long time. A side effect of these chemical reactions is a lot of heat. The fact that the chemical reactions in a fire generate a lot of new heat is what sustains the fire. Many fuels burn in one step. Gasoline is a good example. The heat vaporizes gasoline and it all burns as a volatile gas. There is no char. Humans have also learned how to meter out fuel and control fire. A candle is a tool for slowly vaporizing and burning wax. As they heat up, the rising carbon atoms as well as atoms of other material emit light. This `heat produces light` effect is called incandescence, and it is the same kind of thing that creates light in a light bulb. It is what causes the visible flames. Flame colour varies depending on what you`re burning and how hot it is. Colour variation within a flame is caused by uneven temperature. Typically, the hottest part of a flame -- the base -- glows blue, and the cooler parts at the top glow orange or yellow.

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