If you now toss a piece of wood, or even a sheet of paper, onto this fire, what you will notice is that the new fuel produces a lot of smoke as it heats up. Then, all of a sudden (often with a small pop), it bursts into flame and the smoke disappears. There are four things that you find in any piece of wood:
1.Water - Freshly cut wood contains a lot of water (sometimes more than half of its weight is water). Seasoned wood (wood that has been allowed to sit for a year or two) or kiln-dried wood contains a lot less water, but it still contains some.
2.Volatile organic compounds - When the tree was alive, it contained sap and a wide variety of volatile hydrocarbons in its cells. If you have read How Food Works, you know that cellulose (a chief component of wood) is a carbohydrate, meaning it is made of glucose. A compound is "volatile" if it evaporates when heated. These compounds are all combustible (gasoline and alcohol are, after all, hydrocarbons -- the volatile hydrocarbons in wood burn the same way).
3.Carbon
4.Ash - Ash is the non-burnable minerals in the tree's cells, like calcium, potassium and magnesium.
When you put the fresh piece of wood or paper on a hot fire, the smoke you see is those volatile hydrocarbons evaporating from the wood. They start vaporizing at high temperatures. If the temperature gets high enough, these compounds burst into flame. Once they start burning, there is no smoke because the hydrocarbons are turned into carbon dioxide and water (both invisible) when they burn.
This explains why you see no smoke from a charcoal fire (or a fire that has burned down to embers). Charcoal is created by heating wood to high temperatures in the absence of oxygen.
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