All sorts of things can burn chemically or undergo nuclear reactions
and end up being something besides carbon. For example, hydrogen and
oxygen burn to make water. Nuclear fission and fusion processes make
different elements than the starting elements, but usually not carbon.
Most of the things you burn are left over from some sort of living
thing- maybe a tree or a cow. Our form of life is filled with molecules
largely consisting of carbon, so it is often a prominent ingredient of
Carbon is most often is present in incompletely burned ashes.
Carbon itself burns, combining with oxygen to make CO2 (and sometimes
carbon monoxide). Charcoal production involves incomplete burning of
wood, and the high-carbon product can burn further. Soot is a byproduct
of fires which consists mostly of carbon, but even soot can burn, which
is why it's a good idea to sweep a chimney every so often.
If you burn something completely, the ashes may contain all kinds
of other stuff that didn't burn, and the carbon should burn away. Real
fires tend to burn incompletely.
Mike W. and Tom J.
(republished on 07/24/06)