When carbon burns it seems to disappear, why is this?

Burning is the rapid oxidation of a substance (which may or may not actually involve the addition of oxygen, but that is the most common result).

So when you burn carbon, you get carbon + oxygen, which exists in two forms: carbon monoxide, and carbon dioxide.

Both CO and CO2 are gases. So, they disperse into the air, making it look as if the carbon disappears.

Carbon forms a colorless, odorless gas, Carbon dioxide. Sulfur does the same thing, but Sulfur dioxide is not odorless. Carbon will also actually ignite in an atmosphere of Fluorine gas. The Carbon tetrafluoride produced is also colorless and odorless. The Fluorine has an acrid stench and will burn you very badly. Once there was no Oxygen on earth. When plants evolved, they increased the Oxygen in the atmosphere and it killed nearly everything else on earth. Oxygen is nearly as noxious as Fluorine, but life has adapted to it.