Read it through once

A piece of wood can be burnt up in a fire and very little indeed of it is left. A few ashes will indeed remain, which are the minerals taken in from the earth, but all the rest has vanished into the atmosphere. The water which was contained in the wood has become steam and is evaporated; the woody matter consisted chiefly of compounds of a chemical substance, carbon, which also becomes an invisible gas (carbonic acid gas) in a fire and goes back into the atmosphere.