Gas is a state of matter having neither shape nor volume but having the possibility of indefinite expansion, or diffusion. Cold converts gases into liquid or solid state; heat converts solids and liquids into gases. Air is composed of nitrogen and oxygen gases. Poison gases are used in war, helium employed in balloons, neon in electric signs. The actual discovery of gas was made by a 16th century alchemist, Jean Baptiste Van Helmont. While he was decidedly a mystic, believing in medieval vagaries, Van Helmont was capable of scientific observation. He observed that when coal burned away it left only small residue of cinders and that the rest of the coal disappeared in a volatile form. 'This spirit that is contained in vessels, but that cannot be reduced to a visible body, I called by a new name—Gas,' Van Helmont wrote. He took the name from the Greek word 'chaos,' because he suspected gas to be in the confused state of primordial matter. Later observers found that gas behaves in a well-regulated manner and not as Van Helmont supposed.
