coal gas

Coal gas is a fuel once supplied to most homes and factories but now largely replaced by safer and more energy-rich natural gas. Coal is made by heating coal to about 900°C (1,650°F) in a closed retort and collecting the volatile matter (a process known as destructive distillation); coke remains as a residue. Coal tar is condensed out, and other valuable materials are removed by dissolving them out with water. The remaining mixture of gases, containing methane, carbon monoxide, and hydrogen, together with nitrogen and small amounts of other gases, is coal gas.