Illuminating gas was a synthetic mixture of hydrogen and hydrocarbon gases produced by destructive distillation (pyrolysis) of bituminous coal or peat. It was used for gas lighting, as it produces a much brighter light than natural gas or water gas . Although also sometimes called coal gas, it should not be confused with water gas or syngas, which are made from anthracite coal or coke plus water, and chemically quite different. Illuminating gas was much less toxic than these other forms of coal gas, but less could be produced from a given quantity of coal.
Illuminating gas consists mainly of methane, ethylene and hydrogen. The experiments with distilling coal were described by John Clayton in 1684. George Dixon's pilot plant exploded in 1760, setting back the production of illuminating gas a few years. The first commericial application was in a Manchester cotton mill in 1806. In 1901, studies of the defoliant effect of leaking gas pipes lead to the discovery that ethylene is a plant hormone.
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