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Encyclopedic overview
Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system originating from a gasworks. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous fuels produced for sale to consumers and municipalities.
The original coal gas was produced by the coal gasification reaction, and the burnable component consisted of a mixture of carbon monoxide and hydrogen in roughly equal quantities by volume. Thus, coal gas is highly toxic. Other compositions contain additional calorific gases such as methane, produced by the Fischer–Tropsch process, and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen.
Excerpted from Wikipedia’s “town gas” article, available under the CC BY-SA 4.0 licence.