PF,

Coal gas is a mix of hydrogen, CO and Methane, originally a by-product of coking coal for steelmaking. It was in use in Sydney up to the 70s, where it was bypassed largely by "natural gas" a topped petroleum gas.

In Britain during WW11, some civvy service vehicles were converted to run on coal gas (usually held in balloons attached to the roof of the vehicle). They were mainly delivery vehicles whose routes exceeded their fuel rations, but some doctors etc had them fitted to their cars.

Well spotted and researched Fang.

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