Phlogiston is the miracle substance rarely found in the real world, driving most technology on the Archon. It was identified by J.J. Becher who first published the existance of the substance in 1667. It is likely that he was a Changeling or had access to the hedge in order to identify the substance as he was unable to give any real proof for mortals about the existance of Phlogiston. It was not untill 200 years later that the link between Phlogiston and the gas driving the Archon was made.
Phlogiston is a gas collected from the air and distilled into viles of liquid phlogiston which on it boiled to steam to preassurise the Archon's systems. The reason Phlogiston is used are not fully explored, but it is speculated that it compensates better to the wyrd and because of its rarety it is much harder to manipulate with contracts then other liquids.