I'd like one of the major trade methods in the story I'm writing to be, essentially, blimps/balloons. I'm willing to handwave some of the details of it -- for instance, there's "ports" and trade routs generated by air currents because I said so and it's narratively convenient -- but I'm trying to figure out how they get their gases for the balloons.
Hot air is an option, I suppose, although it seems like that would get cumbersome for long voyages (how would they transport enough fuel?) So the obvious options seem like hydrogen and helium (the former having the fun bonus of potential dramatic explosions/fires).
But I'm not sure how a pre-industrial/medieval society could produce either of those. What I could find seemed to indicate means of production I'd rather not have to deal with (e.g., doing stuff with uranium). It seems like hydrogen could possibly be made from coal? How complicated would that be? What about gathering methane from swamps?
Again, the level of technology is somewhat flexible, and I can use magic if necessary, but in general I'm trying to avoid that. Any thoughts on how a pre-industrial society might produce lighter-than-air gases? Or is this a crazy idea I should just abandon?
Thanks so much!
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