User blog comment:MyOpinion:/Redwall's future/@comment-2065021-20100516132522

Oh, Alcohol! What about alcohol? This was used once as well as a propellant.

And Air? This was used too, for snipers, known as 'Military Reapeating Air Rifle', and produced first in the 16th century.

I also once heard, that the nitrates for gunpowder could also be collected from plants, as an alternative; I'm not sure though. I think I'll go and investigate a little.

Though, I still remember from science, how nitrogen is transferred to nitrate, when entering the earth (so it can be fed to plants right away; unlike pure nitrogen).