RE: Making Charcoal
As Stefan said I recall something about bat guano but also dung heaps being moved so the top soil beneath could be dug up and treated (boiling and catching the condensate?) to recover the nitrates. Similar to the way Arsenic is recovered from the soil beneath lead tailings piles.
>Potasium nitrate is made by pouring this morning's urine over last nights
>ashes, turning a bowl over the slush, and allowing it to evaporate. At the
>end of the day, turn the bowl right side up and collect the crystals that
>have formed on the surface (use a pottery bowl!). the crystals are the salt
>peter you seek.