Vivian said:
>when you speak of "cave earth" or "dirt" you really mean guano, right?
No, dirt from the cave floor. The saltpetre was extracted from the dirt
on the floor of the cave by putting it into big vats and leaching it with
water. The water was then boiled down to crystallize the dissolved saltpetre.
The nitrates in the dirt may have come from bat guano or from other sources.
Several mechanisms for the formation of nitrates in caves have been identified,
including leaching down from organic matter in the outside soil above the cave
and by bacterial fixation of nitrogen or ammonia from the cave atmosphere. Bat
guano was mined directly for fertilizer, but this had nothing to do with making
saltpetre except for the fact that bat caves tended to also have nitrate-rich
soils.
Mark Minton
