3. Make gunpowder.
Before potassium nitrate or saltpeter—which is a main component of gunpowder along with charcoal and sulfur—began to be produced on a large scale in the 20th century, gunpowder makers would make it out of pee, which contains nitrogen and ammonia. The reaction of the ammonia with oxygen forms nitrates. When combined with manure, leaves, and potassium-containing ash, as described by physician and geologist Joseph LeConte in 1862, BOOM!—you’ve got potassium nitrate.

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