Saltpeter is a much sought after commodity. It is used to make gunpowder.
Nitrate, more commonly known as saltpeter, is formed in warm climates by bacterial action during the decomposition of excreta and vegetable refuse. Where people and animals live in close proximity, debris accumulates in and around their homes. The contact between putrefying material, alkaline soil, plant ashes, air and moisture allows 'nitrification' - that is the conversion of nitrogen compounds from animal and plant decay into nitrates which penetrate the soil. Dissolved in rainwater, the deposits evaporate on the surface to form crude saltpeter, as a white flower like powder. This must be washed to remove earth and impurities; then boiled and evaporated to refine it.
Besides selecting their raw materials carefully, the saltpeter producers improve on nature by saturating the matter with blood and urine, mixed with potash-rich ashes. In addition, this slow biological action is sped up with 'nitre beds' - the waste and plant ashes are heaped up together, exposed to the air and watered at intervals. Eventually after the piles had been turned many times, this manure produces saltpeter.