Elizabeth I paid 300 pounds in gold to learn how to grow saltpetre
For centuries, whoever controlled saltpetre controlled gunpowder. England had no supply of its own, so in 1561, at war with Spain and cut off from imports, Elizabeth I paid a German captain 300 pounds in gold for a manual on how to make it grow. The secret ingredient was mostly manure.
Potassium nitrate, the mineral nitre, is a salt of potassium and nitric acid with a sharp, bitter taste. Nitrogen itself was named after nitre, and the name has deep roots: Egyptian and Hebrew words sharing the consonants n-t-r probably fed the Greek nitron. Arabs called it Chinese snow, Persians Chinese salt, and Europeans by the 15th century knew it as saltpetre. Before gunpowder, India's Arthashastra already mentioned its poisonous smoke as a weapon.
The raw material came from unlikely places: crusts on cave walls and piles of bat guano, which in Laos supplied gunpowder for Bang Fai rockets. In 1270 the Syrian engineer Hasan al-Rammah described how to purify crude saltpetre by boiling it and adding wood ash to strip out calcium and magnesium, and his terms suggest the gunpowder recipe came from China. In medieval Christian Europe, according to Michael Scot, one known source was a mountain near the sea in Aragon.
Countries without deposits farmed it. Nitraries buried dung and let saltpetre creep to the surface, while nitre beds, discovered in the early 15th century, relied on soil microbes to turn waste into nitrate. Shortly before the French Revolution, Turgot and Lavoisier set up a royal gunpowder agency whose compost heaps, kept moist with urine, were leached after about a year. The Confederacy, desperate during the Civil War, created a Nitre and Mining Bureau and forced enslaved people to labour in its nitre beds.
Industry finally ended the scramble. From 1903 nitric acid was made from air using an electric arc, and during the First World War the Haber and Ostwald processes let Germany make nitrates after losing Chilean supplies. Until the late 1880s black powder fired every gun on Earth; today the salt mostly goes into fertiliser, fireworks and even the red colour of cured meats.
Source: Potassium nitrate
