among the ancient Greeks and Romans generally meant carbonate of soda,
sometimes carbonate of potash. The Arab chemists, however, clearly
described nitrate of potash. In the works attributed to Geber and
Marcus Græcus, especially, its characters are represented. Raymond
Lully, in the thirteenth century, mentions sal nitri, and evidently
alludes to saltpetre, and Roger Bacon always meant nitrate of potash
when he wrote of nitre. It was not, however, until the seventeenth
century that the term acquired the definite meaning which we attach to
it.
At the beginning of that century there was much discussion as to the
formation of nitre, as it had been held that the acid which combined
with the alkali was ready formed in the atmosphere. Glauber was the
first to argue that vegetables formed saltpetre from the soil. Stahl
taught that the acid constituent of nitre was vitriolic acid combined
with phlogiston emanating from putrefying vegetable matter.
After gunpowder had become a prime necessity of life, saltpetre bounded
upwards in the estimation of kings and statesmen. In France in 1540
an Edict was issued commissioning officials called “salpêtriers” in
all districts who were authorised to seek for saltpetre in cellars,
stables, dovecotes, and other places where it was formed naturally.
No one was permitted to pull down a building of any sort without
first giving due notice to the salpêtriers. The “Salpêtrière” Asylum
in Paris recalls one of the national factories of nitre. During the
French Revolution citizens were “invited” to lixiviate the soil and
ceilings of their cellars, stables, etc., and to supply the Republic
with saltpetre for gunpowder. The Government paid 24 sous, 1s., a pound
for the nitre thus procured, though, as this was no doubt paid in
assignats, it was cheap enough. It was estimated that 16,000,000 lbs. a
year were thus provided.