This substance, known also in commerce by the name of saltpetre, is
brought to this country from India, where in certain places, it forms
a sort of efflorescence on the soil; this is taken off together with
the surface of the soil, and mixed with water, which, after all the
earth has subsided holds the nitre in solution. The water is then
evaporated and the nitre crystallizes in six sided prisms.
On most parts of the continent nitre is manufactured from what are
called nitre beds, these consist of old mortar and other matters
containing lime, as the dry rubbish from old building, &c., together
with manure and other animal refuse. These beds are packed up and
kept from the rain for a certain time, when a small part of the lime
is found to be converted into nitrate of lime, this is the white
substance frequently seen to exude from newly built walls in the
form of crystals like snow. The whole mass of the nitre bed is next
washed; the water used for the first portions being poured over the
next, and so on till it is pretty rich in nitrate of lime, this is
then mixed with carbonate of potash, which decomposes the nitrate
of lime forming nitrate of potash, (nitre), and carbonate of lime,
(chalk); this last settles down and leaves the solution of nitre
clear, which is evaporated, and the nitre got pure.
Nitre is used for making gunpowder and fireworks of different kinds,
also for curing meat, especially pork and beef, to which it imparts a
red color; it is also used for making nitric acid, in the manufacture
of sulphuric acid, and as a medicine.