arc curious o f being more exactly informed, may find at
very accurate account of thefe works in the memoirs
of the academy of fciences by Mr. Petit, to which I refer
them.
In Spain, where a third part of all the lands, and the'
very duft on the roads in the eaftern and fouthern parts
o f the kingdom, contain natural faltpetre, I have feen
them prepare it in the following manner.
They plough the ground two or three times in winter,
atnd fpring, near the villages. In Auguft they pile it
up in heaps of twenty and. thirty feet high: then fill
with this earth a range o f veffels, o f a conic ihape, per*
forated at bottom, obferving to cover the: aperture
with matweed and a few alhes, two or'three fingers deep,
that the. water may juft filter through. They then pour
on the water, (fomctimcs without putting any alhes);
the lye that refults from this operation is put into a boiler.
The common fait, which as we faid before precipitates,
and cryftalizes when warm, falls to the bottom o f the
cauldron in a proportion of 40 lb. to a quintal o f materials
(a) ; then the. liquor is poured into buckets placed
in the ihade, where it ihoots, and cryftalizes into fait-
(a) The Spaniftr quintal is ioolb. weigKt;and abont g) Ib.Engliih. The artobe'of Madrid:
is 25 lb. Spaniih, and four arrobes make one quintal,.
petre.
petre. The great quantity o f common fait which accompanies
the nitre, makes: me think, that the marine acid
with its bafts, is converted into-nitre. The fame earth,
deprived o f its nitrous quality by this procefs, is again
carried back to the fields, and expdfed td the elements,
by which means in the courfe of a twelvemonth, aflifted
by the all-powerful and invifible hand of nature, it again
becomes impregnated with a frelh fupply o f nitre, and
what is ftill more furprifing,. and cannot be obferved
without admiring the wonderful works of the omnipotent
creator, the fame lands have produced-time immemorial
an equal quantity of faltpetre ; fo that i f the fupreme
power was to annihilate all the faditious faltpetre o f
France, and Germany, Spain- alone could fupply the reft'
o f the world* without the aid of a fixed alkali; alhes or
vegetables, if public ceconomy joined hands with induf-
try, and aflifted in bringing-thefe great points to perfection
i I once aiked one o f thefe people the' reafon o f
that .conftant produdion o f faltpetre, but his only anfwer
was, I have two fields, I fow one with corn, and'
“ have a crop, I plough the other, and it furniilies me"
“ faltpetre.”
This faltpetre thus ciyftalized is fimilar to that df Paris
of the firft boiling. In Spain they only boil it once
more, and it becomes perfed, and proper for making o f
gun-powder, aqua fortis, and Other purpofes o f the
F 8 fhops.