belt for every purpofe, fuperior even to that o f Rome*
and only requires to be cleanfed from cafual impurities.
Its fait is found already formed, in the earth like nitre,
and other common falts, in the nitreous and calcareous
earths of Spain ; nothing more being neceifary to refine
it, than a fimple lixivation, to filter, and clear it from the
impurities of the earth.
This lixivium is put into boilers, and evaporated over
the fire, till a thin fcum appears on its furface, like a
cobweb; the liquor is then run off into other velfels,
where, as it cools, it cryftallifes into larger or fmall
rnafles, the form being of no manner o f cdnfequence.
After this is performed, to fave the fait ftill diffolv-
ed in the remaining liquor, they fprinkle this liquor
over the earth, prepared for the lixivium, by which
means, none of the alum is loft. Perhaps if the
earth which has gone through this procefs, was to be
heaped up, in the fame manner as that, out o f which
they get faltpetre, it might again produce a freih ftock of
alum, by fome interior labour o f nature, with the affift-
ance of water, and air, for the kingdom o f Aragon a-
bounds with nitrous foil, from whence they get excellent
faltpetre, as is evident by the gunpowder of Villa Feliche,
the moft famous in Spain. I f any of thefe workmen
would fet about making experiments in this manner,
with alumineous earth, lhould it happen to fucceed, it
would
Would be of great fervice to' the people o f Alcaniz, who
are at prefent in a ftarving condition. I ihall not enter
further into the properties o f alum, which have been
fully defcribed, by chemical writers, particularly Mr.
Maquer, in a memoir read at the academy o f fcierices,
in 1762, and fuch as are defirous to be fully informed
of the nature of thefe works, will find in the memoirs
of the French academy of fciences, for 1750, a defcrip-
tion of the famous alum works of Solfatara, in the kingdom
of Naples, by the Abbe Nollet: thofe of Tolfa, near
Civita-vecchia, in the Roman ftate, have been accurately
defcribed by the Abbe Mazeas, in the fifth volume
o f memoirs o f foreign members of the fame academy.
And with refpetft to the fubjeft at large, Mr. Monet, in
his treatife De la alunation, has collected every necefla-
ry information for a perfect knowledge o f the fubjecft :
an object of confequence to a commercial people, and.
has always been attended to, by enlightened nations.
England, Sweden, Flanders and Italy, are the countries
where alum is principally found ; to fay nothing of
its ufe in medicine, I ihall only add, that it is fo material
an ingredient in commerce, tor dying and colourin
g , that without its aififtance, neither o f thefe branches
can be tolerably performed, it being as ferviceable
and neceifary upon ftuffs, as gum water and glutinous
oil are in painting.
L E T T E R