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They are more ftrongly attacked hy
fal fodæ than by borax, or fufible urinous
fait, becaufe there is moft filiceous
earth in all, which is beft diíTolved by
the folid alkaline fait in the dry way.
Laftly, feveral forts have the quality
of yielding jellies, that is to lay, they
change a proportionable quantity o f
acid to a femi-tranfparent congealed
mafs, which refembles a jelly.
Thefe congelations may in general be
produced in difiereiit ways ; fometimes
the menftruum by length o f time lofes
its power, when the difiblved part is
attacked gradually, though imperfectly,
fo that in a manner it remains
fufpended half difiblved, and after
fome evaporation at laft congeals to a
tough coherent fubftance. This frequently
happened in difiblving tin in
marine acid, or aqna-regia, when the
inflammable fubftance decreafes too
much, and by that means weakens the
connection between the metal and the
folvent.
Sometimes a kind o f gelatinous
congelation is produced by an im-
perfeCt precipitation. For inftance,
when
when the liquor filicum is united with
a certain quantity of acid, ib that tiie
iiliceous earth is not entirely feparated,
but remains fufpended in the liquor.
This much refembles a circurnftance
exhibited by fome zeolites, which I will
now more fully explain.
As the red zeolite o f Adelfors produces
this effecT; more clearly than any
other, it ihall ferve as an in fiance of
it. After this is feparated and freed
as much as pofiible from calcareous
fpar, three or four tea fpootis full of
it muft be thrown into a wine glafs
half filled with common aqua-fortis,
when after a ihort time the whole ib-
lution will be found in the form of
a reddifli gelatinous fubftance, that
nothing of it runs nut i f even the glafs
is turned. To diicover the caufe of
this, I have taken fome of the cleareit
jelly, and difiblved it with boiling water
in a glafs mortar, and left it to dry
on a filtering paper after a perfcfi
filtration, by which means the place
that it occupied was incredibly diminiflied.
I then tried tins fubftance
with acids, but it was not at all at-
A a 3 tacked.