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lèverai parts that compofe it. Some
forts aiford only a gelatinous fub-
llance after a preparatory calcination ;
the caille of which moil probably is
this, tliat the calcareous earth has not
before been enough united with the
Iiliceous earth, at leaft not with the
whole of it. It is well known that
lime and quarz, when expofed to the
operation o f a fire, that has only caufed
tliem to bake together, neverthelefs afterwards
yield a gelatinous fubftance.
Alcaline fait mixed with fand affords
a iimilar demi-concretion, as when we
calcine pot-ailies ; on which account
the cieareil folution a long wliile after
precipitates filiceous powder, in the
fame proportion that the alcaline fait
attracTs fixed air, with which it preferably
unites itfelf. This generally
produces a gelatinous congelation,
when the water is faturated "with alcaline
fait, and alfo is well charged
with iiliceous earth.
From the fame caufe, clay, fpathcfe
Huor, and other fubftances, hard to
be diftblved in acids, may be brought
to a gelatinous congelation, when they
liave
; 377 ]
have before by fuilon been united with
alcaline fait, borax, or calcareous earth :
calcareous earth by itfelf never gives a
gelatinous fubftance in acids, confe-
quently it can ib much the lefs become
a iiliceous earth by this method, as has
however been thought by fome, who
would foon relinquiili their opinion, i f
they would only make experiments
themielves ; where there is no flint before,
it cannot poffibly be produced
by any other acid, but that which is
obtained from Ipathofe fluor.
But at prefent this is enough of the
zeolite, of which I have treated more
extenfively, as it is found in great
abundance in Iceland, and is fuppofed
by fome to be produced in die dry
way ; but I hope that this matter is at
preient entirely determined, not only
by its reparation, but alfo by its pro-
duflion, which happens daily in the
water. See N ° 2.
I have for feveral years pail endeavoured
to difcover the number as well
as the nature o f the Original kinds of
earth. In the year 1758 Mr. Cron-
iledt counted nine ; if he had lived
longer
■ f0l‘ s.•
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