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79 VON TROIL’S LETTERS ON ICELAND.
has been fubject to it? Ifthe Icelandic zeolite has been prepared by fire, we may juftly
queftion how it can produce above five quarts in twenty-five of water in diftilling.
This may likewife be applied to all the other forts, though they generally contain lefs
water, and the red fort from Adelfors only one quart in twenty-five. ‘This is evidently
the water of cryftallization, in proportion to which each kind {wells more or lefs by the
blow-pipe. The Icelandic and Feroe zeolites are moft fubject to this, almoft like borax 5
the Adelfors zeolite fwells much lefs, and that from Upland, and feveral other forts,
fo little, that it ceafes ina moment; and even then produces fo fmall an expanfion of
{pace, that it is fcarcely perceivable to the eye.
Since therefore all zeolites contain this water of cryftallization, which is neither
found nor expected in the productions of fire, it feems to me to be undeniable, that they
have been produced in the way of moifture; befides the zeolites do not confift of a
fimple particular kind of earth, but of three different forts which are mixed together,
and in a manner the one diflolved by the other, in confequence of which thei> connection
cannot be confidered as an original earth. In all, the greateft part ccnfifis of filiceous
earth, the next is argillaceous earth, and the leaft part is calcareous earth. ‘The two
laft forts may be diflolved by acids, and then precipitated by alkali volatile cauflicum,
by which the argillaceous earth, but not the calcareous earth, after being feparated from
the firft by filtrating, may be precipitated by fal fode.
{n this manner I have found that the zeolites defcribed above, contain 48 in 100 of
filiceous earth, 22 of pure argillaceous earth, and from 12 to 14 of calcareous earth.
If thefe numbers were added together, and reckoned with what it contains of water,
the produce is fomething more than oo. This furplus proceeds from the calcareous
earth, that enters into the zeolite without fixed air, with which it is afterwards impreg-
nated during the precipitation. Other zeolites contain exactly the fame fubftances, only
in different proportions.
Of thofe which I have hitherto examined, the Jemtland zeolite contains the greateft
quantity of calcareous earth, that is to fay, 16 parts in 100, and that from Feroe the
leaft, namely, 8in 100. The red zeolite from Adelfors contains the greateft quantity
of filiceous earth to wit 80 in 100, and the Icelandic the leaft, to wit 48in 100.. The
zeolite from Feroe contains moft argillaceous earth, namely, about 25 in 100, and that
from Adelfors the leaft, or about g in 100. When the original compofition of any
kind of {tone is thus known, it is not difficult to determine its qualities.
The zeolites at firft froth and {well in the fire, the caufe of which has been already
explained.
‘They afterward fufe more or lefs perfectly. The fwapparara may be reduced to a
clear glafs, andthe Upland red zeolite can hardly be brought to give any figns of vitri-
fication on the furface.
It is well known that quarz, pure argillaceous earth and lime, cannot feparately be
made to fufe, nor two and two mixed together in many cafes ; but when all three are
compounded, they are more or lefs inclined to fufion. One part of pure argillaceous
earth, with one part of lime, and two and a half to three parts of quarz, afford a mix-
ture, which is eafieft brought to fufe. Ifthe compofition of the zeolites is compared
with this mixture, they are found to be fufible in the fame meafure as the proportion of
their conftituent parts approaches more or lefs to the above-mentioned compofition.
‘They are more ftrongly attacked by fal fode: than by borax, or fufible urinous falt,
becaufe there is in all moft filiceous earth, which is beft diffolved by the folid alkaline
falt in the dry way.
Laftly,
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