Full resolution (JPEG) - On this page / på denna sida - Pages ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
720 VON TROIL’S LETTERS ON ICELANB,
is evidently an incruftation upon mofs and fimilar fubftances, which have been decayed
by length of time, and left thofe cavities. In regard to its compofition, it is of a filiceous
nature as the preceding, and alfo perfectly fimilar in refpect to fire and diffolvents.
I have already mentioned the folution of the flint in fal fodee with the blow-pipe;
and as I fhall hereafter have frequent occafion to refer to it, I will in this place relate
the whole procefs. The late director of the mines ( bergmaftare), Mr. Cron{tedt, makes
mention of this falt in his Mineralogy, but it is very feldom ; and he confiders it as lefs
proper for ufing with the blow-pipe, becaufe it is too foon imbibed by the coals. It
certainly does not afford a very good folution upon coals, and I therefore made ule of a
filver fpoon, made on purpofe; by which method I have been able to make-good ufe of
the fal fod, which in his examinations of the different kinds of earth in this manner, is
very ferviceable, and even indifpenfably neceflary, as I fhall hereafter prove more at
large, in a little diflertation on the blow-pipe, and its proper ule.
[have frequently inferted a fuppofition in my printed works, that though the filiceous
earth cannot be diffolved in the ufual manner in water, yet it might with the help of a
ereat degree of heat ; and that this really happened at Geyfer, is evidently proved by
the above defcribed cruftated ftone. ‘The hot water forms of itfelf the large filiceous
bafon from which it iffues out of the fubftance, that is in a diffolved-ftate at the firft, but
quickly precipitates on account of the heat decreafing in the open air. The heat of the
water was not examined with the thermometer, till fuch time that the bafon was filled,
when it was neverthelefs found at a hundred degrees, according to the Swedifh meafure.
dt is in all probability much greater under the earth ; for its running through cooler
channels, and its fpouting afterwards into the air to a great height, muft neceflarily very
much diminifh the heat on account of the great difperfion.
This quick depofiticn produces both the opacity and irregular form of this ftone, and
prevents the particles from being fo clofely united, as might have been expected from
ihe degree of the hardnefs of each, fuppofing the folvent power had diminifhed more
eradually.
oN Scheele has difcovered the formation of the flint; and I myfelf have found out,
within thefe two years, a method of obtaining, with the help of fome fluor acid, thirteen
precipitated cry{tals of the fize of fmall peas. This artificial pebble in all experiments,
both in the wet and dry method, and even in the focus of a burning-glafs, in a piece that
I fent to Mr. Macquer, difcovered exactly to him the fame qualities as the natural one.
All thefe circumftances, therefore, prove that the pebble is a faline earth, which is
compofed of fluor acid, and an original fub{tance exifling in the watry exhalations. It
is not quite fimple ; but however I have not been able to confider it as any other than
an elementary earth: indeed my judgment is, that it cannot be compounded from any
other principle. ;
I do not in this place mean a finer or coarfer powder, by the denomination of earth,
as is generally under{tood under this appellation ; but I take the word in a chemical fenfe,
to exprefsa fixed principle, which is obtained in analyfing any fubftance, and that can-
not be diflolved in boiling water, after the niceft mechanical divifion. It is well known
that the diffolubility of any fubftance may be leffened by certain compofitions ; and that
a folvent can better attack the fubftance, according to the extent of its furface; and that
la{tly, water in an open veffel will not admit of any greater degree of heat than one
hundred degrees, according to the Swedifh thermometer. A fubftance may, by this rule,
be diffoluble by itfelf, after having gone througha preparatory cleanfing, or a chemical
feparation, or with the afliftance of a greater degree of heat, though it may be indiflo-
Juble without any preparation, or with the ufual method of boiling; and it is with a
view to this circumitance that J call the flint a kind of falt earth.
r3 I have
<< prev. page << föreg. sida << >> nästa sida >> next page >>
