Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 3 - By Alexander Von Humboldt And Aime Bonpland.
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It
Is Also Found In The Chain Of Mica-Slate And Clay-Slate, On The
North-West Coast Of The Island Of Trinidad, At Margareta And Near Cape
Chuparuparu, North Of The Cerro Del Distiladero.* (* Another Place Was
Mentioned To Us, West Of Bordones, The Puerto Escondido.
But that
coast appeared to me to be wholly calcareous; and I cannot conceive
where could be the situation of ampelite and native alum on this
point.
Was it in the beds of slaty clay that alternate with the alpine
limestone of Cumanacoa? Fibrous alum is found in Europe only in
formations posterior to those of transition, in lignites and other
tertiary formations belonging to the lignites.) The Indians, who are
naturally addicted to concealment, are not inclined to make known the
spots whence they obtain native alum; but it must be abundant, for I
have seen very considerable quantities of it in their possession at a
time.
South America at present receives its alum from Europe, as Europe in
its turn received it from the natives of Asia previous to the
fifteenth century. Mineralogists, before my travels, knew no
substances which, without addition, calcined or not calcined, could
directly yield alum (sulphate of alumina and potash), except rocks of
trachytic formation, and small veins traversing beds of lignite and
bituminous wood. Both these substances, so different in their origin,
contain all that constitutes alum, that is to say, alumina, sulphuric
acid and potash. The ores of Tolfa, Milo and Nipoligo; those of
Montione, in which silica does not accompany the alumina; the
siliceous breccia of Mont Dore, which contains sulphur in its
cavities; the alumiferous rocks of Parad and Beregh in Hungary, which
belong also to trachytic and pumice conglomerates, may no doubt be
traced to the penetration of sulphurous acid vapours. They are the
products of a feeble and prolonged volcanic action, as may be easily
ascertained in the solfataras of Puzzuoli and the Peak of Teneriffe.
The alumite of Tolfa, which, since my return to Europe, I have
examined on the spot, conjointly with Gay-Lussac, has, by its
oryctognostic characters and its chemical composition, a considerable
affinity to compact feldspar, which constitutes the basis of so many
trachytes and transition-porphyries. It is a siliciferous subsulphate
of alumina and potash, a compact feldspar, with the addition of
sulphuric acid completely formed in it. The waters circulating in
these alumiferous rocks of volcanic origin do not, however, deposit
masses of native alum, to yield which the rocks must be roasted. I
know not of any deposits analogous to those I brought from Cumana; for
the capillary and fibrous masses found in veins traversing beds of
lignites (as on the banks of the Egra, between Saatz and Commothau in
Bohemia), or efflorescing in cavities (as at Freienwalde in
Brandenburg, and at Segario in Sardinia), are impure salts, often
destitute of potash, and mixed with the sulphates of ammonia and
magnesia. A slow decomposition of the pyrites, which probably act as
so many little galvanic piles, renders the waters alumiferous, that
circulate across the bituminous lignites and carburetted clays.
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