‘Dr. Thompfon, of Naples, on Siliceous Incruftations. 
fobftance of thofe greater ftalaétites of the 
Montamiata, as we have indeed alread 
noticed in thofe fpecimens found in I{chia, 
by Abbate Breiflak (f{. 6.), and as ap-- 
pear more clear in thofe {pecimens of fili- 
ceous ftalactite, tranfparent as glafs, 
found afterwards in the above ftated vifit ' 
to the Zolfatara di Pozzuoli (f{. 7.), when, 
together with Count Redern, I had the 
fortune to inform my/felf of the pheno- 
mena alyeady recited, and befides that, 
to find fulphur and filiceous ftalaétite fo 
intimately combined, that there is no 
longer a doubt of their being produced 
together ; deriving their common origin 
from warm and humid vapours, and hence 
denominated by me thermal: and here 
I obferve, that the moifture apparent in 
drops near the fulphur produced from the 
Zoltfatara, is loaded. with vitrioiic acid, 
while thofe drops which diltil round 
about the filiceous ftalactites of Monticeto, 
where there is no palpable fulphur, are 
infipid, and devoid of fmell. (11.) At 
prefent, we know that Profeflor Black, 
ef Edinburgh, analizing the waters of 
Geyler, difcovered in them the prefence 
of mineral alkali, the known folvent of 
filiceous earth, put into aflign by means 
of fire, or in the dry way.” See Philos, 
‘Trans. of Edinb. (12.) Weknow, like- 
wife, that in the junétures, or knots of 
the cane called bamboo, filiceous earth is 
found, pure and concrete, and of fuch 
hardnefs as to fcrape glafs. See Macie 
upon Tabafheer in the Philos. Trans. of 
London. (13.) This moft interefting 
addition to our knowledge upon the power 
always exifting in the live cane to retain 
filiceous earth in a ftate of liberty, ex- 
cited me to feek that mean which feemed 
to me beft adapted to fuch folution, I 
mean mineral alkali in the frefh juice of 
‘ fome plant which might moft refzmble 
the bamboo, and for this purpofe, I took 
the common:cane of this kingdom (arun- 
do donax (rofeau), and infufing into its 
juice fome few drops of fpirits of fea falt, 
I gained, by flow evaporation,little cubes 
‘of marine falt, a proof of the prefence of 
mineral alkali which f fought for. 
Sufpecting the purity of the acid I 
had employed, which might perhaps hold 
im folution marine falt already formed : 
to convince myfelf more fully, I expofed 
to flow evaporation the decoétion of the 
faid juice, made with diftilled water as 
before, without any infufion of {pirit of 
marine falt; but it happened to me to dif- 
cover, what even until now I have been 
unable to explain, that is, to find cubes 
et fea falt alfo this time, and in fuch 
337 
abundance, that it being impoffible it 
‘fhould have been an error, it is neceflary 
to believe, that not only mineral alkali, 
but likewife alfo marine falt, exifts ef- 
feétively in the live cane; becaufe, with 
this view I colleéted the canes in the val- 
ley between the crater of A ftruni and that 
of the Zolfatara, which is feparated from 
the fea by the whole elevation of the Zol- 
fatara, and by other circumjacent hills, 
which removes the fufpicion that the 
marine falt could be feattered by the fea 
breezes, and had fallen upon the canes : 
this caution I took for greater fecurity, 
becaufe fuch a fufpicion undifputed,would 
have produced other difficulties, and thofe 
not trivial. (14.) It is known, however, ~ 
mott inconteftibly, that almoft, if not all, 
the thermal waters of If{chia, abound 
with mineral alkali, both free, and united 
with marine acid ; it is found alfo in both 
{tates attached to the rock, above the 
{pring called Gorgitello, which furnithes 
its waters to the baths of the neighbour- 
ing beautiful hofpital. We are affured 
that the faid mineral alkali has been 
found, although in one place only, of the 
Zolfatara of Pozzuoli, that is, in the 
glauber falts. See Breiflak fulla Zolfat. 
(15.) The prefenc: of mineral alkali in 
the humid vapaurs of Vefuvius, will not 
be difputed by any one who knows how 
frequent is marine falt cryftallized in 
cubes, atnong the falts. produced ‘from 
fuch vapours as well in the jaft as in other 
eruptions : neverthele{s the orifices, how- 
ever fmall, which now fubfift on the {pot 
where are found the little Vefuvius pearls, 
‘mentioned (fec. 8.) fuffice to bring to our - 
recolleétion the exceffive quantity of fuch 
vapours which evoived themfelves on thofe 
horrible days, when exploded from the 
aby{s, the vifcera of the earth disfigured 
and changed in their nature by fire, were 
feen to melt like glats; a fubject of moft 
interefting contemplation to the minera- 
logift, not, however, unmixed with ap- 
prehenfion, .while he beheld loaded vines, 
cities, the fruits of human ingenuity, over- 
thrown and utterly deftroyed. (16.) The 
origin then of thefe filiceous ftalactites, 
whether tranfparent or fnbdivided and 
fhining with a pearly brightnefs, appears 
to depend on no other caufe than the fo- 
lution of filiceous earth by means of mi- 
neral alkali, and by the humid way, that - 
is, by humid yapours rendered aétive by 
excefs of fire. (17.) The place from 
whence thefe vapours efcape, becoming 
charged from time to time, it becomes 
probable from this (fec. 9.), that the fia- 
lactites found beneath the het bath of 
ae x2 Sau 
