air feparable from the lead ore of Derbyshire, or from Black-Jack, by folution in the acid of vitriol, impregnates common water with the fulphureous findll of Harrogate water; and I have alfo fhewn that the bladder fucus or fea-wrack, by being calcined to a certain point, and put into water, not only gives the water a brackish tafle, but communicates to it, without injuring its tranfparency, the fmell, tafte, and other properties of Harrogate water. Profeffor Bergman impregnated water with a fulphurcous tafe and finell, by means of air feparated by the vitriolic acid from hepar fulphuris, made by fufion of equal weights of fulphur and pot-afhes, and from a mafs made of three parts of iron filings melted with two of fulphur; and he found alfo, that Black-Jack and native Siberian iron yielded hepatic air, by folution in acids. This, I believe, is the main of what is known by chemias on this fubject; what I have to fuggel, relative to the Harrogate waters in particular, may perhaps be of ufe to future enquireis.

"I have been told, that on breaking into an old coal-work, in which a confiderable quantity of wood had been left rotting for a long time, there iffued out a great quantity of water finelling like Harrogate water, and leaving, as that water does, a white fcum on the earth over which it paffed. On opening a well of common water, in which there was found a log of rotten wood, an obfervant phyfician affured me, that he had perceived a frong and diftinct fmell of Harrogate water. Dr. Darwin, in his ingenious account of an Artificial Spring of Water, publifhed in the first part of the LXXVth. Volume of the Philofophical Tranf

actions, mentions his having per ceived a flight fulphureous fmell and tafte in the water of a weil which had been funk in a black, loofe, moift earth, which appeared to have been very lately a morafs, but which is now covered with houfes built upon piles. In the bog or morals above ment oned there is great plenty of fulphureous water which feems to fpr ng from the earth of the rotten wood of which that bog confifts. Thefe facts are not fufficient to make us certain, that rotten wood is efficacious in impregnating water with a fulphureous fiell; because there are many bogs in every part of the world, in which no fulphureous water has ever been difcovered. Nor, on the other hand, are they to be rejected as of no use in the inquiry; becaufe wood, at a particular period of its putrefaction, or when fituated at a particular depth, or when incumbent on a foil of a particular kind, may give an impregnation to water, which the fame wood, under different circumftances, would not give.

"The bilge water, ufually found at the bottom of fhips which are foul, is faid to fmell like Harrogate water: 1 at firft fuppofed, that it had acquired this fmeil in, confequence of tecoming putrid in contact with the timber on which it refted, and this circumftance I confidered as a notable fupport to the conjecture I had formed of rot-. ten wood, being under certain circumitances, inftrumental in generating the fmell of Harrogate water. But this notion is not well founded; for the bilge water is, I fuppofe, falt water; and Dr. Short fays that fea water, which had been kept in a fone bottle fix weeks "itunk not much fhort of Harrogate fulphur water." It has been remarked

temarked above, that calcined fea wrack, which contains a great deal of fea falt, exhales an odour fimilar in all refpects to that of Harrogate water; and in confirmation of the truth of this remark, I find that an author, quoted by Dr. Short, fays, that "Bay falt thrice calcined, diffolved in water, gives exactly the odour of the fulphur well at Harrogate." From thefe experiments confidered together, it may, perhaps, be inferred, that common falt communicates a fulphureous fmell to water both by putrefaction and calcination. Hence fome may think, that there is fome probability in the fuppofition, that either a calcined ftratum of common falt, or a putrefcent falt spring may contribute to the production of the fulphurcous fmell of Harrogate water; efpecially as thefe waters are largely impregnated with common falt. However, as neither the falt in fea-water, nor that of calcined fea-wrack, nor calcined bay falt, are any of them abfolutely free from the admixture of bodies containing the vitriolic acid, a doubt ftill remains, whether the fulphureous exhalation, here fpoken of, can be generated from fubftances in which the vitriolic acid does not exist.

"The fhale from which alum is made, when it is first dug out of the earth, gives no impregnation to water; but by expofure to air and moiture its principles are loofened, it fhivers into pieces, and finally moulders into a kind of clay, which has an aluminous tafte. Alum is an earthy falt, refulting from an nion of the acid of fulphur with pure clay; and hence we are fure, that fhale, when decompofed by the air, contains the acid of fulphur; and from its oily black appearance, and especially from its being in 1786.

flammable, we are equally certain that it contains plogiton, the other conflituent part of fulphur. And indeed, pyritous fubftances, or com binations of fulphur and iron, enter into the composition of many, probably of all forts of fhale, though the particles of the pyrites may not be large enough to be feen in fome of them; and if this be admitted, then we need be at no lofs to account for the bits of fulphur, which are fublimed to the top of the heaps of fhale, when they calcine large quantities of it for the purpose of making alum: nor need we have any difficulty in admitting, that a phlogidic vapour must be difcharged from fhale, when it is decompofed by the air. Dr. Short fays, that he burned a piece of aluminous fhale for half an hour in an open fire; he then powdered and infufed it in common water, and the water fent forth a most intolerable fulphureous fimell, the very fame with Harrogate water.

He burned feveral other peces of fhale, but none of them ftunk fo ftrong as the first. This difference may be attributed either to the different qualities of the different pieces of fhale which he tried, or to the calcination of the first being pushed to a certain definite degree; for the combina. tion of the principles on which the fmell depends may be produced by one degree of heat, and destroyed by another. I have mentioned, briefly, thefe properties of fhale, because there is a itratum of fhale extended over all the country in the neighbourhood of Harrogate; feveral beds of it may be feen in the ftone quarry above the fulphur wells; many of the brooks about Harrogate run upon fhale, and the fulphur wells fpring out of it. They have bored to the depth of twenty yards into this fhale, in different

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places,

places, in fearch of coal, but have have never penetrated through it. Its hardness is not the fame at all depths. Some of it will strike fire, as a pyrites does with steel; and other beds of it are soft, and in a state of decompofition, and the fulphur water is thought to rife out of that fhale which is in the softeft ftate. But whatever impregnation fhale when calcined, or otherwife decomposed to a particular degree, may give to the water which paffes over it, it must not be concluded, that fhale in general gives water a fulphurcous impregnation; fince there are many fprings, in various parts of England, arifing out of fhale, in which no fuch impregnation is obferved.

"I forgot to mention in its proper place, that having vifited the bog, fo often spoken of, after a long feries of very dry weather, I found its furface, where there was no grafs, quite candied over with a yellowish cruft, of tolerable confiftency, which had a strong aluminous tale, and the fmell of honey.

Bergman fpeaks of a turf found at Helfingberg, in Scania, confifting of the roots of vegetables, which was often covered with a pyritous cuticle, which, when elixated, yielded alum; and I make no doubt, that the Harrogate morafs is of the fame kind.

"Whether nature ufes any of the methods which I have mentioned of producing the air by which fulphureous waters are impregnated, may be much questioned; it is of ufe, however, to record the experi ments by which her productions may be imitated; for though the line of human understanding will never fathom the depths of divine wifdom, difplayed in the formation of this little globe which we inhabit; yet the impulfe of attempting an investigation of the works of God is irrefiftible; and every phyfical truth which we difcover, every little approach which we make towards a comprehenfion of the mode of his operation, gives to a mind of any piety the most pure and fublime fatisfaction."

ΤΗ

THE eruption of Mount Vefuvius, which began in the month of November, 1784, nearly at the moment of my return from England to this capital, and which continued in fome degree till about the 2cth of last month has afforded much amufement to travellers unacquainted with this won

derful operation of nature, but no new circumftance that could justify my troubling you with a letter on the fubject. The lava either overhowed the rim of the crater, or iffued from fmall fiffures on its borders, on that fide which faces the mountain of Somma, and ran more or lefs in one, and at

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Aimes in three or four channels, regularly formed, down the flanks of the conical part of the volcano ; fometimes defcending and fpreading itself in the valley between the two mountains; and once, when the eruption was in its greatcft force, in the month of November laft, the lava defcended still lower, and did fome damage to the vine yards, and cultivated parts at the foot of Vefuvius, towards the vil lage of St. Sebaftiano; but generally the lava, not being abundant, ftopped and cooled before it was able to reach the valley. By the accumulation of thefe lavas on the flanks of Vefuvius, its form has been greatly altered; and by the frequent explofion of fcorie and afhes, a confiderable mountain has been formed within the crater, which now rifing much above its rim has likewife given that part of the mountain a new appearance. Juft before I left Naples, in May 1783, I was at the top of Vefuvius. The crater was certainly then more than 250 feet deep, and was impracticable, its fides being nearly perpendicular. This eruption, however, has been as fatisfactory as could be defired by the inhabitants of this city, a prodigious quantity of lava having been difgorged; which matter, confined within the bowels of the earth, would probably have occafioned tremors; and even flight ones might prove fatal to Naples, whofe houfes are, in general, very high, ill built, and a great number in almost every street already fupported by props, having either fuffered by former earthquakes, or from the loofe volcanic foil's having been washed from under their foundations by the torrents of rain water from the high grounds which furround Naples,

and on which a great part of the town itself is built.

"From the time of the laft formidable eruption of Mount Vefuvius, in August 1779 (defcribed in one of my former communications to the Royal Society) to this day, I have, with the afliftance of the Father Antonio Piaggi, kept an exact diary of the operations of Vefuvius, with drawings, fhewing, by the quantity of fimoke, the degrees of fermentation of the volcano; alfo the courfe of the lavas during this laft eruption, and the changes that have been made in the form of the mountain itself by the lavas and fcoriæ that have been ejected. This journal is becoming very curious and interefting; it is remarkably fo with refpect to the pointing out a variety of fingular effects that different currents of air have upon the fmoke that ifiues from the crater of Vefuvius, elevated more than 3600 feet above the level of the fea; bur, except the fmoke increafing confiderably and conftantly when the fea is agitated, and the wind blows from that quarter, the operations of Vefuvius appear to be very capricious and uncertain. One day there will be the appearance of a violent fermentation, and the next all is calmed again: but whenever the fmoke has been attended with confiderable ejections of fcoriæ and cinders, I have conftantly obferved, that the lava has foon after made its appearance, either by boiling over the crater, or forcing its paffage through crevices in the conical part of the volcano. As long as I remain in this country, and have the neceffary affift.nce of the above-mentioned ingenious monk (who is as excellent a draughtsman as he is an accurate and diligent G2 obferver)