of fulphur. Some of these tubs have been in ufe many years, and the adhering cruft is thick in proportion to the time they have been applied to the purpofe; but the fulphur pellicle was fufficiently observable on one which was new in the beginning of this feafon. The water when it is first put into thefe tubs is transparent; when it has been expofed to the air for a few hours, it becomes milky; and, where the quantity is large, a white cloud may be feen flowly precipitating itself to the bottom: this white precipitate confifts partly, I am not certain that it confils wholly, of fulphur; and the fulphur is as really contained in the waters denominated fulphureous, as iron is contained in certain forts of chalybeate waters; in the one cafe the iron is rendered foluble in water by its being united to fixed air, or fome other volatile principle; and in the other fulphur is rendered foluble in water by its being united to fixed air, or fome other volatile principle: neither iron nor fulphur are of themselves foluble in water, but each of them, being reduced into the form of a falt by an union with fome other fubftances, becomes foluble in water, and remains diffolved in it, till that other fubitance either efcapes into the air, or becomes combined with fome other body.

"About forty years ago, they took up the bafon of the third well, and a credible perfon, who was himself prefent at the operation informed me, that in all the crevices of the flone on which the bafon refted, there were layers of pure yellow fulphur. This I can well believe, for I ordered a piece of fhale to be broken off from the bottom of the fourth well; it was fplit, as hale generally is into feveral

thin pieces, and was covered with a whitifh cruft. But laid on a hot iron, in a dark room, it crackled very much, and exhibited a blue flame and fulphureous fmell.

"If the water happens to ftand a few days in any of the weils, without being diffurbed, there is found at the bottom a black fediment; this black fediment alfo marks the courfe of the water which flows from the well, and it may be esteemed characteristic of a fulphur water. The furface of the water alfo, when it is not stirred for fome time, is covered with a whitifh fcum. Dr. Short had long ago obierved, that both the black fediment, and the white fcum, gave clear indications on a hot iron, of their containing fulphur: I know not whence it has come that his accuracy has been questioned in this point; certain I am, that on the repetition of his experiments I found them true. The white fcum alfo, which is found flicking on the grafs over which the water flows, being gently dried, burns with the flame and smell of fulphur. From what has been faid it is clear, that fulphur is found at Harrogate, sticking to the bafon into which the water fprings; fublimed upon the ftones which compofe the edifice furrounding the well; adhering to the fides of the tubs in which the water ftands; fubfiding to the bottom of the channel in which the water runs; and covering the furface of the earth, and of the blades of grafs, over which it flows. It is unneceffary to add another word on this fubject; it remains that I risk a conjecture or two, on the primary caufe of the fulphureous impregnation obfervable in these waters.

"In the Chemical Effay before referred to, I have fhewn, that the

the

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 fmell 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 tafte, but communicates to it, without injuring its tranfparency, the fmell, tafte, and other properties of Harrogate water. Profeffor Bergman impreg nated water with a fulphureous tafe and fmell, by means of air separated by the vitriolic acid from hepar fulphuris, made by fufion of equal weights of fulphur and pot-athes, 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 chemifts on this fubject; what I have to fuggeft, relative to the Harrogate waters in particular, may perhaps be of ufe to future enquirers.

"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 wa ter, in which there was found a log of rotten wood, an obfervant phyfician affured me, that he had perceived a strong and diftinct fmell of Harrogate water. Dr. Darwin, in his ingenious account of an Artificial Spring of Water, published in the first part of the LXXVth. Volume of the Philofophical Tranf

actions, mentions his having perceived a flight fulphureous fmell and taste in the water of a well 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 morafs above mentioned there is great plenty of fulphureous water which feems to fpring from the earth of the rotten wood of which that bog confifts. These facts are not fufficient to make us certain, that rotten wood is efficacious in impregnating water with a fulphureous fmell; 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; because 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: I at firft fuppofed, that it had acquired this fmell in confequence of becoming 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 rotten wood, being under certain circumftances, 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 flone bottle fix weeks

itunk not much fhort of Harrogate fulphur water." It has been remarked

remarked above, that calcined fea wrack, which contains a great deal of fea falt, exhales an odour fimilar in all respects 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 contidered together, it may, perhaps, be inferred, that common falt communicates a fulphureous smell 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 fpring may contribute to the production of the fulphureous fmell of Harrogate water; especially as thefe wa ters 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 fill remains, whether the fulphureous exhalation, here fpoken of, can be generated from fubitances 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 moisture 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 union 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 efpecially from its being in 1786.

flammable, we are equally certain that it contains plogifton, the other conftituent part of fulphur. And indeed, pyritous fubftances, or combinations 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 mak ing alum: nor need we have any difficulty in admitting, that a phlogittic 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 infused it in common water, and the water fent forth a moit intolerable fulphureous fmell, the very fame with Harrogate water. He burned feveral other pieces 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 fliale which he tried, or to the calcipation of the firit 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 deftroyed by another. I have mentioned, briefly, thefe properties of fhale, becaufe there is a ftratum of fhale extended over all the country in the neighbourhood of Harrogate; feveral beds of it may be feen in the tone 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 thale, in different

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 ftate of decompofition, and the fulphur water is thought to rife out of that fhale which is in the fofteft ftate. But whatever impregnation fhale when calcined, or otherwife decompofed 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 fulphureous 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 confitency, which had a strong aluminous tatie, 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 ful phureous waters are impregnated, may be much questioned; it is of ufe, however, to record the experiments 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

In a Letter from Sir WILLIAM JOSEPH BANKS, Bart. P. R.S.

HE 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 20th of laft month has afforded much amufement to travellers unacquainted with this won

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

times in three or four channels, regularly formed, down the flanks of the conical part of the volcano; fometimes defcending and fpreading itfelf in the valley between the two mountains; and once, when the eruption was in its greatest 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 Vesuvius, towards the village of St. Sebastiano; 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 fcoria 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. Just 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, how ever, 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 communica tions to the Royal Society) to this day, I have, with the allitance of the Father Antonio Piaggi, kept an exact diary of the operations of Vefuvius, with drawings, fhewing, by the quantity of fmoke, the degrees of fermentation of the volcano; alfo the courfe of the lavas during this last eruption, and the changes that have been made in the form of the mountain itself by the lavas and feorie that have been ejected. This journal is becoming very curious and interesting; it is remarkably fo with refpect to the pointing out a variety of fingular effects that different currents of air have upon the finoke that iffues from the crater of Veluvius, elevated more than 3600 feet above the level of the fea; b, except the fmoke increafing confiderably and constantly 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 scoriæ 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 affiftince of the above-mentioned ingenious monk (who is as excellent a draughtfman as he is an accurate and diligent G 2 obferver)