In the prefent performance the Author. has taken a wider range than in his former philofophical publications, and has, accordingly, given it a more comprehenfive title. The work is divided into forty fections, the mere titles, or contents, of which would alone nearly occupy the space that we can conveniently allot to an Article. Amidft fuch a multiplicity of matter, it will be most proper to confine ourselves to fome particular subjects, and thofe, too, fuch as may be moft conveniently detached from the rest.

The firft curious obfervation in this volume, that we shall notice, relates to the dephlegmating the vitriolic acid, and the reducing it to a crystalline state; or the converting common oil of vitriol into what we apprehend to be the glacial oil of vitriol, by a very fingular process. This was effected by impregnating ftrong vitriolic acid with what the Author has called Nitrous Acid Vapour; or that peculiar vapour of the nitrous acid, which is produced in confequence of a rapid folution of bismuth in fpirit of nitre. The firft obfervation leading to this subject is to be found in the third volume of the Author's Obfervations on Air, pag. 217.

In one of the proceffes here defcribed, the vitriolic acid had fhot into the most regular and beautiful cryftals refembling a feather; the fibres of which on each fide made an angle with each other (as happens in the ice of water) of about 160 degrees. These were furrounded and covered with a liquor, which, being heated, afforded a large quantity of the pureft nitrous air. In fhort, it appears from this procefs, that, notwithstanding the peculiar avidity with which the vitriolic acid attracts water, the dry nitrous acid vapour had a still superior attraction for that principle; and had accordingly robbed the vitriolic acid of its phlegm, fo as to reduce it to an icy or cryftalline state.

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It appears afterwards, from the Author's very judicious mode of analyfing this curious produce, that the liquor in which these crystals are contained is pure nitrous acid, without any admixture of the vitriolic. For, on putting iron to some of this liquor previously diluted with water, nitrous air only was produced whereas had any of the vitriolic acid ftill remained in this liquor, fome inflammable air would have fucceeded the nitrous air; as happens when these two acids are mixed together, and employed in the folution of iron. The cryftals of vitriolic acid are therefore, in this procefs, precipitated by the nitrous acid vapour, from the water in which they are diffolved; in the fame manner as various falts are precipitated from their aqueous folvents, on the affufion of fpirit of wine, which exerts a fuperior attraction towards the water.

In

In the course of thefe experiments, the Author was led to the difcovery of an eafy method of preparing a refervoir of this pure nitrous acid vapour, by previously impregnating red lead with it ; which is thereby converted into a white fubftance, from which it may afterwards be expelled by heat, whenever it is wanted; free from any admixture with nitrous air, which usually comes over with it, when it is first procured in the process with the nitrous acid and bismuth.

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Paffing over feveral interefting obfervations relating to the nitrous and marine acids, we fhall next take notice of another curious product, the refult of the Author's unufual mode of experimenting. He expofed many liquid fubftances, and aeriform fluids, included in glafs tubes hermetically fealed, to a long continued heat, in a fmall furnace; and, among the reft, about an ounce measure of diftilled water ftrongly impregnated with vitriolic acid air, which had been procured from copper. This, fays the Author, was on the 9th of September 1777, but the result was much more curious than I could poffibly have imagined a priori.-On the 30th of the fame month this impregnated water, which continued tranfparent to the end of the procefs, had depofited a small quantity of black powder; and alfo a bit of matter exactly like fulphur, about one eighth of an inch in diameter, lay among it. Small pieces of the fame matter floated on the furface of the liquor, and ftreaks of the same coated part of the infide of the tube an inch above the liquor. From the top of the tube,' (which was about two feet and an half long) to within about eight inches above the liquor, were beautiful white cryftallizations, like fpicule, difpofed irregularly, but generally in the form of stars, the glafs being perfectly transparent between them-Thefe cryftallizations continually increased to the 20th of January following, when an end was put to the process; at which time the upper half of the tube was pretty thickly and equally covered with these crystals.

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The experiment was repeated with tubes of different lengths and fizes, with the fame general event; though attended with fome variation in the circumftances. The Author kept these tubes a year; in the course of which he fhewed them to several of his chemical friends, who expreffed much furprise at the fight of them. At length he opened the tube that contained the greatest quantity of these cryftals, having previously applied the flame of a candle with a blow pipe to it; when he found that the glass, foftened by the heat, was prefed violently inwards : fo that it was evident that there was a decrease of elaftic matter within the tube, which therefore had probably entered into the cryftals. Accordingly on taking off half of the tube, and opening it under water, it was half filled with water, and the air remaining in it was found to be completely phlogisticated.

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On examining the cryftals, the Author found that they were not diffolved in spirit of falt; and when they had been washed and dried, they had the colour and smell of fulphur; and, being laid on a hot iron, burned with a blue flame, so as to leave no doubt of the identity of the fubftances. To form this fulphur, he conjectures that the phlogifton, which had rendered the acid volatile, in this expanded and confined ftate, had been compelled to form that very different and peculiar union requifite to make fulphur.'

White cryftals were likewife formed in various other tubes, which were expofed to the fame heat, and in which vitriolic acid air, or the elaftic vapour only of the volatile vitriolic acid, was confined. The coating was here, of course, very flight, on account of the small quantity of matter contained in the tube. The Author imagined that it was not fulphur, because spirit of falt feemed to diffolve the whole of it: at leaft, on washing the tube with that fpirit, he could not perceive any fubftance floating in it. He fufpects however, very properly in our opinion, that this circumftance may be owing to the very small quantity of the crystalline fubftance, and the extreme minuteness of its particles. In fact, we can perceive no reason why the products of these two procefies should vary, except with respect to quantity; unless the water in the firit of them fhould produce a difference, which is not very probable; as its presence there feems more likely to prevent than to accelerate the formation of that dry concrete, fulphur.

Thefe experiments, which exhibit the production of a real fulphur, from water containing a combination of vitriolic acid with the inflammable principle in a metal, furnith us with an additional and ftriking proof of the identity of that principle in metals, with that which refides (though blended with various other principles) in oils, coals, and other inflammable fubftances. They fhew that that very principle which metals lose when they are calcined, and which their calces regain by feparating and attracting it from charcoal, when they are reduced, is the very fame with that which is one of the two conftituent principles of fulphur. In fhort, they confirm the beautiful doctrine of Stahl, which has been lately contraverted, on account of fome experiments in which certain metallic calces, or what appear to be fuch, are revived without addition :—a fact which, however difficult it might be to account for it, ought not to weigh against the numerous obfervations on which that luminous theory is established.

The Author obferves, at the end of this work, that thefe experiments may perhaps help to explain the relation that fulphur bears to water, and decide the difputes about the prefence of fulphur in fome mineral waters.'-They certainly point out

one

one of the ways by which the fulphur may be produced that is faid to be found in the vaults of the covered fources, and aqueducts, that convey certain mineral waters-that at Aix la Chapelle in particular.-[See on this head our account of Dr. Williams's Treatife on the Medicinal Virtues of thefe Waters, in our 47th volume, December 1772, pag. 405] On the perufal of that Article, if we are not mistaken, the Reader will be ftruck on feeing nature there defcribed, working in her great fubterraneous laboratory, nearly in the very fame way, and producing the fame effects, but on a larger fcale, that Dr. Prieftley has produced in his artificial fand baths, and glass tubes. Dr. Williams, however, has in that Article only proposed that, as an hypothefis, which Dr. Priestley has here proved by thefe decifive experiments.

The accounts of these proceffes are fucceeded by fome obfervations on the phosphoric acid; which we fhall pass over, in order that we may have more room to relate fome of the Author's very curious experiments made on mercury; the knowledge of which we wish to extend, not only on account of their fingularity, but of their fimplicity likewife, and the facility with which they may be repeated and diverfified by those who are not poffeffed of a regular chemical apparatus.

Of all the numerous fubjects of chemistry, no one perhaps has been more thoroughly inveftigated, by chemifts and alchemifts, than this metallic fubftance, or has been prefented under a greater variety of forms or combinations. Boerhaave's repeated diftillations of this fluid, and agitation of it in a bottle fixed to a windmill, are well known: but a flight hint, fùrnished by accident, and pursued with that ardour and intelligence which fo greatly diftinguifh the prefent Experimentalift, excited in him the idea of fubjecting this femi-metal to the action of air and water, by agitating it together with thefe, and afterwards other, fluids.

Having at one time obferved a larger quantity than usual of a black powder lying on the furface of some mercury, that had been carried from London into the country; the Author firft examined it, by putting a part of it into a glass veffel fitted with a ground ftopper and tube, and then expofing it to the heat of a candle. By this means he expelled air from it, part of which was fixed air, and the refiduum worse than common air. He inferred from hence that this powder had no affinity to the mercurius calcinatus, which yields only the pureft dephlogifticated air. In short, he found that by heat a part of it was reducible to running mercury; while a yellow powder remained, which he afterwards found to be the calx of lead, or fome other metal, with which the mercury had been impregnated. AfterGg 3 wards

wards diffolving a fmall quantity of lead in fome pure mercury, and flightly agitating the fluid in a vial, a black powder refembling the former was immediately produced.

On procuring this black powder, by agitating this amalgam, as we shall call it, in a vial, one-fourth part of which was filled with it, and which he inverted in a bason of quickfilver, he found that, in ten minutes, the air included in the vial was diminished one-fifth. It extinguished a candle, and was found to be completely phlogisticated, or, at leaft, was not at all affected by nitrous air.

Any further agitation of the amalgam in this fame air produced no effect whatever: but if this air was expelled, and fresh air introduced, by means of a pair of bellows or otherwise, the process went on again, and more of this black powder was produced; and at the fame time the air which had been admitted into the vial was phlogisticated, in proportion as the black powder was formed, and till the process was at its maximum, or at a ftand. When fixed air, nitrous, inflammable, or, in fhort, any kind of phlogifticated air, was introduced, no change was effected but with dephlogisticated air the process went on very rapidly.

It now occurred to the Author that the whole of any quantity of lead, or other metal, with which mercury is occafionally impregnated, might be feparated from it by these means; and he accordingly found this to be an easy method, and as effectual as diftillation, of purifying mercury impregnated with certain metals. He added known quantities of lead and tin to mercury, and, by agitating the mixture, feparated them from it in this form. The procefs is to be repeated till the operator finds that no more black matter can be separated from the mixture.

It is not a little remarkable, fays the Author, that the operator will be at no loss to know when the process is completed. 6 For the fame quantity of lead feems to come out of it in equal times of agitation, and, confequently, the whole becomes pure at once. Alfo, whereas, when the lead was in the mercury, it felt, as I may fay, like foft clay; the moment the lead is feparated from it, it begins to rattle as it is fhaken, so that any perfon in the room may perceive when it has been agitated enough.'

In these as well as in fome of the Author's former experiments, on a different fubject, it is very remarkable that water does not prevent, or fenfibly impede, the tranfmiffion of the inflammable principle to the air contained in the vial. If wa ter be added to the impure mercury, the feparation of the metal from the quickfilver is made as effectually as in air alone: provided that there be a fufficient quantity of air left in the vial. This