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In the present performance the Author has taken a wider range than in his former philosophical publications, and has, accordingly, given it a more comprehensive title. The work is divided into forty sections, the mere titles, or contents, of which would alone nearly occupy the space that we can conveniently allot to an Article. Amidst such a multiplicity of matter, it will be most proper to confine ourselves to some particular subjects, and those, too, such as may be most conveniently detached from the rest.

The first curious observation 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 af vitriol into what we apprehend to be the glacial oil of vitriol, by a very singular process. This was effected by impregnating strong 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 solution of bismuth in spirit of nitre. The first observation leading to this subject is to be found in the third volume of the Author's Observations on Air, pag. 217.

In one of the processes here described, the vitriolic acid had Thot into the most regular and beautiful crystals resembling a feather; the fibres of which on each side made an angle with each other (as happens in the ice of water) of about 160 degrees. These were surrounded and covered with a liquor, which, being heated, afforded a large quantity of the purest nitrous air. In short, it appears from this process, 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, so as to reduce it to an icy or crystalline state.

It appears afterwards, from the Author's very judicious mode of analysing this curigus produce, that the liquor in which these crystals are contained is pure nitrous acid, without any admixture of the vitriolic. For, ön putting iron to some of this liquor previously diluted with water, nitrous air only was produced: whereas had any of the vitriolic acid still remained in this liquor, some inflammable air would have succeeded the nitrous air ; as happens when these two acids are mixed together, and employed in the solution of iron. The crystals of vitriolic acid are therefore, in this process, precipitated by the nitrous acid vapour, from the water in which they are dissolved; in the same manner as various salts are precipitated from their aqueous solvents, on the affusion of spirit of wine, which exerts a superior attraction towards the water,

In the course of these experiments, the Author was led to the discovery of an easy method of preparing a reservoir of this pure nitrous acid vapour, by previously impregnating red lead with it; which is thereby converted into a white substance, 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.

Passing over several interesting observations relating to the nitrous and marine acids, we shall next take notice of another curious product, the result of the Author's unusual mode of experimenting. He exposed many liquid substances, and aeriform Auids, included in glass tubes hermetically sealed, to a long continued heat, in a small furnace; and, among the rest, about an ounce measure of distilled water strongly impregnated with vitriolic acid air, which had been procured from copper.-" This, says the Author, was on the gth of September 1777, but the result was much more curious than I could possibly have imagined a priori.–On the 30th of the same month this impregnated water, which continued transparent to the end of the process, had deposited a small quantity of black powder; and also a bit of matter exactly like sulphur, about one eighth of an inch in diameter, lay among it. Small pieces of the fame matter floated on the surface of the liquor, and streaks of the same coated part of the inside 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 crystallizations, like spiculæ, disposed irregularly, but generally in the form of stars, the glass being pera fectly transparent between them.'- These 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.

The experiment was repeated with tubes of different lengths and sizes, with the same general event;

though attended with some variation in the circumstances. The Author kept these

in the course of which he Thewed them to several of his chemical friends, who expressed much surprise at the sight of them. At length he opened the tube that contained the greatest quantity of these crystals, having previously applied the fame of a candle with a blow pipe to it; when he found that the glass, softened by the heat, was pressed violently inwards : so that it was evident that there was a decrease of elastic matter within the tube, which therefore had probably entered into the crystals. 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 crystals, the Author found that they were not dissolved in spirit of salt; and when they had been washed and dried, they had the colour and smell of fulphur ; 'and, being laid on a bot iron, burned with a bļue flame, so as to leave no doubt of the identity of the substances. To form this fulphur, he conjectures that the phlogiston, which had rendered the acid volatile, in this expanded and confined ftate, had been com. pelled to form that very different and peculiar union requisite to make sulphur.'

White crystals were likewife formed in various other tubes, which were exposed to the same heat, and in which vitriolic acid air, or the elastic vapour only of the volatile vitriolic acid, was confined. The coating was here, of course, very light, on account of the small quantity of matter contained in the tube. The Author imagined that it was not sulphur, because spirit of falt seemed to dissolve the whole of it: at least, on washing the Cube with that spirit, he could not perceive any substance floating in it. He suspects however, very properly in our opinion, that this circumstance may be owing to the very small quantity of the crystalline substance, and the extreme minuteness of its particles. In fact, we can perceive no reason why the products of these two proceffes should vary, except with respect to quan. tity; unless the water in the first of them should produce a difference, which is not very probable; as its presence there

ms more likely to prevent than to accelerate the formation of that dry concrete, fulphur.

These experiments, which exhibit the production of a real sulphur, from water containing a combination of vitriolic acid with the inflammable principle in a metal, furnish us with an additional and striking 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 substances. They shew that that very principle which metals lose when they are calcined, and which their calces regain by separating and attracting it from charcoal, when they are reduced, is the very fame with that which is one of the two constituent principles of sulphur. In short, they confirm the beautiful doctrine of Stahl, wisich has been lately contraverted, on account of some experiments in which certain metallic calces, or what appear to be such, are revived without addition :--a fact which, however difficult it might be to account for it, ought not to weigh against the numerous observations on which that luminous theory is established.

The Author obferves, at the end of this work, that these exa periments may perhaps help to explain the relation that sulphur bears to water, and decide the disputes about the presence of sulphur in some mineral waters.'—They certainly point out

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ore of the ways by which the fulphur may be produced that is said to be found in the vaults of the covered sources, and aqueducts, that convey certain mineral waters--that at Aix la Chapelle in particular.-[See on this head our account of Dr. Williams's Treatise on the Medicinal Virtues of these Waters, in our 47th volume, December 1772, pag. 405) On the perusal of that Article, if we are not mistaken, the Reader will be ftruck on seeing nature there described, working in her great fubterraneous laboratory, nearly in the very fame way, and producing the same effects, but on a larger scale, that Dr. Priestley has produced in his artificial fand baths, and glass tubes. Dr. Williams, however, has in that Article only proposed that, as an hypothesis, which Dr. Priestley has here proved by these decisive experiments.

The accounts of these processes are succeeded by some observations on the phosphoric acid ; which we shall pass over, in order that we may have more room to relate some of the Au-. thor's

very curious experiments made on mercury; the knowledge of which we wilh to extend, not only on account of their fingularity, but of their fimplicity likewise, and the facility with which they may be repeated and diversified by those who are not poffefled of a regular chemical apparatus.

Of all the numerous subjects of chemistry, no one perhaps has been more thoroughly investigated, by chemists and alchemifts, than this metallic substance, or has been presented under a greater variety of forms or combinations. Boerhaave's repeated distillations of this fluid, and agitation of it in a bottle fixed to a windmill, are well known : but a flight hint, furnished by accident, and pursued with that ardour and intelligence which so greatly distinguish the prefent Experimentalift, excited in him the idea of subjecting this semi-metal to the action of air and water, by agitating it together with these, and afterwards other, fluids.

Having at one time observed a larger quantity than usual of a black powder lying on the surface of some mercury, that had been carried from London into the country; the Author first examined it, by putting a part of it into a glass veffel fitted with a ground stopper and tube, and then exposing it to the heat of a candle. By this means he expelled air from it, part of which was fixed air, and the residuum worse than common air. He inferred from hence that this powder had no affinity to the mercurius calcinatus, which yields only the pureft dephlogisticated 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 some other metal, with which the mercury had been impregnated. After

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wards dissolving a small quantity of lead in some pure mercury, and nightly agitating the fuid in a vial, a black powder refembling the former was immediately produced.

On procuring this black powder, by agitating this amalgam, as we fall call it, in a vial, one-fourth part of which was õlled with it, and which he inverted in a bason of quicksilver, 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 least, was not at all af. fected by nitrous air.

Any further agitation of the amalgam in this same 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 same 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 stand. When fixed air, nitrous, inflammable, or, in short, any kind of phlogisticated 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 occasionally impregnated, might be separated from it by these means; and he accordingly found this to be an easy method, and as effectual as distillation, of purifying mercury impregnated with certain metals. He added known quantities of lead and tin to mercury, and, by agitating the mixture, separated them from it in this form. The process 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, says the Author, that the operator will be at no loss to know when the process is completed. • For the same quantity of lead seems to come out of it in equal times of agitation, and, consequently, the whole becomes pure at once. Also, whereas, when the lead was in the mercury, it felt, as I may say, like foft clay; the moment the lead is fé. parated from it, it begins to rattle as it is shaken, so that any person in the room may perceive when it has been agitated enough.'

In these as well as in some of the Author's former experiments, on a different subject, it is very remarkable that water does not prevent, or sensibly impede, the transmission of the inflammable principle to the air contained in the vial. If water be added to the impure mercury, the separation of the metal from the quicksilver is made as effectually as in air alone: provided that there be a sufficient quantity of air left in the vial.

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