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that," to acquaint ourselves with the moral duties and virtues. of life, we have nothing more to do than to look into our own hearts, and diligently examine the feelings and fentiments of our own minds." Now we apprehend that the express and pofitive declarations of the will of God, in matters of moral as well as religious practice, were given in aid of human ignorance, and purpofely with a view to prevent our recurrence to apologies fanctified with the names of Nature and Reafon, in order to justify our neglect of duty, or excufe our commiffion of fin. For if the feelings of every man's mind were to be the standard of obligation, what duty that croffes their inclinations will men perform, or what vice that flatters them will they forego, for the fake of what others call Reason, and in deference to an equivocal authority arifing from what philofophy itself, which hath talked moft loudly about this authority, hath not agreed to give any name or definition to? For every man's own feel'ings, i. e. his inclination, will be his ftandard of duty, without a fettled law to which to appeal, a fixed and decifive criterion of good and evil, in fpite of all the fine things that have been faid on the beauty of Virtue-Fitnefs and Unfitnefs-the moral Senfe-and all

" which Theocles in raptur❜d vifion faw."

To clofe this Article, we recommend the perufal of these plain and rational Difcourfes to our Readers; and particularly to minifters, to whom there is given a lesson of most excellent advice on the duty of ftudying the Scriptures with diligence, and explaining them with integrity.

ART. VI. Experiments and Obfervations relating to various Branches of Natural Philosophy; with a Continuation of the Obfervations on Air. By Jofeph Priestley, LL. D. F. R. S. 8vo. 6s. Boards. Johnfon. 1779.

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TOTWITHSTANDING the very fhort interval that has paffed fince we reviewed the Author's third volume of Obfervations; and his intimation, which we then quoted with regret, of a defign to direct his attention to fpeculations of a very different nature'-and which, it is well known, he has pretty Jargely purfued-we now have, nevertheless, the pleasure of again attending this active and fuccefsful investigator, in his philofophical capacity, by announcing to the world a large collection of new and fingular experimental obfervations, made by him on a variety of fubjects. Of the value and importance of thefe obfervations we cannot exhibit a jufter idea, than by reprefenting them as in every refpect worthy to follow thofe with which he has already fo greatly enriched the science of philosophical chemistry.

REV. June, 1779.

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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 fpace that we can conveniently allot to an Article. Amidft fuch a multiplicity of matter, it will be moft proper to confine ourselves to fome particular fubjects, and thofe, too, fuch as may be moft conveniently detached from the rest.

The first curious obfervation in this volume, that we shall notice, relates to the dephlegmating the vitriolic acid, and the reducing it to a cryftalline ftate; or the converting common oil of vitriol into what we apprehend to be the glacial oil of vitriol, by a very fingular procefs. 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 fubject is to be found in the third volume of the Author's Obfervations en 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.

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 spirit of wine, which exerts a fuperior attraction towards the water.

In the course of these experiments, the Author was led to the discovery of an easy 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 firft procured in the procefs with the nitrous acid and bifmuth.

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 Aluids, 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 transparent to the end of the procefs, had depofited a small quantity of black powder; and also a bit of matter exactly like fulphur, about one eighth of an inch in diameter, lay among it. Small pieces of the same matter floated on the furface of the liquor, and ftreaks of the fame 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 fpicula, 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. 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 courfe of which he fhewed them to feveral 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 glafs, foftened by the heat, was preffed violently inwards : fo that it was evident that there was a decrease of elastic 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 fmell 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 least, 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 reafon why the products of these two proceffes fhould vary, except with respect to quantity; unless the water in the first of them should 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 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 fubftances. They fhew 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 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 these experiments may perhaps help to explain the relation that fulphur bears to water, and decide the disputes about the prefence of fulphur in fome mineral waters.'-They certainly point out

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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 propofed that, as an hypothefis, which Dr. Priestley has here proved by these decifive experiments.

The accounts of these proceffes are fucceeded by fome obfervations on the phofphoric acid; which we fhall pafs 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 chemiftry, no one perhaps has been more thoroughly investigated, 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, furnished by accident, and pursued with that ardour and intelligence which fo greatly diftinguish 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 these, and afterwards other, fluids.

Having at one time obferved a larger quantity than usual of a black powder lying on the surface of fome mercury, that had been carried from London into the country; the Author first examined it, by putting a part of it into a glafs 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 dephlogisticated air. In fhort, 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

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