furnish the proper quantity of phlogifton requifite to its fubfequent reduction: for when the experiment is performed in a clean glafs retort, the air which is collected is, in gencral, pure or dephlogifticated.

According to this theory, as crude mercury is a metallic earth. combined with phlogifton; fo mercurius calcinatus is the fame earth, which has loft a part or the whole of its phlogifton, but has, in its room, attracted from the atmosphere air of a certain ftandard; that is, not pure or dephlogifticated, but containing fuch a portion of phlogifton as is fufficient to fupply that which it had loft in the calcination. On applying the proper degree of heat, this new combination of mercurial earth, and air fomewhat impure, is deftroyed. The earth retains the whole of the phlogifton contained in this air, and accordingly recovers its metallic ftate and fluidity; and parts at the fame time with the remaining air, thus completely dephlogisticated. In a fomewhat fimilar manner, plants are fuppofed to attract air, more or lefs pure, from the atmosphere, or from water; and, while they retain the phlogifticated, they are found to emit the dephlogifticated part.

We offer thefe reflections on this fubject, as feeming at leaft to afford a fimple and fatisfactory folution of this great difficulty: nor do we, at prefent at leaft, recollect any phenomena that are irreconcileable with it.

It

The Author's obfervations on fulminating gold contain many curious noveltics; and, in particular, evince ftill more fatisfactorily than even the experiments of the Chevalier Bergman, that the prefence of nitrous acid is not a neceffary circumstance) towards the producing the fulmination of that power. is true, that the Chevalier Bergman made Aurum fulminans from precipitates which did not appear to contain any nitrous acid. He precipitated gold, for inftance, from its common folvent, aqua regia, by a fixed alcali; and then diffolving this precipitate, (firft well edulcorated) in vitriolic, or marine acid, or even in diftilled vinegar, and again precipitating it from these solutions by a volatile alcali, he fill obtained fulminating gold. Nevertheless, we think that a doubt may ftill remain, which we very lately expreffed at fome length [See Appendix to our 63d or laft Volume, December 1780, pag. 505], that, as nitrous acid had been employed in the original folution of the gold in aqua regia, fome of that acid might ftill be retained in the precipitate, and might obftinately adhere to it in all the fubfequent operations upon it. Mr. Scheele's experiments abfolutely remove this doubt. His theory and difcoveries refpe&ting this curious fubject deferve to be abridged, and explained.

Gold is a compound of an earth fui generis, and of phlogifton. It is infoluble in any acids, till it has parted with its phlogifton

to an acid rapacious of that principle. The marine acid has the greatest affinity to its earth, which however it cannot attack till the phlogifton has been detached from it. This laft office is performed by the nitrous acid in the aqua regia, which evidently acquires phlogiston in the procefs; and the marine acid is thus left at liberty to diffolve the earth.

But the Author having difcovered a method, not here indicated, of dephlogisticating marine acid (by means, we believe, of manganefe), found that the marine acid, thus deprived of its own phlogifton, was capable, fingly, of diffolving gold in its metallic ftate; in confequence of the avidity which, by its own dephlogiftication, it had acquired for phlogifton. A folution of gold, thus effected, being diftilled in a retort with a ftrong heat, the gold is reduced without addition: for it recovers back again the very phlogiston which, during its folution, it had before parted with to the marine acid; and the acid accordingly paffes over into the receiver in its prior dephlogisticated state.

Gold, thus diffolved by the dephlogisticated marine acid alone, is actually precipitated, on the addition of a volatile alcali, in the form of fulminating gold. From this procefs it appears clearly that the peculiar qualities of this powder are not to be accounted for from the prefence of any nitrous acid fuppofed to be contained in it.

That the earth of gold † attracts a volatile alcali more ftrongly than the latter is attracted even by the vitriolic acid, the Author thews by digesting this calx in a folution of Glauber's fal ammoniac. In this cafe, this neutral folution of volatile alcali and vitriolic acid became acidulous; in confequence of its parting with a portion of its volatile alcali, which had left the vitriolic acid, and united itself with the earth of gold; conftituting with it a true aurum fulminans, which, from thefe and other experiments, appears evidently to be nothing more than a combination of the earth of gold and volatile alcali;-particularly from the following:

The Author diffolved fulminating gold in marine acid, and put feveral pieces of copper into the folution. The gold was precipitated, on recovering its phlogifton from the copper; and the volatile alcali which had beeh a conftituent part of the fulminating gold, and which had been expelled from it on its reduction, and had entered into the folution, was readily recognifed, on adding fome fixed alcali to expel it from the folution previously evaporated to drynefs.

The Author's analysis of fulminating gold, particularly with

By this term the Author denotes the precipitate thrown down from a folution of gold, on the addition of a fixed alcali; and which is known not to poffefs a fulminating quality,

refpec

refpect to its accenfion, furnishes us, as Mr. Kirwan well obferves in his Notes, with a new and important difcovery;—the decompofition of pure volatile alcali. This calx of gold, at the inftant of its explofion, is fuddenly reduced to a metallic ftate, by means of the phlogifton which it attracts from the volatile alcali: while the other constituent part, or parts, of that faline fubftance appear, from fubfequent experiments, to affume the form of a particular fpecies of air; which Mr. Scheele confiders as agreeing with phlogisticated air in its principal properties. At leaft, a candle was extinguifhed in it; it was not abforbed by water; nor did it make lime-water turbid. The Author refers on this occafion to his Memoir on Manganefe, above alluded to; where he has fhewn, that, whenever a body attracts the phlogifton which is an integrant part of the volatile alcali, fuch air is always produced :-particularly in the diftillation of crocus martis and fal ammoniac; the precipitate thrown down from mercury fublimate by volatile alcali; and in the detonation of nitrum flammans, or nitrous ammoniac.

Paffing over many of the Author's experiments and reafonings, more or less connected with his peculiar theory, we fhall defcribe a fimple and easy method propofed by him, of discovering whether water contains empyreal, i. e. dephlogisticated air, or not. In a preceding experiment, when he was inquiring into the nature of atmospherical air, he found that the green precipitate, formed on adding fixed alcali to a solution of martial or green vitriol, fhut up in a vial containing common air, during a fortnight, had decompounded the air, and had itself acquired the colour of crecus martis: and at the fame time, out of 40 parts of common air, 12 were loft. The air which disappeared was the Author's empyreal air; and the remaining 28 parts were his foul air, in which a candle would not burn. By a mode of trial founded on this experiment, he difcovers whether any particular water contains dephlogisticated air.

To an ounce of the water, for inftance, he adds about four drops of a folution of vitriol of iron, and adds two drops of a folution of falt of tartar fomewhat diluted with water. The dark green precipitate thus formed changes into a yellow colour, in a couple of minutes, if the water contain empyreal air but if the water has been very lately boiled, and cooled without having had free access to the air, or has been lately diftilled; the precipitate retains its green colour, and does not turn yel

*There are fome peculiarities refpecting heat, in the Author's mode of explication, which differ fomewhat from this account: but they cannot be here eafily explained, as they are founded on his particular theory of fire; and the fubject is certainly rendered clearer by the omiflion of them.

low,

low, unless about an hour afterwards; and it never acquires a yellow colour, if it be kept in full glaffes, fo that the air have no access to it.

Before we conclude our Review of the prefent interefting performance, we shall gratify our philofophical Readers by taking notice of a late difcovery of the Author's; though it be here only incidentally mentioned, with a view to corroborate his particular fyftem refpecting the conftitution of empyreal air. It has indeed likewife induced him to propofe this fingular opinion —that metallic and earthy fubftances confift only of acids combined with phlogifton. We allude to his difcoveries relating to that fingular mineral, arfenic; which at once poffeffes the characters of a faline and of a metallic fubftance.

M. Macquer, whofe analyfis of this mineral is well known to our chemical Readers, had indeed detected an acid in it; as forming a conftituent part of it; or rather had discovered that it contained a certain principle, capable of conftituting a neutral falt, when combined with a fixed alcali: but he entertained no fufpicion that this heavy metallic fubftance had not an earth for its bafis. In a Memoir printed in the Tranfactions of the Swedish Academy, the Author has fhewn, that the common arfenic of the fhops confifts only of an acid, fui generis, combined with a certain quantity of phlogifton; and that even the regulus of arfenic, in which this heteroclite fubftance affumes the form of a femi-metal, confifts only of the fame acid, combined with a fill greater portion of phlogiston.

We did not speak at random when, at the beginning of this article, we obferved that chemistry had, in our times, affumed a new face. In the inftance before us, we find a fober and orthodox chemist inferring from his experiments, that all earths are a fpecies of acids; and hinting, that even metals in general confist of acid and phlogifton only. Mr. Scheele founds this opinion not merely on his analyfis of arsenic, but likewise on other facts and obfervations; particularly on his former difcoveries relative to the Sparry acid. He ftill confiders the fluor cruft of earth, as confifting of this acid fixed by an union with water. This conclufion, however, is liable to objections: nevertheless, that great chemist, the Chevalier Bergman, in an excellent prefatory introduction to this work, feems to hold the fame language with the Author, as well with refpect to this fubject, as to his extenfion of the principle to metals, &c. Thefe are his words:

or

• Since the acid of fluor and water, meeting one another in the form of vapours †, coagulate into filiceous earth; and acid

of

+ This is expreffed too generally. From Dr. Priestley's mode of experimenting, it appears that the water need not be in a state of va

pour s

of arfenic with phlogifton coagulates into folid white arfenic'and with ftill more phlogifton (he might have added), into a true regulus or femi-metal; there is fome indication that terreous fubftances, as well as metallic calces, may be confidered in their first principles as acids; which, in the firft cafe, are become fixed by water, and, in the last, by phlogiston.'

The Reader will meet with many obfcurities in this work, befides thofe incidental to a tranflation; and which arife from the Author's great concifenefs on many fubjects, where, it will naturally be wifhed that he had been more explicit and circumftantial; and from the want of a proper arrangement of his materials. Though the philofophical Reader may probably reject the Author's theory of fire; he will here meet with many curious facts, difperfed in various parts of the work, which may, in future, lead to important confequences. In chemiftry,' as the Chevalier Bergman well obferves, there are none of the Veritates Otiofa. The leaft phenomenon, when examined in all its caufes, is always connected with others of the greatest importance; in fuch a manner, that every thing is hewn connected in the great ceconomy of nature.'

pour; as the filiceous earth appears as foon as the fluor acid vapour, or air, reaches the under furface of the water refting on mercury: and from many of his experiments, on other occafions as well as the prefent, it feems probable that the fluor acid air holds the fluor cruft or earth in folution, previously to its meeting with the water; which only decompounds this air by condeafing, and uniting with, its acid: while the earth, deprived of its former aerial folvent, is precipitated, and becomes visible, under the form of fluor cruft.

ART. IV. An Examination of Dr. Crawford's Theory of Heat and Combustion: By William Morgan. Svo. 1 s. 6d. Cadell. 1781.

HOUGH we have, in those parts of our work which are fpecified below*, already given a pretty full account of Dr. Crawford's theory of fire; yet, as the fubject is rather of an intricate nature, we fhall endeavour to throw a little more light upon it, by availing ourfelves of the prefent Author's general expofition of that hypothefis: the refutation of which, at least in fome of its moft effential parts, is the profefled object of this publication. In fhort, we fhall only, except perhaps in a few inftances, take upon us the office of Relaters; and confine ourfelves to fuch parts of the performance as are not much involved in calculation.

* See M. REVIEW, Vol. lxi. November 1779, pag. 378; and Mr. Magellan's explanation of Dr. Crawford's theory of fire, in the Appendix to our 63d volume [1780] pag. 499.

That