tina; one of which, it was afferted, had never been expofed to any operations whatever. His joy, however, on receiving this laft mentioned acceptable prefent was of fhort duration; for, on expofing fome ounces of it to heat, in a glass vessel, mercurial vapours arofe, and were condenfed into globules in the neck of the veffel. He thinks, that it is not probable that platina ever paffes into Europe without having undergone a previous amalgamation with mercury, for the purpose of robbing it of the gold that is mixed with it.

DISSERTATION XIX. On the white Ores of Iron.

30

Among many other curious particulars contained in this Effay, there are feveral relating to manganese, which has been lately discovered to be the calx of a new metal, or metallic fubftance, and is endowed with many remarkable properties. Its reduction to a metallic ftate is effected by expofing it to a moft intense fire, in a clofe crucible, where it is on all fides fure rounded by powdered charcoal. The weight of the metallic fubftance thus procured is found to be parts of the calx employed, and its specific gravity with respect to that of diftilled water is as 6850 to 1000. This regulus poffetles the fingular property of lofing fome of its phlogifton, it expofed for fome time to the atmosphere in a moist place, fo as at length to crumble between the fingers into a powder. The Author fuppofes, that, intenfe as the heat was in which this regulus was procured, it was not quite fufficient to unite all the metallic particles intimately with each other.

The Author well explains the very fingular phenomena which this calx produces on glafs, in the manufacture of which it is much used. It will give various colours to glafs, and yet it is principally employed for the purpose of deftroying the colours with which that substance is tinged. By means of this calx, it has lately been difcovered by M. Scheele, that the common marine acid contains phlogifton as a principle; to which manganefe has fo ftrong an affinity, that it decompofes this acid, and even robs gold of it; to as to enable the marine acid, after having been digested with it, to diff"lve that metal fingly.

DISSERTATION XX. On Nickel.

The difficulty of obtaining this femi-ar tal perfectly pure is very great; particularly of fleeing it from the fulphur, arienic, cobalt, and, above all, the iron contained in it. The fepara

tion of this laft, beyond a certain point, eluded all the fkill and perfeverance of the Author. Different parts of a regulus which he procured of this femi-metal, not only ftrongly adhered to the magnet, and even to common iron, but likewife attracted each other. They were fo ductile, that a globule of a line in diameter bore extenfion under the hammer, fo as to form a plate of three lines in diameter, The Author has not been able to afcer

tain whether it be a diftinct metal, or a peculiar modification of iron, or a compound of various metallic fubftances formed by nature; particularly, as fome have thought, of cobalt, copper, and iron. He failed, however, in producing nickel; though he made various mixtures of these fubftances, and treated them both in the dry and humid way.

DISSERTATION XXI. On Arfenic.

This Differtation contains many curious obfervations on this heteroclite fubftance, which is fo widely diffufed throughout the mineral kingdom; and, in its different ftates, appears under the various forms of a metal, a calx or earth, and a falt or acid. The white arfenic of the fhops is in fact nothing more than an acid of a peculiar nature, different from every other known acid, and which contains just such a quantity of phlogifton as is fufficient to coagulate it. When a ftill greater quantity of phlogifton is added to, and combined with it, it becomes a metal.

According to the Author, 100 parts of white arfenic contain 20 parts of phlogifton. When this principle has, by proper means, been totally expelled, the arfenical acid is left pure. In that ftate, it becomes fixed in the fire; but, on being expofed to a moist air, it deliquefces, and at length is wholly resolved. into a limpid fluid; having attracted to itself about two thirds of its weight of water.

It is nevertheless remarkable, that this pure acid, on being kept in a red heat, even in a clofe veffel, acquires, in fome man. ner or another, as M. Scheele has fhewn [Obfervations, &c. on Air, p. 53.] a certain portion of phlogifton, fufficient even to convert it into white arfenic. To account for this appearance of phlogifton, the Author adopts M. Scheele's fingular hypothefis, concerning the conftituent principles of heat or fire; according to which, the fire, which paffes freely through the fides of the retort, confifts of dephlogifticated air, and phlogiften: but within the body of the retort the fire is decompofed; its phlogiston is attracted by the arfenical acid, with which it forms white arfenic; and its dephlogisticated air may be collected in a bladder fixed to the neck of the retort.

When the arfenical acid has acquired as much phlogiston as is fufficient to faturate it completely, it then affumes, as we have above hinted, its third and laft form, and becomes a metallic fubftance. From this fingular fact principally, and reasoning from analogy, the Author concludes, that it is probable that the different metals are nothing more than different acids, thoroughly coagulated with phlogifton, although the connection of thefe two principles is, in general, fo ftrong, that we are as yet ignorant of the proper means of deftroying it :-the calces of metals always abounding more or less with phlogifton.'-M. Scheele evidently inclines to the fame opinion, and fays- were it pof

fible to separate the phlogifton, fo firmly united with metallic earths, they would probably discover their acid nature more palpably.' [Obf. p. 107.]

Briefly enumerating the various ufes of arfenic, the Author takes notice of the discovery of a new and excellent green colour, which undergoes no change for many years, whether it be ufed as a water or an oil colour. It is a precipitate from a folution of blue vitriol, made by adding to it an aqueous folution of white arfenic and vegetable alcali.

One of the fingular qualities here mentioned of arfenic is, that, on its being fufed, in its metallic ftate, with iron, the compound metal, formed of thefe two fubftances, is not poffeffed of any magnetical qualities, though the quantity of iron contained in it be equal to that of the arfenic, or even conftitute, in fome cafes, two thirds of the mafs. On diffipating, however, a part of the arfenic by heat, though no phlogistic matter be present in the veffel, the iron recovers its magnetic powers.

DISSERTATION XXII. On the Ores of Zinc.

One of the curious particulars contained in this Article is, that the Pfeudogalena, one of the ores of this ufeful femi-metal, being treated either with vitriolic or marine acid, furnishes that particular fpecies of air, firft difcovered by the Author, to which he gave the name of Hepatic Air, as having been originally produced from Hepar Sulphuris, and to which, it is evident, all the hot, and (as it now appears they have been juftly called) the fulphureous mineral waters, owe their principal medicinal efficacy. In our account of the Author's firft volume [M. Review, Vol. LXII. January 1780, p. 74.], we defcribed his method of discovering and precipitating the fulphur contained in these waters. In the prefent differtation he defcribes a method of exhibiting that fubftance, when it exifts under the modification of hepatic air. This is effected by adding, to a quantity of hepatic air contained in an inverted jar, an equal quantity of nitrous air. On their admixture, a real fulphur is precipitated from the first mentioned air; and a thermometer, included in the mixture of these two fpecies of air, rifes feveral degrees. We have formerly obferved, that the Author's theory, with respect to the conftitution of hepatic air, is that it confifts of fulphur, combined with the matter of heat, through the medium of phlogiston. He here explains that idea more fully.

That it contains fulphur, is evident from the precipitation of that fubftance: that latent heat [caler ligatus] is likewife contained in it, is equally evident, he fays, from the rifing of the thermometer, which is caused by that heat being let loofe, or becoming fenfible heat: and that phlogiston (exclufive of that which is contained in the fulphur) is the bond which connects

the two other principles, is apparent, he observes, from hence,— that the hepatic air cannot be decompofed, except by fubftances that greedily attract phlogifton. Thus the concentrated nitrous acid exerts this quality, even in water impregnated with hepatic air; as does nitrous air, though already loaded with phlogifton. Thus, on the feparation of the phlogifton, this compound, confifting of three principles, is deftroyed; for the other two, ful phur and beat, without phlogifton, do not exhibit any hepatic odour.

But M. Bergman endeavours to prove the truth of this hypothefis fynthetically; that is, by fhewing that these three principles are to be found in the Pfeudogalena. He next inquires whether they exift there in a combined ftate, that is, in the form of hepatic air, in the fame manner as fixed air exists in marble; or whether the hepatic air is then only formed, when the acid is applied. In confequence of the refults of certain experiments, he concludes, that it is generated at the time of the experiment. The acid lets loofe the latent heat, and the phlogifon, of the ore: these two principles attack the fulphur contained in it; and, combining with it, conftitute a permanently elaftic fluid.

A fingularity refpecting a particular fpecies of the Pfeudogalena (that of Scharfenburg) deferves particular notice. That ore treated along, with heat, in a clofe veffel, exhibits the very fame kind of finty fublimate, or fluor cruft, as is given by the fparry fluor, or Derbyshire fpar, when treated with oil of vitriol. The Sparry acid, therefore, fays the Author, pre-exifts in this ore, but probably combined with a metallic bafis ;- fo that it can be expelled from it by fire alone, and, united with an aqueous vapour, can generate the fluor crust.'

DISSERTATION XXIII. On Metallic Precipitates.

That man must have been greatly aftonished, as the Author in part obferves, who firft faw fo ponderous and opaque a body as a metal, gradually, and at length totally, disappear in a fluid; the liquor which contained it ftill appearing perfectly limpid and homogenous. Nor would his furprife be lefs, when, merely on the affufion of another tranfparent liquor, he perceived the metal fuddenly to re-appear in its former ponderous and opaque ftate, and foon fall down to the bottom of the veffel, in the form of what is called a precipitate. These two operations, folution and precipitation, are the two moft important in the whole practice of chemistry; and are moft fatisfactorily, though compendiously, treated in this differtation. We must content ourselves with only extracting a particular or two from it.

No metal,' the Author fays, can be diffolved by an acid, while it retains the whole of that quantity of phlogiston, which is effential to its metallic ftate That part of its infiammable principle, which is the obstacle to this procefs, muft therefore neceflarily be re

moved, before any folution can take place. The different acids, by their strong attraction of this principle, produce the folution of the various metals, in proportion to the ftrength with which they refpectively attract it, and, we may add, to the strength with which each metal retains it.

Among the acids, the nitrous attracts phlogifton the most powerfully; and can even rob the vitriolic acid of it. If any one doubts this, fays the Author, let him expofe fulphur to the action of the concentrated nitrous acid, in a gentle boiling heat, and he will find the fulphur at length robbed of all its phlogifton, and the vitriolic acid left naked.

The marine acid, as we have already obferved, contains phlogifton as a proximate principle; but when it has been robbed of it, or dephlogisticated (by manganefe or otherwise), it readily attacks every one of the metals, in confequence of the avidity with which it is difpofed to recover its phlogifton. Gold and platina, which retain their phlogifton fo ftrongly, and on which it could not before act, yield readily to its power, in its dephlogifticated ftate.

In this Differtation, M. Bergman boldly attempts to loofs that most intricate Gordian knot'-the genesis of all the aeriform fluids. But thofe who do not fully adopt the peculiar theory of M. Scheele, on air and fire, will think perhaps that, in this attempt, he has, at least occafionally, practifed the ancient manœuvre of Alexander. This part of the effay, however, highly merits an attentive perusal.

DISSERTATION XXIV. On the Effaying of Metallic Ores, in the Humid Way.

The many difficulties and difadvantages attending the effaying of metallic ores in the dry way, or by fire, have induced the Author to form a regular fyftem, comprehending the various methods by which the fame object may be ftill more easily and accurately obtained, in the humid way, or by folution, precipita tion, &c. He proceeds regularly through the ores of all the metals and femi-metals, in a compendious but inftructive man

ner.

We fhall only extract from this differtation a piece of curious information refpecting one of the ores of lead (plumbum calciforme) which has been discovered by M. Gahn to contain the acid of phofphorus. When the lead has been precipitated, from a folution of the ore in nitrous acid, by means of the vitriolic acid, the remaining liquor, on evaporation, leaves a true acid of phosphorus behind it.

DISSERTATION XXV. and Last. On the Blowpipe, and its Use in the Examination of Bodies, particularly Mineral Subftances. This differtation, which is accompanied with a plate, contains a regular feries of inftructions with refpect to the manage