The affinity which Metalline Substances have with acids is less than that which absorbent earths and fixed alkalis have with the same acids; so that all metalline salts may be decompounded by one of these substances, which will unite with the acid, and precipitate the metal.
Metalline Substances thus separated from an acid solvent are called Magisteries and Precipitates of metals. None of these precipitates, except those of the perfect metals, retain the metalline form: most of their phlogiston hath been destroyed by the solution and precipitation, and must be restored before they can recover their properties. In short, they are nearly in the same state with Metalline Substances deprived of their phlogiston by calcination; and accordingly such a precipitate is called a Calx.
A metalline calx prepared in this manner loses a greater or a less portion of its phlogiston, the more or less effectually and thoroughly the Metalline Substance, of which it made a part, was dissolved by the acid.
Metallic Substances have affinities with each other which differ according to their different kinds: but this is not universal; for some of them are incapable of any sort of union with some others.
It must be observed, that Metallic Substances will not unite, except they be both in a similar state; that is, both in a Metalline form, or both in the form of a Glass; for a Metalline Substance retaining its phlogiston cannot contract an union with any metallic glass, even its own.
CHAP. VII.
Of Metals.
There are six Metals, of which two are Perfect and four Imperfect. The perfect Metals are Gold and Silver; the others are Copper, Tin, Lead, and Iron. Some Chymists admit a seventh Metal, to wit, Quick-silver: but as it is not malleable, it has been generally considered as a metallic body of a particular kind. We shall soon have occasion to examine it more minutely.
The ancient Chymists, or rather the Alchymists, who fancied a certain relation or analogy between Metals and the Heavenly Bodies, bestowed on the seven Metals, reckoning Quick-silver one of them, the names of the seven Planets of the Ancients, according to the affinity which they imagined they observed between those several bodies. Thus Gold was called Sol, Silver Luna, Copper Venus, Tin Jupiter, Lead Saturn, Iron Mars, and Quick-silver Mercury. Though these names were assigned for reasons merely chimerical, yet they still keep their ground; so that it is not uncommon to find the Metals called by the names, and denoted by the characters, of the Planets, in the writings even of the best Chymists. Metals are the heaviest bodies known in nature.
SECTION I.
Of Gold.
Gold is the heaviest of all Metals. The arts of wire-drawing and gold-beating shew its wonderful ductility. The greatest violence of fire is not able to produce any alteration in it. Indeed Mr. Homberg, a famous Chymist, pretended that he had made this metal fume, and even vitrified it, by exposing it to the focus of one of the best burning-glasses, known by the name of the Lens of the Palais Royal: but, there are very good reasons for calling in question the experiments he made on this occasion, or rather for thinking that he was quite mistaken. For,
1. No man hath since been able to vitrify Gold, though several good Experimenters have assiduously tried to effect it, by exposing it to the focus of the same lens, and of other burning-glasses still stronger.
2. It hath been observed, that though Gold, when exposed to the focus of those glasses, did indeed emit some vapours and decrease in weight; yet, those vapours being carefully collected on a piece of paper, proved to be true Gold, in no degree vitrified, and which consequently had suffered no change but that of being carried away by the violence of the heat, its nature not being in the least altered.
3. The small portion of vitrified matter, which was formed on the arm that supported the Gold in Mr. Homberg's experiment, may have come either from the arm itself, or rather from some heterogeneous particles contained in the Gold; for it is almost impossible to have it perfectly pure.
4. Neither Mr. Homberg, nor any that have repeated his experiment, ever reduced this pretended glass of Gold by restoring its Phlogiston, as is done with other metallic glasses.
5. To render the experiment decisive, the whole mass of Gold employed ought to have been vitrified; which was not the case.
Nevertheless, I do not pretend that this metal is in its own nature absolutely indestructible, and unvitrifiable: but there is reason to think that no body hath hitherto found the means of producing those effects on it, probably for want of a sufficient degree of fire; at least the point is very doubtful.
Gold cannot be dissolved by any pure acid: but if the acid of nitre be mixed with the acid of sea-salt, there results a compound acid liquor, with which it has so great an affinity that it is capable of being perfectly dissolved thereby. The Chymists have called this solvent Aqua Regis, on account of its being the only acid that can dissolve Gold, which they consider as the King of Metals. The solution of gold is of a beautiful orange colour.
If Gold dissolved in aqua regis be precipitated by an alkali or an absorbent earth, the precipitate gently dried, and then exposed to a certain degree of heat, is instantly dispersed into the air, with a most violent explosion and noise: Gold thus precipitated is therefore called Aurum Fulminans. But if the precipitated Gold be carefully washed in plenty of water, so as to clear it of all the adhering saline particles, it will not fulminate, but may be melted in a crucible without any additament, and will then appear in its usual form. The acid of vitriol being poured on aurum fulminans likewise deprives it of its fulminating quality.
Gold does not begin to flow till it be red-hot like a live coal. Though it be the most malleable and most ductile of all metals, it has the singular property of losing its ductility more easily than any of them: even the fumes of charcoal are sufficient to deprive it thereof, if they come in contact with it while it is in fusion.
The malleability of this metal, and indeed of all the rest, is also considerably diminished by exposing it suddenly to cold when it is red-hot; for example, by quenching it in water, or even barely exposing it to the cold air.
The way to restore ductility to gold, when lost by its coming in contact with the vapour of coals, and in general to any metal rendered less malleable by being suddenly cooled, is to heat it again, to keep it red hot a considerable time, and then to let it cool very slowly and gradually; this operation frequently repeated will by degrees much increase the malleability of a metal.
Pure sulphur hath no effect on Gold; but being combined with an alkali into a hepar sulphuris, it unites therewith very readily. Nay, so intimate is their union, that the Gold, by means thereof, becomes soluble in water; and this new compound of Gold and liver of sulphur, being dissolved in water, will pass through the pores