larly crystalized; iron in the state of rust, and white or coloured spar, sometimes crystalized. Lead in that of crystalized lime, and of red, green, or white spar; tin in the same variations; zinc in the state of calamine; cobalt in red flowers; and arsenic in white lime. 3. Constitutes that which is most common, where, as in mines, the metals are combined with certain matters, which deprive them of their metallic properties, which they do not regain until they are separated. Sulphur is the substance that most generally unites with metals. The veins of metals are accompanied by stony substances, by quartz and spars, which seem to have been formed at the same time. They in general form two beds; one for the metal to lie upon, and the other as its cover. They do not blend, however, so intimately as the sulphur.

All metallic substances seem to owe their formation to water. The greatest part are to be found crystalized. Some preserve the organization of a vegetable or animal. The fire, indeed, has been supposed to have formed some. Mountains have their substances more immediately for our observation, and particularly those which run in chains. The plants which

* Fourcroy.

which grow on these mountains, are observed to be arid; the trees crooked and ugly; the snow to melt almost as soon as it falls. In fine, the very gravel is frequently seen to exhibit metallic colours. But, as I said before, the mercurial substance, from its amazing weight, its habitual fluidity, its extreme volatility, and the singular alterations it is capable of manifesting, is the most surprizing of all these metallic bodies. Besides the old ideas concerning it, it has been regarded as a metallic water, a water which does not wet one's hands, "Aqua non madefaciens manus." It is true, it does not wet one's hands, or many other bodies which are to be wet by water, by oil, and other liquors. But this phænomenon results merely from its having no affinity with these bodies. For as I have already remarked, when it is in contact. with certain substances, with which it can unite, as gold, silver, tin, &c. then it intimately applies itself, and wets them in such a manner, that they cannot be dried unless by evaporation caused by fire. A phosphoric light, is sometimes to be observed to proceed from mercury, and yet at the same time, a hand plunged into it, is sensible of great cold. A thermometer plunged into it, proves it to be of the temperature of the atmosphere, and no colder.

It

It is found sometimes in large masses. It is generally combined with sulphur, and then it forms what is called cinnabar. The corrosive sublimate is an artifical preparation; as is the amalgam, which is merely an incorporation of mercury with some other metal: this latter, however, can be rendered so powerful, as that metals by amalgamation shall be confounded. and entirely concealed within each other.

Besides the properties of other metals, iron, which next to tin is the lightest of all metals, has three in a great degree its own. One, is the property of being attracted by the magnet, and the power of becoming itself a magnet, by resting in a position south and north, or even by standing perpendicularly. The second, is the property of inflaming, for steel filings, small steel wire, burn by the least approach of ignited bodies; and producing sparks of fire, when struck against a flint, for the sparks are nothing else put particles of steel separated by the hard flint, and set on fire by the violence of the stroke. The third, is its being the only metallic substance that is found in plants and animals, and serves to give colour to a part of their humours. For it gives in reality, all that truly astonishing variety of colours, which are

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comprehended between the blue and the deepest red. It is even probable, that organized bodies, form within themselves this metal, för plants reared in pure water contain iron, as may be proved from their cinders, whence iron is to be extracted. It is very abundant. It is found in almost all coloured stones, bitumens, and mines of other metals. It is not uncommon to see organized matters, such as wood, leaves, barks of trees, and shells, changed into iron. And what is more striking, no organized matter is ever found changed into any other metal, which shews its affinity to those substances. There is scarce any art, in which iron is not employed; M. Macquer calls it the soul of the arts. It is the only metal that has nothing pernicious in it to organized bodies, vegetable or animal.

In decomposition, as you will readily conceive, consists the great art of chymistry, and this proceeds from a knowledge of affinities. Let us suppose, for instance, two bodies which strongly adhere to each other, as an acid and, a metal. Present to them a third substance, which has a stronger affinity with the acid, suppose an alkali; the result will be, the alkali having a superior tendency to unite with the acid, than the acid had with the metal, the

bodies will be separated, and the alkali will take the acid to itself; and the operation of this is called precipitation. It is proved also, in opposition to Stahl and others, that two or more bodies united, form a matter, the properties of which are new, and very different from these, which each of those bodies possessed before their junction. Marine acid and mercury, given separately, and in doses of a few grains in a glass of water, are not capable of injuring the animal economy; while the same dose of corrosive sublimate, formed by the combination of these two substances, and administered in the same manner, is a most violent poison. The oil of vitriol and the oil of tartar, make a solid. The solids of neutral salts combined with ice, make a fluid. But all substances have not an equal tendency to blend. Iron and mercury can never be intimately united.

We have already noticed the difference between the noble and the ignoble metals, and that they were all to be dissolved by aqua fortis, excepting gold. This king of metals, to speak with the ancients, is only to be dissolved by a mixture of the nitrous and the marine acids, though neither of them, when separate, has any effect upon it. It is directly attracted by de

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