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cess to it, that if a glass phial be hermetically closed in that 'heat, and, when cold, hath its neck broken off within a vessel of water, the phial will be so completely filled by the water as to shew that nothing but fire is included in it; no air, but what is attenuated to such a degree of purity as to be no longer distinguishable from fire. When a vessel is closed up without any perceptible air in it, we may then say, that nothing remains in such a space, but the medium, which penetrates all things. Whether the vessel be filled with the sun's rays, or with that invisible fluid which lies hid in the pores of bodies; whether it be dark as ether, bright and shining as the light of the sun, or intensely hot as the medium in the heart of a furnace, we call it fire; that elementary matter which is distinct from earth and water, and is more attenuated and penetrating than air.
It is rather more easy to prove that compound bodies are made up of the above mentioned elements, and are resolved into them again, by proceeding per descensum to discover the simples in the compounds, than to find them separately in their simple form. This may be done by examining the analysis of different bodies from the three kingdoms of fossils, plants, and animals. The articles of the fossil or mineral kingdom are generally more simple than those of the other two, as partaking of earth in a much greater proportion. This element is found under the different forms of metals, stones, gems, and earths of a looser texture, all of which are but earth differently modified: though it must be confessed that they differ from pure virgin earth, in this respect, that with the utmost violence of fire they will for the most part be converted into glass. The substance of glass is extremely different in appearance from the white opaque earth of chalk, lime, bones and wood ashes : yet is it well known that common glass is composed of the two earthy ingredients of sand and alcaline salt, which, being fused together in the fire, settle into that pellucid body, which no art can decompose or bring back again to its constitųent materials. How different in appearance is the glass of lead from the metal in its natural form, and from the powder of red lead : the substance is still the same, but differently modified by the action of fire, which gives a new arrangement to the parts. It may seem strange to call the 'metal of lead by the name of earth; but when this metal
is kept in fusion over the fire, the surface of it is converted into a ponderous dust, very much resembling the dust we tread upon, Quicksilver, which appears as a white shining fluid, may be converted by repeated agitation into a black obscure powder; and a spectator, who should see it only in this latter form, would never think it capable of the former, or believe that the one had any relation to the other. The rust of iron is a
, red earth, which has lost its metallịc form and colour, only by being corroded in a moist air ; and this same red powder, with the addition of any astringent, is the matter which gives blackness to ink.
There is no reason for feigning an elementary mercurial principle as the basis of metals *. It is more reasonable to understand that all metals and minerals are but different modifications of earth : and why should that be supposed in all metals, which cannot be extracted from any one of them, and is producible only from the red ponderous earth of cinnabar? Nature does not M 4
* This doctrine was invented to serve the system of the alchemists: for if all metals have the same metallic basis, it was rendered more probable that they might all be transınụted into one another.
present us with a multitude of principles, but with an endless variety, arising from the different combinations of a few. The three elements of salt, sulphur, and mercury, which the chemists added to the four others of the philosophers, are in reality nothing more than secondary substances : and though it may
very difficult to decompose them with precision, yet in general we may learn their composition very nearly by experiment and rational deduction. Salts are either acid, alcaline, or neutral; the acid is composed of earth, water and air, and so is the neutral; the aloqline is a composition of earth and fire: and some of these are again recompounded, so as to be two removes from the simple elements; which is the case of the ammoniacal salts, and many other heterogeneous bodies. And here it is to be observed, that air and fire are capable of attaching themselves to the other elements, so as to partake of their fixed and quiescent nature, and to become as it were solids themselves in the company of other solids, till by some force they are again resuscitated and enlarged so as to assume their former volatility. One third part of the weight of some bodies is derived from such an accession of air or fire; and hence the chemists, when they decompose such bodies, find the ingredients fail very surprisingly in weight, when compared with the concrete body from which they are taken *. When we say that salts contain air or fire, we mean, in a fixed or quiescent state. Sulphur is composed of an impure earth, an acid salt, and phlogiston, that is fire fixed and intangled in an oleaginous vehicle.
Mercury seems to be the purest metallic earth, unfixed by a cement of sulphur, and owing its fluidity to an etherial or watery principle combined with the solid parts.
Some modern chemists are superseding all the experiments of their predecessors, and would introduce, as primary elements, acid, alkali, and phlogiston : but earth, air, and water will account for the acid; earth and fire for the alkali; and phlogiston is nothing but fixt fire in a resinous or oleaginous vehi. cle, sometimes more sometimes less pure, sometimes gross and solid, as in pitch, tallow, and the sulphur of metals; and in other
* Hence it appears, that most bodies, when once analyzed, can never be recomposed ; because the fire and air, which make a considerable part of them, go off and vanish so as ne. ver to be recovered.