Page:Cyclopaedia, Chambers - Volume 1.djvu/97

Rh therefore, expresses the height at which the Barometer must stand, where the Air would be as heavy as Gold, and the Number $2 51632⁄409640$ Lines, the Thickness to which our Column of 36 Fathoms of Air, would be reduced in the same place.

New, we know, that 409640 Inches, or 43528 Fathoms, is only the 74th Part of the Semidiameter of the Earth: and when you are past that, whatever Matters there be, they must be heavier than Gold: 'Tis not improbable, therefore, that the remaining Sphere of 6451538 Fathoms Diameter, may be full of dense Air, heavier, by many degrees, than the heaviest Bodies among us.—Hence, again, as it is proved, that the more Air is compressed, the more does the same degree of Fire increase the Force of its Spring, and render it capable of so much the greater Effect; and that, for instance, the Heat of boiling Water increases the Spring of our Air, beyond what it ordinarily is, by a Quantity equal to one third of the Weight wherewith it is pressed: We may infer, that a degree of Heat, which in our Orb can only produce a moderate Effect, may have a very violent one in such lower Orb; and that as there may be many degrees of heat in Nature, beyond that of boiling Water, is probable there may be some, whose Violence, thus assisted by weight of the Air, may be sufficient to tear sunder the solid Globe. Mem. de l'Acad. An. 1703.

This elastick Power of the Air, is the second great Source of the Effects of this important Fluid.—In virtue hereof, it infinuates into the Pores of Bodies, carrying with it this prodigious Faculty of expanding; and that so easy to be excited: whence it must necessarily put the Particles of the Bodies it is mix'd withal, into perpetual Oscillations. In effect, the Degree of Heat, and the Air's Gravity and Density, and consequently its Elasticity and Expansion, never remaining the same for two Minutes together; there must be an in- cessant Vibration, or Dilatation and Contraction, in all Bo- dies. See VIERATION.

This Reciprocation we observe in several Instances, par- ticularly Plants, the Tracheæ or Air-Vessels whereof, do the Office of Lungs: For the contained Air alternately ex- panding and contracting, as the Heat increases or diminishes, by turns presses the Vessels, and eases 'em again; and thus promotes a Circulation of their Juices. See VEGETABLE, CIRCULATION, &c.

Hence, we find, that no Vegetation or Germination will proceed in Vacuo.—Indeed, Beans have been observed to grow a little tumid therein; which has led some to attribute that to Vegetation, which was really owing to no other than the Dilatation of the Air within 'em. Sce VEGETATION, GERMINATION, &c.

From the same Cause it is, that the Air contain'd in theBubbles in Ice, by its continual Action, bursts the Ice: And thus Glasses and other Vessels frequently crack, when their contained Liquors are frozen. Thus, also, entire Columns of Marble sometimes cleave in the Winter time, from some little Bubble of included Air's acquiring an increased Elasticity.

From the same Principle arises all Putrefaction and Fermentation; neither of which will proceed, even in the best dispofed Subjects, in Vacuo. See PUTREFACTION, and FERMENTATION.

In this we have a singular Instance of the wonderful Efficacy of Air, that it can change the two Kingdoms, and convert Vegetable Substances into Animal, and Animal into Vegetable. See ANIMAL, &c.

In effect, all natural Corruption and Alteration seems to depend on Air; and Metals, particularly Gold, only seem to to be durable and incorruptible, in Virtue of their not being pervious to Air—Accordingly, Names slightly wrote in the Sand, or Dust, on the Tops of high Mountains, have been known to remain 40 Years, without being in the leaf alter'd or effaced. See CORRUPTION, ALTERATION, &c.

Effects of the peculiar Ingredients of the Air.

Air not only acts by its common Properties of Gravity, and Elasticity, but there are numerous other Effects, ari- sing from the peculiar Ingredients whereof it consifts. Thus, 1$o$, it not only dissolves and attenuates Bodies by its Pressure and Attrition; but as a Chaos, containing all Kinds of Menstruums, and consequently having wherewithal to dissolve all Kinds of Bodies. See DISSOLUTION.

"Tis known, that Iron and Copper readily diddolve, and become rudty in Air, unleds well defended with Oil-Boerhaave assures us, he has seen Pillars of Iron so reduced by Air, that one might crumble 'em to Dust between the Fingers; and for Copper, it is converted by the Air into a Substance much like the Verdegrease produced by Vinegar. See IRON, COPPER, VERDEGREASE, &c.

Mr. Boyle relates, that in the Southern English Colonies, the great Guns rust so fast, that after a few Years lying in the Air, large Cakes of Crocus Martis may be easily beat off 'em.—Acosta adds, that in Peru the Air dissolves Lead, and considerably increaſes its weight—Yet Gold is gene- rally esteem'd indissoluble by Air, being never found to contract Rust, the exposed ever so long. The Reason hereof is, that Sea Salt, which is the only Menstrum capable of acting on Gold, being very difficult to volatilize; there is but a small Proportion of it in the Atmosphere. In the Chymists Laboratories, where Aqua Regia is preparing; the Air becoming impregnated with an unusual Quantity of this Salt; Gold contracts a Rust like other Bodies. See GOLD, &c.

Stones also undergo the common Fate of Metals. Thus, Purbeck Stone, whereof Salisbury Cathedral consists, is observed gradually to become softer, and moulder away in the Air; and the like Mr. Foyle relates of Blackington Stone. See STONE.—He adds, that Air may have a notable Operation on Vitriol, even when a strong Fire could act no further on it. The same Author has even found the Fumes of a sharp Liquor to work more suddenly and manifestly on a certain Metal, when sustained in the Air, than the Menstruum it self did which emitted those Fumes, on those Parts of the Metals it cover'd.

2$o$, Air volatilizes fix'd Bodies.—Thus Sea Salt being first calcined, then fused by the Fire, and when fused exposed to the Air to liquify; when liquified set to dry again, then fu- sed again; and, the Operation thus repeated: will by de- grees he almost wholly evaporated; nothing remaining but a little Earth behind. See VOLATILITY, VOLATILIZATION, &c.

Helmont mentions it as a mighty Arcanum in Chymistry, to render fixed Salt of Tartar volatile: but the thing is easily effected by Air alone; for if some of this Salt be exposed to the Air in a Place replete with acid Vapours, the Salt draws the Acid to it self, and when saturated therewith, is volatile. See TARTAR, &c.

3$o$, Air also fixes volatile Bodies.—Thus, the Nitre or Aquafortis readily evaporate by the Fire; yet, if there be any putrified Urine near the Place, the volatile Spirit will be fix'd, and fall down in form of Aqua secunda. See FIXITY.

4$o$, Add, that Air brings many quiescent Bodies into Ac- tion, i. e. excites their latent Powers. Thus, if an acid Va- pour be diffused thro' the Air, all the Bodies whereof that is a proper Menstruum, being dissolved thereby, are brought in- to a State proper for Action. See SALT, &c.

In Chymistry, not only the Presence or Absence of the Air, but even its being barely open, or inclosed, is of great consequence. Thus, Camphire fired in a close Vessel, runs wholly into Salts; whereas, if during the Process, the Cover be removed, and a Candle applied, the whole flies off in Fume. So to make Sulphur inflammable, it requires a free Air : in a close Cucurbit, it may be sublimed a thousand times without kindling. Sulphur being put under a glass Bell, and a Fire applied, rises into Spirit of Sulphur per Campanam: But if there be the least Chink whereby the included Air communicates with the Atmosphere, it im- mediately kindles. So an Ounce of Charcoal, inclosed in a Crucible well luted, will remain without loss for fourteen Days in the intensest Heat of a melting Furnace; tho the thousandth Part of the Fire in open Air, will presently turn it into Ashes.—Helmont adds, that the Charcoal remains all that while without any Alteration of its black Colour; but that if the minute Air is let in, it falls instantly into white Ashes. The same holds of the Parts of all Animals and Vegetables, which can only be calcined in open Air: In close Vessels they never become any other than black Coals. See CALCINATION, COAL, &c.

The Air is liable to abundance of Alterations, not only in respect of its Mechanical Properties, Gravity, Density, &c. but also in respect of the Ingredients it consists of Thus, in Places abounding with Marcasites, a fretting vitrio- lick Salt is observed to predominate in the Air, which rets the Hangings, and is often seen lying on the Ground in a whitish Efflorefcence.-At Fa$o$blun in Sweden, noted for Copper Mines, the mineral Exhalations affect the Air so sensibly, that their Silver Coin is frequently discoloured in their Purses; and the same Eruvia change the Colour of Brass. Mr. Boyle was assured by a Gentleman who pos- sess'd some Ground wherein there were several Veins of Merals, and other Minerals, that he had frequently seen Pillars of Fumes ascending thence; some having no Scent, some an ill one, and some few a good one.—In Carniola, Campania, &c. where there are Mines of Sulphur, the Air at times becomes very unwholesom; whence frequent epi- demick Diseases, &c.—Tis added, that the Mines near the Cape of Good Hope, emit such horrible Fumes from the Arsenic that abounds there, that no Animal can live near them; so that such as have at any time been opened, were obliged to be immediately closed again.

The Effluvia of Animals also have their Effect in varying the Air; as is evident in contaginus Diseases, Plagues, Murrains, and other Mortalities which are spread by the Air. See PLAGUE. The