COROLLARY.

This experiment renders it unneceffary to fly to a Fuga vacui for a reafon why two flat polifh'd marbles, when they adhere, require a confiderable force to disjoin them; they being preffed together by air of an immenfe height, after a like manner with our valve, and the inftrument, here, by water; which requires the great weight L, to over-balance it, fo as to force them afunder.

STATICS.

HYDROSTATICS

Applied to

ORES,

And to the

MATERIA MEDICA

Fofils, their medicinal virtue,

whence?

A

SECT. I.

S the virtues of gems proceed, chiefly, from the metalline and mineral fubftances, that, whilft their original matter remain'd either fluid or foft, are incorporated therewith, and afterwards hardned into ftones; fo it feems very probable, that feveral boles, clays, earths, and efpecially minerals, &c. may be endow'd with confiderable medicinal virtues, and, perhaps, greater than thofe of the finer gems; because herein are often found, more of the metallic and mineral parts, which, whilst in folutis principiis, might very plentifully infinuate themselves into the more open bodies, and there fit loofer than in diamonds, rubies, fapphires, &c. which Aqua fortis, itself, is unable to penetrate and diffolve.

A new way of I, therefore, thought it might be of ufe to phyficians, mineralifts, and examining them miners, to advance a new way of examining foffils; for tho' the method hydroftatically. itfelf pretends not, directly, to difcover more than one quality of the body it examines; yet that quality, being its fpecific gravity, is fo confiderable, that it may lead one farther than might, at firft, be imagined.

Its foundation. Reflecting that rock-cryftal is of the moft pure, and homogeneous kind of ftones; I pitched upon this for the ftandard, whereby to adjust and afcertain the purity and fimplicity of other mineral fubftances.

By

By carefully weighing feveral pieces of native cryftal, clear and colour- STATICS. lefs, firft in air, and then in water, we found its proportion to clear water, of the fame bulk, as 2 to 1, nearly. Thus, if a hollow, metalline cube be exactly fill'd by one ounce of water; and afterwards, again, as exactly fill'd by a cubical piece of rock-cryftal, that bulk of the ftone will weigh about two ounces and a half. Some of my trials, indeed, made with tender balances, reprefented the proportion of these two bodies, with a very inconfiderable variation; but 'tis probable, that different pieces of cryftal, tho' of equal bulk, may not have precifely the fame weight: however, the difference is fo fmall, that it may here be fafely neglected.

And to prevent any fcruple about the origin and nature of cryftal, I fhall add, that I procured fome ftrong ificles, that had been faften'd to vaults, c. as bodies that would be acknowledg'd true ftones, and yet to have once been in a liquid form and having hydroftatically examin'd thefe concretions, their fpecific gravity appear'd to be little differing from that of cryftal.

To apply this fundamental obfervation to the present occafion; when I would, with probability, difcover whether the mere ftony matter of a mineral body were mix'd with fome adventitious substance of a metalline nature, or of fome other mineral more ponderous than cryftal; I carefully weigh'd it, as we faid, in air, and then in water: when, if its proportion to water of the fame bulk, exceeded that of 2 to 1, or 5 to 2, I conclude it probable, that the concrete had in it a portion of foreign matter fpecifically heavier than cryftal, proportionably to the excefs of the weight of the folid body above that of an equal bulk of water. To illuftrate this procedure by example.

illuftrate the

The magnet, upon account of its great hardness, is ufually reckon'd Examples to among ftones; but having obferv'd a particular kind thereof, to be appa- doctrine. rently more ponderous than common ftone, of equal bulk, we weigh'd them in air and water; and found the fpecific gravity of fome of them fo far to exceed that of cryftal, or marble, that we concluded they contain❜d a confiderable quantity of metalline matter, which, by collateral experiments appear'd to be of a ferruginous nature.

Emeri is commonly reputed a mere ftone; but finding its weight in water confiderably to exceed that of an equal bulk of cryftal; for it was to that liquor nearly as 4 to 1; I conjectured, that it contain'd a metalline fubftance; as afterwards, by proper trials, I found it did.

By the weight, alfo, of Lapis Hamatites on my hand, I conjectured, it largely partook of a metalline ingredient; and prefently I difcover'd that iron or fteel was contain'd therein. And, in general, I have frequently fufpected different bodies to be of a metalline or mineral nature, and was feldom mistaken in my conjecture; tho' they have commonly been thought to contain no fuch fubftance. The fame thing I, likewife, found true, even in granats and American talc, from which I have extracted metalline parts. But we muft here fet down fome preliminary obfervations. And firft, Preliminary obif a proposed foffil be much lighter than an equal bulk of cryftal, it is fervations, h

Sf 2

almoft

STATICS. almoft certain it cannot be a metalline ore; and this negative proof is here ufually ftronger than the affirmative kind. Thus, for inftance, when I find that jet, tho' a foffil, has a far lefs fpecific gravity than cryftal, I conclude it to be no metalline body. The like determination I make as to foffil-amber, Sulphur vivum, common fulphur, English and Venetian talc, and fome other firm concretions, which are dug out of the earth: among which, I alfo rank black-lead. For having found its weight to that of water as 1.86 to 1, I afterwards difcover'd it to be not lead-ore, but a particular kind of mineral, and near allied to a fort of talc that I have met with.

2. We muft diftinguish between the feveral ufes to be made of foffils by men of different profeffions. So that if a fofiil be found very little heavier in fpecie than cryftal or marble, it may, poffibly, have a metalline or mineral portion, which, however fmall in quantity, will perhaps entitle it to the efteem of a jeweller, physician, or chymift. But if this excefs of its fpecific gravity be inconfiderable, the foffil itself will prove of little price to a mineralift; for if it be poor in metalline fubftance, it may chance to be hardly worth the working.

3. But tho' the great ponderofity of a foffil generally proceeds from a proper metalline fubftance embody'd with the other parts thereof, which fhews it not to be a mere ftore; yet this, alone, is not a fure fign that the mineral part is properly metalline: and, therefore, where any doubt arifes, we fhould have recourfe to collateral figns. For, befides metalline ores, properly fo call'd, there are other foffils, which, tho' of affinity to metals, may be diftinguifh'd from true metalline ores; fuch, for inftance, are antimony, bifmuth, Lapis Calaminaris, and marcafites. But there will not, perhaps, occur many cafes, wherein we need to have recourfe to collateral figns, to fhew whether the mineral part of a foffil be, in a strict sense, of a metalline nature, or not. For fuch femi-metals are moft commonly found either in veins, maffes, or great lumps of their refpective kinds; and eafily discover to what fpecies they belong. I have, indeed, receiv'd a lump of matter from Devonshire, wherein I found fome antimony mix'd with lead, which was the predominant body. But fuch mixtures occur fo feldom in England, that our way of eftimating ponderous foffils, will, nevertheless, be useful on moft occafions.

4. Two different eftimates may be made of the fpecific gravity of ores; one, when the body propofed is weigh'd in its natural ftate, that is, as it comes out of the earth, accompanied with the fpar, or other heterogeneous matter, that firmly adheres to it; and the other, after it has been beaten fmall, and feparated from heterogeneous fubftances by the help of water, after being skilfully agitated, wherein there is a remarkable difference in weight between thefe and the genuine parts of the ore; which being thus fever'd from the reft, are call'd wafhed. "Tis fometimes, alfo, very proper to prepare the ore by roafting it once or more, or by keeping it for feveral hours in a competently ftrong fire; as is ufually practifed in preparing copper-ore; efpecially if it be ftubborn. I purpofely mention thefe

two

two ftates, wherein the weight of an ore may be taken, because I have STATICS. obferv'd, that, in feveral cafes, 'tis of great importance to diftinguish them carefully. For feveral ores, which, in their natural ftate, have too little fpecific gravity, to make them judg'd worth the charge of being wrought, may yet, after they are prepar'd by water and fire, afford a metalline portion, fo ponderous, as to allow one to fufpect they contain either filver or gold. I remember, that a piece of lead-ore, brought from Ireland, feem'd to me fo light in the lump, that I thought it deferv'd not to be wrought for lead; yet, afterward, upon trial, it appear'd fo well ftor'd with particles of filver, that I encourag'd the owner of the mine to work

it.

5.

metalline ores..

There is one kind of minerals that I have obferv'd to impofe upon men To distinguish fo frequently, that I shall take a particular notice of it. For, not to men- marca fites from tion examples from travels, and voyages, I have myself met with numbers who had great expectations from marcafites. And I have receiv'd not only from places near home, but even from the Indies, foffils, whereof my opinion was defir'd; which I found to be only marcafites. Many of these foffils have two qualities, that make them fit to delude the vulgar; for, they fhew a multitude of fhining ftreaks, refembling gold; or have, at the fame time, a weight equal to that of true metalline ores. Marcasites, then, being thus adapted to impofe upon the unwary, I have had much ado to undeceive fome perfons, as to the pleafing confidence they had entertain'd, that thefe promifing foffils were lumps of rich gold, or filverore. Wherefore, fince their weight, the criterion of minerals, is one of the two things that delude fo many, I fhall give a few inftances of the fpecific gravity of marcafites, to make it appear, that fome of them are, bulk for bulk, far more ponderous than true metalline ores. And, indeed, the great ponderofity of foffils, has feveral times occafion'd me to determine, before trial, that they were marcafites. But, to prevent being impos'd on, by this, or the like fpecious fubftance, it is but placing it in a strong fire, and blowing, now and then, with a pair of bellows; for, by this means, the fulphur wherewith marcafites abound, will take fire, and burn with a flame for the moft part blue, like that of common fulphur: fo that once, by diftillation, in a clofe veffel, I obtain'd four ounces of good brimftone, from three pounds of thefe ftones. And, if when this foflik ceafes to flame, and fmoke, it be taken out of the fire, and fuffer'd to cool, it will be depriv'd of all its gaudy appearance, and turn'd to a brittle, blackish fubftance, very different from that of a proper metalline ore. Marcalites, however, may be look'd upon as a kind of metalline bodies; for, I have found feveral of them to contain, not only particles of copper, but also of iron, or fteel; for, after calcination, applying the pulveriz'd remains, to a vigorous load-ftone, great multitudes of chalybeate corpufcles quickly adhered thereto. And, I remember, in a catalogue of the foffils of Mifnia, published by Kentmannus, under the head of Pyrites, he places feveral marcafites; fome whereof contain'd copper, others filver, others gold, and others, again, both filver and gold. Having prefented a very fine marca