of examination may be of fingular fervice. For the fpecific gravity of per- STATICS. fectly refined gold to water, being known; 'tis, thence, eafy to examine its degrees of fineness. And, when once the true fpecific gravity of a parcel of fand-gold is known, together with its degree of fineness, gain'd by collateral trials; this fpecific gravity may be used as a standard, whereby to try the fineness of other parcels of the like native gold: whence the fraud of the Negroes may, in this cafe, be prevented; who often clandeftinely mix with the right fand-gold, filings of copper, or brafs; whofe fpecific gravity is not half fo great as that of fine gold. Aquafortis, alfo, would immediately difcover this fraud, which will not work upon gold; but corrodes brafs, and thereby gains a colour betwixt blue and green; tho' if much filver be naturally mix'd with the gold, this proof, by Aqua fortis, will require skill: and, therefore, good fpirit of urine may be fubftituted in its ftead, occafionally; for this will readily work upon filings of copper or brafs in the gold, and gain from them a fine blue colour. And, to haften the operation of this liquor on filings of brafs, or copper; 'tis but fpreading them thin, upon a piece of white paper, and moistening them throughly therewith, that the air may promote its action; for, by this means, I have often produced, in a few minutes time, a pleasant blue colour upon the paper. Spirit of hart's-horn, or other volatile alkalies, or even ftale rank urine, will ferve in time of need, and yield the fame phenomenon. But if a folid fubftance be defired for this purpofe, common fal-armoniac may be used, by making a strong folution thereof in water, and applying it as any of the former; for this alfo, will foon gain a greenish colour, or a blue, from brafs or copper, and without affecting the gold. I have obferv'd fuch a variety of appearances and difguizes in metalline All minerals bodies, and other minerals, that I would advise the fearchers after mineshould be care fully examined, to have their eyes always open, and ready to take notice of any un-and, if fondeknown, or uncommon foffil; and not neglect to weigh it in their ros, hydrostatically. hands; and if it feem to exceed the weight of cryftal, or marble, to examine it hydroftatically. For there are in England, and feveral other countries, ufeful foffils, usually overlook'd by the unskilful. I have found, in this kingdom, eagle-ftones even upon the high-ways; and fome other minerals that were not fufpected to be of English growth. And, I remember, that paffing by a potter's work-house, and viewing the ground attentively, I made a difcovery of manganefe, a mineral very proper for glazing and colouring of earthen veffels, which the potter, afterwards, gladly used for that purpofe. The fame perfon fhew'd me a place that contain❜d great ftore of a foffil fubftance, unknown in England, that ran very far under ground, like a vein of metalline ore; by fome eafy trials I found it abounded with vitriolate falt, much more than any marcafite I had examin'd in the form of ftones: whence I concluded, it might more profitably be employ'd to make vitriol, than the marcafites ufed for that purpose in the works at Deptford, or elsewhere, in England. STATICS. I remember, alfo, that a mineral of an odd appearance, being fent me, as unknown to the miners who dug it up ; I found it to be the ore of bifmuth, tho' the vein that afforded it was very fmall. But the chief reafon for which I give this particular caution, is, that an application of our general remark upon the fpecific gravity of foffils, may be extended to a new and confiderable ufe; for we need not confine ourfelves to examine only thofe foffils, whereof we can obtain pieces fufficiently large to be fingly weigh'd in water; becaufe, not to mention the minerals that may be found ufeful to the phyfician, the drugfter, or the mineralift; the ores of metals may be often found difguiz'd in the form of earth, or mud, that is eafily dry'd; which foffils, tho' unfit to be immediately fufpended by a foft fubftances, horfe-hair, may conveniently be examin'd by means of a glafs jar-bucket, hydrostatically. of a known specific gravity: for, this veffel being almoft fill'd therewith, and that matter, carefully counterpois'd in air, and made thoroughly wet with water, and the whole warily let down in the fame fluid, and there kept fufpended by a horse-hair, tied to a tender balance, the difference between the weight of the mineral, and veffel in air and water, will be obtain'd; the weight, therefore, of the veffel, in water, being fubftracted from that difference, will give the weight of the foffil in water, and, confequently, its fpecific gravity in water. How to examine earths, or Colour'd fands, and gravel. And to fhew that this method wants not proper fubjects, whereto it may be apply'd; we are told, that one of the beft forts of Swedish iron is often found in the form of a red mud, at the bottom of lakes, or other ftagnant water: and I have obferv'd English okers to be richer in iron, than fome ores of that metal. And, an experienc'd writer, upon the gold and filver mines of America, takes notice, that gold, itself, is often found difguized in a reddifh earth. Vannochio, alfo, a famous Italian mineralift, tells us, that a reddish fort of earth, fometimes, contains the richeft metals. I, myself, have obferv'd fome finely figur'd crystals, to grow in a red earth. And, laftly, a traveller prefented me with a certain earth, which he affirm'd to come from the diamond-mines; and this, alfo, I found to be red. But a mineralift may make a more advantagious ufe of our hydroftatical bucket, by employing it in weighing colour'd fands and gravel. And, to fhew how apt we are to over-look fands, for want of trying them by weight; I have, fometimes, feen a fort, flighted as worthlefs, which being wafh'd, and view'd thro' a microfcope, appear'd like a heap of fmall granats, and, perhaps, were really fo. But what is more extraordinary, having obferv'd, that the black fand, ufually employ'd to dry fresh writing, feem'd, manifeftly, heavier than the common; I examin'd it by the hydroftatical bucket, which gave us its fpecific gravity to water, as about 4.6 to 1; and, by melting it down, with two or three parts of antimony, and cafting it into an iron cone, I found it of an irony nature; and, by applying it to a load-ftone, to be far richer in metal, than any of our English iron-ores; for, at leaft, feven parts in eight, would eafily be taken up by the magnet. But fuch obfervations as thefe, are not my chief motives to recommend the examination of fands and gravel to the mineralift. 'Tis 'Tis well known, that European traders yearly bring large quan- STATICS. tities of gold from the coaft of Guinea, which is wash'd, or pick'd out of the fand. And, even in Europe, there are rivers whofe fand is inrich'd by grains of gold. For this, the Tagus, that runs by Lisbon, and Pactolus, were famous among the ancients. An induftrious chymift affur'd me, he got gold, with profit, from the fand found on the banks of the Rhine : and there is a little river in Savoy, on the banks whereof, after a landflood, I faw poor people employ'd in feeking for grains of gold. Some trial, alfo, that I caufed purpofely to be made, confirm'd me in a perfuafion, that the fands, of many places, if skilfully treated, by chymistry, may afford much more gold than is got from them in form of grains. For, befides that there may be many particles of gold, fo very minute, and clofely fix'd to grains of fand, as not to be taken notice of by the eye, or prove feparable by washing or picking; there may, as I conceive, be many fmall portions of that metal incorporated with the body of the fand; which a skilful artist, by the help of proper additions, might feparate to good advantage; efpecially, if with litharge, or minium, the fand be firft reduced to a glass; and then care be taken to get the volatile gold, by giving it a pure body, fit to retain, and fix it; fuch, for example, is fine filver; out of which, I remember, we feparated, by quartation, from a crucible full of vitrified fand, and two or three fluxing materials, of fmall price, fixteen grains of pure gold. Volatile gold is, I know, by many learned men, look'd upon as a fictitious thing; yet I have, by the help of an addition, inconfiderable as to bulk, and more fo, as to weight, without a naked fire, and in a glass retort, fublimed crude gold; fometimes in the form of a yellow falt; and fometimes, when the operation fucceeded better, in that of thin crystals, prettily fhaped, gloffy, and as red as rubies: this by the bye. It may, perhaps, be more useful to fearchers after rich foffils, to obferve, that when they meet with fands, earths, mineral fragments, &c. whofe fpecific gravity but little exceeds that of cryftal,; and yet, by the place wherein they are found, or by other tokens, give hopes of their containing particles of gold, they fhould not haftily reject them. For, having fometimes difcover'd corpufcles of iron, and steel, in a vast variety of foffils, and difguizes, I fufpect that fome golden particles may lie conceal'd in feveral bodies, which are thought to contain no metal; and ftill more in metalline ores. But thofe who would apply hydroftatics to ores in general, fhould en- and has of lead Ores in general; deavour to procure fpecimens of different mines, efpecially if they be in particular. found in the fame country; and either by trial, or ftrict inquiry, inform themselves what proportion of the refpective metal they contain. For thefe portions of ores, and minerals, being carefully weigh'd in air and water, and their fpecific gravities thereby known, may ferve for a kind of ftandard, wherewith to compare, hydroftatically, the metalline portions contain'd in other parcels of ore, of the fame fpecies. Thus, for inftance, all our English lead-ores,worth taking notice of,may be divided into three STATICS. three kinds; and, in each of thefe, a latitude allow'd for greater or lefs degrees of goodness. Of the firft fort are thofe that, in the ordinary ways of melting, hold, fome of them, from thirty to forty pounds of lead in an hundred weight; and others, to forty-five pounds; which are often flighted, as fcarce worth the working. The fecond fort may reach from fortyfive to fixty pounds in a hundred ; but the moft ufual proportion, I have found, in my trials, hath been about half the weight of the ore, in clean and malleable lead. These are thought indifferently good, and worth the working; but others, comprized in this fecond fort, hold about fifty-five, and fome near fixty pounds; and thefe we look'd upon as pretty rich. As for the third fort, it may confift of thofe that yield from fixty to eighty pounds in the hundred; and fuch ores are juftly reputed very rich, efpecially if they come near up to eighty pounds. I confefs, I never met with any that reach'd fo far; but was affur'd by the mafter of his majefty's mint, that he had found fome fuch. These look as if they were all metal; and I have obferv'd fome lumps thereof to be compos'd of feveral large cubes, very firmly adhering to one another. The bydrostatical balance applied to the Materia firft, to the La Ás to the ores, prefented me from different countries, I have inferted their fpecific gravities, in the table annexed to this treatife; fuppofing it may be of ufe, in making a conjecture, with other concurrent circumftances, whether a mine may be advantagiously wrought; but, concurrent circumstances are, by no means, to be neglected. W SECT. II. E come now to the fecond part of our defign; that is, to apply the hydroftatical balance to the Materia medica. And firft, there is a medica; and deeply red, and opake hard mineral, call'd, in the fhops, by the name of Pis Hæmatites. Lapis Hamatites, which, tho' little ufed by our English phyficians, is, in several places abroad, highly esteem'd, and, in my opinion, not without caufe; particularly for the fomniferous quality to be obferv'd in fome of its preparations. Of the English fort of this foffil, we weigh'd, in a tender baÎance, a piece that chanc'd to amount to three ounces, two drams, first in the air, and then in water; and found its proportion to that liquor, as 4.15 to 1; that is, almoft twice as heavy as a mere ftone of equal bulk. So great a weight, confirm'd me in the conjecture I had made, that this ftone contain❜d a large proportion of metalline fubftance. I therefore fublimed it, when finely powder'd, and diligently mix'd it with a double weight of fal-armoniac,and found it,as I expected, very aftringent upon the tongue, like feveral preparations of iron; and, for a farther proof, having put lefs than a grain of it into a fpoonful, or two, of a strong infufion of galls, it immediately produced a black and inky mixture. To the Lapis Lapis Lazuli is fometimes ufed by European, but more frequently by the Arabian, and other eaftern phyficians; and, particularly, as an emetic; which faculty I thought it poffefs'd, upon account of fome metalline ingredient; and, accordingly, having hydroftatically examin'd a piece, that was judg❜d moderately rich, we found the proportion thereof to an equal bulk bulk of water, as 3 to 1; which argues, that notwithstanding its brisknefs STATICS. in operation, it contain'd a much fmaller proportion of metalline fubftance, than Lapis Hamatites, or feveral lefs violent minerals. The load-ftone is applicable to medicinal uses, and may have fenfible The magnet. operations upon the human body; for which reafon we examin'd it hydroftatically, and found the weight of a lump thereof, that I judg'd to be either English, or Norwegian, was, in proportion to water of the fame magnitude, as 4.93 to 1. Lapis Calaminaris, is frequently ufed in phyfic, efpecially by chymifts, Calamine. to abforb acidities; for which purpofe I prefer it to feveral more famous drugs; but though 'tis ufually employ'd only as an external remedy, yet fome uncommon chymical preparations of it, make me think it deferves to be further examin'd. A famous empiric candidly affured me, that the medicine he with great fuccefs made ufe of, against fluxes, was nothing but pure, and well-ground Lapis Calaminaris; hence I readily conjectur'd, that it participates of a metalline nature: which may alfo be argued from its operation upon copper, which it turns into brafs: wherefore, weighing a piece of this foffil, we found it to water, as 4.69 to I. Let it be here obferv'd, that tho' when a hard foffil is found to be much heavier than cryftal, of the fame bulk, 'tis very probable, the folid concrete contains a confiderable portion of fome metalline, or ponderous mineral body; whence its good or bad qualities, with regard to the animal œconomy, may, probably, be deduced; yet 'tis very poffible, for a foffil to be endow'd with medicinal virtues, or noxious qualities, on account of its extraneous matter, tho' its fpecific gravity but little exceeds that of crystal, or the difference be inconfiderable; for a very fmall proportion of adventitious metalline, or mineral fubftance, if it be of a violent nature, may, in fome cafes, diffuse it self thro' the reft of the mass, and impregnate it with active qualities; as we fhall fee hereafter. But further, this method of examination, may affift us to guess, with Red coral. probability, whether a mineral body be of a ftony nature, or not. Thus coral, for inftance, is, by fome, thought to be a plant; by others, a Lythodendron; but, by the greater number, a precious ftone; in which difference of opinions, its fpecific gravity may prove of confiderable fervice. We, therefore, weigh'd a piece of choice, and well-colour'd red coral, firft in air, and then in water, and found its proportion, to an equal bulk of the latter, to be as 2.68 to 1: whence their opinion, who take it for a stone, feems most probable; fince its fpecific gravity exceeds that of cry ftal. Pearls, because of their hardness, are often thought of a ftony na- Pearl. ture. A monftrous one being prefented me, that was taken out of an oyfter, its shape irregular, its magnitude extraordinary, and its aerial weight amounting to 206 grains; I weigh'd it in water, and found it to be thereto as 2.51 to 1: fo that its fpecific gravity nearly equall'd that of cry ftal. Calcula |