Medicina hydrostatica, or, Hydrostaticks applyed to the materia medica shewing how by the weight that divers bodies, us'd in physick, have in water : one may discover whether they be genuine or adulterate : to which is subjoyn'd a previous hydrostatical way of estimating ores / by the Honourable Robert Boyle ...

CHAP. VI.

BUT the Second thing compri∣zed in our Corlolary, may in divers Cases be of much greater Uti∣lity and Importance, as being very

proper to help us to discern genuine Stones, whether Animal or Mineral, from counterfeit Ones; which too often pass for true, to the great pre∣judice of Physicians and Patients, and the great Loss of Lapidarie's, and their Customers. For as there are few Qua∣lities appertaining to ponderable Bo∣dies here below, that are so radi∣cated, (if I may so speak) as their Ponderosity is. So there is scarce any Quality, wherein 'tis so difficult for Impostors, to make a notable Al∣teration unperceivedly, as the speci∣fick Gravity. I said, for Impostors because, tho' in several Cases, 'tis not so very difficult, to alter the speci∣fick Weight belonging to this, or that, kind of Bodies; yet in those ve∣ry Cases, it may be exceeding diffi¦cult, and perhaps impractible, to make a considerable Change in tha•• Quality, but by such Additions, o•• Operations, as will make a sensible Change in some other Qualities too and thereby expose the Fallacy to b•• discovered. And this will especiall••

prove difficult in many Cases to vul∣gar Cheats, and Counterfeiters, or Adulterators of Gems, and other va∣luable Minerals; because the little knowledge they have of the Nume∣rousness, and Variety, of Natural and Artificial Productions, confines them to a small Number and Diversity of Means, to accomplish their fradulent Designs. And whilst they are in∣tent, but upon counterfeiting the more obvious Qualities of things; and perhaps of eluding the known and vulgar Tryals Men are wont to acquiesce in; they are not like to take Care to maintain the specifick Gra∣vity, and secure their adulterated Wares, against an Hydrostatical Way of Examen, which, probably, they never so much as heard of. By this means, several Perls, for Instance, may be discovered to be Counter∣terfeit, without, in the least, injuring them. And I remember, That some factitious Corals, that, for Divertise∣ment, I made, to shew what might be done in that kind; were, notwith∣standing

their fine Colour, Shape, and Glossiness, easily discoverable, by their having a specifick Weight manifestly exceeding That, which be∣longs to natural Corals.

Before I knew better Ways, I have sometimes, for Recreation, by the help of Minium made Pastes, or factitious Gems, which, tho' transparent, and finely enough coloured, yet, because they contained some vitrified Lead, added to the other Ingredients to pro∣mote the Fusion, were liable to be de∣tected by an easie Hydrostatical Tryal of their Ponderosity. I have likewise seen a fair Bezoar Stone, that so re∣sembled a genuine Stone, That a great Price was set upon it. But be∣ing brought me to be judged of, I made little doubt of its being Coun∣terfeit, by reason of its appearing to me as heavy as a Mineral Stone of that Bulk; tho' the Possessor being loth to expose it to an uncommon Tryal, I could not so cogently evince, that I had a clear Reason to disadvise the purchase of it.

Notes

• Use IV.