VOL* XXIV.J PHILOSOPHICAL TRANSACTIONS. 103 



which was so rich, that lOOcwt. of it contained near 50 gilders of silver, and 

 30 in gold; the piece was about the size of a common bean, and putting it 

 over a pretty smart fire, the sulphur, of which there was a great deal in the 

 mineral,* stood in bubbles, and remained on the stone in the figure of round, 

 black, burnt globules; I then dropped it red hot into water, where it remained 

 whole, only with this difference, that whereas before it was very hard, now 

 it became very brittle; and having broken it, I perceived it to consist chiefly of 

 irregular particles, though some few were of an exact diamond-cut; and I couid 

 see, much more plainly than before, the globules of gold and silver, lying 

 separately from one another, some of the former of which were so exceedingly 

 small, that they almost escaped the sight in the microscope; and as gold is 

 not near so easy to be melted as silver, I saw some that the fire had not force 

 enough to reduce to globules, and upon it lying a small globule of silver, which 

 the fire had brought into that figure; and though the gold and silver touched 

 each other, yet they were not united, because the fire where that gold lay, 

 was not strong enough to reduce it to a fluid body, 



I have often observed in these mineral stones, that one part of them was 

 white, and another, a little lower in the same stone, a dark grey colour; and 

 that they are brought to us in little pieces, the largest not exceeding a joint of 

 one's finger; and that in some few pieces there were little cavities or breaches, 

 without any metal, either of gold or silver, (for in that mineral there is no 

 other") but oftentimes with very small crystals; which I call so, because of the 

 analogy of their figures with those of rock crystal, being, like them, transpa- 

 rent, hexangular, and ending into a point or spire. These crystals were in the 

 white part of the stone; for those that were in the grey were not pellucid. 

 RSTV, fig. 22, represent a small particle of such crystal, clear and transparent. 



Some believe that these crystals are formed by the exhaling damps, or mois- 

 tures, deep in those mines, from whence the mineral stone is dug; but this is 

 contrary to my opinion; for upon that hypothesis, the whole cavities should 

 be filled with the particles; whereas we find the contrary; for I have observed 

 that not one fourth part of the cavities are filled with them; and I have found 

 some of the said crystals in such small cavities, that a pin's head would have 

 filled them, and in breaches of the mineral stone that were not so broad as the 

 thickness of a small pin; whereas I could meet with none of these crystals in 

 other cavities that were much larger. I rather suppose that most of the stony 

 matter where those cavities are found, was of the same configuration as the 

 said crystals; and at the time of the coalition or union of the particles of stone, 

 the intercepted air occasioned some cavities, in which the crystals were inclosed, 

 and in which they acquired the figure which they now retain; in the mean 



