MAGNETiCAL PYRITES. *267 



f* called Mynydd Mawr. Thefe mountains form thaentrance 

 V into a little clofe valley, which leads to Cy wellin lake, near 

 tf Snowdon, a little beyond the hamlet of Bettvvs. 



" The vein appears to be fome yards in depth and breadth, 

 <s and feems to run from north to fouth, as it is found on 

 " Mynydd Mawr, which is acrofs the narrow valley, and 

 ** oppofite to Moel iElia." 



Mr. R. Greville, in another part of his letter, ftates that 

 copper ore has been worked in feveral of the adjacent places, 

 and that, many years ago, Capf. Williams, of Glan yr Avon, 

 employed fome miners at the place where this pyrites is found, 

 but the undertaking proved unproductive. Yellow copper ore 

 is certainly in the vicinity ; for fome portions of it were adhering 

 to the fpecimens which have been mentioned ; and I fhall here 

 obferve, that the ftone which accompanies the magnetical 

 pyrites, is a variety of the lapis ollaris or pot-ftone, of a pale 

 grayiih-green, containing fr*ooth cubic cryftals of common 

 pyrites. 



§ III. 



From the appearance of thofe parts of the magnetical pyrites MagnetVpy- " 



which have been expofed to the weather, it feems to be !iable m . e3 1S A'ghtiy 

 ... , ..... oxidable by die 



to oxidizement, but not to vitnoliza'ion. weather. 



The fpecific gravity, at temperature 65° of Fahrenheit, is Sp. gravity. 



4518. 



When expofed to the blowpipe, it emits a fulphureous odour, EfFeft of mere 



and melts into a globule nearly black, which is attracted by the k^ h ? Wow " 



b ' J pipe: 



magnet. 



Five hundred grains, in coarfe powder, were expofed) in a — in a crucible; 

 (mall earthen, retort, to a red heat, during three hours. By 

 this operation, the weight of the powder was very little di- 

 minifhed; neither was there any appearance of fulphur in the 

 receiver, which however fmelt ftrongiy of fulphureous acid. 



Five hundred grains of the fame were put into a flat porce inthemufH:. 



Iain crucible, which was kept in a red heat, under a muffle, 

 during four hours. The powder then appeared of a dark gray, 

 ■with a tinge of deep red, and weighed 432.50 grains. The 

 lofs was therefore 67.50 — I 3.50 per cent, but, upon examining 

 therefiduum, I found that only part of the fulphur had been 

 thus feparated. 



The 



