2%2 Of the Vitriol 



Yet this gilding happens not fo well in the 

 groove, as at the day, unlefs there happen to be 

 there dry places, or warm weather. From the 

 Rothe-grube, at Friberg, I have procured much 

 of this black-grey vitriolic mineral, where, indeed, 

 the mify, called the uppermofl zone, or layer (zo- 

 na fuprema) of the atr amentum metallicum, was al- 

 ways wanting, but foon appeared again, upon ex- 

 poiure, for a little time only, in fome degree of 

 warmth. And at Braunfdorff, a mile from Fri- 

 berg, I have taken up a black fhivery rock, in 

 which I have obferved both chalcitis, cabled the 

 middle zone (zona media) and fory, called the under 

 zone (zona infima) ; nay, after repeated elixations, 

 being kept for a few weeks under cover, it was 

 again found over-cafl with white and yellow, but 

 with this difference, that it proved a good, or, gene- 

 rally, a pure iron-vitriol, as was that from the Rothe- 

 grube abovementioned, in the open air, not fo 

 much yellow, as white ; but if mixt, as was that of 

 Braunfdorff, and in particular aluminous, the 

 yellow foon fhews itfelf in the fame air as that 

 in which I lay the piece from the Rothe-grube: 

 but in a warm room, efpecially if placed near the 

 fire, vitriols, whether of one fort or another, pure 

 or mixt, do, at laft, all of them turn yellow •, never- 

 thelefs I have not been able to obferve any orpi- 

 ment, confequently nothing arfenical in what fo 

 eafily, even in the cool air, as that of a cellar or 

 vault, turns to mify, though I have carefully exa- 

 mined it, as many others, and I myfelf at firft 

 might imagine ; efpecially as the Braunfdorff py- 

 rites-work readily does, and is really very arfeni- 

 cal, of which hereafter, in particular, when I come 

 to examine the queltion, whether arfenic contri- 

 butes to the vitriol-mate, as fuch. 



The 



