8 The Subject Propounded. 



fibre or vein without it, and of fuch extenfive 

 ufefulnefs, fupplying us with fulphur, arfcnic and 

 vitriol, thofe capital inftruments both in nature 

 and chemiftry, and with one of the mod power- 

 ful fluxes (efpecially with us in Germany) for 

 forcing flubborn ores to give forth their contents ; 

 yet its nature is hitherto ib little underflood, and all 

 the accounts we have of it are fo very lame, no one 

 having either clearly defcribed, or accurately dif- 

 tinguifhed it, that an attempt to put it in its pro- 

 per light fhould feem to want no apology. 



But to give the reader a Hill nearer view of my 

 manner of managing this fubjecl: j I have exa- 

 mined upwards of 60 different famples of pyrites, 

 procured from different parts •, confidered each 

 fample apart in its colour, texture, and fpecific 

 gravity •, expofed a little of each to the air, in or- 

 der to difcover which fort would, and which would 

 not, be affected and opened by it ; to the fire, 

 for its contents $ to the action of the magnet for its 

 iron, both in the crude and calcined flate of the 

 fample ; to aqua fortis and aqua regia, for the 

 gold and filver ; nay, to vinegar and fpirit of 

 fal ammoniac, for difcovering the copper in it : 

 fome famples I have boiled with alcaline lixiviums, 

 with lixiviums of common fait and allum -, the one 

 to feparate the fulphur from its metallic earth, and 

 form a hepar fulphuris ♦, the other, for the vitriol 

 .acid to lay hold on the alcaline earth, and dif- 

 jcharge the acid of the common fait •, confe- 

 quently to exhibit an Epfom, or the like fait of 

 a mineral water, or a Glauber fait •, and thus 

 to ferve to eftabliih my conjectures on the origi- 

 nal of aciduU. I have combined the feveral 

 parts of the pyrites with each other, and with 

 other bodies ♦, nay, the entire pyrites itfelf. I have 

 examined the capita mortua of "the pyrites, in the fame 

 manner as the pyrites itfelf: in particular, I have 



mixed 



