MINERALOGY. 22 j 



S E C T. CCXLV. 



"Observations on Arsenic. 



Such ores as confift of arfenic united fclely with 

 iron, or with iron and ftdphur, cannot be enaplov- 

 ed to any other life than to the preparation of ar- 

 fenical products ; for which reaibn they ought to 

 be ranged among the arfenic ores. Some have 

 indeed denied this difference .between the arienical 

 pyrit^e ; but it is however necefiary to make feme 

 difference, with refpect to the prefence or abfence 

 of fuiphur, although the greateft quantity of arfe- 

 nic is got from the calcination of the cobalt ores, 

 and that the true arfenical pyritas do not deferve to 

 be feparately employed. 



Although it is difficult to reduce the arfenic by 

 way of precipitation, one cannot for that reafon 

 deny it to be of a metallic nature*, for the fame 

 way of reafoning might have been uied againfc the 

 zink in the -calamine, before the method to extract 

 that femi-metal in its metallic flate, now known, 

 was diicovered : But thofe who know that metals 

 only can be mixed with metals, fo as to preferve 

 the folidity and fome ductility in the compound, 

 and who at the fame time are ignorant /of any me- 

 tallic earth, which cannot be reduced to its me- 

 tallic ftate again, could never entertain kich 

 notions. 



It is indeed tpje, that fuiphur, in regard to the 

 brittlenefs which .it produces in metals, is of no 

 worfe effect than arlenic •, but this laft may by it- 

 fclf, and mixed only with a pure phlogifton, be 

 fubiimed into a metallic form, which is more plain- 

 ly feen in the Scherbencobolt (Sect, cexxxix. ). I 

 eafily perceive that it may be objected by thofe, 



Q 3 wha 



