in the P y R I T £ s. 123 



be burnt away, and to icorify, nay, from inatten- 

 tion and negligence in the operator. The fame 

 may with more propriety be faid of tin, whole 

 proper, pure ore, called tin- ft one, alfo tin-gra- 

 nates, conftantly give the fame, and that a rich 

 yield, namely, above a half. This great variety 

 in the copper-yield of pyrites affording us no certain 

 axioms or truths, puts us upon the neceflity of 

 framing fo many claries of them, as there are dif- 

 ferent yields ; and therefore copper is to be cond- 

 dered as fomething incidental to pyrites. 



It were to be wifhed we had forne external figns 

 or characters, whereby to afcertain the different 

 yields of the copper-pyrites. The denfity, clofenefs, 

 and weight of the ores are not always to be de- 

 pended on. Their ftructure, which is either ftel- 

 late, teftaceous, or run, or melted together, as it 

 were, io far manifefts the difference of their inter- 

 nal fubftance, as to fhew that the flellate pyrites 

 commonly contains no copper at all, or but very 

 little •, thole confiding ot different coats, to be 

 generally arfenical ; in which refpect they are here 

 ac Friberg called cobaldijh, nay cob aid itfclf ; but as 

 to thofe maffes of pyrites, which appear melted, or 

 run together, it ftill remains a difficulty to deter- 

 mine their yield. The colour proves a furer guide 

 in this cafe; the more yellow and green ifli thepy- 

 rites (hews, the richer it proves in copper : yet, 

 from the abfence of thefe colours, the abfence of 

 copper muft not be inferred. For though this in- 

 ference might in mod inftances hold good, efpe- 

 cially in regard to fome one particular mine-work ;. 

 for inftance, that of Friberg •, yet the above-men- 

 tioned fampJe of a certain copper-ore confiderably 

 white, fuch as I never once after faw, heard, or 

 read of, might caution us againft entirely ana 



folclv 



