in the Pyrites. 129 



neither be called fulphur, nor arfenic, nor a me- 

 tallic earth : and, to confirm this, I examined 

 other ores, and found a like earth in cobaid 

 and biimuth ores. Cobaid, which is uled for 

 making fmalt, tolerably refembles the ar fenic-py rites ^ 

 of the white fyritcs, or miJJ-ickeU both externally 

 and internally ; only that this lalt turns to a very 

 dark glafs, whereas the firft has its earth changed 

 to a beautitul blue glals. Now as the white, or 

 arfenic pyrites, has fome iron for its grcund~earth y 

 which undoubtedly is the caufe of the black co- 

 lour of its glais ; and as the tint and colour of 

 glafles commonly bewray lbmething metallic, as 

 appears, not only by analyfis, but by fynthefis, as 

 in the making of fmalts, or enamels •, lb all blue 

 mineral colours, whether natural or artificial, as 

 laful-ftone, copper-blue, mountain-blue, blue 

 vitriol, arife only from copper. And laftly, as 

 copper fhews itfelf plainly in that fort of cobaid, 

 called kupferniekel, it is not improbable, fmalt 

 may be produced from an earth, not only, in ge- 

 neral, metallic, but, in particular, coppery : but 

 as from cobaid, by any method hitherto under- 

 ttood, only a very fmall quantity of metal, either 

 of copper, or any other mineral, is procurable, 

 tha: bears any proportion to its earth, we muft 

 needs fuppofe its giound-carth, if not all, yet moil 

 of it, to be wimctallic, crude, vague, or undeter- 

 mined-, particularly, crude-earthy, fandy, and thus 

 taiily vitrifiable : but the cobaid to be employed, 

 : be no mixt- r j;ork, but fuch as is highly pure, 

 carefully feparated from its quartz, which 

 only externally adheres thereto, but often 

 very tenderly and inieparably interfperfed cr 

 mixed amongft it; otherwife it would yield an 

 over-quantity of unmetalUc earth. This genuine 

 fmalt-earth is generally as one to three, in regird 

 Bi die volatile, arfcnicaj, portion -, the arfenic be- 

 lt ing 



