in the PvRitEs. if% 



often appearing like a fine-grained mock- lead, we 

 fhall find reafon to clafs it amongft arfenics ; nay, 

 fometimes it mews lb like a foflile mock-lead, and 

 a mineralifed body, as to impofe on the mofl in- 

 telligent in ores. The origination of this, indeed, 

 rather than of the preceding calamy matter, feems 

 to be owing to a caking or running together ; yet 

 it is alfo of various forts, and, upon properly view- 

 ing many a iample of it, we muft allow it rather 

 to be aggregated together in the way of a damp, 

 or vapour. For, though we find amongft: it 

 pieces not only caked together, but quite vitri- 

 fied, as may be eafily conjectured from the run- 

 ning together of quartzy, efpecially if fomewhac 

 leady, and thus pofTc fifed of vitrifying particles, 

 yet the principal part is of quite another, or rather 

 a new appearance. 



It appears black and grey, flakey, and almoft 

 like a mock-lead, though very different, it being 

 more kindly and light. It is not only, in fome 

 meafure, of the nature of zink, or calamy, which 

 cannot be faid of any one fort of mock-lead, but 

 contains as much, if not more arfenic than the 

 meagre, lean mock lead. In a word, 'tis a kind 

 of fly-ftone fublimate, riling up entirely at the 

 lail, but to no very great height ; which, toge- 

 ther with its calamy and arfenkal, or, volatile 

 portion, has taken along with it, by the violence 

 of the fire, fomething of a crude, earthy, and, , 

 perhaps alfo, of a mock- leady nature, whence it 

 happens to confift of fo coarfe a mixture, as to be 

 of mounting high •, and this is (imply 

 called furnace- fragment ', as it mutt be broke off, in 

 order to clear and fit the furnace for a new opera- 

 - •, a nam.: which may fufficiently diftinguifh it 

 from the abovementioned grey, white, yettowifli 



N matter, 



