in the Pyrites. 175 



They are generally, though falfely, confldered 

 as a proper but fume, or arfenic, efpecialiy when 

 they affume appearances of a grey mea] : but, not 

 to iniift that experience fhews quite the contrary, 

 we may eafily imagine, volatile matters, that 

 mould fland and hold out, when fettled in the con- 

 fines of the ftrongeft glow of a furnace, to be 

 fomething d(t than arfenical ; and hence we need 

 not wonder, they deftroy neither mice, nor rats. 



This zinky matter manifefts itfelf in tall fmelt- 

 ing furnaces, particularly in thofe where the ope- 

 ration of crude fmelting is performed ; that is, where 

 fmall or poor ores, which are commonly quartzy, 

 mock-leady, and fyrity, alfo, incidentally, fome- 

 what glittery, are fmelted and concentrated from a 

 large quantity of ore, to a regulus, or cake. It 

 takes its place in the lower parts of the furnace, 

 particularly on the fides, having under it, for its 

 ftool, that mock-leady, ftoney, and hard matter, 

 of which hereafter. 



The manner of its origination muft, doubtlefs, be 

 like that of arfenic, namely, in the way of a fume and 

 vapour, feeing no part of it is obferved to be run. 

 When expofed long to the air and weather, it opens, 

 that is, becomes tender and porous, and fit for 

 making brafs ; the reafons of which are not pro- 

 per here to be given, as I now only confider it on 

 account of its arjenic. At our huts it is thrown away, 

 and as it muft be knocked and broke off* the fur- 

 nace, 'us called furnace-fragments, by many calamy, 

 though improperly, on account of its very diffe- 

 rent admixture ; wherefore that appellation ought 

 to be qualified by the epithet calamy -furnace -frag- 

 ment, or furnace-calamy ; nav, it mould juftly 



be 



