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ckntly hard to extradl fparks from fteel, 

 that is to fay, to melt it : on the contrary, I 

 was never able to extrad: the fmallefl: fpark 

 from the pitch-flpne lavas above mentioned, 

 though I made the experiment on them 

 with the heft fteel. They are therefore lefs 

 hard than volcanic glafs, as is indeed appa- 

 rent from the facility v/ith which pieces fly 

 off at every ftroke. To thefe evident diffi- 

 milarities we may likewife add the weight, 

 which in pieces of the fame iizt is always 

 greater in volcanic glafs than in pitch-ftone 

 lavas. 



Father Terzl may, however, eafily con- 

 vince himfelf that thole veins of the Euga- 

 nean mountains which he calls glafs, are by 

 no means entitled to that appellation, if he 

 will fufe a fmall portion of them in the fur- 

 nace. He will then find the prcdudl a true 

 enamel, exhibiting a vitreous afped: not at 

 all difcoverable in the pitch-flone lava from 

 which it was produced. This is true, like- 

 wife, of the veins of Monte Muffato ; and 

 fhews that the pitch-ftone lavas rauft not 



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