The Sulphureous Copper Ore.-^Tkeory of the Earth. 153 



cliquating (darren)* and melting the lead with the black-copper, in which it is contained \ 

 (4) All the lofs of lead, occafioned by its fufion with the copper at its eliquation, its re- 

 fining, and the fcratch-work with the brufb in cleaning ; (5) Likewife the lofs of lead 

 poor in filver, which is obtained by eliquation from copper, and ought not to be enriched 

 with filver in that degree, as may be done according to my method. And if it (hould be 

 found advifeable to refine the -work lead direftly in the fmelting houfe, there would then 

 (6) be faved the charges of tranfporting the black copper to the houfe, in which it is 

 to be eliquated. 



To this may be added, that by my method of proceeding the quality of the copper is 

 improved, which is always the chief object of the fmelting houfe. The copper obtained 

 by eliquation is well known to contain lead, and this proportion of lead imparts to it a 

 noxious property, diminiflies its dudtility, and even that of the brafs, prepared from if. 

 This contamination of the copper with lead cannot take place in my procefs ; becaufe by 

 that management no lead can combine with the copper of the copper-mat made ufe of, 

 when the fulphur of this laft has been fufTiciently diminilhed in its quantity by the 

 roafling. 



II. 



Obfervations on the Proofs of the Hutlonian TJieory of the Earthy adduced by Sir Jamef 



Hall-, Bart. By R. Kirwan, Es(i. Communicated by the Author. 



{Concluded from page 102.) 



EXPERIMENT THE FIRST. 



'RUNSTEN, a compound of felfpar and hornblend Intimately mixed with each 

 other, was the fubjeft of this experiment. ' 



Its colour, black, or greenifh black, intermixed with pale reddifli brown ; both the 



felfpar and hornblend imperfeftly and confufedly cryftalized in minute grains ; the 



fraElure partly ftriated and partly foliated. Lujlre moderate : Its hardnefs 7, or almoft 8. 



Gives an earthy fmell when breathed upon, and frequently contains fmall fpecks of 



pyrites. Ibid. p. 7. 



This fubftance he vitrified by a (trong heat and fubfequent rapid cooling, p. 9. A frag» 

 ment of the glafs thus produced being introduced under a narrow muffle, and heated to 

 2 1 . in one minute became fo foft as to yield readily to the preflure of an iron rod, but after 

 a fecond minute it became quite hard, though the temperature had been fliationary. The 

 fubftance thus hardened underwent a thorough change, it loft its vitreous charafter, its 

 fradure was like that of porcelain (that is even) and it was fufible only in a heat of 31. 

 page II. 



* CreiCs Principles ofChm. §. 1490. 



Vol. IV ^JuLY 1800. X In 



