868 Dr. Watson’s Experiments and 
2.7 23. ‘; the medium of the four is 2.700. Mr. cotes 
fixes the fpecific gravity of Iceland cryftal at 2.720, and 
wallerius fixes it at 2.700. 
The fpecific gravities of four pieces of the fame lump 
of cubical fpar were 3.204, 3.218, 3.222, 3.231; the 
medium of the four is 3.219. 
Six ounces of fine tefiellated lead ore were put into a 
crucible and expend, at firft, to a gentle, afterwards to a 
ftrong fire : the ore grew red, and emitted fumes which 
fmelled of fulphur ; at length it melted, and the fumes 
became very copious; they were accompanied with a 
yellowifh flame upon the furface of the melted ore, and 
when collected had a whitifh appearance. The crucible, 
after the ore had continued a full hour in perfect fufion 
Was taken from the fire, and when it was cold it was 
broken. The mafs which it contained weighed five 
ounces and an half; there were no fcoria ohfervable on 
its furface, nor were any particles of metal formed, it 
was ftill an ore of lead. 
The mafs remaining from the laft experiment was put 
into a frefh crucible, and expofed to a ftrong melting 
heat; the fumes which arofe from it feemed to be 
heavy ; they brooded over the furface of the melted mafs 
in undulating flames, which now and then appeared like 
burning zinc. The lead was now formed, and many 
particles 
