Objervations oH Lead Ore. 873 
heterogeneous mixture, yet the following experiments 
fhew how much we fhould be deceived in forming fuch 
a conjecture, and how rightly it is denominated crude 
fulphur. 
From one hundred and twenty parts, by weight, of 
lead ore, I obtained, by folution in acid of nitre, fubfe- 
quent wafhing in hot water, and drying by a gentle fire, 
forty parts of a fubftance which looked like fulphur : 
thefe forty parts were put on a red-hot iron, the fulphur 
was made manifeft by a blue flame and pungent frnell. 
When the flame went out, there remained upon the iron 
unconfirmed twenty-fix parts of a greyifh calx ; the 
weight of the fulphur which was confirmed muffc there- 
fore have amounted to fourteen parts, or between one 
eighth and one ninth part of the weight of the ore. It 
has been obferved, that the weight of the matter, fepara- 
ble from lead ore by folution in acid of nitre, fometimes 
exceeded, and fometimes fell flrort of, one third part of 
the weight of the ore; this variety, as far as I .have been ■ 
able to obferve, does not extend to the quantity of ful- 
phur contained in a given quantity of ore, but depends 
upon the quantity of calx remaining after the burning of 
the fulphur. Different lead ores will, doubtlefs, contain 
different quantities of fulphur; but that the fulphur con- 
tained in the lead ore which I examined conftitutes be- 
tween one eighth and one ninth part of the weight of 
Vo l, LX VIII. * 5 Q the 
