Obfervations on Lead Ore. 877 
glafs, the acid having abforbed the water which held it 
in folution. When lead is diflolved in the manner here 
mentioned, by a very diluted acid of nitre, there is no 
appearance of fulphur upon the furface of the men- 
ftruum, there is found at its bottom a black matter which 
is the fulphur. 
But though lead and fulphur, a liquid and air, are un- 
queftionably conftituent parts of lead ore, I do not take 
upon me to fay, that they are the only conftituent parts : 
it is well known, that, during the fmelting of lead ore, a 
third part or more of its weight is fomehow or other loft, 
fince from one and twenty hundred weight of ore they 
feldom obtain above fourteen hundred weight of lead. 
What is loft partly confifts of a fcoria which floats upon 
the furface of the lead during the operation of fmelting, 
and partly of what is fublimed up the chimney and diffi- 
pated in the air. The fcoria, I apprehend, would be very 
little even from a ton of ore, if the ore was quite free from 
fpar: it is the fpar which is mixed with the ore that con- 
ftitutes the main portion of the fcoria. I have in my 
pofleflion a folid mafs of fcoria, which accidentally 
flowed out from a fmelting furnace, and which in colour 
and confiftency perfectly refembles grey lime-ftone; it 
receives a polifh as fine as marble, and it might, perhaps, 
with advantage be caft into molds for paving ftones, 
2 chimney 
