876 Dr. watson’s Experiments and 
than if it be moderate ; and I am not certain whether the 
experiment might not be fo managed, that there would 
be little or no calx remaining ; that is, a given quantity 
of ore might be fo diffolved in the acid of nitre, that 
nothing would remain undiffolved except the fulphur. 
But 1 have not yet perfectly fatisfied myfelf as to the 
conftituent parts of lead ore. I am certain that it con- 
tains lead and fulphur, a liquid and air: of the exiftence 
of the three firft there can be no doubt, from what has 
been faid, and the air is rendered beautifully apparent 
by the following experiment. 
Let fome lead ore be reduced into a fine powder, put 
it into a narrow-bottomed ale glafs, fill the glafs three 
parts with water, drop into the water a portion of the 
ftrong acid of nitre, you may judge of the requifite 
quantity by feeing the folution commence, and you will 
obferve the ore univerfally covered with bubbles of air, 
thefe will buoy the ore up in large tufts to the furface, 
and the air will continue to be feparated from the ore till 
the acid becomes faturated with the lead. The fait 
arifing from the union of the nitrous acid to the lead 
often appears cryftallized upon the furface of the men- 
ftruum in this experiment; and if, when the menftruum. 
is in that ftate, a little frefii acid be added, the fait in- 
ftantly cryftallizes and falls down to the bottom of the 
glafs. 
