go2 ESSAYS ann OBSERVATIONS 
fufficient time for the folution of the iron, 
and precipitation of the copper, put into 
the folution a piece of lime-fione ; the aqua 
fortis immediately works upon it with frefh 
vigour: laftly, add fome falt of tartar, or 
oleum tartari, p. d.; this precipitates the fto- 
ny matter, and renews the effervefcence. 
This feems to finifh the work, and quite to 
abforb the acid, and deftroy all its folvent 
powers: yet even here the acid only lurks 
and conceals itfelf by its {trict union with an 
oppofite falt. But art can again produce it to 
view, and reftore all its former powers. If 
in this procefs, five or fix ounces of /pir. ni- 
tri, or aqua fortis, were employed in the be- 
ginning, and, after the laft ftep, the liquor 
is diluted with fome more water, ftrained 
thro’ brown paper, fully fatiated with the 
alcaline liquor or falt, and then flowly eva- 
porated and chryftallized: there will be pro- 
cured a falt perfectly refembling common 
falt-petre, in the fhape of the chryftals, ex- 
plofive quality, and other marks. This, fa- 
Gtitious falt-petre, then may be employed in 
place of the common ; and I diftilled fome 
ounces of a falt, made much in the fame | 
way (for I imagine the intermediate fteps 
will 
