292 ESSAYS ann OBSERVATIONS 
deprived of its fluidity, and turned into a red 
- eal, or has been firft diffolved in agua fortis, 
and afterwards, by evaporation and calcina- | 
tion, freed from the acid, and reduced to a 
red powder ; if either of thefe red powders, 
I fay, is digefted with oil of vitriol, and made 
to boil, this liquor will not now diffolve the 
-mercury, or fo much as change its colour. 
On the other hand, tho’ /pir. fal. mar. is not 
efteemed a proper menffruum of quick-filver 
in the immerfive way, but when applied toit 
in form of vapour in fublimation ; yet if this 
fpirit is poured upon the red precipitate mer- 
cury, it prefently changes its colour to 
white, and quickly diffolves it. Again, /pir. 
fal. mar. readily diffolves clean and freth file- 
ings of iron: yet if thefe are frequently moift- 
ened with water, and by trituration and cal- 
cination turned toa crocus ; [p. fal. mar. poured 
upon this, raifes an eflervefcence indeed, but 
does not feem to make a folution ; for the 
iron lies at the bottom not fenfibly diminifhed, ~ 
and the colour of the liquor is not changed. 
Some ores, as they are taken from the mine, 
tho’ they appear pretty rich and clean, yet will 
not readily diffolve in the fame menjftrua, 
which are fit to diffolve the pure metals, un-— 
til 
