icjB Mr. Gregor on a native Arseniate of Lead. 
III. 
A fragment of crystal exposed to the flame of the blow- 
pipe in a gold spoon, melted into a brownish yellow mass, which 
on cooling did not assume any angular figure. It remained in 
a state of ignition apparently unaltered ; but when a piece of 
it was exposed to the flame on charcoal, a rapid decomposi- 
tion took place, arsenical vapours were extricated, and globules 
of a metal, possessing the common properties of lead, were 
left behind. 
This mineral, in a state of fine powder, is soluble in nitric 
acid, even without the aid of heat. Care, however, must be 
taken, that it does not concrete into lumps. The vessel there- 
fore which contains it must be frequently shaken, and the 
nitrat of lead produced must be, from time to time, dissolved 
in water, and poured off' from the residuum. The process of 
solution is, however, accelerated by a digesting heat. Some 
silica remains, which, as the quantity of it is variable accord- 
ing to circumstances, appears not to be an essential ingredient 
of this fossil. 
The nitric solution is colourless ; its transparency is not 
disturbed by nitrat of barytes. Nitrat of silver renders it tur- 
bid, and a small quantity of white curdly matter is deposited. 
Sulphuric acid and the liquid sulphats, produce copious preci- 
pitates of a white heavy matter. If the fluid be poured off 
from this subsided matter, and it be freed from the super- 
fluous sulphuric acid, by the means of nitrat of barytes, it will 
yield, on the affusion of liquid nitrat of lead, an abundant white 
precipitate, which urged by the flame of the blow-pipe on a 
support of charcoal, resolves itself into reduced lead and ar~ 
senical vapours. 
