203 
Mr. Gregor on a native Arseniate of Lead. 
silver was more abundant in the cases, where I employed a 
vessel with a long neck for the solution, and did not expose it 
to heat. 
I concluded therefore, that when the process was conducted 
under different circumstances, the predominating mass of nitric 
acid produced its effect, and volatilized a portion of the mu- 
riatic. 
Another source of error I found in the following anomalous 
circumstance, viz. a simultaneous precipitation of a portion of 
arseniat of lead takes place with that of the muriat of silver. 
Whatever combination this may be, it is a weak one, and may 
be severed by nitric acid, which dissolves the arseniat and 
leaves the muriat ; or by ammonia, which takes up the mu- 
riat, to the exclusion of the arseniat. 
The conclusion, to which many experiments have led me, 
is this, that the muriat of silver produced in the nitric solution 
of one hundred grains of arseniat of lead by nitrat of silver, 
amounts to about 9.5. 
E. 
In order to prove that the acid, which is combined with the 
oxide of lead in this mineral, is the arsenic acid, and that it is 
not combined with phosphoric, I decomposed some of its acid, 
which had been combined with lead in the foregoing experi- 
ments, by means of sulphuric acid, and filtered off the sulphat 
of lead. The fluid which passed through the filter was eva- 
porated nearly to dryness, and it assumed the appearance of 
crystalline grains. Some of it was exposed to the flame of 
the blow-pipe in a gold spoon ; at first it became like a white 
dry powder, which melted before an increased heat : placed 
