100 grains of solid arsenical acid gave 297 grains of solid 
arseniat of lead after moderate drying, and hence 100 
grains of the arseniat contain 33*66 of arsenic acid.* 
For the analysis, the ore being first dissolved in nitric 
acid* the solution was accurately neutralized with carbon- 
ated potash* and then acetited lead was added till all pre- 
cipitation ceased, a little of this salt remaining in excess. 
The precipitate of arseniated lead when washed and dried 
indicated the proportion of arsenic acid in the ore. The 
solution now contained acetic and nitric acids, united with 
oxyd of copper and potash, and a little acetited lead ; 
from which the lead was first separated by sulphat of soda, 
that precipitated it in the form of an insoluble sulphat, af- 
ter which a little sulphuric acid was added to engage the 
copper, and this metal in its turn was separated by polish- 
ed iron in the usual manner. The copper however is thus 
obtained in the metallic state, but in the ore it is an oxyd, 
and therefore one-fourth of the weight of the copper must 
foe added for oxygen, that is (as in the actual analysis) for 
40 parts of metallic copper, 50 of the oxyd of copper 
must be estimated. It is necessary to neutralize the ni- 
trous solution at first, as the arseniated lead is very solu- 
ble in acids, and therefore would not otherwise be pro- 
perly collected. 
Where iron is suspected in the ore, the solution instead 
of being finally precipitated by polished iron may be de- 
composed by ammonia, and the copper separated from 
the iron by an excess ©f the alkali. 
As many acids form a white precipitate with the solu- 
tions of lead, the powder in question is proved to be ar- 
seniat of lead by digesting with sulphuric acid, which 
displaces the former acid, and leaves it uncombined in 
the liquor ; and arsenic acid is detected by various me- 
thods mentioned under that article, particularly by giving 
* Klaproth, voL if 14% 
