318 Chemical Composition of the Brown Lead Ore. 
either by the addition of sulphuric acid, or of oxalate of potash. 
Nor was any precipitate of sulphuret of arsenic produced by a 
stream of sulphuretted hydrogen passed through the solution. From 
these experiments, the entire absence of fluoric acid, arsenic acid 
and lime in this lead ore was clear; while it contains, as is sufficiently 
proved, only chlorine, lead and phosphoric acid. 
According to two trials, in each of which four grammes of crys- 
tallized pieces were employed, previously freed from their ferruginous 
coatings, the Brown Lead Ore of Poullaouen contains in one hun- 
dred parts: 
Oxide of lead, - - - - - 82.301 
Muriatic acid, 1.989 
Phosphoric acid with traces of i iron ‘aa Weaes 15.710 
100.000 
or 
1 atom chloride of lead = - - - 10.09 
3% atoms phosphate of lead = - Bei 89.91 
100.00 
8. Amorphous Brown Lead Ore of Poullaouen.—In order to ar- 
rive at complete certainty respecting the absence of fluorine and cal- 
cium in the Brown Lead Ores of Poullaouen, and to establish upon 
as many data as possible a correct opinion of the chemical composi- 
tions of this mineral species, I have subjected still another variety 
from this celebrated locality, to analysis. The specimens examined, 
consisted of a compact, but superficially drusy mass, which in some 
spots exhibited a yellowish grey, in others, a hair-brown, color. Its 
specific gravity, I found to be 7.050. Before the blowpipe, it con- 
ducts exactly like the crystallized variety ; also, it affords no odor 
of arsenic, when melted along with, carbonate of soda. Heat- 
ed in the state of powder with sulphuric acid in a platina capsule, 
it occasioned no corrosion to a glass plate held over its surface. 
Repeated researches, conducted in various ways upon its solution, 
afforded me no evidence of the presence of lime: by means of 
caustic ammonia only a slight precipitate of oxide of iron was thrown 
wn. 
ant 
a 
