Chemical Composition of the Brown Lead Ore. 313 
The chemical composition of the Polyspharite reckoned after the 
last mentioned formula is as follows : 
Chloride of lead, 10.838 containing 8.073 lead. 
Fluoride of calcium, 1.094 «“ 0.567 calcium. 
Basic phosphate of lead, 77.015 $s 58.918 oxide of lead. 
———— lime, 11.053. S 6.025 lime. 
100.000 
The result thus obtained, not only confirms in the highest degree the 
supposition which we have made respecting the mode of combination 
among the constituents, but shows at the same time the correctness 
of the chemical analysis ; since the quantity of lime as ascertained 
from calculation corresponds very well with that found by analysis, 
when we take into consideration, that the determination of the base 
could not, in the present instance, be so accurately ascertained as that 
- of the chlorine and of the oxide of lead. 
But if we adopt the view, that the fluorine in this mineral, instead of 
the chlorine is united to the lead, which, however, I have already 
remarked is the less probable state of the case, and if we enter into 
a similar computation as above, founding the estimate upon the quan- 
tities of chlorine and oxide of lead ascertained from the analysis, we 
have the following as the chemical constitution of the Polysphirite : 
Chloride of lead, 10.838 containing 8.073 lead.) _ 
Fluoride of |“ 3.398 * 2.871 “ }66.991. 
Basic phosphate of lead, 73.255 “ 56.047 « 
————_—_—_—— lime, 12.509 ys 6.815 lime. 
: 100.000 
As the preceding chemical examination of the variety of Brown 
Lead Ore, called Polyspbarite shows, that in it, a part of the chlorine 
is replaced by fluorine without occasioning a disturbance in the con- 
stituents, or a variation of the formula which expresses the compo- 
‘sition of the Green Lead Ore, it appeared highly probable, that cal- 
cium and fluorine might enter into the constitution of more varieties 
of Green and Brown Lead Ore. 
This induced me, in the first place, to analyze more Brown Lead 
Ores from different localities ; and I especially directed my attention 
to such as were possessed of a diminished specific gravity. 
As I have pursued the same method of investigation as has been 
detailed above, I shall refrain from mentioning the individual steps 
taken in the following analyses. 
