320 Chemical Composition of the Brown Lead Ore. 
2. In most of the Brown Lead Ores, a part of the lead is replaced 
by lime, and a part of the chlorine by fluorine. Hence the supposi- 
tion made by Mr. G. Rose in his investigation of the Apatite, that it 
was not improbable that Green Lead Ores would be found, which 
should contain lime, is in reality confirmed. 
3 Brown Lead Ores are like the Green Lead Ores, isomor- 
phous with Apatite, and constitute, if we may so speak, the connecting 
link between both species; which is not only true as respects their 
chemical composition, but as respects their specific gravity also, 
which is intermediate between the two, 
4. The specific gravity is, in the six examined varieties, notably 
less than that of the Green Lead Ore ; and sustains an inverse relation 
to the fluorine and calcium which they contain. The greater the 
quantity of fluorine and calcium in Brown Lead Ore, so much the 
less is the specific gravity, and the reverse. 
5. It is obvious, that the existence of fluoric acid determines the 
presence of lime, or that the reverse takes place ; since all the Brown 
Lead Ores examined by me, in which fluoric acid was found, contained 
also lime, and on the contrary, those which contained lime contained in 
like manner fluoric acid. This led me to regard the fluorine as uni- 
ted to the calcium, and conformably to this idea to conduct the cal- 
culation of the Brown Lead Ore,—considering that quantity of the 
calcium which remained after the saturation of the fluorine, as united 
with phosphoric acid. 
6. None of the Brown Lead Ores analyzed, contain arsenic acid 5 
and in them, : 
7. Chlorine is isomorphous with fluorine, and oxide of lead with 
lime. : : 
The results of these researches may possess some interest in a 
chemical point of view, as well as affording a new example of the 
isomorphism of lime and oxide of lead; since, except the instance 
in which lime and lead are isomorphous in Arragonite and White 
Lead Ore, from whence Mr. Mitscherlich derived the fact, and which 
stood a long time as a solitary case, there were only three other ex- 
amples known to me corroborative of the same thing; viz. the iso- 
morphism of the sub-sulphate of lead and the sub-sulphate of lime, _ 
ascertained by Mr. Heeren; thatof the Green Lead Ores and the 
Apatites proved by Mr. G. Rose; and that of the tungstate of lead 
and tungstate of lime observed by Mr. Levy. . The present research- 
es afford us a fourth example that lime and lead are isomorphous. 
