Chemical Composition of the Brown Lead Ore. 307 
ment. I think they will be found very useful to Engineers and Ar- 
chitects.” ; 
We coincide fully with Mr. Miller as to the importance of elici- 
ting this species of knowledge, in our country, and the Editor will 
feel much obliged by communications on this subject from all able 
Engineers who may. deem this Journal a suitable vehicle for their 
observations. 
Art. IX.—*On the Chemical Composition of the Brown Lead Ore ; 
by C. Kersten, of Freyberg. Translated from the German of 
the Neues Jahrbuch der Chemie und Physik, Band II. Heft 1. 
by Cuarztes U. SHeparp. 
In the following brief memoir, I am permitted to give, in succes- 
sion according as they were obtained, the results of a chemical 
analysis of the principal varieties of the Brown Lead Ore from va- 
rious localities——commencing with a short historical notice of that 
variety which from its interesting chemical composition led to these 
inquiries. 
Several months ago, there was found in the Sonnenwirbel mine 
at Freiberg a mineral, which in its external appearance resembled 
the so called, botryoidal Brown Lead Ore, but which presents an es- 
sential difference in its inferior specific gravity. Prof. Breithaupt 
subjected it to a mineralogical examination, and communicated a de- 
scription of its external characters in the third number of this Jour- 
nal for 1830, from which the following account is borrowed. This 
mineral occurs in distinct balls and globular masses, whose interior 
exhibits a fine concentric texture; in consequence of which, Prof. 
Breithaupt was led to denominate it Polyspharite. It belongs, ac- 
cording to him, to the order of Spar, but to the order Baryte in the 
system of Mohs. It possesses a greasy lustre, and a brown color 
which runs from a clove-brown into Isabella-yellow. It occurs only 
in balls and globular masses, upon whose exterior are seen small, but 
undeterminable crystals. ‘These masses rarely unite to give rise to 
kidney-shaped pieces. It presents a moderate degree of lustre, and 
an asteriated or radiating fracture, which sometimes becomes nearly 
invisible, and from thence passes to the compact conchoidal fracture. 
Its hardness =4, according to the scale of Breithaupt, or 3 by the 
standard of Mohs. Its specific gravity, when perfectly free from 
foreign substances =6.092. 
