Chemical Composition of the Brown Lead Ore. 317 
Chloride of lead, - - - - 10.074 
Fluoride of calcium, - - - 0.130 
Basic phosphate of lead, -" = - 89.110 
ge G lime, - - - 0.682 
99.996 
6. Amorphous Brown Lead Ore from the Niclas mine, Freiberg .— 
This variety of Brown Lead Ore, I owe to the politeness of Mr. Frei- 
esleben, Counsellor of mines; it is described in his Geological Re- 
searches (Bd. 6. S. 147.) Its behavior before the blowpipe is simi- 
lar to that of the varieties already described, and it exhibits no trace 
of arsenic. Heated with sulphuric acid in a platina capsule, it at- 
tacks with energy a glass plate held over the mixture. In a solution 
of it, in nitric acid from which the lead had been removed in the 
manner before described, sulphuric acid as well as oxalate of pot- 
ash, produced a white precipitate. Nitrate of silver, added with 
suitable caution, occasioned a yellow precipitate. ‘Therefore this 
Brown Lead Ore is constituted like those before examined, and con- 
tains lime and fluoric acid. ‘The small quantity of the mineral at my 
command prevented me from undertaking its quantitive analysis. 
7. Crystallized Brown Lead Ore of Poullaouen (dep. Finesterre.) 
—This variety of Brown Lead Ore which is the best known and char- 
acterized of the species, occurs in long, distinct prisms, often many 
lines in length, which are generally very irregular, and in which the 
regular terminations are not often distinguishable. ‘This is more com- 
mon than it is to observe a face perpendicular to the axis of the prism. 
The single erystals are for the most part furnished with an opaque, 
brown covering, which I have found to be composed of a mixture of 
phosphate of iron and phosphate of lead. 
The specific gravity when pure, and in crystals freed from the 
coating alluded to, is according to Prof. Breithaupt, 7.0485. 
Alone before the blowpipe, it melts into a polyhedral mass and 
at the same time feebly tinges the flame with a green color. Ifa 
fragment of it is treated with salt of phosphorus, a brisk effervescence 
takes place. With soda upon charcoal, metallic lead was obtained, 
but no,evidence of the presence of arsenic. 
Heated with sulphuric acid ina platina capsule, no extrication of 
fluoric acid fumes, nor any corrosion of a glass plate held over the 
capsule, was perceptible. No change was occasioned in the solu- 
tion of the mineral freed from lead, although it was concentrated, 
Vol. XXII.—No. 2. 41 
