188 
‘© The mineral which I lately sent to you was raised in 
across lode of Huel Unity in the parish of Gwennap in 
Cornwall. At what depth or under what circumstances I 
am unable to discover. A very small quantity only of it 
has been raised. [I shall briefly mention some of the rea- 
sons which induced me to pronounce this fossil to be an 
Arseniate of Lead. A small fragment of it exposed to the 
flame of a blowpipe in a golden spoon loses its yellowish 
brown colour, and becomes white. Urged still further it 
melts into a brownish mass, and continues in this fused 
state without decomposition. If this mass be detached 
from the spoon and placed upon charcoal, and if the flame 
be directed upon it, a decomposition rapidly takes place, 
and fumes, evidently arsenical, are extricated. Globules of 
a fused metal are left upon the charcoal, which is marked 
with that yello,.ish hue which indicates the presence of 
- Lead. This fused metal is malleable: it ts soluble in 
Nitric Acid, and forms with it a crystallized salt, the so- 
Jution of which is rendered turbid by a drop of liquid Sul- 
phate of Soda, and a heavy white matter subsides. A 
piece of the mineral does not appear to be acted upon by 
Nitric Acid in the cold. By long digestion, however, in 
a sand-bath, the solution is effected. The transparency of 
this solution is not disturbed by a-drop of liquid Muriate 
of Barytes. Some crystals, however, appeared in small 
quantity, after some hours, at the bottom of the glass. 
A drop of liquid Nitrate of Silver caused the nitric solution 
to assume an opalescence, scarcely however perceptible. 
The purest crystals were selected ; but it is impossible to 
free them perfectly from all the stony matter which adheres 
to them. With a view to this extraneous increment, I 
weighed 26-2 grains, and exposed the powder in a platinum 
crucible to a very low heat, in which the bottom of the 
vessel was scarcely red, for half an hour. I proceeded thus 
cautiously, because the Arsenic Acid is decomposed under 
