187 
TAB. CCXCV. 
PLUMBUM Arseniatum. 
Arseniate of Lead. 
~ Class 3. Metals. Order 1. Homogeneous. 
Gen. Lead. ; Spec. Arseniate. 
Div. 1. Crystallized. 
$$ —____ 
‘Tuts new and at present very rare substance, but lately 
discovered in Cornwall, is a token of our possessing in our 
island some substances that are not found elsewhere. I 
am obliged to the Rev. William Gregor (who has been 
mentioned as the first person who analysed the Menacha- 
nite, fab. 277.) for ascertaining what this substance is, 
and also for the delicate specimen figured. In colour and 
form of the crystal it somewhat resembles Phosphate of 
Lead.—see tal. 84,—which, however, is seldom so brown 
as this, and is less transparent: besides, the crystals of 
Arseniate have some characters which I do not know to 
occur in the Phosphate of Lead, such as the fasciculated 
structure found in most of the crystals, even where the two 
ends are apparently regular ; also a considerable degree of 
lustre, transparency, and neatness at the terminal edges: 
besides, it is considerably softer than Phosphate of Lead, 
and rather harder than Sulphate of Lead. The crystals are 
scattered upon a gangue of white Quartz. 
With the specimen sent by Mr. Gregor, he favoured 
me with the following account, which, as it is likely to 
be very useful to the science, I consider it proper to publish 
in nearly his own words. 
