*99 
Mr. Gregor on a native Arseniate of Lead . 
These preliminary experiments led me to the probable 
conclusion, that this fossil chiefly consisted of oxide of lead, 
arsenic acid, and a small quantity of the muriatic acid. 
IV. Analysis. 
A. 
1. Fifty grains, carefully selected from crystals of a pale 
Isabella-colour, were reduced to a fine powder and exposed 
to a low red heat for about an hour. Their weight was dimi- 
nished by 0.15 of a grain. 
2. The yellowish powder was now transferred to a vessel 
of pure silver, and mixed with a lixivium containing fifty 
grains of potash, prepared by the means of alcohol; a quan- 
tity, which I had previously ascertained to be sufficient to effect 
a complete decomposition of this mineral. The ley was gra- 
dually evaporated to dryness in a sand-bath. The soluble 
part was extracted by distilled water, and poured off from a 
yellowish white matter, which was sufficiently edulcorated 
(#). 
g. Liquid nitrat of ammonia was now dropped into the al- 
kaline fluid, as long as it produced any cloudiness : the clear 
fluid was now decanted from a small quantity of white matter, 
which had subsided, and rendered acid by nitric acid ; ammo- 
nia, added to excess, produced a slight turbidness. These 
precipitates, after sufficient edulcoration, were added to the 
yellowish white residuum (tf). 
4. The liquid was now rendered slightly acid by nitric acid, 
and a solution of nitrat* of lead in distilled water was dropped 
* If the colourless liquid oxynitrat of lead be dropped into a dilute solution of ar- 
senic acid, or of arseniat of potash acidulated by nitric acid, no immediate precipita- 
D d 2 
