189 
certain circumstances, and it was a greater object with me 
to ascertain the quantum of acid than of the water of 
crystallization, The matter lost 0:48 of a grain. I have 
reason to think that all the water of crystallization was not 
expelled. It was now transferred to a silver crucible, and a 
ley containing about 20 grains of Potash was gradually 
digested with it, to dryness, and the crucible was at last 
exposed for a few minutes on an open fire. All the soluble 
part was elixated by distilled water, and the solid matter 
left behind weighed 19°50 grains. I found that the alka- 
line ley held a small portion of the mineral in solution: this 
was previously separated : it consisted of Oxide of Lead, 
Silica, and very slight traces of Alumina and [ron. After 
being neutralized with Nitric Acid, liquid Nitrate of Lead 
was dropped into it, as long as any precipitate was pro- 
duced. The precipitated white matter weighed 14 grains, 
which, according to the calculation of Mr. Chenevix, indi- 
cates 4:62 of Arsenic Acid. In order to be certified that it 
contained Arsenic Acid, I decomposed it by means of half 
its weight of Sulphuric Acid. I obtained a dry granulated 
matter which attracted the moisture of the atmosphere. 
It had acid properties. . Dissolved in water, it precipitated 
Cxide of Titanium from a solution of its Sulphate. Some 
of this acid was exposed to the flame by the blowpipe in a 
golden spoon: it bore ignition, and appeared to be a dry 
pulverulent matter; but being heated on charcoal it was 
speedily dissipated m copious arsenical vapours. Some of 
the Acid was neutralized hy Carbonate of Soda. A solution 
of this Salt, mixed with liquid Nitrate of Silver, produced 
a copious precipitate of a brick-colour. As 1 thought 
it possible that-all the ‘acid had not been extracted, I 
boiled the 19°50 grains with a fresh ley of Potash. Some 
of the mineral was again dissolved, but not the smallest 
quantity of Arsenic Acid was obtained. The remaining 
matter was dissolved in Nitric Acid, except.a small portion 
of Quartz. The matter, also, which had been separated from 
