erable quantity in
nature, chiefly combined with sulphur or metals.

Arsenic, in the metallic state, is of a whitish-grey color, high
lustre, and is crystalline, of a foliated structure, and is so brittle
that it can be pulverized. It does not melt, but is volatilized at
356 deg.. Its vapor has a strong alliaceous odor. Arsenic sublimes in
irregular crystals. By exposure to the air it soon tarnishes, and is
coated black. Being mixed with nitrate of potassa and inflamed, it
detonates with vehemence. Mixed with carbonate of potassa, it is
inflamed by a stroke of the hammer, and detonates violently.

Heated in oxygen gas, it is inflamed, and burns with a pale blue flame
to arsenious acid.

([beta].) _Arsenious Acid_ (AsO^{3}).--This acid crystallizes in
octahedrons, or, when fused, forms a colorless glass, which finally
becomes opaque and enamel-like, or forms a white powder. It sublimes
without change or decomposition. When heated for a longer while below
the temperature of sublimation, it melts into a transparent,
colorless, tough glass. The opaque acid is sparingly soluble in cold
water, and still more soluble in hot water. It is converted, by
continued boiling, into the transparent acid, which is much more
soluble in water. Arsenious acid is easily dissolved by caustic
potassa. It is also soluble in hydrochloric acid. This acid occurs
associated with antimonious acid, protoxide of tin, protoxide of lead,
and oxide of copper. It occurs likewise in very small quantity in
ferruginous mineral springs.

([gamma].)_Arsenic Acid_ (AsO^{5}) is a white mass, which readily
absorbs moisture and dissolves. It will not volatilize at a low red
heat, nor will it decompose. Exposed to a strong heat, it is
decomposed, yielding oxygen, and passing into arsenious acid.

_Reactions before the Blowpipe._

Metallic arsenic, heated in a glass tube closed at one end, yields a
black sublimate of a metallic lustre, and at the same time gives out
the characteristic alliaceous odor. This is the case too with alloys
of arsenic, if there is a maximum quantity of arsenic present.

When heated in a glass tube open at both ends, metallic arsenic is
oxidized to arsenious acid, which appears as a white crystalline
sublimate on the sides of the glass tube. This deposit will occur at
some distance from the assay, in consequence of the great volatility
of the arsenic. The sublimate can be driven from one place upon the
tube to another, by a very l