fused with nitre, it forms chromate
of potassa. It is unaltered in the blowpipe flame.

_Sesquioxide of Chromium_ (Cr^{2}O^{3}).--This oxide forms black
crystals of great hardness, and is sometimes seen as a green powder.
Its hydrate (Cr^{2}O^{3} + 6HO) is of a bluish-grey color. It forms
with acids two classes of isomeric salts, some of which are of a
green color, and the others violet-red or amethyst. The neutral and
soluble salts have an acid reaction upon blue litmus paper, and are
decomposed by ignition.

Sesquioxide of chromium in the oxidation and reduction flames is
unchangable. When exposed to heat, the hydrate loses its water, and
gives a peculiarly beautiful flame. In the oxidation flame borax
dissolves the sesquioxide of chromium slowly to a yellow bead (chromic
acid) which is yellowish green when cold. Upon the addition of more of
the oxide, the bead is dark red while hot, but changes to green as it
becomes cold.

In the reduction flame the bead is of a beautiful green color, both
while hot and when cold. It is here distinguished from vanadic acid,
which gives a brownish or yellow bead while hot.

With microcosmic salt it fuses in the oxidation flame to a clear
yellow bead, which appears, as it cools, of a dirty-green, color, but
upon being cool is of a fine green color. If there be a superabundance
of the oxide, so that the microcosmic salt cannot dissolve it, the
bead swells up, and is converted into a foamy mass, in consequence of
the development of gases.

In the reduction flame it fuses to a fine green bead. The addition of
a little tin renders the green still deeper.

Sesquioxide of chromium fuses with carbonate of soda upon platinum
foil to a brown or yellow bead, which, upon cooling, appears of a
lighter color and transparent (chromate of sodium).

When fused with soda upon charcoal, the soda is absorbed, and the
green oxide is left upon it, but is never reduced to the metallic
state.

_Chromic Acid_ (CrO^{3}) crystallizes in the form of deep ruby red
needles. It is decomposed into sesquioxide and oxygen when heated.
This decomposition is attended with a very lively emission of light,
but this is not the case if the chromic acid has been attained by the
cooeperation of an aqueous solution, unless the reduction is effected
in the vapor of ammonia. Before the blowpipe chromic acid produces the
same reactions as the sesquioxide.

(_l._) _Manganese_ (Mn).--This metal occurs in considerable