The glass, which has been treated in the oxidizing flame, becomes, when the acid is not present in too large a quantity, brown, and when in large quantity, perfectly opaque.  In a strong flame, oxide of molybdenum is formed which is visible in the yellow glass in the form of black flakes.  If the glass appear opaque, it should be flattened with the forceps.

  Behavior with Mic.  Salt on Platinum wire

    in the oxidizing flame.

Dissolves to a clear glass, which, when sufficient acid is present, is of a yellowish-green color when warm, and becomes nearly colorless on cooling.  On charcoal, the glass becomes dark, and when cool has a beautiful green color.

    in the reducing flame.

The glass becomes of a bottle-green color, which on cooling, changes to a brilliant green, similar to that produced by oxide of chromium.  The reaction on charcoal is precisely similar.  Tin renders the color somewhat darker.

* * * * *

31.  Vanadic Acid, VaO^{8}.

  Behavior with Borax on Platinum wire

    in the oxidizing flame.

      Dissolves to a clear glass, which is colorless when only a small
      quantity of acid is present, and yellow when containing a larger
      proportion.

    in the reducing flame.

      The yellow color of the glass changes to a brown when warm and a
      chrome-green on cooling.

  Behavior with Mic.  Salt on Platinum wire

    in the oxidizing flame.

      As with borax.

    in the reducing flame.

      As with borax.

* * * * *

32.  Oxide of Chromium, Cr^{2}O^{3}.

  Behavior with Borax on Platinum wire

    in the oxidizing flame.

Affords an intense color, but dissolves slowly.  A small proportion colors the glass yellow when warm, and yellowish green when cold; a larger addition produces a dark red color when warm, which, on cooling, becomes yellow and finally a brilliant green with a tinge of yellow.

    in the reducing flame.

      A small quantity of the oxide renders the glass beautifully
      green both when warm and when cold.  A larger addition changes it
      to a darker emerald green.  Tin produces no change in the color.

  Behavior with Mic.  Salt on Platinum wire

    in the oxidizing flame.

      Dissolves to a clear glass which has a pink tinge while warm,
      but on cooling becomes dusky green, and finally brilliantly
      green.

    in the reducing flame.

      As in the oxidizing flame, except that the colors are somewhat
      darker.  Tin produces no further change.

* * * * *

33.  Arsenious Acid, AsO^{3}.