n with carbonate of soda in the oxidation and reduction
flames, the silver oxides are instantly reduced to metallic silver,
which fuses into one or more grains.

(_c._) _Gold_ (Au).--This metal occurs mostly in the metallic state,
but frequently mixed with ores, and with other metals. Gold
crystallizes in cubes and octahedrons, is of a beautiful yellow color,
great lustre, and is the most malleable and ductile of all the metals.
It melts at a higher temperature than copper, gives a green colored
light when fused, and contracts greatly when cooling. It does not
oxidize at ordinary temperatures, nor when heated much above them. It
is soluble in nitro-hydrochloric acid (_aqua regia_).

([chi].) _Protoxide of Gold_ (Au^{2}O).--This oxide is a dark violet
colored powder which is converted by a temperature of 540 deg. into
metallic gold and oxygen. It is only soluble in aqua regia. Treated
with hydrochloric acid, it yields the chloride of gold and the metal.
With aqua ammonia, it yields the fulminating gold, which is a blue
mass and very explosive.

([chi].) _Peroxide of Gold_ (Au^{2}O^{3}).--This oxide is an
olive-green or dark brown powder, containing variable quantities of
water. Decomposed at 530 deg., it yields metallic gold and oxygen.

_Reactions before the Blowpipe._--Oxides of gold are reduced, in both
the oxidation and reduction flames, to the metal, which fuses to
grains.

_Borax_ does not dissolve it, but it is reduced to the metallic state
in this flux in either flame. The reduced metal fuses upon charcoal to
a grain.

_Microcosmic Salt_ presents the same reactions as borax.

When fused with soda, upon charcoal, the soda is absorbed, and the
gold remains as a metallic grain.

TENTH GROUP.--MOLYBDENUM, OSMIUM.

These metals are not volatile, and are infusible before the blowpipe;
but some of their oxides are volatile, and can be reduced to an
infusible metallic powder.

(_a._) _Molybdenum_ (Mo) occurs in the metallic state; also combined
with sulphur, or as molybdic acid combined with lead. It is a white,
brittle metal, and is unaltered by exposure to the air. When heated
until it begins to glow, it is converted into a brown oxide. Heated at
a continued dull red heat, it turns blue. At a higher temperature, it
is oxidized to molybdic acid, when it glimmers and smokes, and is
converted into crystallized molybdic acid upon the surface.

([chi].) _Protoxide of Molybdenum_ (MoO).--This oxide is a black