incrusts the charcoal, at a small distance from the assay, with
molybdic acid, which, near the assay, forms transparent crystalline
scales, and is elsewhere deposited as a fine powder. The incrustation,
while hot, is of a yellow color, but becomes white after cooling. It
may be volatilized by heating with either flame, and leaves the
surface of the charcoal, when perfectly cooled, of a dark-red copper
color, with a metallic lustre, due to the oxide of molybdenum, which
has been formed by the reducing action of the charcoal upon the
molybdic acid. In the reducing flame, metallic molybdenum remains
unchanged.

SILVER.--This metal, when fused alone, and kept in this state for some
time, under a strong oxidizing flame, covers the charcoal with a thin
film of dark reddish-brown oxide. If the silver be alloyed with lead,
a yellow incrustation of the oxide of that metal is first formed, and
afterwards, as the silver becomes more pure, a dark red deposit is
formed on the charcoal beyond. If the silver contains a small quantity
of antimony, a white incrustation of antimonious acid is formed, which
becomes red on the surface if the blast be continued. And if lead and
antimony are both present in the silver, after the greater part of
these metals have been volatilized, a beautiful crimson incrustation
is produced upon the charcoal. This result is sometimes obtained in
fusing rich silver ores on charcoal.


SULPHIDES, CHLORIDES, IODIDES, AND BROMIDES.

In blowpipe experiments, it rarely occurs that we have to deal with
pure metals, which, if not absolutely non-volatile, are recognized by
the incrustation they form upon charcoal. Some compound substances,