finity for oxygen, under the influence of
the intense heat of that part of the flame. The substance is thus
deprived of a part, or the whole, of its oxygen, and becomes _reduced_
according to the strength of the affinity which the substance itself
has for oxygen. If the reduction of a substance is undertaken on
platinum, by fusion with a flux, and if the oxide is difficult to
reduce, the reduction will be completely effected only in the luminous
part of the flame. But if a substance be reduced on charcoal, the
reduction will take place in the blue part of the flame, as long as
the access of air is cut off; but it is the luminous part of the flame
which really possesses the greatest reducing power.

The following should be observed in order to procure a good reduction
flame:

The wick should not be too long, that it may make a smoke, nor
too short, otherwise the flame will be too small to produce a
heat strong enough for reduction.

The wick must be free from all loose threads, and from
charcoal.

The blast should be continued for a considerable time without
intermission, otherwise reduction cannot be effected.

For the purpose of acquiring practice, the student may fuse the oxide
of manganese with borax, upon a platinum wire, in the oxidation flame,
when a violet-red glass will be obtained; or if too much of the oxide
be used, a glass of a dark color and opaque will be obtained. By
submitting this glass to the reduction flame, it will become colorless
in correspondence to the perfection with which the flame is produced.
Or a piece of tin may be fused upon charcoal, and kept in that state
for a considerable time, while it presents the appearance of a bright
metal on the surface. This will require dexterity in the operator;
for, if the oxidation flame should chance to touch the bright metal
only for a moment, it is coated with an infusible oxide.

COMBUSTION.--Any flame of sufficient size can be used for blowpipe
operations. It may be either the flame of a candle of tallow or wax,
or the flame of a lamp. The flame of a wax candle, or of an oil lamp
is most generally used. Sometimes a lamp is used filled with a
solution of spirits of turpentine in strong alcohol. If a candle is
used, it is well to cut the wick off short, and to bend the wick a
little toward the substance experimented upon. But candles are not the
best for blowpipe operations, as the radiant heat, reflecting from the
su