resemble each other very closely, when examined in regard to
their physical appearance, but the blowpipe will quickly discriminate
them, for if a small piece of the former mineral be placed in the
flame of oxidation, a bright green color will be communicated to the
flame beyond it, while in the latter there will be no color. Thus, in
a very short time, these two minerals can be distinguished from each
other by aid of the blowpipe, while no amount of physical examination
could determine that point. The blowpipe is equally an indispensable
instrument in the determination of certain minerals which may exist in
others as essential or non-essential constituents of them. For
instance, should a minute quantity of manganese be present in a
mineral, it must be fused with twice its bulk of a mixture of two
parts of carbonate of soda, and one part of the nitrate of potassa, in
the flame of oxidation upon platinum foil. The manganate of soda thus
formed will color the fused mass of a bluish-green tint.

Or a slight quantity of arsenic may be discerned by the following
process recommended by Plattner:[4] one grain of the finely pulverized
metal is mixed with six grains of citrate of potassa, and slowly
heated on the platinum spoon. By this means the metals are oxidized,
while the arseniate of potassa is obtained. Then boil the fused mass
in a small quantity of water in a porcelain vessel till all tho
arseniate is dissolved. The metallic oxides are allowed to subside,
and the above solution decanted off into another porcelain vessel. A
few drops of sulphuric acid are added, and the solution boiled to
expel the nitric acid, after which it is evaporated to dryness. In
this operation, the sulphuric acid should be added only in sufficient
quantity to drive off the nitric acid, or, at the utmost, to form a
bisulphate with the excess of potassa. When dry, the salt thus
obtained is pulverized in an agate mortar, and mixed with about three
times its volume of oxalate of potassa, and a little charcoal powder.
The mixture is introduced into a glass bulb having a narrow neck, and
gently warmed over a spirit-lamp in order to drive off the moisture,
which must be absorbed by a piece of blotting-paper in the neck of the
bulb. After a short time, the temperature is increased to a low red
heat, at which the arsenious acid is reduced and the metallic arsenic
sublimed, and which re-condenses in the neck of the bulb. If there
the arsenic be so small in