water, filtered and neutralized while hot with carbonate of ammonia,
until it ceases to give an acid reaction with test-paper. This must
now be filtered again, and carbonate of potassa added to the filtrate
as long as a precipitate is produced. This precipitate is brought upon
a filter and washed thoroughly, and then dissolved in diluted nitric
acid. This is evaporated to dryness, and one part of it is dissolved
in ten parts of water for use.

The oxide of cobalt combines, with strong heat in the oxidation flame,
with various earths and infusible metallic oxides, and thus produces
peculiarly colored compounds, and is therefore used for their
detection; (alumina, magnesia, oxide of zinc, oxide of tin, etc.) Some
of the powdered substance is heated upon charcoal in the flame of
oxidation, and moistened with a drop of the solution of the nitrate of
cobalt, when the oxidation flame is thrown upon it. Alumina gives a
pure blue color, the oxide of zinc a bright green, magnesia a light
red, and the oxide of tin a bluish-green color; but the latter is only
distinctly visible after cooling.

The dropping bottle, is the most useful apparatus for the purpose of
getting small quantities of fluid. It is composed of a glass tube,
drawn out to a point, with a small orifice. This tube passes through
the cork of the bottle. By pressing in the cork into the neck of the
bottle, the air within will be compressed, and the liquid will rise in
the tube. If now we draw the cork out, with the tube filled with the
fluid, and pressing the finger upon the upper orifice, the fluid can
be forced out in the smallest quantity, even to a fraction of a drop.


10. _Tin._--This metal is used in the form of foil, cut into strips