ted. These solutions
have a fine red color.

_Protoxide of Cobalt_ (CoO).--It is an olive-green powder, but, by
exposure to the air, it becomes gradually brown. Its hydrate is a rich
red powder. The solution of its salts is red, but the aqueous solution
is often blue.

When heated in the oxidation flame, the protoxide is converted into
the black proto-sesquioxide (CoO + Co^{2}O^{3}). In the reduction
flame it shrinks and is reduced without fusion to the metallic state.
It is now attracted by the magnet and acquires lustre by compression.

Borax dissolves it in the oxidation flame, and produces a clear,
intensely colored blue bead, which remains transparent and of the same
beautiful blue when cold. This blue is likewise manifest even if the
bead be heated intermittingly. If the cobalt exists in considerable
quantity, the color of the bead is so intense as to appear almost
black.

This reaction of cobalt is so characteristic and sensitive that it can
detect a minute trace.

With microcosmic salt the same reaction is exhibited, but not so
sensitive, nor is the bead so intensely colored when cold as that with
borax.

By fusion with carbonate of soda upon a platinum wire, with a very
small portion of cobalt, a bright red colored mass is produced which
appears grey, or slightly green when cold. By fusion upon platinum
foil the fused portion floats down from the sides, and the foil is
coated around the undissolved part, with a thin, dark-red sublimate.
When fused upon charcoal, and in the reduction flame, it is reduced
with soda to a grey powder, which is attracted by the magnet, and
exhibits the metallic lustre by compression.

_Sesquioxide of Cobalt_ (Co^{2}O^{3}).--It is a dark brown powder. Its
hydrate (2HO + Co^{2}O^{3}) is a brown powder. It is soluble only in
acetic acid as the acetate of the sesquioxide. All other acids
dissolve its salts to protoxide, the hydrochloric acid producing
chloric gas. By ignition in the oxidation flame, it is converted into
the proto-sesquioxide (CoO + Co^{2}O^{3}) and produces with reagents
before the blowpipe the same reactions as the protoxide.

(_c._) _Nickel_ (Ni).--This metal occurs invariably associated with
cobalt, and in analogous combinations, chiefly as the arsenical
nickel. In the metallic state it is greyish, silver-white, has a high
lustre, is hard, and malleable both cold and hot. At common
temperatures, it is unalterable either in dry or moist air. When
ignited,