In the reduction flame no change is visible if the quantity of iron be small.  By the addition of more iron, the hot bead appears red, and while cooling, changes to yellow, then green, and, when cold, is of a dull red.  By fusing the bead on charcoal with a small addition of tin, it exhibits, while cooling, a bluish-green color, but, when cold, is colorless.

The oxides of iron are not dissolved in the oxidation flame by fusion with carbonate of soda.  By ignition with soda upon charcoal in the reduction flame, they are absorbed and reduced to the metallic state.  Cut out this portion of the charcoal; grind it with the addition of some water in an agate mortar, for the purpose of washing off the carbon particles, when the iron will remain as a grey magnetic powder.

(b.) Cobalt (Co) occurs in combination with arsenic and sulphur, and associated with nickel and iron.  It is found occasionally in combination with selenium, and there are a traces of it in meteoric iron.  In the metallic state it is of a light, reddish-grey color, rather brittle, and only fusible at a strong white heat; at common temperatures it is unalterable by air or water.  At a red heat, it oxidizes slowly and decomposes water; at a white heat it burns with a red flame.  Cobalt is soluble in dilute sulphuric or hydrochloric acid by the aid of heat, whereby hydrogen is eliminated.  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.