Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

MOLYBDENUM COMPOUNDS FROM MOLYBDENITE. 225

the powder in a small evaporating dish, heating strongly with a

Fletcher burner, and stirring frequently until the mass has been

largely converted into yellow molybdenum trioxide and the sul-

phur has escaped as sulphur dioxide. Carried out in this manner

the roasting consumes from four to six hours; if it is carried out

in a porcelain tube, in which a better circulation of air is obtained,

the same result is accomplished in from thirty minutes to an
hour. The tube should be about 25 cm. long and 3 cm. in diam-
eter, and should be placed in a slightly inclined position within
an asbestos heating chamber (Fig. 4, p. 3).
Extract the roasted product with 2-normal ammonia solution,
dry the dark-colored residue, roast it, and extract it again with
ammonia; finally repeat the process once more, when nothing
but a grayish gangue remains.
To the entire ammoniacal extract add three drops of ammo-
nium sulphide to precipitate traces of copper; after standing

twelve hours, filter, add a drop of bromine to the filtrate, and

evaporat3 until crystallization takes place, adding at the last a

few drops of concentrated ammonia. The addition of a little

alcohol aids the separation of crystals. Dry the product in the

air. Yield, 35 to 40 g. of small flake-like crystals; theoretical

yield from pure molybdenite, 47.5 g.

A dilute solution of ammonium molybdate slightly acidified

with hydrochloric acid, gives a dark-blue color when treated with

one drop of stannous chloride; upon further addition of this

reagent it becomes a dirty green. Dependent preparation: Molyb-

denum Blue, No. 24.

(b) Oxides of Molybdenum.

Molybdenum Trioxide, MoO 3. Ignite some ammonium molyb-

date at first gently and then strongly in an evaporating dish.

The ignited product usually contains some lower oxide; to

change this completely to the trioxide, place the material in a
combustion tube and heat in a slow current of oxygen, using

a row burner (Fig. 2) and covering the tube with an asbestos

mantle. Do not heat the substance sufficiently to volatilize

the molybdenum trioxide.

Molybdenum Dioxide, MoO 2. Place 2 g. of molybdenum triox-

ide in a weighed glass tube, about 35 cm. long, which has been