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

226 COMPOUNDS OP THE RARE ELEMENTS.

drawn out a little at one end, and fill the tube with hydrogen

which has been washed successively with caustic soda solution,

silver nitrate, potassium permanganate, and sulphuric acid.

Heat in the atmosphere of hydrogen for 15 minutes to moder-

ate redness so that the temperature surely exceeds 470°. When

cold, determine the loss in weight, and if necessary repeat the

heating until finally the change in weight corresponds to the

change from the trioxide to the dioxide. In this way a reddish-

brown glistening powder is obtained.

1

Stronger ignition in

hydrogen causes the formation of metallic molybdenum.

(c) Chlorides of Molybdenum.

Molybdenum Dioxydichloride, MoO 2 Cl 2 - Place 2 g. of molyb-

denum dioxide in a glass tube about 50 cm. long, and pass over it

a current of chlorine which is dry and entirely free from air.

After the air is completely expelled from the tube, heat gently by

means of a Bunsen burner with a flame spreader. The volatile

molybdic acid chloride sublimes and deposits as a loose mass of

pinkish-white plates in the colder parts of the tube. After the

reaction is ended replace the chlorine with dry carbon dioxide, and

when cold, cut the tube at a point between the residue and the

sublimed product. Transfer the crystals immediately to a glass-

stoppered tube, since they are very hygroscopic, and make the

stopper air-tight with a little vaseline.

Molybdenum Pentachloride, MoCl 5. First prepare the neces-

sary metallic molybdenum by heating 15 g. of molybdenum tri-

oxide in a current of hydrogen as hot as possible in a combustion

furnace until no more water vapor is evolved. This method of

reduction requires about three hours, and even then it is expedi-

ent to pulverize the product and to heat it a second time in hydro-

gen. Molybdenum reduced by the Goldschmidt method (see

footnote below) may also be pulverized and used.

Meanwhile construct, under a hood with a strong draft, the

apparatus represented in Fig. 26. Make as indicated two con-

(^1) Molybdenum dioxide, being non-volatile, is especially suited for the
aluminothermic production of the fused metal. Place a mixture of 80 g. of
molybdenum dioxide and 21 g. of aluminum powder in a clay crucible
embedded in sand, and start the reaction by means of some fuse powder (cf.
No. 2). Yield, 70 to 80%.