228 COMPOUNDS OF THE RARE ELEMENTS.
occasionally playing a Bunsen flame over the constriction at B,
bring the product into the section of the tube BC where it pre-
cipitates in a shower of very minute crystals. Avoid heating too
strongly. At the end of the operation only a few gray flocks
remain behind to the left of B. During the process the end of
the tube at C is connected with a wide glass tube leading into
the flue.
Allow the crystals to cool in a current of carbon dioxide, close
C with a cork, and, with a blast lamp, fuse the tube together
at B. By repeatedly tapping the tube loosen the crystals and
transfer them to a preparation tube which is made ready as fol-
lows: Close one end of a fusible glass tube 35 cm. long and of
the same width as the combustion tube, and make a constriction
20 cm. above the closed end. Fill the tube with carbon dioxide,
and place the open end over the narrowed end C of the com-
bustion tube. As soon as the substance is transferred seal the
constricted part of the preparation tube. Dissolve the residue
adhering within the combustion tube in alcohol; considerable
heat is evolved, and an emerald-green solution is obtained which,
when treated with ammonia, gives a grayish-brown flocculent
precipitate.
Molybdenum Trichloride, MoCl 3. In an apparatus like that
used for the preparation of the pentachloride, substitute a com-
bustion tube prepared as shown in Fig. 27. The lengths of th»A
0
Fig. 27.three sections of the tube are 32 cm., 8 cm., and 60 to 75 cm.
respectively, and the inside diameter at the constrictions A, B,
and C is from 1.0 to 1.2 cm. Proceed at first, exactly as directed
above, to prepare molybdenum pentachloride from 6 g. of molyb-
denum, and allow the greater part of this product to sublimeinto the longest section of the tube, while a small amount con-
denses in the 8 cm. section. Allow the tube to cool, replace the
chlorine by carbon dioxide and the latter by hydrogen. Then
place the combustion tube in a somewhat inclined position so
that D is higher than A. Heat the tube at C, while a fairly
strong current of hydrogen is passing, until the pentachloride