218 METAL-ORGANIC COMPOUNDS.
box^1 (cf. Fig. 4, p. 3) around the combustion tube and insert
a thermometer into the chamber. Heat the tube by means of
a Bunsen burner with a flame spreader, but do not place the
flame immediately under the lower opening of the box. Clamp
the combustion tube so that it slants downward a little and pro-
vide an extra burner to expel any water which may condense
inside the tube.
Place 5 to 7 g. of nickel oxalate in the tube between two looseplugs of asbestos, replace the air completely with hydrogen, and
heat the charge to 300° in a current of hydrogen until it has
become black and no more water vapor escapes. Avoid a higher
temperature, as the nickel would then lose its condition of fine
subdivision. Then allow the temperature to sink to between 80°
and 100°, and replace the hydrogen by means of a current of air-
free carbon monoxide (the wash bottles and connections should
be filled with carbon monoxide before beginning the operation).Test the escaping gases for nickel carbonyl as follows:
- Insert into the end of the combustion tube a cork carrying
a tube drawn out to a capillary jet; set fire to the escaping gas;
it burns with a brilliantly luminous flame from which metallic
nickel is deposited upon a cold piece of porcelain in a form resem-
bling soot.- Connect the combustion tube by means of rubber tubing
with a carefully cleaned glass tube, and heat the latter gently
with a Bunsen burner; a mirror of nickel is deposited in the
heated part. If the tube is heated to redness the nickel is then
precipitated in the form of a powder.
If the procedure above outlined is carried out on a larger scale
the nickel carbonyl vapor issuing from the apparatus may be
condensed by passing it into a vessel surrounded by a freezing
mixture. Nickel carbonyl is a colorless liquid which boils at 43°
under 751 mm. pressure, and solidifies at —25° to a mass of needle-
shaped crystals.
1
The openings in the cover of the heating box should be covered with
discs of asbestos to avoid drafts.