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

NICKEL CARBONYL. 217

the deep lemon-yellow crystals, wash them with a little alcohol,

and dry them at a gentle heat. The product melts with decom-

position^1 at 105 to 107°. The yield is not quite quantitative, as

some lead iodide is always formed.

161. Nickel Carbonyl,^2 N1(CO) 4.

When carbon monoxide is conducted over very finely divided nickel,
four molecules of the gas combine below 100° with one atom of nickel to form
nickel carbonyl (boiling-point, 43°). At higher temperatures this compound
dissociates and the nickel separates in the form of a dust, or deposits as a
mirror on the walls of the vessel. In making the preparation a careful main-
tenance of the proper temperature and a state of very fine subdivision of the
metal are important; nickel is obtained in the desired condition by reducing
nickel oxalate in a current of hydrogen.

Treat a hot solution of nickel sulphate with oxalic acid, then

add ammonia, but without entirely neutralizing the solution.

The precipitation of nickel oxalate in this way is not quite

quantitative, but the product can be washed readily by

decanting with hot water. By draining the precipitate and

drying it in the hot closet, a light-green, loose powder is

obtained.

The carbon monoxide may be prepared by allowing 30 g. con-

centrated formic acid to slowly drop from a dropping funnel into

a distilling flask containing 100 g. concentrated H 2 SO 4 at about
100°, and passing the gas through two wash-bottles containing
concentrated sodium hydroxide solution. Collect the carbon mon-

oxide in a gasometer.

The reduction of the nickel oxalate and the synthesis of the

nickel carbonyl may be accomplished in the same apparatus.

Connect two sulphuric acid wash bottles in series at one end of a

combustion tube about 26 cm. long, and beyond them place a

three-way cock through which either hydrogen from a Kipp gen-

erator or carbon monoxide from the gasometer may enter. The

carbon monoxide, before entering the tube, must be further purified

from traces of carbon dioxide by passing through two bottles

containing caustic soda solution. Place an asbestos heating

(^1) Diphenyl is formed: (C
6 H 6 ) 2 PbI 2 = Pbl 2 -I- C 6 H 5 .C 6 H 5. The same
decomposition takes place slowly even in a solution of diphenyl-lead-iodide.
The diphenyl is easily recognized by its characteristic odor.
(^1) Mond, Langer, and Quincke, Chem. News, 62, 97 (1890).