96 PHOSPHIDES.
oxygen, while the remainder combines with the nitrogen that is
left. By the hydrolysis of the nitride, ammonia and the hydrox-
ide of the metal are formed. The possibility of obtaining ammonia
from the nitrogen of the air, with the intermediate formation of a
nitride, was first pointed out by Wohler in 1850 when his method
of preparing boron nitride was published.
- Chromium Nitride, CrN.
Heat 5 to 10 g. of violet, anhydrous chromium chloride (No. 44)
in a 25 to 50 cm. tube of difficultly fusible glass, at first gently
and then strongly with a row burner (Fig. 3, p. 2). Meanwhile pass
through the tube a current of ammonia gas, which is obtained by
heating a concentrated solution of ammonia and drying the gas
successively in a lime-tower and a U-tube containing lime. Leave
the reaction tube entirely open at one end, since if an ordinary
delivery tube is used to carry away the waste gases, it soon becomes
stopped with sublimed ammonium chloride. Carry out the
experiment under the hood and continue the heating until no more
vapors of ammonium chloride escape. After cooling, pulverize
the reaction product and once more ignite it in an atmosphere of
ammonia. Yield, nearly theoretical.
Chromium nitride is very stable towards warm caustic soda
solution, and hot concentrated sulphuric acid reacts with it but
slowly. To test its purity, boil a small sample with chloride-free
caustic soda and test the solution obtained for chloride. If it is
desired to remove traces of chromium chloride from the prepara-
tion, it may be treated in the cold with dilute hydrochloric acid
and a little tinfoil, then washed with water, drained, and dried at
110° to 120°.
Chromium nitride, on being heated upon a porcelain crucible
cover over the blast lamp, changes to dull, grayish-green chromic
oxide.
(e) Phosphides. - Magnesium Phosphide, Mg-J",.
Draw out one end of a 35 cm. long combustion tube so that its
diameter is 0.6 to 0.9 cm., and connect this end by a piece of
rubber tubing with two drying bottles and a Kipp hydrogen
generator. Insert two porcelain boats into the tube, the one