MAGNESIUM NITRIDE. 95
in the cover. After drying, make a perforation in this last mass
of asbestos by means of a fine needle. Dry the crucible, with its
contents, in the hot closet.
Place the crucible in a hole made in a piece of heavy asbestos
board, so that its greater part hangs below the asbestos, and
direct the flame of a, blast lamp sidewise against it. By this
arrangement the flame gases are kept well away from the cover
of the crucible. Turn the asbestos board with the crucible from
time to time so that all sides are heated equally. Continue the
heating for 30 minutes.
After cooling, remove the cover of the crucible and the upper
layer of white magnesium oxide. Beneath the latter lies a light
yellowish-green mass of nearly pure magnesium nitride, which is
obtained to about 80% of the theoretical yield. If the heating is
not continued long enough, dark places are found in the mass,
caused by the presence of unchanged magnesium.
Magnesium nitride reacts violently with water with the forma-
tion of ammonia. To obtain the ammonia, place the whole con-
tents of the crucible (without separating the oxide from the
nitride) in a round-bottomed flask which is provided with a
separatory funnel and with a right-angled tube leading to a con-
denser. Prolong the condenser with an adapter that just dips
into 100 c.c. of water in a small flask. Cool the evolution flask
by placing it in a dish of cold water, and then, at first slowly and
later more rapidly, allow 75 c.c. of water to drop upon the nitride.
1
Finally, heat the contents of the flask with a small flame as long
as ammonia continues to be evolved. Yield, 3 to 4 g. of ammonia,
as determined by titrating an aliquot part of the distillate with
0.5 normal acid.
Calcium Nitride. Place a small shaving of metallic calcium
on an inverted porcelain cover and set fire to it with a match.
It burns with a light, yellowish-red flame, and both oxide and
nitride are formed. Moisten the white combustion product with a
few drops of water, and test with Nessler's reagent for ammonia.
The chemical reaction is the same for both the magnesium and
calcium nitrides. A part of the metal serves to free the air of(^1) Since the reaction produces intense heat, it is well, in order to avoid
breaking the flask, to place in the bottom of the flask a layer of sand and on
top of this the nitride mixed with sand.