94 NITRIDES.
each of mercuric cyanide in a test tube fitted with a delivery tube.
Finally, saturate the solution once more with hydrogen sulphide.
After standing for some time a mass of small crystals is deposited;
boil the mother liquor with bone-black and evaporate the filtrate
in order to obtain another crop of crystals. Recrystallize the
product from alcohol, or from a mixture of acetone and chloroform.
Yield, 3.5 to 4 g.- Treat an aqueous solution of 25 g. copper vitriol with con-
centrated ammonia until the precipitate, which first forms, just
disappears; decolorize the liquid by the addition of a barely suffi-
cient amount of potassium cyanide solution (about 26 g. KCN)
and then saturate with hydrogen sulphide. The solution first
becomes yellow, then it appears red, and finally a red, crystalline
powder separates. After standing for several hours in the ice-
chest, separate the crystals from the liquor and recrystallize them
from a little alcohol. The yield is small (about 0.5 g.) because
in aqueous solution the greater part of the cyanogen is reduced to
hydrocyanic acid. This is the reason for the use of alcohol in
the first method. - Boron Nitride, BN.
Heat an intimate mixture of 5 g. finely powdered, anhydrous
borax and 10 g. ammonium chloride, as hot as possible with the
blast lamp in a covered platinum crucible surrounded by a clay
mantle. After cooling, pulverize the porous contents of the
crucible, and extract it several times with water containing a
little hydrochloric acid. Boil the residue with pure water, collect
it on a filter and dry it. Yield, about 0.3 g. The nitride prepared
in this way always contains a little oxide.
Boron nitride is insoluble in water and in acids; on being
boiled with caustic soda solution, it decomposes slowly, evolving
ammonia; it is attacked more rapidly by fusion with sodium
carbonate on platinum foil. - Magnesium Nitride, Mg-N;; Ammonia from the Atmosphere.
Fill a small iron crucible (3 cm. high and 5 cm. wide at the
top) to two-thirds with 8 to 9 g. of magnesium powder, and make
a tight joint with the cover by means of wet asbestos pulp. Like-
wise close with asbestos pulp a small hole which has been made