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NITROUS OXIDE.
473
should not give a precipitate when added to the nitrate of am-
monia; should it do so, then sulphuric acid is present; or the
nitrate of ammonia may be tested by a solution of nitrate of silver,
which will also give a precipitate, if chlorine is present. The
test with nitrate of silver may be made by dissolving a drachm or
the nitrate of ammonia in half a glass of distilled water and adding a
few crystals of the nitrate of silver. If the nitrate of ammonia is
pure, the solution will remain perfectly clear; but should chlorine
be present, it will show a clouded appearance, and should be dis-
carded, as it is not fit to generate the gas from.
The salt nitrate of ammonia is a white, crystalline substance,
formed by neutralizing dilute nitric acid by means of carbonate
of ammonia, and is so constituted as to be resolved into nitrous
oxide and water. A pound of the salt will generate about thirty
gallons of the gas. In generating nitrous oxide gas, care must
be taken to preserve its purity; consequently it becomes im-
portant to maintain, as nearly as possible, an equal temperature
during its manufacture ; and should any nitric oxide—binoxide of
nitrogen—be formed, which may be done by too high a heat
under the retort, it is necessary to remove it and other impurities,
by the aid of solutions of caustic potash and copperas; the caustic
potash neutralizing any free nitric acid present, and the copperas
removing either chlorine or nitric oxide. The salt nitrate of
ammonia is perfectly fused at 226° F., emits white fumes at
302° F., and begins to evolve gas at 460° F. At 500° F. the
impurity, nitric oxide^ is given ofF; hence the temperature during
the process should not be permitted to rise above 482° F., which
can be determined by thermometers prepared for the purpose.
No red fumes should pass from the_retort.
Liquefied Nitrous Oxide.—Nitrous oxide gas, as principally used
at the present time, is in the form of condensed gas, being lique-
fied and solidified under great pressure, and secured in iron
cylinders, from which it escapes into an inhaling bag when
needed for use by turning a stop-cock. Liquefied nitrous oxide
is a colorless fluid, having specific gravity of 0.908, and at a very
low temperature (148° F.) it congeals into a transparent crys-
talline solid. It is prepared by condensing the gas by a pressure