3. That of the hydrogene of ammoniac for the oxygene
of nitric acid.
4. That of the nitrogene of ammoniac for the nitrous gas
of nitric acid.
At temperatures below 300°, the salt, from the equilibrium between
these affinities, preserves its existence.
Now when its temperature is raised to 400°, the attractions of
hydrogene for nitrogene,[90] and of nitrous gas for oxygene,[91] are
diminished; whilst the attraction of hydrogene for oxygene[92] is
increased; and perhaps that of nitrogene for nitrous gas.
[90] As is evident from the decomposition of ammoniac by heat.
[91] Nitric acid is phlogisticated by heat, as appears from Dr.
Priestley’s experiments. Vol. 3, p. 26.
[92] As is evident from the increase of temperature required for the
formation of water.
Hence the former equilibrium of affinity is destroyed, and a new one
produced.
The hydrogene of the ammoniac combines with the oxygene of the nitric
acid to generate water; and the nitrogene of the ammoniac enters into
combination with the nitrous gas to form nitrous oxide: and the water
and nitrous oxide produced, most probably exist in binary combination
in the aëriform state, at the temperature of the decomposition.
But when a heat above 800° is applied to nitrate of ammoniac, the
attractions of nitrogene and hydrogene for each other, and of
oxygene for nitrous gas,[93] are still more diminished; whilst that
of nitrogene for nitrous gas is destroyed, and that of hydrogene
for oxygene increased to a great extent: likewise a new attraction
takes place; that of nitrous gas for nitric acid, to form nitrous
vapor.[94] Hence a new arrangement of principles is rapidly produced;
the nitrogene of ammoniac having no affinity for any of the single
principles at this temperature, enters into no binary compound: the
oxygene of the nitric acid forms water with the hydrogene, and the
nitrous gas combines with the nitric acid to form nitrous vapor. All
these substances most probably exist in combination at the temperature
of their production; and at a lower temperature, assume the forms of
nitrous acid, nitrous gas, nitrogene, and water.
[93] For ammoniac and nitrous oxide are both decomposed at the red
heat, and oxygene given out from nitric acid when it is passed through
a heated tube.
[94] Whenever nitrous acid is produced at high temperatures, it is
always highly phlogisticated, provided it has not been long in contact
with oxygene. When Dr. Priestley passed nitric acid through a tube
heated red, he procured much oxygene, and phlogisticated acid; and the
water in the apparatus employed was fully impregnated with nitrous air.
Hence it would appear, that heat diminishes the attraction between
oxygene and nitrous gas, and increases the affinity of nitrous gas for
nitrous acid. Mr. JAMES THOMSON, whose theory of the Nitrous Acid I
have already mentioned, from some experiments on the phlogistication
of Nitric Acid by heat, which he has communicated to me, concludes
with great justness, that a portion of the acid is always completely
decomposed in this process: the oxygene liberated, and the nitrous gas
combined with the remaining acid.
I have avoided entering into any discussions concerning the light
and heat produced in this process; because these phænomena cannot be
reasoned upon as isolated facts, and their relation to general theory
will be treated of hereafter.