The decomposition of nitrate of ammoniac has been supposed by
Cornette[78] to take place at temperatures below 212°, and its
sublimation at 234°.
Kirwan, from the non-coincidence in the accounts of its composition,
has imagined that it is partially decomposable, even by a heat of
80°.[79]
[78] Mem. Par. 1783. See Irish Trans. vol. 4.
[79] Addit. Obs. pag. 120.
To ascertain the changes effected by increase of temperature in this
salt, a glass retort was provided, tubulated for the purpose of
introducing the bulb of a thermometer. After it had been made to
communicate with the mercurial airholder, and placed in a furnace,
the heat of which could be easily regulated, the thermometer was
introduced, and the retort filled with the salt, and carefully luted;
so that the appearances produced by different temperatures could be
accurately observed, and the products evolved obtained.
From a number of experiments made in this manner on different salts,
the following conclusions were drawn.
1st. Compact, or dry nitrate of ammoniac, undergoes little or no change
at temperatures below 260°.
2dly. At temperatures between 275° and 300°, it slowly sublimes,
without decomposition, or without becoming fluid.
3dly. At 320° it becomes fluid, decomposes, and still slowly sublimes;
it neither assuming, or continuing in, the fluid state, without
decomposition.
4thly. At temperatures between 340° and 480°, it decomposes rapidly.
5thly. The prismatic and fibrous nitrates of ammoniac become fluid at
temperatures below 300°, and undergo ebullition at temperatures between
360° and 400°, without decomposition.
6thly. They are capable of being heated to 430° without decomposition,
or sublimation, till a certain quantity of their water is evaporated.
7thly. At temperatures above 450° they undergo decomposition, without
previously losing their water of crystalisation.
II. _Decomposition of Nitrate of Ammoniac; production of respirable
Nitrous Oxide; its properties._
200 grains of compact nitrate of ammoniac were introduced into a
glass retort, and decomposed slowly by the heat of a spirit lamp.
The first portions of the gas that came over were rejected, and the
last received in jars containing mercury. No luminous appearance was
perceived in the retort during the process, and almost the whole of the
salt was resolved into fluid and gas. The fluid had a faint acid taste,
and contained some undecompounded nitrate. The gas collected exhibited
the following properties.—
_a._ A candle burnt in it with a brilliant flame, and crackling noise.
Before its extinction, the white inner flame became surrounded with an
exterior blue one.
_b._ Phosphorus introduced into it in a state of inflammation, burnt
with infinitely greater vividness than before.
_c._ Sulphur introduced into it when burning with a feeble blue flame,
was instantly extinguished; but when in a state of active inflammation
(that is, forming sulphuric acid) it burnt with a beautiful and vivid
rose-colored flame.
_d._ Inflamed charcoal, deprived of hydrogene, introduced into it,
burnt with much greater vividness than in the atmosphere.
_e._ To some fine twisted iron wire a small piece of cork was affixed:
this was inflamed, and the whole introduced into a jar of the air. The
iron burned with great vividness, and threw out bright sparks as in
oxygene.
_f._ 30 measures of it exposed to water previously boiled, was rapidly
absorbed; when the diminution was complete, rather more than a measure
remained.
_g._ Pure water saturated with it, gave it out again on ebullition, and
the gas thus produced retained all its former properties.
_h._ It was absorbed by red cabbage juice; but no alteration of color
took place.
_i._ Its taste was distinctly sweet, and its odor slight, but agreeable.
_j._ It underwent no diminution when mingled with oxygene or nitrous
gas.
Such were the obvious properties of the NITROUS OXIDE, or the gas
produced by the decomposition of nitrate of ammoniac in a temperature
not exceeding 440°. Other properties of it will be hereafter
demonstrated, and its affinities fully investigated.
III. _Of the gas remaining after the absorption of Nitrous Oxide by
Water._
In exposing nitrous oxide at different times to rain or spring water,
and water that had been lately boiled, I found that the gas remaining
after the absorption was always least when boiled water was employed,
though from the mode of production of the nitrous oxide, I had reason
to believe that its composition was generally the same.
This circumstance induced me to suppose that some of the residuum
might be gas previously contained in the water, and liberated from
it in consequence of the stronger affinity of that fluid for nitrous
oxide. But the greater part of it, I conjectured to consist of
nitrogene produced in consequence of a complete decomposition of part
of the acid, by the hydrogene. It was in endeavoring to ascertain the
relative purity of nitrous oxide produced at different periods of the
process of the decomposition of nitrate of ammoniac, that I discovered
the true reason of the appearance of residual gas.
I decomposed some pure nitrate of ammoniac in a small glass retort;
and after suffering the first portions to escape with the common air,
I caught the remainder in three separate vessels standing in the same
trough, filled with water that had been long boiled, and which at
the time of the experiment was so warm that I could scarcely bear my
hands in it. The different quantities collected gave the same intense
brilliancy to the flame of a taper.
26 measures of each of them were separately inserted into 3 graduated
cylinders, of nearly the same capacity, over the same boiled water.
As the water cooled, the gas was absorbed by agitation. When the
diminution was complete, the residuum in each cylinder filled, as
nearly as possible, the same space; about two thirds of a measure.
To each of the residuums I added two measures of nitrous gas; they gave
copious red vapor, and after the condensation filled a space rather
less than two measures.
Hence the residual gas contained more oxygene than common air.
I now introduced 26 measures of gas from one of the vessels into a
cylinder filled with unboiled spring water of the same kind.[80] After
the absorption was complete, near two measures remained. These added to
two measures of nitrous air, diminished to 2,5 nearly.
[80] Two measures of air dispelled from this water by boiling, mingled
with 2 of nitrous gas, diminished to 2,4 nearly.
These experiments induced me to believe that the residual gas was not
produced in the decomposition of nitrate of ammoniac, but that it was
wholly liberated from the water.
To ascertain this point with precision, I distilled a small quantity
of the same kind of water, which had been near an hour in ebullition,
into a graduated cylinder containing mercury. To this I introduced
about one third of its bulk, i. e. 12 measures of nitrous oxide, which
had been carefully generated in the mercurial apparatus. After the
absorption, a small globule of gas only remained, which could hardly
have equalled one fourth of a measure. On admitting to this globule a
minute quantity of nitrous gas, an evident diminution took place.
Though this experiment proved that in proportion as the water was free
from air, the residuum was less, and though there was no reason to
suppose that the ebullition and distillation had freed the water from
the whole of the air it had held in solution, still I considered a
decisive experiment wanting to determine whether nitrous oxide was the
only gas produced in the slow decomposition of nitrate of ammoniac, or
whether a minute quantity of oxygene was not likewise evolved.
I received the middle part of the product of a decomposition of nitrate
of ammoniac, under a cylinder filled with dry mercury, and introduced
to it some strong solution of ammoniac. After the white cloud produced
by the combination of the ammoniacal vapor with the nitric acid
suspended in the nitrous oxide, had been completely precipitated, I
introduced a small quantity of nitrous gas. No white vapor was produced.
Now if any gas combinable with nitrous gas had existed in the cylinder,
the quantity of nitrous acid produced, however small, would have
been rendered perceptible by the ammoniacal fumes; for when a minute
globule of common air was admitted into the cylinder, white clouds were
instantly perceptible.
It seems therefore reasonable to conclude,
1. That the residual gas of nitrous oxide, is air previously contained
in the water, (which in no case can be perfectly freed from it by
ebullition), and liberated by the stronger attraction of that fluid for
nitrous oxide.
2. That nitrate of ammoniac, at temperatures below 440°, is
decompounded into pure nitrous oxide, and fluid.
3. That in ascertaining the purity of nitrous oxide from its absorption
by water, corrections ought to be made for the quantity of gas
dispelled from the water. This quantity in common water distilled
under mercury being about ¹/₅₀; in water simply boiled, and used when
hot, about ¹/₃₆; and in common spring water, ¹/₁₂.