From the phænomena mentioned in Res. I. Divis. III.[166] it appears
that the combustible bodies burn in nitrous oxide at certain
temperatures. The experiments in this Division were instituted for the
purpose of investigating the precise nature of these combustions, with
a view of ascertaining exactly the composition of nitrous oxide.
[166] Section 2.
It will be seen hereafter that very high temperatures are required for
the decomposition of nitrous oxide, by most of the combustible bodies,
and that in this process heat and light are produced to a very great
extent. These agents alone are possessed of a considerable power of
action on nitrous oxide; of which it is necessary to give an account,
that we may be able to understand the phænomena in the following
sections.
II. _Conversion of Nitrous Oxide into Nitrous Acid, and a Gas analogous
to Atmospheric Air, by Ignition._
_a._ Dr. Priestley asserts, that nitrous oxide exposed for a certain
time to the action of the electric spark, is rendered immiscible with
water, and capable of diminution with nitrous gas, without suffering
any alteration of volume; and likewise that the same changes are
effected in it by exposure to ignited incombustible bodies.[167]
[167] Vol. ii. pag. 91.
The Dutch chemists state, that the electric spark passed through
nitrous oxide, occasions a small diminution of its volume, and that the
gas remaining is analogous to common air.[168] They conclude that this
change depends on the separation of its constituent parts, oxygene and
nitrogene, from each other.
[168] Journal de Physique, tom. xliii, part ii. pag. 330. They effected
the same change by passing it through a heated tube. Dr. Priestley had
published an account of similar experiments more than two years before.
None of these chemists have suspected the production of nitrous acid in
this process.
_b._ Nitrous oxide undergoes no change whatever from the simple action
of light. I exposed some of it, confined by mercury, for many days to
this agent, often passing through it concentrated rays by means of a
small lens. When examined it appeared, as well as I could estimate, of
the same degree of purity as at the beginning of the experiment.
_c._ A temperature below that of ignition effects no alteration in the
constitution of nitrous oxide. I passed nitrous oxide from a retort
containing decomposing nitrate of ammoniac, through a green glass
tube, strongly heated in an air-furnace, but not suffered to undergo
ignition. The gas, received in a water apparatus exhibited the same
properties as the purest nitrous oxide; some of it absorbed by water,
left a residuum of not quite one thirteenth.
_d._ The action of the electric spark for a long while continued,
converts nitrous oxide into a gas analogous to atmospheric air, and
nitrous acid.
I passed about 150 strong shocks from a small Leyden phial, through 7
ten grain measures of pure nitrous oxide. After this it filled a space
rather less than six measures: the mercury was rendered white on the
top, as if it had been acted on by nitric acid. Six measures of nitrous
gas mingled with the residual gas of the experiment, over mercury
covered by a little water, gave red fumes, and rapid diminution. In
five minutes the volume of the gases nearly equalled ten. Thermometer
in this experiment was 58°.
Electric sparks were passed for an hour and half through 7 ten grain
measures of nitrous oxide over mercury covered with a little red
cabbage juice, previously saturated with nitrous oxide, and rendered
green by an alkali. After the process the gas filled a space equal
to rather more than six measures and half, and the juice was become
of a pale red. The gas was introduced into a small tube filled with
pure water, and agitated; no absorption was perceptible: 7 measures
of nitrous gas added to it gave red fumes, and after six minutes a
diminution to 9¼ nearly. 6½ measures of common air from the garden,
with 7 of nitrous gas, gave exactly 9.
In this experiment it was evident that nitrous oxide was converted into
a gas analogous to atmospheric air, at the same time that an acid was
formed. There could be little doubt but that this was the nitrous acid.
To ascertain it, however, with greater certainty, the electric spark
was passed through 6 measures of nitrous oxide, over a little solution
of green sulphate of iron, confined by mercury. As the process went on,
the color of the solution became rather darker. When the diminution
was complete, a little prussiate of iron was added to the solution. A
precipitate of pale blue prussiate of potash was produced.
_c._ Nitrous oxide was passed from decomposing nitrate of ammoniac,
through a porcelain tube well glazed inside and outside, strongly
ignited in an air-furnace, and communicating with the water apparatus.
The gas collected was rendered opaque by dense red vapor. It appeared
wholly unabsorbable by water. After the precipitation of its vapor, a
candle burnt in it with nearly the same brilliancy as in atmospheric
air. 20 measures of it that had been agitated in water immediately
after its production, mingled with 40 measures of nitrous gas,
diminished to about 47.5; whereas 20 measures that had remained
unagitated for some time after their generation, introduced to the same
quantity of nitrous gas, gave nearly 49. 20 measures of atmospheric
air, with 40 of the same nitrous gas, were condensed to 46.
The water with which the gas had been in contact, was strongly acid. A
little of it poured into a solution of green sulphate of iron, and then
mingled with prussian alkali, produced a green precipitate. Hence the
acid it contained was evidently nitrous.
That no source of error could have existed in this experiment from
fissure in the tube, I proved, by sending water through it whilst
ignited, after the process, from the same retort in which the nitrate
of ammoniac had been decomposed; a few globules of air only were
produced, not equal to one tenth of the volume of the water boiled, and
which were doubtless previously contained in it.
I have repeated this experiment two or three times, with similar
results; whenever the air was agitated in water immediately after its
production, it gave _almost_ the same diminution with nitrous gas as
common air; when, on the contrary, it has been suffered to remain for
some time in contact with the phlogisticated nitrous acid suspended
in it, the condensation has been less with nitrous gas by five or
six hundred parts. Hence I am inclined to believe, that if it were
possible to condense all the nitrous acid formed, immediately after
its generation, so as to prevent it from absorbing oxygene from the
permanent gas, this gas would be found identical with the air of the
atmosphere.
The changes effected by fire on nitrous oxide are not analogous to
those produced by it in other bodies; for the power of this agent
seems generally _uniform_, either in wholly separating the constituent
principles of bodies from each other, or in making them enter into more
intimate union.[169]
[169] On the one hand, it decomposes ammoniac into hydrogene and
nitrogene, whilst on the other, it converts free oxygene and nitrogene
into nitrous acid. It likewise converts nitrous gas into nitrous acid
and nitrogene. Till we are more accurately acquainted with the nature
of heat, light, and electricity, we shall probably be unable to explain
these phænomena.
It is a singular phænomenon, that whilst it condenses one part of the
oxygene and nitrogene of nitrous oxide, in the form of nitrous acid;
it should cause the remainder to expand, in the state of atmospheric
air. Does not this fact afford an inference in favor of the _chemical_
composition of atmospheric air?
III. _Decomposition of Nitrous Oxide by Hydrogene, at the temperature
of Ignition._
In the following experiments on the decomposition of nitrous oxide
by hydrogene, the gases were carefully generated in the mercurial
apparatus, and their purity ascertained by the tests mentioned in
Research I. They were measured in small tubes graduated to grains, and
then transferred into the detonating tube, which was eight tenths of an
inch in diameter, and graduated to ten grain measures.
The space occupied by the gases being noted after the inflammation by
the electric shock, green muriate of iron, and prussiate of potash,
were successively introduced, to ascertain if any nitrous acid had
been formed. The absorption, if any took place, was marked, and the
gases transferred into a narrow grain measure tube, and their bulk and
composition accurately ascertained.
_b._ The hydrogene employed was procured from water by means of zinc
and sulphuric acid. 50 grain measures of it fired by the electric
spark, with 30 grain measures of oxygene containing one eleventh
nitrogene, gave a residuum of about 4. Nitrous gas mingled with those
4, indicated the presence of rather less than 1 of unconsumed oxygene.
In another experiment 23 of it, with 20 of the same oxygene left rather
more than 6 residuum.
The nitrous oxide was apparently pure, for it left a remainder of about
,05 only, when absorbed by common water.
_c._ 30 of hydrogene were fired with 40 of nitrous oxide; the
concussion was very great, and the light given out bright red; no
perceptible quantity of nitrous acid was formed; the residual gas
filled a space equal to 52. No part of it was absorbable by water, it
gave no diminution with nitrous gas, when it was mingled with a little
oxygene, and again acted on by the electric spark, an inflammation and
slight diminution was produced.
_d._ 33 of hydrogene were fired with 35 of nitrous oxide: nitrous acid
was produced in very minute quantity; the gas that remained was not
absorbable by water, and filled a space equal to 37 grains. Nitrous gas
mingled with these, underwent a very slight diminution.
_e._ 46 hydrogene were fired with 46 nitrous oxide. The quantity of
nitrous acid formed was just sufficient to tinge the white prussiate
of potash. The gases filled a space equal to 49, gave no perceptible
diminution with nitrous gas, and did not inflame with oxygene.
_f._ 40 hydrogene were fired with 39 nitrous oxide; no perceptible
quantity of nitrous acid was formed. The residual gas filled a space
equal to 41; was unabsorbable by water, underwent no diminution when
mingled with nitrous gas; or when acted on by the electric spark in
contact with oxygene.
_g._ 20 hydrogene were fired with 64 nitrous oxide; after detonation
the expansion of the gases was greater in this experiment than any of
the preceding ones; dense white fumes were observed in the cylinder,
and a slow contraction of volume took place. After a little green
muriate of iron had been admitted, the gases filled a space equal
to 73: prussiate of potash mingled with the muriate, gave a deeper
blue than in any of the preceding experiments. The residual gas was
unabsorbable by water: 65 of it, mingled with 65 of nitrous gas,
diminished to 93; whilst 65 of common air, with 65 of nitrous gas, gave
84.
_h._ 8 of hydrogene were fired with 54 of nitrous oxide; the same
phænomena as were observed in the last experiment took place; nitrous
acid was formed; after the absorption of which the residual gas filled
a space equal to 55. 50 of this, with an equal quantity of nitrous gas,
diminished to 76. In these processes the temperatures were from 56° to
61°.
These experiments are selected as the most accurate of nearly fifty,
made on the inflammation of different quantities of nitrous oxide and
hydrogene.
As Mr. Keir found muriatic acid in the fluid, produced by the
inflammation of oxygene and hydrogene in closed vessels, in Dr.
Priestley’s experiments, I preserved the residual gas of about 3 cubic
inches of nitrous oxide, that had been detonated at different times
with less than a cubic inch and half of hydrogene; but solution of
nitrate of silver was not clouded when agitated in this gas, nor when
introduced into the detonating tube in which the inflammation had been
made.
From these experiments we learn that nitrous oxide is decomposable at
the heat of ignition, by hydrogene, in a variety of proportions.
When the quantity of hydrogene very little exceeds that of the nitrous
oxide, both of the gates disappear, water is produced, no nitrous acid
is formed, and the volume of nitrogene evolved is rather greater than
that of the nitrous oxide decomposed.
When the quantity of hydrogene is less than that of the nitrous oxide,
water, nitrous acid, oxygene and nitrogene, are generated in different
proportions; one part of the nitrous oxide is most probably wholly
decomposed by the hydrogene, and the other part converted into nitrous
acid and atmospheric air, in consequence of the ignition.
From experiments _c_, _d_, and _e_, the composition of nitrous oxide
may be deduced. In experiment _d_, 39 of nitrous oxide were decomposed
by 40 of hydrogene, and converted into 41 of nitrogene.
Now from _b_ it appears that 40 of hydrogene require for their
condensation about 20.8 of oxygene in volume; so that founding the
estimation upon the quantity of hydrogene consumed, 100 parts of
nitrous oxide would consist nearly of 63.1 of nitrogene, and 36.9 of
oxygene. But 41 of nitrogene weigh 12.4, Res. I. Div. I. Consequently,
deducing the composition of nitrous oxide from the quantity of
nitrogene evolved, 100 parts of it would consist of 63.5 nitrogene, and
36.5 oxygene.
These estimations are very little different from those which may be
deduced from the other experiments, and the coincidence is in favor of
their accuracy.
From the following experiment it appears that the temperature required
for the decomposition of nitrous oxide by hydrogene must be higher
than that which is necessary to produce the inflammation of hydrogene
with oxygene. I introduced into small tubes filled with equal parts of
nitrous oxide and hydrogene, standing on a surface of mercury, iron
wires ignited to different degrees, from the dull red to the vivid
white heat. The gases were always inflamed by the white and vivid
red heats; but never by the dull red heat, though the last uniformly
inflamed mixtures of oxygene and hydrogene, and atmospheric air and
hydrogene.
Dr. Priestley[170] first detonated together nitrous oxide and
hydrogene; his experiment was repeated by the Dutch chemists, who found
that when a small quantity of hydrogene was employed, the nitrous
oxide was partially converted into a gas analogous to common air. Their
estimation of its composition, which is not far removed from the truth,
was founded on this phænomenon.[171]
[170] Vol. ii. pag. 83.
[171] Journal de Physique, tom. xliii. part 2, pag. 331. They supposed
it to consist of about 37,5 oxygene, and 62,5 nitrogene. The nearness
of this account to the truth is singular, when we consider that they
were neither acquainted with the specific gravity of nitrous oxide, nor
with the production of nitrous acid in this experiment.