_a._ When nitrous gas, is exposed to wetted iron filings, a diminution
of its volume slowly takes place; and after a certain time, it is found
converted into nitrous oxide.
In this process ammoniac[138] is formed, and the iron partially
oxydated.
[138] As was first observed by Priestley and Austin, and as I have
proved by many experiments.
The water in contact with the iron is decomposed by the combination of
its oxygene with that substance, and of its hydrogene with a portion
of the oxygene and nitrogene of the nitrous gas, to form water and
ammoniac.
That the iron is not oxydated at the expence of the oxygene of the
nitrous gas, appears very probable from the analogy between this
process, and the mutual decomposition of nitrous gas and sulphurated
hydrogene. Besides, dry iron filings effect no change whatever in
nitrous gas, at common temperatures.
I have generally found about 12 of nitrous gas converted into 5 of
nitrous oxide in this process; which is not very different from the
diminution by sulphurated hydrogene. It takes place equally well in
light and darkness; but more rapidly in warm weather than in cold.
_b._ Nitrous gas exposed to a large surface of zinc, in contact with
water, is slowly converted into nitrous oxide; at the same time that
ammoniac is generated, and white oxide of zinc formed. This process
appears to depend, like the last, upon the decomposition of water by
the affinities of part of the oxygene and nitrogene of nitrous gas,
for its hydrogene, to form ammoniac and water; and by that of zinc
for its oxygene. Zinc placed in contact with water, and confined by
mercury,[139] decomposes it at the common temperature. Zinc, when
perfectly dry, does not in the slightest degree act upon nitrous gas.
[139] As I have found by experiment.
I have not been able to determine exactly the diminution of volume of
nitrous gas, during its conversion into nitrous oxide by zinc. In one
experiment 20 measures of nitrous gas, containing about,03 nitrogene,
were diminished to 9, after an exposure of eight days to wetted zinc;
but from an accident, I was not able to ascertain the exact quantity of
nitrous oxide formed.
_c._ It is probable that most of the imperfect metals will be found
capable of oxydation, by the decomposition of water, when its
hydrogene is attracted by the oxygene and nitrogene of nitrous gas.
I have this day (April 14, 1800), examined two portions of nitrous
gas, one of which had been exposed to copper filings, and the other to
powder of tin, for twenty-three days.
The gas that had been exposed to copper was diminished nearly two
fifths. The taper burnt in it with an enlarged flame, blue at the
edges. Hence it evidently contained nitrous oxide.
The nitrous gas in contact with tin had undergone a diminution of one
fourth only, and did not support flame.
VI. _Miscellaneous Observations on the conversion of Nitrous Gas into
Nitrous Oxide._
_a._ Dr. Priestley found nitrous gas exposed to a mixture of iron
filings and sulphur, with water, converted after a certain time, into
nitrous oxide. Sulphurated hydrogene is always produced during the
combination of iron and sulphur, when they are in contact with water;
and by the hydrogene of this in the nascent state, the nitrous gas is
most probably decomposed.
_b._ Green oxide of iron moistened with water, exposed to nitrous gas,
slowly gains an orange tinge, whilst the gas is diminished. Most likely
it is converted into nitrous oxide; but this I have not ascertained.
_c._ I exposed nitrous gas, to the following bodies over mercury
for many days, without any diminution, or apparent change in its
properties. Alcohol, saccharine matter, hydrocarbonate, sulphureous
acid, and phosphorus.
_d._ Crystalised sulphate, and muriate of iron, absorb a small quantity
of nitrous gas, and become dark colored on the outside; but after this
absorption, (which probably depends on their water of crystalisation,)
has taken place, no change is effected in the gas remaining.
_e._ The power of iron to decompose water being much increased by
increase of temperature, nitrous gas is converted into nitrous oxide
much more rapidly when placed in contact with a surface of heated
iron, than when exposed to it at common temperatures. During the
decomposition of nitrous gas in this way, ammoniac[140] is formed.
_f._ The curious experiments of Rouppe,[141] on the absorption of gases
by charcoal, compared with the phænomena noticed in this Division,
render it probable that hydrogene in a state of loose combination with
charcoal, will be found to convert nitrous gas into nitrous oxide.
[140] As was observed by Milner. Nitrous gas passed over heated zinc,
or tin, I doubt not will be found converted into nitrous oxide.
[141] Annales de Chimie, xxxii. p. 3.
VII. _Recapitulation of conclusions concerning the conversion of
Nitrous Gas into Nitrous Oxide._
_a._ Certain bodies having a strong affinity for oxygene, as the
sulphites, dry sulphures, muriate of tin, &c. convert nitrous gas into
nitrous oxide, by simply attracting a portion of its oxygene; whilst
the remaining oxygene enters into combination with the nitrogene, and
they assume a more condensed state of existence.
_b._ Nitrous gas is converted into nitrous oxide by hydrogene, in a
peculiar state of existence, as in sulphurated hydrogene; and that by
a series of very complex affinities. Both oxygene and nitrogene are
attracted from the nitrous gas by the hydrogene, in such proportions
as to form water and ammoniac, whilst the remaining oxygene and
nitrogene[142] assume the form of nitrous oxide.
[142] The decomposition and recomposition of water, in this process,
are analogous to some of the phænomena observed by the ingenious Mrs.
Fulhame.
_c._ Nitrous gas placed in contact with bodies, such as iron and
zinc decomposing water, is converted into nitrous oxide, at the same
time that ammoniac is formed. It is difficult to ascertain the exact
rationale of this process. For either the nascent hydrogene produced by
the decomposition of the water by the metallic substance may combine
with portions of both the oxygene and nitrogene of the nitrous gas; and
thus by forming water and ammoniac, convert it into nitrous oxide. Or
the metallic substance may attract at the same time oxygene from the
water and nitrous gas, whilst the nascent hydrogene of the water seizes
upon a portion of the nitrogene of the nitrous gas to form ammoniac.
The degree of diminution, and the analogy between this process and the
decomposition of nitrous gas by sulphurated hydrogene, render the first
opinion most probable.
VIII. _The production of Nitrous Oxide during the oxydation of Tin,
Zinc, and Iron, in Nitric Acid._
_a._ Dr. Priestley discovered, that during the solution of tin, zinc,
and iron, in nitric acid, certain portions of nitrous oxide were
produced, mingled with quantities of nitrous gas, and nitrogene,
varying in proportion as the acid employed was more or less
concentrated.
It has long been known that ammoniac is formed during the solution of
tin, zinc, and iron, in diluted nitric acid. Consequently, in these
processes water is decomposed.
I had designed to investigate minutely these phænomena, so as to
ascertain the quantities of water and acid decompounded, and of the new
products generated. But after going through some experiments on the
oxydation of tin without gaining conclusive results, the labor, and
sacrifice of time they demanded, obliged me to desist from pursuing the
subject, till I had completed more important investigations.
I shall detail the few observations which have occurred to me, relating
to the production of nitrous oxide from metallic solutions.
_b._ When tin is dissolved in concentrated nitric acid, such as of
1.4, nitrous oxide is produced, mingled with generally more than twice
its bulk of nitrous gas. In this process but little free nitrogene is
evolved, and the tin is chiefly precipitated in the form of a white
powder. If the solution, after the generation of these products, is
saturated with lime, and heated, the ammoniacal smell is distinct.
When nitric acid of specific gravity 1.24, is made to act upon tin;
in the beginning of the process, nearly equal parts of nitrous gas
and nitrous oxide are produced; as it advances, the proportion of
nitrous oxide to the nitrous gas increases: the largest quantity of
nitrous oxide that I have found in the gas procured from tin is ¾, the
remainder being nitrous gas and nitrogene.
When tin is oxydated in an acid of less specific gravity than 1.09, the
quantities of gas disengaged are very small, and consist of nitrogene,
mingled with minute portions of nitrous oxide, and nitrous gas.
Whenever I have saturated solutions of tin in nitric acid of different
specific gravities, with lime, and afterwards heated them, the
ammoniacal smell has been uniformly perceptible, and generally most
distinct when diluted acids have been employed.
_c._ When zinc is dissolved in nitric acid, whatever is its specific
gravity, certain quantities of nitrous oxide are produced.
Nitric acids of greater specific gravity than 1.2, act upon zinc with
great rapidity, and great increase of temperature. The gases disengaged
from these solutions consist of nitrous gas, nitrous oxide, and
nitrogene; the nitrous oxide rarely equals one third of the whole.
When nitric acid of 1,104 is made to dissolve zinc, the gas obtained in
the middle of the process consists chiefly of nitrous oxide. From such
a solution I obtained gas which gave a residuum of one sixth only when
absorbed by water. The taper burnt in it with a brilliant flame, and
sulphur with a vivid rose-colored light.
100 grains of granulated zinc, during their solution in 300 grains
of nitric acid, of 1,43, diluted with 14 times its weight of water,
produced 26 cubic inches of gas. Of this gas ⁷/₃₆ were nitrous, ¹⁷/₃₆36
nitrous oxide, and the remainder nitrogene. The solution saturated with
lime and heated, gave a distinct smell of ammoniac.
_d._ During the solution of iron in concentrated nitric acid, the gas
given out is chiefly nitrous; it is however generally mingled with
minute quantities of nitrous oxide. When very dilute nitric acids
are made to act upon iron, by the assistance of heat, nitrous oxide
is produced in considerable quantities, mingled with nitrous gas
and nitrogene; the proportions of which are smaller as the process
advances.[143] The fluid remaining after the oxydation and solution of
iron in nitric acid, always contains ammoniac.
[143] From one of Dr. Priestley’s experiments, it appears that
hydrogene gas is sometimes disengaged during the solution of iron in
very dilute nitric acid by heat. This phænomenon has never occurred to
me.
_e._ As during the solution of tin, zinc, and iron, in nitric acid, the
quantity of acid is diminished in proportion as the process advances,
it is reasonable to suppose that the relative quantities of the gases
evolved are perpetually varying. In the beginning of a dissolution,
the nitrous gas generally predominates, in the middle nitrous oxide,
and at the end nitrogene.
_f._ During the generation of nitrous gas, nitrous oxide, and ammoniac,
from the decomposition of solution of nitric acid in water, by tin,
zinc, and iron, very complex attractions must exist between the
constituents of the substances employed. The acid and the water are
decomposed at the same time, and in proportions different as the
solution is more concentrated, by the combination of their oxygene with
the metallic body.
The nitrous gas is produced by the combination of the metal with
³²/₁₀₀ of the oxygene of the acid. The nitrous oxide is most probably
generated by the decomposition of a portion of the nitrous gas
disengaged, by the nascent hydrogene of the water decompounded; some
of it may be possibly formed from a more complete decomposition of the
acid.
The production of ammoniac may arise, probably from two causes; from
the decomposition of the nitrous gas by the combination of the nascent
hydrogene of the water, with portions of its oxygene and nitrogene at
the same time; and from the union of hydrogene with nascent nitrogene
liberated in consequence of a complete decomposition of part of the
acid.