_a._ When nitric acid is combined with muriatic acid, or sulphuric
acid,[144] the quantities of nitrous oxide produced from its
decomposition by tin, zinc, and iron, are rather increased than
diminished. The nitrous oxide obtained from these solutions is,
however, never sufficiently pure for physiological experiments. It is
always mingled with either nitrous gas, nitrogene, or hydrogene, and
sometimes with all of them.
[144] As was discovered by Priestley, and the Dutch Chemists.
_b._ From the solutions of bismuth, nickel, lead, and copper, in
diluted nitric acid, I have never obtained any perceptible quantity
of nitrous oxide: the gas produced is nitrous, mingled with different
portions of nitrogene. Antimony and mercury, during their solution in
aqua regia, give out only nitrous gas.
Probably none of the metallic bodies, except those that decompose
water at temperatures below ignition, will generate nitrous oxide from
nitric acid. On cobalt and manganese I have never had an opportunity of
experimenting: manganese will probably produce nitrous oxide.
_c._ During the solution of vegetable matters[145] in nitric acid, by
heat, very minute portions of nitrous oxide are sometimes produced,
always however mingled with large quantities of nitrous gas, and
carbonic acid.
[145] Such as the leaves, bark, and wood, of trees.
When nitric acid is decompounded by ether, fixed oils, volatile oils,
or alcohol, towards the end of the process small quantities of nitrous
oxide are produced, and sometimes sufficiently pure to support the
flame of the taper.[146]
_d._ When green oxide of iron is dissolved in nitric acid, nitrous
oxide is produced, mingled with nitrogene and nitrous gas.
_e._ During the conversion of green sulphate, or green muriate of iron
into red, by the decomposition of dilute nitric acid, nitrous oxide is
formed, mingled with different proportions of nitrous gas and nitrogene.
_f._ When solution of green nitrate of iron is heated, a part of the
acid is decomposed, red oxide is precipitated, red nitrate formed, and
impure nitrous oxide evolved.
_g._ When iron is introduced into a solution of nitrate of copper, the
copper is precipitated in its metallic state, whilst nitrous oxide,
mingled with small portions of nitrogene, is produced.[147]
[146] As I have observed after Priestley.
[147] As was discovered by Priestly.
Both zinc and tin precipitate copper in its metallic form from
solution in the nitric acid. During these precipitations, certain
quantities of nitrous oxide are generated, mingled however with larger
quantities of nitrogene than that produced from decomposition by iron.
In all these processes ammoniac is formed, and water consequently
decomposed.
The decomposition of water and nitric acid, during the precipitation
of copper from solution of nitrate of copper, by tin, zinc, and iron,
depends upon the strong affinity of those metals for oxygene, and their
powers of combining with a larger quantity of it than copper.
X. _Decomposition of Aqua Regia by Platina, and evolution of a Gas
analogous to Oxygenated Muriatic Acid, and Nitrogene._
_a._ De la Metherie, in his essay on different airs, has asserted that
the gas produced by the solution of platina in nitro-muriatic acid, is
identical with the dephlogisticated nitrous gas of Priestly. He calls
it nitrous gas with excess of pure air, and affirms that it diminishes,
both with nitrous gas and common air.
_b._ I introduced into a vessel containing 30 grains of platina,
2050 grains of aqua regia, composed of equal parts, by weight, of
concentrated nitric acid of 1,43, and muriatic acid of 1,16. At the
common temperature, that is, 49°, no action between the acid and
platina appeared to take place. On the application of the heat of a
spirit lamp, the solution gradually became yellow red, and gas was
given out with rapidity. Some of this gas received in a jar filled
with warm water, appeared of a bright yellow color. On agitation,
the greater part of it was absorbed by the water, and the remainder
extinguished flame. When it was received over mercury, it acted upon it
with great rapidity, and formed on the surface a white crust.
As the process of solution advanced, the color of the acid changed
to dark red, at the same time that the production of gas was much
increased; more than 40 cubic inches were soon collected in the water
apparatus.
Different portions of the gas were examined, it exhibited the following
properties:
1. Its color was orange red,[148] and its smell exactly
resembled that of oxygenated muriatic acid.
2. When agitated in boiled water, it was rapidly absorbed,
leaving a residuum of rather more than one twelfth.
3. The taper burnt in it with increased brilliancy,
the flame being long, and deep red at the edges.
4. Iron introduced into it ignited, burnt with a dull
red light.
5. Green vegetables exposed to it were instantly
rendered white.
6. It underwent no diminution, mingled with
atmospheric air.
7. When mingled with nitrous gas, it gave dense red
vapor, and rapid diminution.
[148] This deep color depended, in some measure, upon the
nitro-muriatic vapor suspended in it. I have since observed that it is
more intense in proportion as the heat employed for the production of
the gas has been stronger. The natural color of the peculiar gas is
deep yellow.
_c._ From the exhibition of these properties, it was evident that the
gas produced during the solution of platina in aqua regia, chiefly
consisted of oxygenated muriatic acid, or of a gas highly analogous to
it. It was, however, difficult to conceive how a body, by combining
with a portion of the oxygene of nitro-muriatic acid, could produce
from it oxygenated muriatic acid, apparently mingled with very small
portions of any other gas.
_d._ To ascertain whether any permanent gas was produced during the
ebullition of aqua regia, of the same composition as that used for the
solution of the platina; I kept a large quantity of it boiling for some
time, in communication with the water apparatus; the gas generated
appeared to be wholly nitro-muriatic, and was absorbed as fast as
produced, by the water.
_e._ To determine whether any nitrous oxide was mingled with the
peculiar gas, as well as the nature and quantity of the unabsorbable
gas, nitrous gas was gradually added to 21 cubic inches of the gas
produced from a new solution, till the diminution was complete: the gas
remaining equalled 2,3 cubic inches; it was unabsorbable by water, and
extinguished flame.
In another experiment, when the last portions of gas from a solution
were carefully received in water previously boiled, 12 cubic inches
agitated in water left a residuum of 1.3; whilst the same quantity
decomposed by nitrous gas, containing,02 nitrogene, left about 1.5.
Hence it appeared that the aëriform products of the solution consisted
of the peculiar gas analogous to oxygenated muriatic acid, and of a
small quantity of nitrogene.
_f._ Consequently a portion of the nitric acid of the aqua regia had
been decomposed; but if it had given oxygene both to the platina and
muriatic acid, the quantity of nitrogene evolved ought to have been
much more considerable.
_g._ To ascertain if any water had been decomposed, and the nitrogene
condensed in the solution by its hydrogene, to form ammoniac, I
saturated a solution with lime, and heated it, but no ammoniacal smell
was perceived.
_h._ To determine if any nitrogene had entered into chemical
combination with muriatic acid and oxygene, so as to form an aëriform
triple compound, analogous in its properties to oxygenated muriatic
acid, I exposed some of the gas to mercury, expecting that this
substance, by combining with its oxygene, would effect a complete
decomposition; and this was actually the case: for the gas was at
first rapidly diminished, and the mercury became oxydated; its volume,
however, soon increased; and the residual gas appeared to be nitrous,
mingled with much nitrogene. The exact proportions of each, from an
accident, I could not determine.
This experiment was inconclusive, because the nitro-muriatic acid
suspended in the peculiar gas, from which it can probably be never
perfectly freed, acted in common with it upon the mercury, and produced
nitrous gas: and this nitrous gas, at the moment of its production,
formed nitrous acid by combining with the oxygene of the peculiar
gas; and the nitrous acid generated[149] was again decomposed by the
mercury; and hence nitrous gas evolved, and possibly some nitrogene.
[149] The decomposition of aëriform nitrous acid by mercury, was first
noted by Priestley; vol. iii. pag. 101. This decomposition I have often
had occasion to observe. In reading Humbolt’s paper on eudiometry,
Annales de Chimie, xxviii, pag. 150, I was not a little surprised to
find that he takes no notice of this fact. He seems to suppose that
nitrous acid can remain aëriform, and even be condensed, in contact
with mercury, without alteration. He says, “In mingling 100 parts of
atmospheric air with 100 of nitrous air, the air immediately became
red, but all the acid produced remained aëriform; and after eighteen
hours some _drops_ only of acid were formed, which _swam_ upon the
mercury.”
_i._ Peculiar circumstances prevented me at this time from completely
investigating the subject. It remains doubtful whether the gas consists
simply of highly oxygenated muriatic acid and nitrogene,[150] produced
by the decomposition of nitric acid from the coalescing affinities of
platina and muriatic acid for oxygene; or whether it is composed of a
_peculiar_ gas, analogous to oxygenated muriatic acid, and nitrogene,
generated from some unknown affinities.[151]
[150] Lavoisier has said concerning aqua regia, “In solutions of metals
in this acid, as in all other acids, the metals are first oxydated,
by attracting a part of the oxygene from the compound radical. This
occasions the disengagement of a particular species of gas not hitherto
described, which may be called nitro-muriatic gas. It has a very
disagreeable smell, and is fatal to animal life when respired; it
attacks iron, and causes it to rust; it is absorbed in considerable
quantities by water.” Elem. Eng. 237.
[151] I have no doubt but that the gas procured from the solution of
gold in aqua regia, is analogous to that produced from platina.
Some very uncommon circumstances are attendant on the solution of
platina:
1st. The immense quantity of acid required for the solution of a minute
quantity of platina.
2d. The great quantity of gas produced during the solution of this
minute quantity.
3d. The intense red color of the solution, and its perfectly acid
properties after it ceases to act upon the metal.
XI. _On the action of the Electric Spark on a mixture of Nitrogene and
Nitrous Gas._
Thinking it possible that nitrous gas and nitrogene might be made to
combine by the action of the electric spark, so as to form nitrous
oxide, I introduced 20 grain measures of each of them into a small
detonating tube, graduated to grains, standing over mercury, and
containing a very small quantity of cabbage juice rendered green by an
alkali. After electric sparks had been passed through the gases for an
hour and half, they were diminished to about 32, and the cabbage juice
was slightly reddened. On introducing about 10 measures of hydrogene,
and passing the electric spark through the whole, no inflammation or
diminution was perceptible. Hence the condensation most probably arose
wholly from the formation of nitrous acid,[152] by the more intimate
union of the oxygene of nitrous gas with some of its nitrogene, as in
the experiments of Priestley.
[152] For if nitrous oxide had been formed, it would have been
decomposed by the hydrogene.
As the nascent nitrogene, in the decomposition of nitrate of ammoniac,
combines with a portion of oxygene and nitrogene, to form nitrous
oxide; it is probable that nitrous oxide may be produced during the
passage of nitrous gas and ammoniac through a heated tube.