_a._ The opinions of Priestley[132] and Kirwan,[133] relating to the
causes of the conversion of nitrous gas into nitrous oxide, were
founded on the theory of phlogiston. The first of these philosophers
obtained nitrous oxide by placing nitrous gas in contact with moistened
iron filings, or the alkaline sulphures. The last by exposing it to
sulphurated hydrogene.
[132] Vol. ii. pag. 55.
[133] Phil. Trans. vol. lxxvi. pag. 133.
The Dutch chemists,[134] the latest experimentalists on nitrous oxide,
have supposed that the production of this substance depends upon the
simple abstraction of a portion of the oxygene of nitrous gas. They
obtained nitrous oxide by exposing nitrous gas to muriate of tin, to
copper in solution of ammoniac, and likewise by passing it over heated
sulphur.
[134] Journal de Physique, tom. xliii. 323.
The diminution of volume sustained by nitrous gas during its conversion
into nitrous oxide, has never been accurately ascertained; it has
generally been supposed to be from two thirds to eight tenths.
_b._ Nitrous gas may be converted into nitrous oxide in two modes.
First, by the simple abstraction of a portion of its oxygene, by bodies
possessing a strong affinity for that principle, such as alkaline
sulphites, muriate of tin, and dry sulphures.
Second, by the combination of a body with a portion both of its oxygene
and nitrogene, such as hydrogene, when either in a nascent form, or a
peculiar state of combination.
_c._ Each of these modes will be distinctly treated of; and to prevent
unnecessary repetitions, I shall give an account of the general manner
in which the following experiments on the conversion of nitrous gas
into nitrous oxide, have been conduced.
Nitrous gas, the purity of which has been accurately ascertained by
solution of muriate of iron, is introduced into a graduated jar filled
with dry mercury. If a fluid substance is designed for the conversion
of the gas into nitrous oxide, it is heated, to expel any loosely
combined air which might be liberated during the process; and then
carefully introduced into the jar, by means of a small phial. After
the process is finished, and the diminution accurately noted, the
nitrous oxide formed is absorbed by pure water. If any nitrous gas
remains, it is condensed by solution of muriate of iron; other residual
gases are examined by the common tests. The quantity of nitrous oxide
dissolved by the fluid is determined by a comparative experiment; and
the corrections for temperature and pressure being guessed at, the
conclusions drawn.
If a solid substance is used, rather more nitrous gas than that
designed for the conversion, is introduced into the jar. The substance
is brought in contact with the gas, by being carried under the mercury;
and as a little common air generally adheres to it, a small portion
of the nitrous gas is transferred into a graduated tube, after the
insertion, and its purity ascertained. In other respects the process is
conducted as mentioned above.
II. _Of the conversion of Nitrous gas into Nitrous Oxide, by Alkaline
Sulphites._
The alkaline sulphites, particularly the sulphite of potash, convert
nitrous gas into nitrous oxide, with much greater rapidity than any
other bodies.
At temperature 46°, 16 cubic inches of nitrous gas were converted, in
less than an hour, into 7,8 of nitrous oxide, by about 100 grains of
pulverised sulphite of potash, containing its water of crystalisation.
No sensible increase of temperature was produced during the process,
no water was decomposed, and the quantity of nitrogene remaining after
the experiment, was exactly equal to that previously contained in the
nitrous gas.
The nitrous oxide produced from nitrous gas by sulphite of potash, has
all the properties of that generated from the decomposition of nitrate
of ammoniac. It gives, as will be seen hereafter, the same products by
analysis. Phosphorus, the taper, sulphur, and charcoal, burn in it with
vivid light. It is absorbable by water, and capable of expulsion from
it unaltered, by heat.
Nitrous gas is converted into nitrous oxide by the alkaline sulphites
with the same readiness, whether exposed to the light, or deprived of
its influence.
The solid sulphites act upon nitrous gas much more readily than
their concentrated solutions; they should however always be suffered
to retain their water of crystalisation, or otherwise they attract
moisture from the gas, and render it drier, and in consequence more
condensed than it would otherwise be. In case perfectly dry sulphites
are employed, the gas should be always saturated with moisture after
the experiment, by introducing into the cylinder a drop of water.
The sulphites, after exposure to nitrous gas, are either found wholly,
or partially, converted into sulphates. Consequently the conversion of
nitrous gas into nitrous oxide by these bodies, simply depends on the
abstraction of a portion of its oxygene; the nitrogene and remaining
oxygene assuming a more condensed state of existence.
If we reason from the different specific gravities of nitrous oxide and
nitrous gas, as compared with the diminution of volume of nitrous gas,
during its conversion into nitrous oxide, 100 parts of nitrous gas,
supposing the former estimation of the composition of nitrous oxide
given in Division III, accurate, would consist of 54 oxygene, and 46
nitrogene; which is not far from the true estimation. Or assuming the
composition of nitrous gas, as given in Division IV, it would appear
from the diminution, that 100 parts of nitrous oxide consisted of 38
oxygene, and 62 nitrogene.
III. _Conversion of Nitrous Gas into Nitrous Oxide, by Muriate of Tin,
and dry Sulphures._
_a._ Nitrous gas exposed to dry muriate of tin, is slowly converted
into nitrous oxide: during this process the apparent diminution is
to about one half; but if the products are nicely examined, and the
necessary corrections made, the real diminution of nitrous gas by
muriate of tin, will be the same as by the sulphites; that is, 100
parts of it will be converted into 48 of nitrous oxide.
During this conversion, no water is decomposed, and no nitrogene
evolved. Solution of muriate of tin converts nitrous gas into nitrous
oxide; but with much less rapidity than the solid salt.
_b._ Nitrous gas exposed to dry and perfectly well made sulphures,
particularly such as are produced from crystalised alumn[135] and
charcoal not sufficiently inflammable to burn in the atmosphere, is
converted into nitrous oxide by the simple abstraction of a portion of
its oxygene, and consequently undergoes a diminution of ⁵²/₁₀₀.
It is probable, that all the bodies having strong affinity for oxygene
will, at certain temperatures, convert nitrous gas into nitrous oxide.
Priestley, and the Dutch chemists, effected the change by heated
sulphur. Perhaps nitrous gas sent through a tube heated, but not
ignited, with phosphorus, would be converted into nitrous oxide.
[135] That is, alumn containing sulphate of potash.