In agitating nitrous gas over spring water, the diminution rarely
amounts to more than one thirtieth, the volume of water being taken as
unity. I at first suspected that this great differcnce in the quantity
of gas absorbed by spring water, and pure water, depended on carbonic
acid contained in the last, diminishing the attraction of it for
nitrous gas: but by long boiling a quantity of spring water confined
by mercury, I obtained from it about one twentieth of its bulk of air,
which gave nearly the same diminution with nitrous gas, as atmospheric
air.
This fact induced me to refer the difference of diminution to the
decomposition of the atmospheric air held in solution by the water,
the oxygene of which I supposed to be converted into nitric acid, by
the nitrous gas, whilst the nitrogene was liberated; and hence the
increased residuum.
_a._ I exposed to pure water, that is, water procured by distillation
under mercury, nitrous gas, containing a known quantity of nitrogene.
After the absorption was complete, I found the same quantity of
nitrogene in the residuum, as was contained in a volume of gas equal to
the whole quantity employed.
_b._ Spring water boiled for some hours, and suffered to cool under
mercury, absorbed a quantity of nitrous gas equal to one thirteenth of
its bulk; which is not much less than that absorbed by pure water.
_c._ I exposed to spring water, 10 measures of nitrous gas; the
composition of which had been accurately ascertained; the diminution
was one twenty-eighth, the volume of water being taken as unity. On
placing the residuum in contact with solution of sulphate of iron,
the nitrogene remaining was nearly one twentieth more than had been
contained by the gas before its exposure to water.
_d._ Distilled water was saturated with common air, by being agitated
for some time in the atmosphere. Nitrous gas placed in contact with
this water, underwent a diminution of ¹/₁₈; the volume of water being
unity. The gas remaining after the absorption contained about one
twenty-seventh nitrogene more than before.
_e._ Nitrous gas exposed to water combined with about one fourth of its
volume of carbonic acid, diminished to ¹/₃₂[112] nearly. The remainder
contained little or no superabundant nitrogene.
[112] The water still being unity.
From these observations it appears, that the different degrees of
diminution of nitrous gas by different kinds of water, may depend upon
various causes.
1. Less nitrous gas will be absorbed by water holding in solution
earthy salts, than by pure water; and in this case the diminution of
the attraction of water for nitrous gas will probably be in the ratio
of the quantities of salt combined with it. _a._ _b._
2. The apparent diminution of nitrous gas in water, holding in solution
atmospheric air, will be less than in pure water, though the absolute
diminution will be greater; for the same portion will be absorbed,
whilst another portion is combined with the oxygene of the atmospheric
air contained in the water; and from the disengagement of the nitrogene
of this air, arises an increased residuum. _c._ _d._
3. Probably in waters containing nitrogene, hydrogene, and other gases,
absorbable only to a slight extent, the apparent diminution will be
less, on account of the disengagement of those gases from the water, by
the stronger affinity of nitrous gas for that fluid.
4. In water containing carbonic acid, and probably some other acid
gases, the diminution will be small in proportion to the quantity of
gas contained in the water: the affinity of this fluid for nitrous gas
being diminished by its greater affinity for the substance combined
with it. _e._
The different diminution of nitrous gas when agitated in different
kinds of water, has been long observed by experimenters on the
constituent parts of the atmosphere, and various solutions have been
given of the phænomenon; the most singular is that of Humbolt.[113] He
supposes that the apparent diminution of nitrous gas is less in spring
water than distilled water, on account of the decomposition of the
carbonate of lime contained in the spring water, by the nitrous acid
formed from the contact of nitrous gas with the water; the carbonic
acid disengaged from this decomposition increasing the residuum.
[113] He says “100 parties de gaz nitreux, (à 0.14 d’azote) secouées
avec l’eau distillée, récemment cuite, diminuent en volume de 0.11, ou
0.12. Ce même gaz, en contact avec l’eau de puits, ne perd que 0.02. La
cause de cette différence de 0.9, ou 0.10, ne doit pas être attribuée
ni à l’impurité de l’air atmosphérique, contenu dans les interstices
de l’eau, ni à la décomposition de cette eau même. Elle n’est
qu’apparente; car l’acide nitrique, qui se forme par le contact du gaz
nitreux avec l’eau de puits, en décompose le carbonate de chaux. Il se
dégage de l’acide carbonique, qui, en augmentant le volume du residu,
rend l’absorption du gaz nitreux moins sensible. Pour déterminer la
quantité de cet acide carbonique, je lavai le résidu avec de l’eau de
chaux. Dans un grand nombre d’expériences, le volume diminua de 0.09,
ou 0.07. Il faut en conduire que l’eau de puits absorbe réellement 9 +
2, ou 7 + 2 parties de gas nitreux, c’est-à-dire, à peu-près la même
quantité que l’eau distillée.”
Annales De Chimie, xxviii. pag. 154.
This opinion may be confuted without even reference to my
observations. It is, indeed, altogether unworthy of a philosopher,
generally acute and ingenious. He seems to have forgotten that carbonic
acid is absorbable by water.
VII. _Of the absorption of Nitrous Gas, by solution of pale green
Sulphate of Iron._
_a._ The discovery of the exact difference between the sulphates of
iron, is owing to Proust.[114] According to the ingenious researches of
this chemist, there exist two varieties of sulphate of iron, the green
and the red. The oxide in the green sulphate contains ²⁷/₁₀₀ oxygen.
This salt, when pure, is insoluble in spirit of wine; its solution in
water is of a pale green color; it is not altered by the gallic acid,
and affords a white precipitate with alkaline prussiates.
[114] Nicholson’s Phil. Jour. No. 1, p. 453.
The red sulphate of iron is soluble in alcohol and uncrystalizable; its
oxide contains ⁴⁸/₁₀₀ oxygene. It forms a black precipitate with the
gallic acid, and with the alkaline prussiates, a blue one.
The common sulphates of iron generally consist of combinations of these
two varieties in different proportions.
The green sulphate may be converted into the red by oxygenated muriatic
acid or nitric acid. The common sulphate may be converted into green
sulphate, by agitation in contact with sulphurated hydrogene.
The green sulphate has a strong affinity for oxygene, it attracts it
from the atmosphere, from oxygenated marine acid, and nitric acid. The
alkalies precipitate from it a pale green oxide, which if exposed to
the atmosphere, rapidly becomes yellow red.
The red sulphate of iron has no affinity for oxygene, and when
decomposed by the alkalies, gives a red precipitate, which undergoes no
alteration when exposed to the atmosphere.[115]
[115] I have been able to make these observations on the sulphates of
iron, most of them after Proust.
_b._ The absorption of nitrous gas by a solution of sulphate of iron,
was long ago discovered by Priestley. During this absorption, he
remarked a change of color in the solution, analogous to that produced
by the mixture of it with nitric acid.
This chemical fact has been lately applied by Humbolt, to the discovery
of the nitrogene generally mingled with nitrous gas.
Vauquelin and Humbolt have published a memoir, on the causes of the
absorption[116] of nitrous gas by solution of sulphate of iron. They
saturated an ounce and half of sulphate of iron in solution, with 180
cubic inches of nitrous gas.
[116] Annales de Chimie, vol. xxviii. pag. 182.
Thus impregnated it strongly reddened tincture of turnsoyle; when
mingled with sulphuric acid, gave nitric acid vapor; and saturated with
potash, ammoniacal vapor.
By analysis, it produced as much ammoniac as that contained in 4 grains
of ammoniacal muriate, and a quantity of nitric acid equal to that
existing in 17 grains of nitre. Hence they concluded, that the nitrous
gas and a portion of the water of the solution, had mutually decomposed
each other; the oxygene of the water combining with the oxygene and a
portion of the nitrogene of nitrous gas to form nitric acid; and its
hydrogene uniting with the remaining nitrogene, to generate ammoniac.
They have taken no notice of the nature of the sulphate of iron
employed, which was most probably the common or mixed sulphate; nor of
the attraction of the oxide of iron in this substance for oxygene.
_c._ Before I was acquainted with the observations of Proust, the
common facts relating to the oxygenation of vitriol of iron induced
me to suppose, that the attraction of this substance for oxygene was
in some way connected with the process of absorption. The comparison
of the experiments of Humbolt and Vauquelin, with the observations of
Proust, enabled me to discover the true nature of the process.
I procured a solution of red sulphate of iron, by passing oxygenated
muriatic acid through a solution of common sulphate of iron, till it
gave only a red precipitate, when mingled with caustic potash. To
nitrous gas confined by mercury, a small quantity of this solution was
introduced. On agitation, its color altered to muddy green; but the
absorption that took place was extremely trifling: in half an hour it
did not amount to,2, the volume of the solution being unity, when it
had nearly regained the yellow color.
I now obtained a solution of green sulphate of iron, by dissolving iron
filings in diluted sulphuric acid. The solution was agitated in contact
with sulphurated hydrogene, and afterwards boiled; when it gave a white
precipitate with prussiate of potash.
A small quantity of this solution agitated in nitrous gas, quickly
became of an olive brown, and the gas was diminished with great
rapidity; in two minutes, a quantity equal to four times the volume of
the solution, had been absorbed.
These facts convinced me that the solubility of nitrous gas in common
sulphate of iron, chiefly depended upon the pale green sulphate
contained by it; and that the attraction of one of the constituents of
this substance, the green oxide of iron, for oxygene, was one of the
causes of the phænomenon.
_d._ Green sulphate of iron rapidly decomposes nitric acid. It was
consequently difficult to conceive how any affinities existing between
nitrous gas, water, and green sulphate of iron, could produce the
nitric acid found in the experiments of Vauquelin and Humbolt.
To ascertain if the presence of a great quantity of water destroyed the
power of green sulphate of iron to decompose nitric acid, I introduced
into a cubic inch of solution of green sulphate of iron, two drops of
concentrated nitric acid.
The solution assumed a very light olive color; prussiate of potash
mingled with a little of it, gave a dark green precipitate. Hence
the nitric acid had been evidently decomposed. As no nitrous gas was
given out, which is always the case when nitric acid is poured on
crystalised sulphate of iron, I suspected that a compleat decomposition
of the acid had taken place; but when the solution was heated, a few
minute globules of gas were liberated, and it gradually became slightly
clouded.
Having often remarked that no precipitation is ever produced during the
conversion of green sulphate of iron into red, by oxygenated muriatic
acid, or concentrated nitric acid, I could refer the cloudiness to no
other cause than to the formation of ammoniac.
To ascertain if this substance had been produced, a quantity of slacked
caustic lime was thrown into the solution. On the application of heat,
the ammoniacal smell was distinctly perceptible, and the vapor held
over orange nitrous acid, gave dense white fumes.
_e._ When I considered this fact of the decomposition of nitric acid
and water by the solution of green sulphate of iron, and the change
of color effected in it by the absorption of nitrous gas, exactly
analogous to that produced by the decomposition of nitric acid; I
was induced to believe that the nitric acid found in the analysis of
Vauquelin and Humbolt, had been formed by the combination of some
of the nitrous gas thrown into the solution with the oxygene of the
atmosphere: and that the absorbability of nitrous gas, by solution of
green sulphate of iron, was owing to a decomposition produced by the
combination of its oxygene with the green oxide of iron, and of its
nitrogene with the hydrogene disengaged from water, decompounded at the
same time.
To ascertain this, I procured a quantity of nitrous gas: it was
suffered to remain in contact with water for some hours after its
production. Transferred to the mercurial apparatus, it gave no
white vapor when placed in contact with solution of ammoniac; and
consequently held no nitric acid in solution.
Into a graduated jar filled with mercury, a cubic inch of concentrated
solution of pure green sulphate of iron was introduced, and 7 cubic
inches of nitrous gas admitted to it. The solution immediately became
dark olive at the edges, and on agitation this color was diffused
through it. In 3 minutes, when near 5¾ cubic inches had been absorbed,
the diminution ceased. The solution was now of a bright olive brown,
and transparent at the edges. After it had rested for a quarter of an
hour, no farther absorption was observed; the color was the same, and
no precipitation could be perceived. A little of it was thrown into a
small glass tube, under the mercury, and examined in the atmosphere.
Its taste was rather more astringent than that of solution of green
sulphate; it did not at all alter the color of red cabbage juice. When
a little of it was poured on the mercury, it soon lost its color, its
taste became acid, and it quickly reddened cabbage juice, even rendered
green by an alkali.
To the solution remaining in the mercurial jar, a small quantity of
prussiate of potash was introduced, to ascertain if any red sulphate of
iron had been formed; but instead of the production of either a blue,
or a white precipitate, the whole of the solution became opaque, and
chocolate colored.
Surprised at this appearance, I was at first induced to suppose,
that the ammoniac formed by the nitrogene of the nitrous gas and the
hydrogene of the water, had been sufficient to precipitate from the
sulphuric acid, the red oxide of iron produced, and that the color of
the mixture was owing to this precipitation. To dissolve any uncombined
oxide that might exist in the solution, I added a very minute quantity
of diluted sulphuric acid; but little alteration of color was produced.
Hence, evidently, no red oxide had been formed.
This unexpected result obliged me to theorise a second time,
by supposing that nitrate of ammoniac had been produced, which
by combining with the white prussiate of iron, generated a new
combination. But on mingling together green sulphate of iron, prussiate
of potash, and nitrate of ammoniac in the atmosphere, the mixture
remained perfectly white.
To ascertain if any nitric acid existed, combined with any of the
bases, in the impregnated solution, I introduced into it an equal bulk
of diluted sulphuric acid: it became rather paler; but no green or blue
tinge was produced.
That the prussic acid had not been decomposed, was evident from the
bright green produced, when less than a grain of dilute nitric acid was
admitted into the solution.
_f._ From these experiments it was evident, that no red sulphate of
iron, or nitric acid, and consequently no ammoniac, had been produced
after the absorption of nitrous gas by green sulphate of iron. And when
I compared them with the observations of Priestley, who had expelled
by heat a minute quantity of nitrous gas from an impregnated solution
of common sulphate of iron, and who found common air phlogisticated by
standing in contact with it, I began to suspect that nitrous gas was
simply dissolved in the solution, without undergoing decomposition.
_g._ To determine more accurately the nature of the process, I
introduced into a mercurial cylinder 410 grains of solution of green
sulphate of iron, occupying a space nearly equal to a cubic inch and
quarter; it was saturated with nitrous gas, by absorbing 8 cubic
inches. This saturated solution exhibited the same appearance as
the last; and after remaining near an hour untouched, had evidently
deposited no oxide of iron, nor gained any acid properties.
Into a small mattrass filled with mercury, having a tight stopper
with a curved tube adapted to it, the greater part of this solution
was introduced; judging from the capacity of the mattrass, about 50
grains of it might have been lost. To prevent common air from coming in
contact with the solution, the stopper was introduced into the mattrass
under the mercury; the curved tube connected with a graduated cylinder
filled with that substance; and the mattrass brought over the side of
the mercurial trough. But in spite of these precautions a large globule
of common air got into the top of the mattrass, from the curvature of
the tube. When the heat of a spirit lamp was applied to the solution,
it gave out gas with great rapidity, and gradually lost its color.
When 5 cubic inches were collected it became perfectly pale green,
whilst a yellow red precipitate was deposited on the bottom of the
mattrass.
On pouring a little of the clear solution into prussiate of potash, it
gave only white prussiate of iron.
But on introducing a particle of sulphuric acid into the solution,
sufficient to dissolve some of the red precipitate, and then pouring
a little of it into a solution of prussiate of potash, it gave a fine
blue prussiate of iron.
Hence the red precipitate was evidently red yellow oxide of iron.
I now examined the gas, suspecting that it was nitrous oxide. On
mingling a little of it with atmospheric air, it gave red vapor, and
diminished. Solution of sulphate of iron introduced to the remainder,
almost wholly absorbed it: the small residual globule of nitrogene
could not equal one thirtieth of a cubic inch.
Consequently it was nitrous gas, nearly pure.
Caustic potash was now introduced into the solution, till all the oxide
of iron was precipitated. The solution, when heated, gave a strong
smell of ammoniac, and dense white fumes when held over muriatic acid.
It was kept at the heat of ebullition till the evaporation had been
nearly compleated. Sulphuric acid poured upon the residuum gave no
yellow fumes, or nitric acid vapor in any way perceptible; even when
heated and made to boil, there was no indication of the production of
any vapor, except that of the sulphuric acid.
_h._ This experiment, compared with the others, seemed almost to prove,
that nitrous gas combined with solution of pale green sulphate of
iron, at the common temperature, without decomposition; and that when
the impregnated solution was heated, the greater portion of gas was
disengaged, whilst the remainder was decompounded by the green oxide of
iron; which attracted at the same time oxygene from the water and the
nitrous gas; whilst their other constituent principles, hydrogene and
nitrogene, entered into union as ammoniac.
Whilst, however, I was reasoning upon this singular chemical change,
as affording presumptive proofs in favor of the exertion of simple
affinities by the constituent parts of compound substances, a doubt
concerning the decomposition of the nitrous gas occurred to me. As
near as I could guess at the quantity of nitrous gas contained by
the impregnated solution, at least ¾ of it must have been expelled
undecompounded.
More than a quarter of a cubic inch of common air had been present in
the mattrass: the oxygene of this common air must have combined with
the nitrous gas, to form nitric acid. Might not this nitric acid have
been decomposed, and furnished oxygene to the red oxide of iron, and
nitrogene to the small quantity of ammoniac found in the solution, as
in _d_?
_i._ I now introduced to a solution of green sulphate confined by
mercury, nitrous gas, perfectly free from nitric acid. When the
solution was saturated, a portion of it was introduced into a small
mattrass filled with dry mercury, in the mercurial trough. The curved
tube was closed by a small cork at the top, and filled with nitrous
gas; it was then adapted to the mattrass, which was raised from the
trough, and the solution thus effectually preserved from the contact of
the atmosphere.
When the heat of a spirit lamp was applied to the mattrass, it began to
give out gas with great rapidity. After some time the solution lost its
dark color, and became turbid. When the production of nitrous gas had
ceased, it was suffered to cool. A copious red precipitate had fallen
down; which, examined by the same tests as in the last experiment,
proved to be red oxide of iron.
The solution treated with lime, as before, gave ammoniac; but with
sulphuric acid, not the slightest indications of nitric acid.
_k._ Having thus procured full evidence of the decomposition of
nitrous gas in the heated solution, in order to gain a more accurate
acquaintance with the affinities exerted, I endeavoured to ascertain
the quantity of nitrous gas decomposed by a given solution, under known
circumstances.
Into a cylinder of the capacity of 20 cubic inches, inverted in
mercury, 1150 grains of solution of green sulphate of iron, of specific
gravity 1,4, were introduced. Nitrous gas was admitted to it, and after
some time 21 cubic inches were absorbed.
The impregnated solution was thrown into a mattrass, in the same manner
as in the last experiment, and the same precautions taken to preserve
it from the contact of atmospheric air. A quantity was lost during
the process of transferring, which, reasoning from the space occupied
in the mattrass by the remaining portion, as determined by experiment
afterwards, must have amounted nearly to 240 grains.
The curved tube from the mattrass was now made to communicate with
the mercurial airholder. By the application of heat 12,5 cubic inches
of nitrous gas were collected, after the common temperature had been
restored to the mattrass; which was suffered to remain in communication
with the conducting tube.
The solution was now pale green, that is, of its natural color, and a
considerable quantity of red oxide of iron had been deposited.
Solid caustic potash was introduced into it, till all the green oxide
of iron had been precipitated, and till the solution rendered green,
red cabbage juice.
A tube was now accurately connected with the mattrass, bent, and
introduced into a small quantity of diluted sulphuric acid. Nearly half
of the fluid in it was slowly distilled into the sulphuric acid, by
the heat of a spirit lamp. The impregnated acid evaporated at a heat
above 212°, and gave a small quantity of crystalised salt, which barely
amounted to two grains and quarter: it had every property of sulphate
of ammoniac. Sulphuric acid in excess was poured on the residuum, and
the whole distilled by a heat not exceeding 300°, into a small quantity
of water. This water, after the process, tasted strongly of sulphuric
acid; it had no peculiar odor. Tin thrown into it when heated, was not
perceptibly oxydated; mingled with strontitic lime water, it gave a
copious white precipitate, and after the precipitation became almost
tasteless. Hence it evidently contained no nitric acid.
The 12,5 cubic inches of undecompounded gas that came over were
examined; and accounting for the small quantity of common air
previously contained in the airholder, must have been almost pure.
_l._ Now supposing 927 grains of the impregnated solution (including
the weight of the nitrous gas), to have been operated upon, this must
have contained about 16,7 cubic inches of nitrous gas. But 12,5 cubic
inches escaped undecompounded: hence 4,2 were decomposed; and these
weigh 1,44 grains, and are composed of,8 oxygene, and,64 nitrogene.[117]
Consequently, the nitrous gas must have furnished,8 of oxygene to the
green oxide of iron.
But,64 of nitrogene require,15 of hydrogene to form,79 of
ammoniac:[118] consequently 1 of water was decompounded, and this
furnished,85 of oxygene to the green oxide of iron.
[117] Division IV. Section 5.
[118] Division II. Section 1.
The green oxide of iron contains ²⁷/₁₀₀ oxygene; the red ⁴⁸/₁₀₀. But
the whole quantity of oxygene supplied from the water and nitrous
gas is 0,8 + 0,85 = 1,65; and calculating on the difference of the
composition of the red and green oxide of iron, 5,7 grains of red oxide
must have been deposited, and consequently these would saturate as
much acid as,79 grains of ammoniac, or 4,1 grains of green oxide of
iron.[119]
And supposing the ammoniac in sulphate of ammoniac to be to the acid
as 1 is to 3,[120] 3.2 grains of sulphate of ammoniac must have been
formed, containing about 2,4 grains acid; and then 6,5 grains of green
sulphate of iron must have been decomposed.
[119] No precipitation takes place during the conversion of solution of
green sulphate into red; and the acid appears saturated.
[120] Division II, Section 6.
Hence we gain the following equation:
6,5 green s. = 2,41 sul. acid + 4,1 gr. ox. iron.
+
1,44 nit. gas = ,64 nitrogene + ,8 oxygene.
+
1 water = ,85 oxygene, + ,15 hydrogene,
equal
3,2 sul. am. = 2,41 s. acid + ,64 nit. + ,15 hyd.
+
5,7 r. ox. iron = 4,1 gr. ox. iron + 1,6 oxyg.
Though the estimation of the quantities in this equation must not
be considered as strictly accurate, on account of the degree of
uncertainty that remains concerning the exact numerical expression of
the quantities of the constituents of water, ammoniac, and the other
compound bodies employed; yet as founded on a simple quantity, that is,
the nitrous gas decomposed, it cannot be very distant from the truth.
The sulphate of ammoniac given by experiment, is considerably less than
that which was really produced; much of it was probably carried off
during the evaporation of the superabundant acid.
The conclusions that may be drawn from this experiment, afford a
striking instance of the importance of the application of the science
of quantity to the chemical changes: for the data being one chemical
fact, the decomposition of a given quantity of nitrous gas by known
agents; the composition of nitrous gas, of water, ammoniac, the oxides
of iron, and sulphate of ammoniac; we are able not only to determine
the quantities of the simple constituents that have entered into new
arrangements, but likewise the composition of two compound bodies, the
green and red sulphates of iron.[121]
[121] According to the estimation in the equation, 6.5 of dry green
sulphate of iron contain 4.1 green oxide of iron, and 2.4 of Kirwan’s
real sulphuric acid; and 8.1 red sulphate of iron, contain 2.4 acid,
and 5.7 red oxide of iron.
_m._ Though from the experiments in _e_ it appeared that no
decomposition of nitrous gas had been produced during or even after its
absorption by solution of sulphate of iron at the common temperature;
yet a suspicion that it might take place slowly, and that indications
of it might be given by deposition, induced me to examine minutely
two impregnated solutions, one of which had been at rest, confined by
mercury, for 19 hours, and the other for 27. In neither of them could I
discover any deposition, or alteration of color, which might denote a
change.
Two cubic inches of oxygene were admitted to half a cubic inch of one
of these solutions. The oxygene was slowly absorbed, and the solution
gradually lost its color.
To ascertain if during the conversion of the nitrous gas held in
solution by sulphate of iron, into nitric acid, by the oxygene of the
atmosphere at the common temperature, any water was decomposed; I
suffered an impregnated solution, weighing nearly two ounces, to remain
in contact with the atmosphere at 57°-62°, till it was become perfectly
pale. It then had a strong acid taste, effervesced with carbonate
of potash, and gave a blue precipitate with prussiate of potash.—It
was saturated with quicklime, and heated: slight indications of the
presence of ammoniac were perceived.
As in this experiment the nitric acid had been most probably decomposed
by the green oxide of iron, as in _f_, I sent oxygenated muriatic acid
through an impregnated solution, till all the green oxide of iron was
converted into red, and all the nitrous gas into nitric acid.
This solution saturated with potash, and heated, gave no ammoniacal
smell.
From these experiments we may conclude,
1st. That solution of red sulphate of iron has little or no affinity
for nitrous gas[122]; and that solution of common sulphate absorbs
nitrous gas only in proportion as it contains green sulphate.
[122] The muddy green color produced in a solution of red sulphate of
iron agitated in nitrous gas, depended upon impurities in the mercury.
I have since found, that when the solution is completely oxygenated,
the diminution is barely perceptible.
2dly. That solutions of green sulphate of iron dissolve nitrous gas in
quantities proportionable to their concentration, without effecting
any decomposition of it at common temperatures. And the solubility
of nitrous gas in solution of green sulphate, may be supposed to
depend on an equilibrium of affinity, produced by the following simple
attractions:
1. That of green oxide of iron for the oxygene
of nitrous gas and water.
2. That of the hydrogene of the water
for the nitrogene of the nitrous gas.
3. That of the principles of the sulphuric
acid, for nitrogene and hydrogene.
3dly. That at high temperatures, that is, from 200° to 300°, the
equilibrium of affinity producing the binary combination between
nitrous gas and solution of green sulphate of iron is destroyed; the
attraction of the green oxide of iron for oxygene being increased;
whilst probably that of nitrogene for hydrogene is diminished.
Hence the nitrous gas is either liberated,[123] in consequence of the
affinity between oxygene and hydrogene, and oxygene and nitrogene not
following the same ratio of alteration on increased temperature; or
decomposed, because at a certain temperature the green oxide exerts
such affinities upon water and nitrous gas, as to attract oxygene from
both of them to form red oxide; whilst the still existing affinity
between the hydrogene of the one, and the nitrogene of the other,
disposes them to combine to form ammoniac.
[123] Perhaps the liberation of nitrous gas from the solution takes
place at a lower temperature than its decomposition. I have always
observed that the quantity of yellow precipitate is greater when the
solution is rapidly made to boil. Were it possible to heat it to a
certain temperature at once, probably a compleat decomposition would
take place.
4thly. That the change of color produced by introducing nitric acid
to solution of common sulphate of iron, exactly analogous to that
occasioned in it by impregnation with nitrous gas, is owing to the
decomposition of the acid, by the combination of its oxygene with the
green oxide of iron, and of its nitrous gas with the solution.
5thly. That nitrous gas in combination with solution of green sulphate
of iron, is capable of exerting a strong affinity upon free or loosely
combined oxygene, and of uniting with it to form nitric acid.
_n._ The products obtained from a solution of sulphate of iron
saturated with nitrous gas, by Vauquelin and Humbolt, and their
consequent mistake with regard to the nature of the process of
absorption,[124] must have arisen from exposure of their impregnated
solution to the atmosphere.
[124] Annales de Chimie. T. 38, pag. 187.
Indeed, from the acidity of it, on examination, from the small portion
of ammoniac, and the large quantity of nitric acid obtained, it appears
most probable that the whole of the nitrous gas employed was converted
into nitric acid, by combining with atmospheric oxygene; for no nitric
acid could have been obtained in the mode in which they operated,
unless the green oxide of iron in the solution had been previously
converted into red.
VIII. _On the absorption of Nitrous Gas by solution of green Muriate of
Iron._
_a._ The analogy between the affinities of the constituents of the
muriate and sulphate of iron, induced me to conjecture that they
possessed similar powers of absorbing nitrous gas; and I soon found
that this was actually the case; for on agitating half a cubic inch
of solution of muriated iron, procured by dissolving iron filings
in muriatic acid, in nitrous gas, the gas was absorbed with great
rapidity, whilst the solution assumed a deep and bright brown tinge.
_b._ Proust,[125] who as I have before mentioned, supposes the
existence of two oxides of iron only, one containing ²⁷/₁₀₀ oxygene,
the other ⁴⁸/₁₀₀, has assumed, that the muriatic acid, and most other
acids as well as the sulphuric, are capable of combining with these
oxides, and of forming with each of them a distinct salt. He has,
however, detailed no experiments on the muriates of iron.
[125] Annales de Chimie, xxiii. pag. 85; or Nicholson’s Phil. Journal
vol. i. pag. 45.
As these salts are still more distinct from each other in their
properties than the sulphates, and as these properties are connected
with the phænomenon of the absorption and decomposition of nitrous gas,
I shall detail the observations I have been able to make upon them.
_c._ When iron filings have been dissolved in pure muriatic acid, and
the solution preserved from the contact of air, it is of a pale green
color, and gives a white precipitate with alkaline prussiates. The
alkalies throw down from it a light green oxide of iron.
When evaporated, it gives crystals almost white, which are extremely
soluble in water; but insoluble in alcohol.
The solution of green muriate of iron has a great affinity for oxygene,
and attracts it from the atmosphere, from nitric acid, and probably
from oxygenated muriatic acid.
When red oxide of iron is dissolved in muriatic acid, or when nitric
acid is decomposed by solution of green muriate of iron; the red
muriate of iron is produced. The solution of this salt is of a deep
brown red, its odor is peculiar, and its taste, even in a very diluted
state, highly astringent. It acts upon animal and vegetable matters in
a manner somewhat analogous to the oxygenated muriatic acid, rendering
them yellowish white, or yellow.[126]
[126] Probably by giving them oxygene; whereas the green muriate and
sulphate blacken animal substances; most likely by abstracting from
them oxygene.
Sulphuric acid poured upon it, produces a smell resembling that of
oxygenated muriatic acid. Evaporated at a low temperature, it gives an
uncrystalisable dark, orange colored salt, which is soluble in alcohol,
and when decomposed by the alkalies, gives a red precipitate. With
prussiate of potash it gives prussian blue.
The common muriate of iron consists of different proportions of these
two salts. It may be converted into red muriate by concentrated nitric
acid, or into green by sulphurated hydrogene.
_d._ To ascertain if solution of red muriate of iron was capable of
absorbing nitrous gas, I introduced into a jar filled with mercury, a
cubic inch of nitrous gas, and admitted to it nearly half a cubic inch
of solution of red muriate of iron. No discoloration took place. By
much agitation, however, an absorption of nearly,2 was produced, and
the solution became of a muddy green. But this change of color, and
probably the absorption, was in consequence of the oxydation of either
the mercury, or some imperfect metals combined with it, by the oxygene
of the red muriate. For I afterwards found, that precisely the same
change of color was produced when a solution was agitated over mercury.
_e._ I introduced to a cubic inch of concentrated solution of green
muriate of iron, 7 cubic inches of nitrous gas, free from nitric acid;
the solution instantly became colored at the edges, and on agitation
absorbed the gas with much greater rapidity than even sulphate of iron;
in a minute, only a quarter of a cubic inch remained.
The solution appeared of a very dark brown, but evidently no
precipitation had taken place in it, and the edges, when viewed against
the light, were transparent and puce colored.
Five cubic inches more of nitrous gas were now dissolved in the
solution. The intensity of the color increased, and after an hour no
deposition had taken place. A little of it was then examined in the
atmosphere; it had a much more astringent taste than the unimpregnated
solution, and effected no change in red cabbage juice. When prussiate
of potash was introduced into it, its color changed to olive brown. A
few drops of the solution, that had accidentally fallen on the mercury,
soon became colorless, and then effervesced with carbonate of potash,
and tasted strongly acid.
The remainder of the impregnated solution, which must have nearly
equalled,75 cubic inches, was introduced into a mattrass, having a
stopper and curved tube, as in the experiments on the solution of
sulphate of iron; great care being taken to preserve it from the
contact of air.
The mattrass was heated by a spirit lamp, the curved tube being in
communication with a mercurial cylinder. Near 8 cubic inches of nitrous
gas were collected, when the solution became of a muddy yellow. It was
suffered to cool, and examined. A small quantity of yellow precipitate
covered the bottom of the mattrass; the fluid was pellucid, and
light green. A little of it thrown on prussiate of potash, gave a
white precipitate, colored by streaks of light blue. When the yellow
precipitate was partly dissolved by sulphuric acid, a drop of the
solution, mingled with prussiate of potash, gave a deep blue green.
Hence, evidently, the precipitate was red oxide of iron.
Caustic potash in excess was introduced into the remainder of the
solution, and it was heated. It gave an evident smell of ammoniac, and
dense white fumes, when held over strong phlogisticated nitrous acid.
When half of it was evaporated, sulphuric acid in excess was poured on
the remainder; muriatic acid was liberated, not perceptibly combined
with any nitric acid.
_f._ In an experiment that I made to ascertain the quantity of nitrous
gas capable of combining with solution of green muriate of iron; I
found that,75 cubic inches of saturated solution absorbed about 18
of nitrous gas, which is nearly double the quantity combinable with
an equal portion of the strongest solution of sulphate of iron. A
part of this impregnated solution, heated slowly, gave out more
gas in proportion to the quantity it contained, than the last, and
consequently produced less precipitate; so that I am inclined to
suppose it probable, that at a certain temperature, all the dissolved
nitrous gas may be dispelled from a solution.
From these experiments we may conclude,
1st. That the solution of green muriate of iron absorbs nitrous gas in
consequence of nearly the same affinities as solution of green sulphate
of iron; its capability of absorbing larger quantities depending
most probably on its greater concentration (that is, on the greater
solubility of the muriate of iron), and perhaps, in some measure, on a
new combining affinity, that of muriatic acid for oxygene.
2dly. That at certain temperatures nitrous gas is either liberated from
solution of green muriate, or decomposed, by the combination of its
oxygene with green oxide of iron, and of its nitrogene with hydrogene,
produced from water decompounded by the oxide at the same time.