OXYGENATION
OF
_COMBUSTIBLE BODIES_.
It has been shown, in the preceding chapters, that water is essential
to the reduction of metals; that it is always decomposed in that
process; and that the reducing substances are oxygenated by the oxygen
of the water, while the hydrogen of the latter reduces the metals.
That water is also decomposed in every instance of oxygenation, and
that the oxygen of water alone oxygenates combustible bodies, will
appear from the following observations.
AZOTE.
The first case of oxygenation, we shall consider, is that of _azote_,
in an experiment of Dr. Priestley, which has been urged by Mr. Kirwan
with great success against the Antiphlogistians.
“If the electric spark be taken in nitrous air, it will be reduced to
⅓ of its bulk, and the residuum is mere phlogisticated air, and a
little acid is deposited. Now the Antiphlogistians own that nitrous
air contains both pure air and phlogisticated air; since, therefore,
this pure air disappears, is it not evident that it was converted
into water? and since the formation of water requires the presence of
inflammable air, does it not follow that the nitrous air contained this
also[27]?”
To this objection M. Berthollet replies, that the diminution of the
nitrous gas “is owing to the combination of the mercury with the
oxygene, which existed in the gas[28].”
But this answer is insufficient; as it does not account for the
water, and acid, that appeared: and indeed, by this experiment,
the Antiphlogistians are refuted on their own principles, and the
decomposition of water is incontestably proved; for as nitrous acid
could not be formed without more oxygen than what existed in the
nitrous air, is it not evident, that this oxygen must be derived from
the water contained in the nitrous air? It is obvious then, that the
water of the gas was decomposed; which seems to have been effected in
the following manner.
The electric spark diminishes the attraction of the constituent
principles of the water for each other; hence the azote of the gas
unites with the oxygen of the water, while the hydrogen of the latter
combines with the oxygen of the gas; and thus water and nitrous acid
are formed.
The formation of nitrous acid in Mr. Cavendish’s noted experiment,
cannot be explained on any other principle than the decomposition of
water: when the electric spark is taken in a mixture of azotic gas,
and vital air; the water of these airs is decomposed: the electric
flame lessens the force, with which the oxygen and hydrogen of the
water adhere; hence the azote seizes the oxygen of the water, and forms
nitrous acid, while the hydrogen of the water unites with the oxygen of
the vital air, and forms a quantity of water equal to that decomposed.
When nitrous, and vital air, are mixed; the whole mass “hisses, turns
red, grows warm, and contracts in bulk,” the azote of the nitrous air
attracts the oxygen of the water, and forms nitrous acid, while the
hydrogen of the water unites in its nascent state with the oxygen of
the vital air, and forms a quantity of water equal to that decomposed.
Hence while the azote of the nitrous air is oxygenated; the caloric is
restored to its combustible state.
“But it is to be observed,” says M. Bergman, treating of this
experiment, “that the decomposition of nitrous air is the effect of a
double attraction; the phlogiston is attracted by the vital air, and
the acid part by the water. Therefore, when the mixture is made in a
phial immersed in mercury, the experiment fails[29].”
HYDROGEN.
The combustion of hydrogen gas with vital air is explicable only on the
decomposition of the water contained in these airs: thus when flame,
or a glowing body is applied to a mixture of them; the attraction of
the principles of the water for each other is diminished; therefore
the hydrogen of the inflammable air unites with the oxygen of the
water, while the hydrogen of the latter seizes the oxygen of the
vital air: thus the whole bulk of the airs, which are changed into
water, disappears; and their light, and caloric, are restored to the
combustible state.
Hence it appears that water is not formed during the combustion of
vital, and inflammable air, in the manner the Antiphlogistians suppose.
Indeed it is obvious, that, if these airs contained no water, they
could never be burned: for since they are already saturated with light,
and caloric, they can have no attraction for any additional quantity
of these fluids; and consequently can suffer no other change from
the light, or caloric, of a glowing body, than a greater degree of
expansion, and therefore could never unite.
The same reasoning applies to the combustion of all elastic fluids.
PHOSPHORUS.
Vital air always contains a large proportion of water: when phosphorus
is burned in this air, it attracts the oxygen of the water, and forms
phosphoric acid, while the hydrogen of the water unites with the oxygen
of the gas, and forms water, which unites with the acid.
Hence the weight of the acid formed is equal to the weights of the
oxygen gas, and phosphorus, consumed; and the light and caloric, which
appear during the combustion, are restored to their combustible state.
This explanation is confirmed by an observation of Mr. Bergman, who
says,
“In vital air, without the aid of external heat, phosphorus is consumed
very slowly, and scarce at all, unless water be present[30].”
Therefore the phosphorus does not unite to the oxygen of the vital air,
as M. Lavoisier supposes, but to the oxygen of the water contained in
the oxygen gas.
SULPHUR.
When sulphur is burned in vital air, it attracts the oxygen of the
water, and forms sulphuric acid, while the hydrogen of the water
attracts the oxygen of the gas, and forms a quantity of water equal to
that decomposed: the light and caloric are at the same time restored to
their combustible state.
The sulphur then does not unite with the oxygen of the vital air,
as the Antiphlogistians imagine, but with the oxygen of the water
contained in that gas.
CHARCOAL.
In like manner during the combustion of charcoal in vital air, the
carbone attracts the oxygen of the water, and forms carbonic acid,
while the hydrogen of the water unites with the oxygen of the vital
air, and forms a new quantity of water equal to that decomposed.
Hence the carbone of the charcoal does not unite with the oxygen of the
vital air, as M. Lavoisier supposes, but with the oxygen of the water
contained in that gas.
That water is decomposed in every instance of combustion, is further
proved by attending to what passes during the burning of a common fire:
the carbone of the fuel combines with the oxygen of the water, and
forms carbonic acid, while the hydrogen of the water unites partly
with the oxygen, and partly with the azote of the atmosphere, and forms
water, and the ammonia, which abounds in soot.
From these observations it is evident, that M. Lavoisier’s account of
the formation of water, and acids, is erroneous, and inadequate to
explain the phenomena.
The different kinds of fermentation are so many instances of the
decomposition of water: in every case of them, combustible bodies are
oxygenated by the oxygen of the water, while others are restored by its
hydrogen to their combustible state.
Hence the azote, ammonia, and carbonic acid of fermentation, the
inflammable air of marshes, mines, &c. the azotic, and hydrogen
gas, ascending into the atmosphere, and there meeting the vital air
discharged from the water of plants, &c. form new quantities of air,
and water.
When the azote is oxygenated, it unites with the oxygen of the water
contained in the air, and forms atmospheric air, and sometimes perhaps
nitrous acid, the hydrogen of the water combines, at the same time,
with the oxygen of the vital air, and forms a quantity of water equal
to that decomposed.
But when the hydrogen is oxygenated, a quantity of water double that
decomposed is regenerated; for the hydrogen of the gas unites with the
oxygen of the water, while the hydrogen of the latter seizes the oxygen
of the vital air: and thus a quantity of water double that decomposed
is formed, and that part of it which the atmosphere cannot suspend
descends in the form of rain.
When these decompositions are rapid, the phenomena of thunder and
lightning appear.
This account of the renovation of our atmosphere explains why the
phenomena of thunder and lightning appear sometimes with, and sometimes
without rain, and also accounts for the production of the nitrous acid,
which Mr. Margraaf discovered in the purest snow.
The breathing of fishes is a striking proof of the decomposition of
water in respiration.
For this view of the formation of our atmosphere I am indebted to a
friend well acquainted with the experiments related in this essay, and
also for the application of the opinion which I venture to advance, to
the respiration of animals.
The phenomena of vegetation cannot be explained on any other principle,
than the decomposition of water by heat, and light, which uniting to
the oxygen of the water contained in vegetables change it into streams
of vital air, that serve to renovate our atmosphere: the hydrogen of
the water, at the same time, contributes to form the oil and other
principles of plants, and when these are decomposed by the various
processes of combustion, forms a quantity of water equal to that
consumed in their formation.
The changes, which nitric acid suffers by exposure to heat, or light,
are explained with ease on this principle: the light unites with the
oxygen of the water contained in the nitric acid, and forms vital air,
while the hydrogen of the water combines with the oxygen of the acid,
and forms a new quantity of water equal to that decomposed: thus the
nitric is converted into the ruddy nitrous acid.
METALS.
According to the Antiphlogistians, “In every metallic solution by an
acid, the metal, in order to become oxided, decomposes either the acid
itself, or the water of solution, or it obtains from the atmosphere the
requisite quantity of oxygene. In the second case, hydrogenous gas, in
a state of greater or less purity is disengaged; and the acid remains
entire without decomposition, which is proved by the quantity of alkali
necessary to saturate it. In the first case, one of the principles of
the acid, or the acid deprived of part of its oxygene, is disengaged,
and fused in the caloric, which is separated at the same time; such are
nitrous gas, and sulphurous acid gas. In the third case, neither the
water nor the acid are changed; such is the solution of copper by the
acetous acid.
“The muriatic acid, and the vegetable acids, which are formed of
radicals, or acidifiable principles, which have more affinity with
oxygene, than the metals have, are not decomposed by these metals,
and the oxygene is always afforded to these last by the water or
atmosphere. Hence the solutions by these acids afford only hydrogenous
gas, or do not effervese at all.
“There are some cases in which the water and the acid are at the same
time decomposed by the metal, as in the solution of tin in the nitric
acid, according to the observation of M. De Morveau.”
“Tin is so greedy of oxygene, and requires so large a quantity for its
saturation, that after having absorbed that of the nitric acid, and
reduced it to the state of azote, it decomposes likewise the water,
and disengages hydrogene. These two principles being separated from
their first compounds, unite together, and immediately form ammoniac.
Hence there is no disengagement of elastic fluid. In this case it
appears, that the formation of ammoniac, in the solution of tin by the
nitric acid, always takes place; for by throwing quicklime, or caustic
fixed alkali, into this solution, there is always a disengagement of
ammoniac[31].”
It is evident, then, that this account of the oxygenation of metals,
given by the Antiphlogistians, is equally complex, as their account
of metallic reduction, and improbable; since every case, in which
they deny the decomposition of water, and derive the oxygen from other
sources, is easily, and naturally explained on that principle, as will
appear from what follows.
Thus when mercury, or silver, is dissolved in nitric acid; the metal
attracts the oxygen of the water, while the hydrogen of the latter
unites with, and separates, more or less of the oxygen of the acid,
which is thus changed into nitrous air.
The same thing happens during the solution of other metals in this
acid; the only difference being the greater or less energy, and
rapidity, with which they combine with the oxygen of the water.
This decomposition of water is confirmed by the solution of tin in this
acid; in which the Antiphlogistians allow the decomposition of the
acid, and the water too; for ammonia is formed by part of the hydrogen
of the water, and azote of the acid.
In every case of metallic solution by sulphuric, and muriatic acids,
whether concentrated, or diluted, water is decomposed: the metals
attracting the oxygen of the water, while its hydrogen escapes in
the form of inflammable air, or unites partly with the oxygen of the
acid, and partly with caloric: hence the volatile sulphurous acid, and
muriatic acid air, obtained, always contain some hydrogen gas, as
appears from the following observation of M. Bergman.
“By means of vitriolic acid, inflammable air is obtained from zinc,
and iron, as also by means of marine acid; but, from the other metals
dissolved in vitriolic acid, we obtain another species of air, called
_vitriolic acid air_; and, by the marine acid, another similar to
the former, called _muriatic air_, but both more or less mixed with
_inflammable air_[32].”
Again, when copper is dissolved in the acetous acid; the copper
attracts the oxygen of the water, while the hydrogen of the latter
unites with the oxygen of the atmosphere, and forms water: hence no
effervescence appears.
When alkalies dissolve metals, the latter are always oxygenated at the
expence of the water, which holds the alkali in solution: thus when
lead, and copper, are dissolved; the metals combine with the oxygen of
the water, while its hydrogen unites to the oxygen of the atmosphere,
and forms water: hence no hydrogen gas appears.
The oxygenation of metals, and other substances by heat, and air, is
easily explained on the same principle: the metals, &c. unite with the
oxygen of the water contained in atmospheric air, while the hydrogen
of the water combines with the oxygen of the air, and forms a quantity
of water equal to that decomposed.
This explanation is clearly proved by an experiment of Mr. Bergman on
the regulus of manganese, which, if kept in a dry place, retains its
metallic splendour; but, if exposed to moisture, is soon oxygenated,
and loses its lustre[33].
It is further confirmed by the authority of the distinguished Mr.
Scheele, who says, that “the water contained in common atmospheric air
is the chief cause of the ignition of pyrophorus,” which he proved by
the following experiment.
“I made a very dry air by putting some very small pieces of quicklime
into a small matrass: then I put the neck of another matrass into
that of the first, so that the air of both might communicate; and I
luted the crevices with wax. Two days afterwards I separated the empty
matrass, and poured half an ounce of pyrophorus from my phial into
it, and immediately carefully shut the aperture up: but I did not
observe, that it grew in the least warm: an hour after this, I put a
sponge moistened in water into the matrass, and shut it up again: a few
minutes after the pyrophorus began strongly to be heated, and some
pieces kindled spontaneously[34].”
Many other facts might be adduced to prove, that oxygenation cannot
take place without water, as the combustion of mixtures of iron
filings, sulphur and water, of alkaline sulphure and water, &c. in
which the water is decomposed, and the combustible bodies oxygenated by
its oxygen.
It is evident then from the experiments and observations related in
this essay, that water is essential to the oxygenation of combustible
bodies; and that it is the only source of the oxygen that oxygenates
them: it is also evident, that when one body is oxygenated, another,
at least, is restored to the combustible state: hence it appears that
the oxygenation of combustible bodies is never effected by a single
affinity.
The Antiphlogistians treating of the precipitation of metals by each
other, say,
“Since the metals cannot remain united to the acids, but in the state
of oxides of a determinate degree, it is easily conceived, that by
plunging into a metallic solution a metal which has a stronger affinity
with oxygene than that which is dissolved, the former must deprive
the latter of its oxygene, take its place in the acid, and cause the
second to subside in a form more or less metallic, accordingly as it
has deprived it of more or less oxygene. This is the reason of the
precipitation of silver by copper, copper by iron[35],” &c.
But this account of the precipitation of metals by one another cannot
be admitted; for it has been proved in every instance of reduction
related in this essay, that water is decomposed, and that its hydrogen
is the only substance that restores bodies to their combustible state.
There is no reason then to suppose that nature deviates, in this
particular case, from that uniform simplicity, which she constantly
observes in all her operations.
Therefore it is obvious, that, when one metal precipitates another in
a form more or less metallic; the precipitant unites with the oxygen
of the water, while the hydrogen of the latter combines with, and
separates, the oxygen of the precipitated metal, and thus reduces it.
The experiments made with phosphorus and metallic solutions in ether,
alcohol, and water, prove the truth of this explanation; and show that
when one metal precipitates another in the metallic form, it acts like
a stick of phosphorus, decomposing the water.
This account of the reduction of one metal by another is supported by
the opinion of Mr. Bergman, who says,
“It is well known, that the calx of copper, dissolved in vitriolic
acid, is precipitated in its metallic form on the addition of iron; and
that by means of a double elective attraction; for the iron dissolving
in the acid would form an inflammable air by its phlogiston, were not
the copper present, which takes it up[36].”
The same author remarks, that a small excess of acid is necessary, and
that without it no precipitation begins.
Now since water is decomposed by iron and sulphuric acid, it must be
allowed, that, when iron is immersed in a solution of sulphate of
copper, the water is decomposed by the iron and excess of acid, the
iron attracting the oxygen of the water, while the hydrogen of the
latter, unites to the oxygen of the copper, reduces it, and forms a
quantity of water equal to that decomposed.
The precipitation of silver in its metallic form by iron and other
metals is to be explained in the same manner: and not by a single
affinity, as the Antiphlogistians imagine.
The reduction of gold, and some other metals, by solutions of sulphate
of iron, and muriate of tin, is readily accounted for on the principles
advanced here; for fresh made solutions of sulphate of iron, and
muriate of tin, contain hydrogen, and have the power of decomposing
water: the oxygen of which unites with the iron, and tin, while its
hydrogen seizes the oxygen of the gold, &c. reduces it, and forms a
quantity of water equal to that decomposed.
The decomposition of water is further proved by the large dilution
necessary to form the arbor Dianæ, the purple precipitate of Cassius,
and other instances of the reduction of metals by one another.