REDUCTION OF METALS
BY
_PHOSPHORATED HYDROGEN GAS_.
The effects of hydrogen gas and phosphorus on the reduction of metals
in the fibres of silk have been treated of separately in the two
first chapters; in this, I shall briefly treat of their effects, when
combined in the form of phosphorated hydrogen gas, which from its high
degree of inflammability seemed well adapted to this purpose.
The spontaneous inflammation of this kind of air was known to M.
Gengembre in 1783; and his experiments were published in Rosier’s
journal for October 1785.
Mr. Kirwan also, without any knowledge of M. Gengembre’s experiments,
discovered the same air, which he calls phosphoric air, and published
his experiments in the 76th volume of the Philosophical Transactions
for 1786.
This elastic fluid may be obtained by digesting a solution of potash in
water with about half its weight of phosphorus in a heat sufficient to
melt the latter; and may be received in glass vessels over mercury.
But finding it inconvenient to introduce pieces of silk prepared for
these experiments over mercury in close vessels, I exposed them to the
gas, as it issued from the neck of the phial in which it was prepared.
Part of this elastic fluid is spontaneously inflammable; but the other
has not that property, which M. Gengembre imputes to the presence of
carbonic acid; for the sake of brevity, I shall design the latter by
the term _gas_, or _phosphorated hydrogen gas_; and the former by the
epithets _spontaneously inflammable_, or _detonating_ gas, which, I
found, does not burn or scorch silk wetted with metallic solutions.
EXP. 1. GOLD.
A piece of silk, which was immersed in a solution of nitro-muriate of
gold in distilled water, and suspended in the air twelve hours to dry,
was divided into three parts.
One of these was exposed to a stream of phosphorated hydrogen gas: the
silk became brown, and its margins, which happened to touch the sides
of the phial, acquired a violet tinge: but no reduction took place.
Another of these parts was wetted with alcohol, and exposed to the gas;
but no signs of reduction could be perceived.
The remaining part was wetted with water, and was no sooner exposed to
the gas, than the reduction commenced over the whole silk, which was
soon covered with a bright coat of reduced gold.
EXP. 2. SILVER.
A piece of silk was dipped in a solution of fused nitrate of silver in
alcohol, and dried in the air: it was then divided into three parts.
One of these, in order to dissipate moisture more effectually, was
dried still better by a gentle heat, and exposed to the gas; the silk
acquired a brownish dark colour: but no other alteration could be
perceived.
Another of these parts, which was also better dried by a gentle heat,
was wetted with alcohol, and exposed to the gas: the silk acquired a
dark brown colour; but no other change could be observed.
The remaining part was wetted with water, and exposed to the gas: the
reduction commenced immediately, and in a short time the silk was
covered with reduced silver.
EXP. 3. PLATINA.
A piece of silk was immersed in a solution of nitro-muriate of the
ore of platina in distilled water, and dried in the air; it was then
divided into three parts.
One of these parts was exposed to the gas; but suffered no visible
change.
Another of them was wetted with alcohol, and exposed to the gas; but
underwent no perceptible change.
The remaining part was wetted with water, and exposed to the gas: in
about three or four minutes, a bright metallic film, of great lustre,
appeared on the side of the silk, opposed to the gas.
Another bit of silk, which was dipped in the same solution of platina,
and exposed, while wet, to the spontaneously inflammable gas, was
immediately covered with reduced platina, which being transferred
to the surface of water looked bright as silver, and retained the
impression of the silk.
EXP. 4. MERCURY.
A bit of silk, which was immersed in a solution of nitrate of mercury
in distilled water, and dried in the air, was exposed to the gas; but
underwent no visible change.
Another bit of silk was dipped in the same solution of mercury, and
dried: it was then wetted with alcohol, and exposed to the gas; but no
sign of reduction appeared.
Another bit of silk was immersed in the same solution of mercury, and
exposed to the gas; the metal was instantly reduced all over the silk;
a great variety of beautiful colours attending.
A piece of silk was dipped in a solution of oxygenated muriate of
mercury in distilled water, and dried in the air: it was then divided
into two parts.
One of these was exposed to the gas: no change appearing, it was wetted
with alcohol, and exposed again to the gas; but still no alteration
could be perceived.
The remaining part was wetted with water, and was no sooner exposed to
the gas, than the mercury was reduced over the whole silk. No colours
attended the reduction.
Mr. Kirwan introduced some precipitate per se to a small portion of
phosphoric air: the precipitate soon grew black; and a white smoke
appeared; in two days the precipitate remained solid; yet acquired a
pale white colour, like that of steel: the air lost its spontaneous
inflammability[17].
EXP. 5. COPPER.
A piece of silk, which was immersed in a solution of sulphate of copper
in distilled water, and dried in the air, was divided into two parts.
One of these was exposed to the gas; but no visible change occurred.
The remaining part was wetted with water, and exposed to the gas: in
a few minutes a brownish matter appeared in the silk; but nothing
metallic could be seen: the silk was then dipped in a glass of clear
water, and transferred a small white metallic pellicle to its surface.
In another experiment, made with the spontaneously inflammable gas,
a white metallic pellicle was immediately formed, attended with a
brown stain; this pellicle resembled silver, or a white metal: but the
gas soon reacted on it, and formed a disagreeable brown matter in the
fibres of the silk.
EXP. 6. LEAD.
A bit of silk, which was dipped in a solution of acetite of lead in
distilled water, and dried in the air, was exposed to the gas; but
suffered no visible change.
Another bit of silk was immersed in the same solution of lead, and
exposed, while wet, to the gas; but nothing metallic could be seen: the
silk, however, on immersion in water, transferred a few minute bright
films to the surface of that fluid.
In another experiment, made with the detonating gas, the reduced films
were more evident.
EXP. 7. TIN.
A bit of silk, which was dipped in a solution of muriate of tin in
distilled water, and dried in the air, was exposed to the action of the
gas, without suffering any visible alteration.
Another piece of silk was immersed in the same solution of tin, and
exposed, while wet, to the gas; but no signs of reduction could be
perceived: the silk was then immersed in water, and transferred a
delicate metallic film to its surface.
EXP. 8. ARSENIC.
A bit of silk, which was immersed in a solution of muriate of arsenic
in distilled water, and dried in the air, was exposed to the gas; but
no change could be perceived.
Another bit of silk, immersed in the same solution of arsenic, and
exposed, while wet, to the gas, acquired in a few minutes a brown
stain; but nothing metallic could be seen on the silk; which, however,
on being dipped in water, transferred a very minute film of reduced
arsenic to its surface.
In another experiment, made with the detonating gas, the films of
reduced arsenic were much more evident, of greater brilliance, and
attended with a brown stain produced in the fibres of the silk.
EXP. 9. BISMUTH.
A piece of silk, which was dipped in a solution of nitrate of bismuth
in distilled water, and dried in the air, was exposed to the gas; but
no alteration could be observed.
Another bit of silk was immersed in the same solution of bismuth, and
exposed, while wet, to the gas: the silk in two or three minutes got a
brown stain, which gradually became more intense; and a very delicate
metallic film appeared: the silk was then immerged in water, and
transferred a bright film of reduced bismuth to the surface of that
fluid: the film retained the impression of the silk.
EXP. 10. ANTIMONY.
A bit of silk, immersed in a solution of tartarite of antimony in
distilled water, and dried in the air, was exposed to the gas; but
suffered no apparent change.
Another piece of silk was dipped in the same solution of antimony, and
exposed, while wet, to the gas; but no signs of reduction appeared:
the silk was then immerged in water, to the surface of which, it
transferred one small spangle.
This experiment was repeated with the detonating gas, which with
difficulty produced some sparkling films: the silk was immersed in
water, and transferred the films to its surface.
A white matter was visible in the fibres of the silk.
EXP. 11. COBALT.
A piece of silk, immersed in a solution of muriate of cobalt, and dried
in the air, was exposed to the gas; but suffered no visible alteration.
Another bit of silk was dipped in the same solution of cobalt, and
exposed, while wet, to the gas: but no sign of reduction appeared; nor
did the silk transfer a film to water.
Another bit of silk was immersed in a solution of nitrate of cobalt,
and exposed, while wet, to the detonating gas: no signs of reduction
were visible for some time; but at length a few small spangles of
the metal appeared on the silk, and were very brilliant, and when
transferred to water, were still more so: a white matter could be seen
in the fibres of the silk.
EXP. 12. IRON.
A bit of silk was immersed in a largely diluted solution of sulphate of
iron in distilled water, and dried: it was then exposed to the action
of the gas; but no alteration could be perceived.
Another bit of silk was dipped in the same solution of iron, and
exposed, while wet, to the gas: in a few minutes some parts of the silk
acquired a light brown colour; but no reduced iron could be seen on the
silk, which however transferred a very minute, and delicate film to
water.
This experiment was repeated with a strong detonating gas, and a very
brilliant metallic film about four lines in diameter was reduced on the
silk accompanied with a brown stain: but nothing like the black oxid of
iron appeared.
EXP. 13. ZINC.
A bit of silk, which was immersed in a largely diluted solution of
muriate of zinc, was exposed dry to the gas; but underwent no visible
alteration.
Another piece of silk was dipped in the same solution of zinc, and
exposed wet to the gas; no signs of reduction appearing, the silk was
immerged in water, and left a very minute metallic film on its surface,
which could with difficulty be seen.
The experiment was repeated with the detonating gas, and a very bright
metallic film of zinc, four or five lines in diameter, was reduced on
the silk.
This experiment succeeded also with a largely diluted solution of
sulphate of zinc.
The silk, viewed by transmitted light, exhibited a brown stain beneath
these films of iron and zinc.
The experiments detailed in this chapter show,
1. That water is essential to the reduction of metals by phosphorated
hydrogen gas.
2. That alcohol does not promote these reductions, without the aid of
water.
3. That this elastic fluid does not reduce metals by giving them
phlogiston; nor by combining with, and separating, their oxygen; for
were either of these suppositions true, it should reduce them as well
with alcohol, as with water.
After explaining the manner, in which sulphurated hydrogen gas reduces
the metals; the mode of agency of phosphorated hydrogen gas is
sufficiently obvious.
The gas attracts the oxygen of the water, while the hydrogen of the
latter unites, in its nascent state, with the oxygen of the metal, and
reduces it.
Hence it follows, that the hydrure of phosphorus, which constitutes the
base of this gas, is oxygenated by the oxygen of the water, while the
metal is, at the same time, restored to its combustible state.
By hydrure of phosphorus is meant, a combination of hydrogen and
phosphorus, containing less caloric, than is necessary to the gazeous
state.