_Reduction of Metals by Alkaline Sulphure._
The Sulphure, I made use of, was prepared by fusing equal parts of
carbonate of potash, and flowers of sulphur, till the effervescence
ceased.
M. Gengembre has made a very important observation on alkaline
sulphure, prepared in this way, which is, that this substance has no
smell, and that it exhales no gas, while it continues dry; but that,
when it is dissolved in water, or attracts humidity from the air, it
diffuses an offensive smell.
From this circumstance M. Gengembre inferred, that the disengagement of
this gas depended on the decomposition of water; for he discovered both
by analysis, and synthesis, that this air consists of hydrogen, one of
the principles of water, combined with sulphur, and caloric.
There can then be no doubt, but alkaline sulphure has the power of
decomposing water; and may therefore be happily employed to illustrate
the mode of action of sulphur, and other combustible substances,
treated of in this essay.
When dilated acids are poured on solid alkaline sulphure, the
decomposition of the water is promoted, and accelerated, sulphurated
hydrogen gas being formed in great abundance.
I made two solutions of this alkaline sulphure, one in water, and the
other in alcohol.
EXP. 1. GOLD.
A bit of silk was immersed in the solution of sulphure in alcohol, and
then a solution of gold in ether was applied: a brown matter was formed
in the silk; but no reduced gold could be perceived.
Another bit of silk was dipped in the same solution of sulphure in
alcohol, and a solution of nitro-muriate of gold in water was applied;
a white metallic film was slowly formed; but no other signs of
reduction were visible.
This experiment was repeated on another bit of silk, with this
difference, that the solutions of the gold, and sulphure, were both in
water; and the white metallic film was instantly formed, accompanied by
a considerable precipitate of a brown matter.
It is obvious then, that water accelerates, and is necessary to the
appearance of this film: for when both solutions were in water, it
appeared much sooner.
EXP. 2. GOLD.
A piece of silk was immersed in an aqueous solution of gold, in which
the acid predominated, then a few drops of the aqueous solution of
sulphure were applied: a white pellicle, which looked like silver, was
immediately formed, and the silk got a deep brown colour.
To another piece of silk, dipped in the same solution of gold,
the solution of sulphure in alcohol was applied, a white metallic
film appeared; but not so evident, or so soon, as in the preceding
experiment, wherein the solution of sulphure in water was used:
beside the film produced by the aqueous solution of sulphure was more
permanent, and the stain, which the silk acquired, was more intense,
than those produced by the solution of sulphure in alcohol.
EXP. 3. SILVER.
I immersed a piece of silk in a solution of the sulphure in alcohol,
and after most of the spirit evaporated, a solution of nitrate of
silver in alcohol was applied: nothing appeared on the silk, but a
brown stain. The nitrate of silver, used in this experiment, was fused,
to expel as much water as possible.
Another piece of silk was dipped in the same solution of sulphure; when
most of the alcohol evaporated, a solution of crystallized nitrate of
silver in water was applied to the silk; and instantly the metallic
lustre of the silver appeared, attended with a brown stain.
EXP. 4. SILVER.
A piece of silk was dipped in the solution of alkaline sulphure in
water, and an aqueous solution of crystallized nitrate of silver was
applied; the silver was immediately reduced in greater quantity than
in the preceding experiment, in which the alkaline sulphure employed
was dissolved in alcohol. The stain produced in the silk was also more
intense.
EXP. 5. SILVER.
A bit of silk was immersed in a solution of the sulphure in water,
and then a solution of nitrate of silver in alcohol was applied: but
nothing appeared on the silk, except a brown stain. The nitrate of
silver, used in this experiment, was fused, which deprived it of a
great part of its acid. That this was the circumstance, which prevented
the reduction of the silver, appears from the following experiment.
A bit of silk was immersed in the same solution of silver in alcohol,
then some diluted nitric acid was applied, lastly the aqueous solution
of sulphure was dropped on the silk: and instantly the silver was
restored to its metallic splendour. It is evident then, that acids
contribute to the reduction of silver by alkaline sulphure, which they
effect by promoting the decomposition of water.
In some time the reduced silver disappears for the most part: and
indeed the white metallic films, which were produced in the experiments
on gold, totally disappeared.
EXP. 6. PLATINA.
A bit of silk was immersed in a solution of nitro-muriate of the ore of
platina in distilled water, and dried; then the solution of sulphure in
alcohol was dropped on the silk: nothing appeared but a brown stain.
Another bit of silk was dipped in the aqueous solution of sulphure, and
a little of the solution of platina applied; in a short time, a film of
reduced platina appeared.
To another bit of silk, which was dipped in the solution of platina, a
few drops of distilled vinegar were applied, and then the solution of
sulphure in water was added; a brown stain was immediately produced,
and more platina reduced than in the preceding experiment.
EXP. 7. MERCURY.
To a bit of silk, which was immersed in a solution of oxygenated
muriate of mercury in water, and dried in the air; some of the solution
of sulphure in alcohol was applied; but no change, except a light
yellowish brown, was produced.
After the silk was some time exposed to the air, some very faint shades
of black were visible on parts of it.
To a piece of silk, which was immersed in the solution of sulphure in
water, some of the same solution of mercury was applied; immediately
the metal was restored to its metallic lustre, in a very striking
manner; and it was remarkable, that the precipitate on the silk was
very small.
This experiment was repeated with this difference, that the silk
was first wetted with distilled vinegar: and more of the mercury
was reduced, than in the preceding experiment, attended with an
olive precipitate, which gradually turned blackish: the quantity
of precipitated matter in this was much greater than in the former
experiment; but the reduced metal was not so bright.
EXP. 8. MERCURY.
A bit of silk, which was dipped in a solution of nitrate of mercury,
and dried in the air, had no change produced on it by a solution of
sulphure in alcohol, except a stain compounded of the slate colour,
which the nitrate imparts, and the yellow of the sulphure.
To another bit of silk, which was immersed in the aqueous solution of
sulphure, some of the same solution of mercury was applied: the metal
was immediately reduced; and a very black stain attended the reduction.
EXP. 9. COPPER.
A piece of silk was dipped in a solution of sulphate of copper, and
dried in the air; a solution of the sulphure in alcohol was applied to
it; but no change, except a brown stain, was produced.
To another bit of silk, immersed in the aqueous solution of sulphure,
some of the same solution of copper was applied: a white metallic film
was slowly formed, attended with a brown colour.
On another bit of silk, which was dipped in the same solution of
copper, and placed on a saucer, some distilled vinegar was dropped,
and then a few drops of the aqueous solution of sulphure were added:
immediately a white metallic film appeared in greater quantity than in
the preceding experiment.
EXP. 10. LEAD.
A piece of silk was immersed in a solution of acetite of lead in
distilled water, and dried in the air; then the solution of sulphure in
alcohol was applied: but nothing appeared on the silk, except a brown
stain.
A bit of the same silk was dipped in the same solution of lead, then
the solution of sulphure in water was applied: the lead was soon
reduced to its metallic state: a brown stain, and precipitate of the
same colour, attending the reduction.
The same experiment was repeated with this difference, that the silk
was first wetted with distilled vinegar, and instantly the lead was
reduced of greater lustre, and in greater quantity, than in the
preceding experiment.
This experiment was tried on a bit of white calico, dipped in distilled
vinegar, and placed on the palm of my hand; and instantly the metallic
lustre of the lead, which was reduced in great quantity, appeared in a
very remarkable manner, attended with a brown stain.
EXP. 11. TIN.
To a bit of silk dipped in a solution of muriate of tin in distilled
water, and dried in the air, the solution of sulphure in alcohol was
applied: nothing appeared but a brown stain.
Another bit of silk was immersed in the solution of sulphure in water,
then the same solution of muriate of tin was applied; in a short time
some reduced tin appeared on the silk. Vinegar promoted the reduction
of this metal also, in a remarkable manner.
EXP. 12. ARSENIC.
A bit of silk was immersed in a solution of muriate of arsenic in
distilled water, and dried in the air: the solution of sulphure in
alcohol was then applied: the silk first looked yellow, in a short
time the yellow colour almost entirely disappeared, leaving behind a
whitish precipitate; but no other change was produced.
Another bit of silk was dipped in the solution of sulphure in water;
then some of the same solution of arsenic was applied; a yellow
precipitate was formed; and shortly after, this precipitate was
surrounded by a violet margin; but no other change could be observed.
I immersed another bit of the same silk in the same solution of
arsenic, some distilled vinegar was then dropped on it; and lastly the
aqueous solution of sulphure was applied: after some time, a few minute
films of reduced arsenic bright as silver were visible.
Some attention is necessary to discover the reduced arsenic, as the
particles reduced are few, and minute; and sometimes none can be seen.
EXP. 13. BISMUTH.
To a bit of silk, which was dipped in a solution of nitrate of Bismuth
in distilled water, and dried in the air, the solution of sulphure in
alcohol was applied: the silk appeared first yellow, then brown; but no
farther change could be observed.
Another bit of silk was immersed in the solution of sulphure in water;
some of the same solution of bismuth was then applied to it; the metal
was immediately reduced; and a brown precipitate was formed. Vinegar
seems neither to promote, nor retard the reduction.
Two bits of white calico were dipped in the same solution of bismuth;
to one of these placed on a saucer some distilled vinegar was added;
then a single drop of the solution of sulphure in water was applied;
and the whole of the calico, except that part on which the drop fell,
was covered with reduced bismuth, which looked exceedingly bright: the
same appearance was observed on the other bit, to which no vinegar was
added.
EXP. 14. ANTIMONY.
To a bit of silk, which was dipped in a solution of tartarite of
antimony in distilled water, and dried in the air, the solution of
sulphure in alcohol was applied; the silk got a yellow colour, whose
margins, some time after, acquired an orange hue; but no other change
was perceived.
Another bit of the same silk was immersed in the aqueous solution of
sulphure, the same solution of antimony was then applied: part of the
metal was reduced, though in small quantity, attended with an orange
precipitate.
The acids of vinegar, and tartar, seemed to impede the reduction; the
muriatic acid also seemed to have the same effect, though not in so
great a degree as the two former.
EXP. 15. COBALT.
To a bit of silk, which was dipped in a solution of nitrate of cobalt,
and dried in the air, the solution of sulphure in alcohol was applied;
the silk soon became brown; but no farther change could be perceived.
To another bit of silk, which was immersed in the solution of sulphure
in water, a few drops of the same solution of cobalt were applied: the
silk immediately acquired a dark colour, and, in a little time, some
of the metal was reduced, attended with a dull blue precipitate, which
changed to a blackish brown.
Muriate of cobalt was reduced in the same manner: vinegar promoted the
reduction of both these preparations of cobalt.
EXP. 16. IRON.
To a piece of silk, which was immersed in a solution of sulphate of
iron largely diluted, and dried in the air, the solution of sulphure in
alcohol was applied: the silk soon became black; but no other change
could be perceived.
Another bit of silk was dipped in the solution of sulphure in water,
some of the same solution of iron was then applied: the silk instantly
assumed a black colour; but no reduced iron appearing, it was immerged
in a glass of water, and transferred a bright film of reduced iron to
the surface of that fluid.
Sometimes part of the film has not the metallic lustre, which is very
evident in other parts of it; so that the parts completely reduced can
be easily distinguished from the dull and imperfectly reduced black
oxid of iron, intermixed with these bright films.
The same experiments were repeated on bits of calico with the same
result: the calico from its spongy texture is better suited to produce
strong films than silk is.
Vinegar did not promote the reduction of iron in these experiments.
EXP. 17. ZINC.
To a bit of silk, which was immersed in a largely diluted solution of
muriate of zinc, and dried in the air, some of the solution of sulphure
in alcohol was applied; nothing appeared on the silk, but the yellow
colour, which the solution of sulphure imparts.
Another bit of silk was dipped in the solution of sulphure in water,
and some of the same solution of zinc was applied: the yellow colour,
which the solution of sulphure gave the silk, soon became white; but
no reduced zinc could be seen. The silk was then immerged in a glass
of clear water, and transferred a bright film of reduced zinc to its
surface.
In another experiment, made with white calico, the pellicle transferred
to the surface of water was brighter; and more zinc was reduced, than
in the preceding experiment.
Sulphate of zinc also was reduced both on silk, and calico, with this
difference that black, and olive, precipitates, attended the reduction.
EXP. 18. MANGANESE.
I dipped a bit of silk in a diluted solution of nitrate of manganese,
and dried it in the air; the solution of sulphure in alcohol was then
applied: the silk acquired a yellow colour, which soon disappeared; but
no other change could be observed.
To another bit of silk, which was immersed in the solution of sulphure
in water, a drop of the same solution of manganese was applied:
instantly a pearl-white precipitate was formed, the margin of which
soon acquired a bright film of reduced manganese. Under this film a
violet tinge was evident.
The nitrate of manganese used in this experiment was very acid.
A solution of alkaline sulphure in water after a certain length of time
loses the power of reducing the metals, in which respect it resembles
an old solution of sulphate of iron.
Having procured a more neutral solution of nitrate of manganese, I
immersed a bit of silk in the solution of sulphure in alcohol, when
most of the spirit evaporated; a single drop of this solution of
manganese was applied; instantly a bright film of reduced manganese
appeared, attended with a violet tinge, and a brown precipitate. After
some time the violet tinge disappears.
On another bit of silk immersed in the same solution of sulphure in
alcohol, a drop of a solution of sulphate of manganese in distilled
water was applied: instantly films of reduced manganese bright
as silver appeared, accompanied with a faint violet tinge, and a
pearl-white precipitate. These films soon disappear.
A solution of alkaline sulphure in alcohol does not by age lose its
power of reducing the metals, as that in water does; I kept the former
solution more than two years, and found it, at the end of that time, as
capable of reducing the metals, as when it was made.
It is manifest from the experiments related in this chapter,
1. That water is essential to the reduction of metals by alkaline
sulphure.
2. That alcohol does not promote these reductions, without the aid of
water.
3. That alkaline sulphure does not reduce the metals by giving them
phlogiston; nor by uniting with, and separating, their oxygen; for
were either of these opinions true, a solution of alkaline sulphure in
alcohol should reduce them as effectually, as a solution of the same in
water does.
4. That acids contribute to these reductions by promoting the
decomposition of water.
Now since M. Gengembre has demonstrated, that water is decomposed
by alkaline sulphure; who can doubt, that it is decomposed in these
reductions?
The manner, in which metals are reduced by this substance, seems to be
the following.
An hydrure of sulphur, that is, a combination of hydrogen, and sulphur,
is formed: this hydrure of sulphur 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.
The experiments in this chapter leave us no room to doubt of the
decomposition of water in metallic reductions by alkaline sulphure,
and serve to illustrate, and confirm, the manner, in which sulphur,
phosphorus, and other combustible bodies, effect the reduction of
metals.