REDUCTION OF METALS
BY
_CHARCOAL_.
Finding several combustible bodies, as hydrogen, phosphorus, sulphur,
and combinations of these, capable of reducing the metals in the
ordinary temperature of the atmosphere; I was desirous of knowing, if
Charcoal also possessed that power.
Charcoal may be applied with this view in several forms. M. Rouelle has
observed that caustic fixed alkali dissolves a considerable quantity of
this substance.
Charcoal also exists in a very attenuated state in ether, alcohol, gum,
&c.
I have examined some of its effects on the reduction of metals, in
these different forms, in which it probably exists combined with
hydrogen, and also some of its effects in the solid form.
EXP. 1. GOLD.
A small bit of well burned charcoal was suspended by a thread in
a phial containing a diluted solution of nitro-muriate of gold in
distilled water: some air bubbles soon appeared on the charcoal: and
in about two hours reduced gold was evident on its lower surface, and
increased gradually, till the charcoal was nearly coated with gold of
its proper colour.
This experiment was repeated with a richer solution of gold; the
reduction did not commence near so soon, nor was the quantity reduced
so great, or brilliant, as in the preceding experiment.
EXP. 2. GOLD.
A small bit of charcoal was suspended in a solution of gold in
ether: an effervescence immediately commenced, and continued for a
considerable time: but the solution suffered no change of colour; nor
was there a particle of the gold reduced.
I should not be surprised, if the gold were reduced in this experiment,
as charcoal contains a large quantity of water, which it powerfully
attracts from the surrounding air: however not a vestige of reduced
gold could be perceived.
Bits of charcoal were suspended in the same manner in most of the
metallic solutions treated of in this essay: no change was perceived on
those immersed in solutions of arsenic, manganese, and fused nitrate of
silver in water: but a bit immersed in a solution of the same nitrate
in alcohol, had parts of it covered with bright sparkling particles,
which seemed to vegetate from the charcoal, and were evidently reduced
silver: for they were not soluble in water, on the surface of which the
bit of charcoal deposited some small spangles of great lustre. The bits
immersed in solutions of sulphate of iron and zinc exhibited some very
faint signs of reduction.
But these experiments were not repeated, nor sufficiently varied, to
enable us to form a just opinion of the power of charcoal in reducing
metals in this way.
A small quantity of charcoal, reduced to fine powder, was digested
several days in a strong solution of caustic potash in alcohol; the
phial was frequently shaken to promote the solution.
Some of the clear solution, which was of a reddish colour, was poured
into a phial for use.
EXP. 3. GOLD.
A few drops of this solution of charcoal, or carbone, were applied to a
bit of silk; after the alcohol evaporated, a solution of gold in ether
was dropped on, and immediately produced a brown, which, in about half
an hour, was changed to a purple hue, owing to water attracted from the
air; but no other sign of reduction appeared.
Another bit of silk was immersed in the solution of carbone, and when
the alcohol evaporated, a few drops of an aqueous solution of gold
were applied; a brown stain was instantly formed; the silk was kept wet
with water; the stain gradually assumed a purple tinge, and, in about
five minutes, some reduced gold of its proper splendour, and colour,
appeared: and in some time after every part of the silk, to which the
solutions of carbone and gold were applied, was coated with reduced
gold, which remained permanent. During the experiment, it is necessary
to keep the silk constantly wet with water.
If the solution of gold be applied before the alcohol evaporates,
a black precipitate is formed, along with the brown stain. In an
experiment made in this manner, a metallic film, whitish, and obscure,
appeared in the beginning; but soon vanished: and in some time after
the gold was reduced of its proper colour; and a speck of ruby red
appeared on the margin.
The silk viewed by transmitted light presented various colours, as
purple, blue, and some green.
EXP. 4. SILVER.
A few drops of the solution of carbone were applied to a bit of silk;
when the alcohol evaporated, a solution of fused nitrate of silver in
alcohol was applied: a light brown stain was immediately produced in
the silk; but no reduced silver could be seen.
The solution of carbone was applied to another bit of silk, and when
the alcohol evaporated, an aqueous solution of fused nitrate of silver
was dropped on: a brown stain was instantly formed, and, in about ten
minutes, minute films of reduced silver were visible.
The silk was kept wet with water during the experiment; and the brown
stain was gradually changed to black. In some little time the metallic
films disappeared.
If the solution of silver be applied to the silk, before the alcohol
evaporates, black and brown precipitates are immediately formed; and
commonly no reduced silver can be seen; but sometimes very minute films
appear.
EXP. 5. PLATINA.
To a bit of silk, which was immersed in a solution of nitro-muriate of
platina in distilled water, and dried in the air, a few drops of the
solution of carbone were applied; but no visible change was produced.
Another bit of silk was dipped in the solution of carbone, and when
the alcohol evaporated, a few drops of the solution of platina were
applied: a yellow precipitate was immediately formed, and, in about ten
minutes delicate films of reduced platina were visible: these metallic
films soon vanished; and nothing but a yellow stain and the precipitate
remained.
A bit of calico, on which this experiment was repeated, transferred a
bright film of reduced platina to the surface of water.
During the experiments, the silk and calico were kept wet with water.
EXP. 6. MERCURY.
On a bit of silk, which was immersed in a solution of oxygenated
muriate of mercury in distilled water, and dried in the air, a little
of the solution of carbone was dropped; but the silk underwent no
visible change.
Another bit of silk was dipped in the solution of carbone, and, when
the alcohol evaporated, a little of the same solution of mercury was
applied; a yellow precipitate was immediately formed; and soon after
small films of reduced mercury appeared on the margin of the stain.
This experiment was repeated with a solution of nitrate of mercury, and
the reduction of the metal was very evident on the margin of the stain,
which was black: the precipitate on the bit of silk was of the colour
of sulphur.
EXP. 7. COPPER.
To a bit of calico, which was immersed in a solution of acetite of
copper in distilled water, and dried in the air, a few drops of the
solution of carbone were applied; but no visible change was produced.
On another bit of calico, which was dipped in the same solution
of copper, some of the solution of carbone was dropped: the calico
acquired a slight tinge of brown; it was kept wet with water; and, in
about twenty minutes, several white metallic films were evident.
A bit of silk, on which this experiment was made, acquired a beautiful
red colour, similar to the ruby red, with which copper tinges glass,
and depending on the same cause, viz. the quantity of oxygen combined
with the metal.
EXP. 8. LEAD.
A bit of white calico was immersed in a solution of acetite of lead in
distilled water, and dried in the air: then a few drops of the solution
of carbone were applied; but no visible alteration took place.
On another bit of the same calico, which was dipped in the solution
of carbone, a little of the same solution of lead was dropped; and
in a few seconds films of reduced lead, bright as silver, appeared:
the calico was then immerged in water, and transferred a continuous
pellicle of reduced lead to its surface.
This experiment was often repeated both on silk, and calico: sometimes
the lead is reduced in an instant; but at other times five or six
seconds elapse, before any reduced lead becomes visible.
I also found, that a solution of potash in alcohol reduces lead;
but not so soon, or effectually, or in such quantity, as the former
solution does; but it is evident, that these solutions differ only in
the quantity of carbone, which they contain.
EXP. 9. TIN.
To a bit of calico, which was immersed in a solution of muriate of
tin in distilled water, and dried in the air, some of the solution of
carbone was applied: but no signs of reduction appeared, nor was the
colour of the calico much altered.
On another bit of calico, which was dipped in the solution of carbone,
some of the same solution of tin was dropped: a white precipitate was
instantly formed, attended with bright films of reduced tin: the calico
was immerged in water; and left a bright metallic film on the surface
of that fluid.
The same experiment succeeds on silk.
EXP. 10. BISMUTH.
A piece of silk, which was immersed in a solution of nitrate of
Bismuth in distilled water, and dried in the air, suffered no visible
alteration, on applying the solution of carbone.
To a bit of calico, which was dipped in the solution of carbone, a few
drops of the same solution of bismuth were applied; and immediately
films of reduced bismuth were evident. The calico was immerged in
water, and transferred a bright metallic film to its surface.
This experiment succeeded also on silk.
EXP. 11. ARSENIC.
A bit of silk was immersed in a solution of muriate of arsenic in
distilled water, and dried in the air, then a little of the solution of
carbone was dropped on the silk; but no visible alteration took place.
Another bit of silk was dipped in the solution of carbone, and when the
alcohol evaporated, some drops of the same solution of arsenic were
applied; and in a short time a few minute metallic films were visible
on the silk, which, when transferred to water, were still more so.
Tartarite of antimony, treated in the same manner, transferred a very
delicate film, scarcely visible, to the surface of water.
EXP. 12. IRON.
A bit of calico, which was dipped in a largely diluted solution of
sulphate of iron, and dried in the air, suffered no perceptible change,
on applying the solution of carbone, except a slight tinge of brown.
Another bit of calico was immersed in the same solution of iron, and
placed on a bit of deal board, a few drops of the solution of carbone
were then applied: the calico was kept constantly wet with water, and
in about fifteen minutes films of reduced iron were visible: the calico
was immersed in water, and left a bright metallic film on its surface.
EXP. 13. ZINC.
To a bit of silk, which was dipped in a largely diluted solution of
muriate of zinc, and dried in the air, a few drops of the solution of
carbone were applied; but scarce any alteration of colour, or other
visible change, occurred.
A piece of calico was immersed in the same solution of zinc, and placed
on a bit of thin deal board, a few drops of the solution of carbone
were then applied: the calico was kept constantly wet with water; and
in about fifteen minutes films of reduced zinc were evident: the calico
was immerged in water, and transferred a very bright metallic film of
the colour of zinc to its surface.
I also reduced muriate of cobalt in this manner.
EXP. 14. MANGANESE.
To a bit of silk, which was dipped in a diluted solution of nitrate of
manganese, and dried in the air, some drops of the solution of carbone
were applied; but nothing appeared, except a brown stain.
Another bit of silk was immersed in the solution of carbone, when the
alcohol evaporated, a few drops of the same solution of manganese were
applied: a brown stain was soon produced; the silk was kept wet with
water, and in about twenty minutes films of reduced manganese of a
bluish white colour were evident on the silk.
This experiment did not succeed with a strong solution of nitrate of
manganese.
The same experiment succeeds also on linen, and calico, both with
nitrate, and sulphate of manganese; the reduction is attended with
violet, and purple, colours, such as this metal imparts to glass,
and other substances, in which it exists combined with different
proportions of oxygen: this difference is the cause of the different
colours, which solutions of manganese assume.
The bright films of reduced manganese soon disappear, the cause of
which has been explained in the first chapter of this essay: the
explanation there offered is confirmed by the following facts.
“Regulus of Manganese,” says Mr. Bergman, “when well fused generally
persists in a dry place, but sometimes undergoes spontaneous
calcination, and falls down in a brownish black powder.
“Moisture, but particularly the access of aerial acid, assists this
operation. A small piece, put into a dry bottle, well corked, remained
perfect for the space of six months, but afterwards, exposed to the
open air of a chamber for two days, contracted a browness on its
surface, together with so much friability as to crumble between the
fingers. The internal parts, however, retained an obscure metallic
splendour, which disappeared in a few hours[18].”
I shall now relate a few experiments made with ether, alcohol, and gum.
EXP. 15. GOLD.
I evaporated a solution of gold in nitro-muriatic acid to dryness,
and dissolved the salt in pure alcohol: the solution was poured into
a phial carefully dried in hot sand, and rinced with pure alcohol:
the solution filled about ¾ of the phial, which was carefully corked,
and though it was nine months exposed to the gray light, no films of
reduced gold appeared.
Part of the same solution was poured into a phial, and diluted with
water; films of reduced gold soon appeared.
EXP. 16. GOLD.
A phial half filled with a solution of gold in sulphuric ether was
exposed nine months to the gray light; but no films of reduced gold
were produced.
On a bit of silk, which was dipped in part of the same solution of
gold, and exposed to the gray light, and kept wet with water, reduced
gold appeared in the space of a few hours.
EXP. 17. GOLD.
I mixed an aqueous solution of gold with a solution of gum arabic in
distilled water, in such proportion, as to prevent the solution from
spreading in the silk.
With this solution I drew several stripes on a piece of silk, and
exposed it to the gray light of a chambre: in some time the gold was
reduced attended with blue, and purple, colours.
Similar stripes were drawn on another piece of silk, which, after the
stripes became sufficiently dry, was placed over the vapour of hot
water; and in about fifteen minutes the gold was reduced in a beautiful
manner.
This solution was applied to another bit of silk, which, after it
became sufficiently dry, was placed between the leaves of a blank book,
to exclude the action of light; the gold, after some time, was reduced.
I found that small stripes, and spots, made with this solution, were
reduced by breathing on them for some time.
Sugar also, mixed with the solution of gold, promotes the reduction;
but not so well as gum.
A bit of silk was dipped in a solution of nitrate of silver in
distilled water, and exposed, while wet, to the smoke of a common fire;
in a short time reduced silver appeared.
The following inferences are deducible from the experiments related in
this chapter.
1. Charcoal is capable of reducing the metals in the ordinary
temperature of the atmosphere.
2. Water is essential to the reduction of metals by charcoal: for these
experiments prove, that the reduction cannot be effected without water.
3. Charcoal does not reduce the metals by giving them phlogiston; nor
by uniting with, and separating, their oxygen; for were either of these
opinions true, metallic solutions in ether, and alcohol, should be as
effectually reduced by charcoal, as metallic solutions in water are.
4. Ether, and alcohol do not promote the reduction of metals without
the aid of water: but when this is present in sufficient quantity, they
effect the reduction, in the same manner, that charcoal, and other
combustible bodies do.
It is evident then that charcoal reduces the metals by decomposing
water; which seems to be effected in the following manner.
The carbone of the charcoal 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 carbone is oxygenated by the oxygen of the
water, and forms carbonic acid, while the metal is restored to its
combustible state.
This explanation is supported by the following fact: M. Gengembre
has observed, that if charcoal be immersed in water, and kept at a
temperature of 30 degrees of the thermometer of M. De Reaumur, the
water is gradually decomposed, and inflammable gas is formed[19].
That charcoal effects the reduction of metals, in high degrees of heat
also, by decomposing water, is evident from the following observations.
The great force with which charcoal attracts water is a fact
sufficiently established; Dr. Priestley is so convinced of this, that
he expresses himself in the following strong terms. “I did not know,
nor could believe the powerful attraction, that charcoal, or iron,
appear to have for water; when they are intensely heated, they will
find, and attract it in the midst of the hottest fire through any pores
in the retort[20].”
Now since water is essential to the reduction of metals in low degrees
of heat; and since that fluid is always present, when metals are
reduced by charcoal in high degrees of heat; it is manifest, that
charcoal acts in the same manner in both these temperatures; and since
water is easily, and instantly, decomposed by charcoal at a red heat,
as the Antiphlogistians themselves allow; it clearly follows that their
theory of metallic reduction is erroneous: for since the water is
instantly decomposed by the charcoal, it is a necessary consequence,
that its carbone must unite with 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, forming a new quantity of water equal to
that decomposed: this new quantity of water may be decomposed in its
turn: so that a thimble full of water would be sufficient to reduce any
quantity of metal; provided the water were prevented from escaping, and
time enough allowed.
Beside this source of water, the air of the atmosphere, which
contributes to support the fire is an inexhaustible magazine of water:
and the hotter the air is, the more water it holds in solution; as
M. Le Roy has demonstrated[21]. Moreover all metallic oxids and ores
contain a large proportion of water.
From this view it appears, that the manner, in which charcoal, and
other combustible bodies, effect the reduction of metals, is by
assisting to decompose water, the hydrogen of which is therefore the
only reducer of the metals.
In order to point out the difference between this opinion, and that of
the Antiphlogistians, I shall present the reader with M. Lavoisier’s
idea of metallic reduction.
“It can not be doubted,” says that celebrated chymist, “that charcoal
at a red heat takes oxygen from all metallic substances: this is a fact
against which no exception can be made: and it is the foundation of the
whole theory of metallic reduction.”
But the experiments in this essay demonstrate, that this assertion
is erroneous in every instance of metallic reduction: for so far is
it from being true, that charcoal takes oxygen from all metallic
substances, that it never does so in one single instance; since its
carbone always unites with the oxygen of the water, the hydrogen of
which unites immediately to the oxygen of the metal, and reduces it.
“But this action of charcoal on oxygen,” adds M. Lavoisier, “this
property, which it possesses of taking it from metallic subsubstances,
is not so strong in the cold, as at a red heat, since we are
unacquainted with any metallic revivification effected by charcoal
without heat[22].”
It is evident that this mode of reasoning is no longer of any weight;
since charcoal does reduce metals in the ordinary temperature of the
atmosphere.
The reason charcoal is more powerful in high degrees of heat, than
other reducers of the metals, is its great fixity in the fire, and
the immense force, with which it attracts, and imprisons water in its
pores: thus preventing its escape till it be decomposed by an affinity,
which is much more complex than has been hitherto imagined.
Another reason of the superior power of charcoal in metallic reduction
is, that it forms a volatile elastic fluid with the oxygen of the
water, which flies off; and consequently does not react on the metal,
or disturb, or impede, by its presence, the action of the reducing
powers: advantages that phosphorus, or any other combustible substance,
which forms a fixed acid, that reacts on the metal, can never possess.