_Reduction of Metals by Phosphorus._
The next substance, of whose effects in reducing metals in the fibres
of silk, I shall treat, is Phosphorus, one of the most inflammable
substances, we are acquainted with.
I was for some time at a loss, how to apply it to this purpose; but
learning from a note of Mr. Lewis, that it is soluble in ether; I
dissolved a small quantity of it in that fluid, which can be easily
effected, if the ether be good. The solution is considerably promoted
by a gentle heat, as that of the hand, and may be made in a small
phial, which should be nearly filled with the ether, and accurately
corked: a common cork is preferable, for this purpose, to a glass
stopper; and a single grain of phosphorus is sufficient for a great
number of experiments.
I sometimes applied a much greater degree of heat than the above, by
placing the phial in hot sand, pressing on the cork at the same time
with my finger, to prevent its being forced out by the expansion of the
ether, part of which is converted into an elastic fluid, and holds some
phosphorus in solution: the ether soon begins to boil; the phosphorus
melts; and a strong solution is obtained in a few minutes by shaking
the phial. If the solution be removed to a cool place it frequently
deposits crystals.
This manner of preparing the solution is attended with some danger; for
should the phial burst, or the cork be extruded, the contents will be
thrown out with considerable force, and that part of the phosphorus not
dissolved by the ether burn with great violence.
The only objection to this preparation of phosphorus is the ether,
which must necessarily modify the result, and prevent that simplicity
so desirable in experiment.
But, after some observation, it was perceived, that the ether flies
off, and leaves the phosphorus pure, and minutely divided in the fibres
of the silk: the ether, from its great volatility, first evaporates,
and, at the same time, produces a very considerable degree of cold,
which effectually prevents the evaporation, and combustion, of the
phosphorus.
After the ether evaporates; the cold ceases, and the combustion of the
phosphorus commences, attended with white fumes, which continue till
the whole is consumed, if no other power intervene.
Hence it is evident, that this preparation of phosphorus has a
simplicity, and elegance, not always to be obtained.
It has also another great advantage in experiments of this kind; for
it does not change, in the smallest degree, the white colour of silk,
during its slow combustion, which is not attended with heat sufficient
to affect the most delicate colour. This property of not affecting the
colour of the silk renders observation, and experiment, more accurate;
as whatever change supervenes, must depend either on the metallic
solution itself, or on the action of the phosphorus on the same. But
this advantage is confined to a certain range of the thermometer; for
if the heat be increased to about 86° of Fahrenheit, and the silk be
dry, the phosphorus is apt to set fire to it.
EXP. 1. GOLD.
I immersed a bit of silk in a solution of gold in ether, and after the
ether evaporated, dropped on it some of the solution of phosphorus,
which diffused itself through the silk, like a drop of oil, and formed
a circumscribed spot, whose limits, as the ether evaporated, assumed
a brown colour, which soon diffused itself equally over every part,
to which the solution of phosphorus was applied; but the parts of the
silk, to which the latter did not reach, retained the yellow colour,
which the solution of gold gave them.
The silk viewed by transmitted light presented the same colours, except
that the limits of the brown appeared more intense, and seemed to
border on a faint purple.
Examining the silk next day, I found, that the whole of the brown stain
acquired a faint shade of purple, which was most evident on the margins
of the stain.
EXP. 2. GOLD.
I dipped a bit of silk in the solution of gold in ether, and after it
was well dried, half of it was wetted with distilled water; the other
half remaining dry: the solution of phosphorus was applied to both the
moist and dry parts of the silk: instantly the part wetted with the
water began to acquire a purple colour; and, soon after, the metallic
splendour of the gold appeared; but that part, which was kept dry,
acquired only a brown stain, similar to that described in the preceding
experiment.
I repeated these experiments many times, and always found, that the
gold was reduced only in proportion to the water applied.
Finding water promoted the reduction of gold by phosphorus, I began to
form various conjectures about its mode of action: I first supposed,
it acted by holding the particles of the salt minutely divided, thus
diminishing their attraction of cohesion, and consequently increasing
their chymical attraction.
The truth of this supposition might, I thought, be decided by using
ether, and alcohol, instead of water, to wet the silk, avoiding
aqueous moisture, as much as possible; accordingly, I made the
following experiments, which were frequently repeated with nearly the
same result.
EXP. 3. GOLD.
A piece of silk was immersed in the solution of phosphorus; as soon as
the ether evaporated, and the phosphorus began to fume, an ethereal
solution of gold was dropped on the silk, which immediately got a brown
colour; the piece was kept constantly wet with ether; in some time a
purple tinge appeared on parts of the silk; and, shortly after, small
films of reduced gold appeared: the silk was now remarkably wet, and
seemed to have a great power of collecting water; this, I supposed, was
partly attracted from the air by the salt, and phosphorous acid formed
during the combustion, which has a powerful attraction for water; and
partly deposited in the silk by the ether during its evaporation.
In order to determine if the ether during its evaporation deposited
water in the silk, I kept a bit of silk wet with ether for a few
minutes, and found, that, after the evaporation ceased, the silk was
moist: but this humidity was not so great, as that observed in the
silk, to which the ethereal solutions of phosphorus, and gold, were
applied.
Another bit of silk was dipped in the ethereal solution of gold, and
after the ether evaporated, the solution of phosphorus was applied: a
brown colour was produced; the silk was kept wet with ether, and, in a
short time, a purple tinge appeared on parts of it; but chiefly at the
margin of the stain, which gradually diffused itself over the whole.
The only difference between this and the preceding experiment on gold
is the order, in which the solution of gold, and phosphorus, were
applied to the silk; but there is a considerable difference in the
result; for in this the brown and purple colours were formed much more
slowly, and no particles of reduced gold appeared till after a much
longer time.
EXP. 4. GOLD.
A piece of silk was immersed in the solution of phosphorus, and when
the white fumes began to rise, a solution of gold in alcohol was
applied to the silk, which was kept wet with alcohol; a brown tinge,
which soon changed to a purple, appeared on different parts; and, in a
little time after, a very small film of reduced gold was visible on a
part of the margin.
In another experiment, conducted in the same manner, the reduction was
more evident.
The solution of gold used in this experiment was very rich; and had
a great attraction for water; for bits of silk tinged with it, could
not be dried without difficulty; and after they were removed to a cool
place, they very soon became moist again. This is more or less the case
with solutions of gold in general.
EXP. 5. GOLD.
A bit of silk was dipped in a solution of gold in alcohol, and dried;
then some of the solution of phosphorus was poured on the silk; a
brown, and then a purple colour, appeared; and in some parts a small
portion of the gold was reduced: the reduction was very obscure; but
became gradually more evident, in proportion as it attracted water from
the air. The silk was occasionally wetted with alcohol.
This experiment was repeated, with this difference, that the silk was
not kept wet with alcohol; and no reduced gold could be perceived.
EXP. 6. GOLD.
In order to exclude water more effectually, a small phial was carefully
dried by placing it in hot sand, and then corked, to prevent the access
of moisture from the air; when the phial cooled, it was nearly filled
with ether, and a small bit of phosphorus dropped into it; it was then
corked, and replaced on the hot sand; the phosphorus soon melted, and
a strong solution was obtained by shaking the phial.
Into this solution a small bit of silk, which was dipped in a rich
solution of gold, and carefully dried, was introduced: the silk
immediately got a brown tinge; but not a particle of reduced gold could
be perceived. The solution in a short time became turbid, and deposited
a brown powder. The colour of the precipitate was exactly the same, as
that which the silk acquired. The experiment was continued about three
months, and carefully observed; but no other change could be perceived:
at the end of this time the silk was taken out of the phial; and the
solution of phosphorus was found capable of reducing gold and silver by
the aid of water.
EXP. 7. GOLD.
In order to contrast the effects of water with those of ether, and
alcohol, more fully, a piece of silk was immersed in a solution of
nitro-muriate of gold in water, and dried in the air about twelve
hours; during which time the yellow tinge, the solution of gold gave
the silk, remained unchanged: the solution of phosphorus was then
applied; a brown stain appeared; the ether soon evaporated; the
phosphorus began to fume; and the silk acquired a purple colour; but
not a particle of reduced gold could be perceived. The purple tinge
in this bit of silk was much more intense, and more equal, than in the
pieces, in which ether and alcohol were used.
EXP. 8. GOLD.
I dipped a piece of silk in the solution of phosphorus, when the ether
evaporated, and the phosphorus began to fume, a solution of gold in
water was applied; instantly the silk was covered with a splendid coat
of reduced gold.
Nothing can be more striking than this experiment, which was repeated
times without number, or demonstrates the necessity of water in these
reductions in a more convincing manner.
This piece, viewed by transmitted light, had a purple colour with a
considerable tinge of blue; and the margin of the reduced gold was
fringed with purple.
EXP. 9. GOLD.
Thinking that phosphorus applied in the form of vapour through the
medium of water might be more effectual than a solution of it in ether,
I immersed a small bit of silk in an aqueous solution of gold, and
suffered it to dry a little; it was then suspended in a phial over
a little water, into which a small bit of phosphorus was previously
introduced: the phial was then corked, and placed on hot sand: the
phosphorus began to melt, and ascend in white vapours, which, as soon
as they reached the lower end of the silk, gave it a brown tinge,
succeeded by a purple; and the gold began to assume its metallic
splendour: in a short time these appearances were evident over the
whole silk.
The following propositions are deducible from these experiments.
1. Water does not promote the reduction of gold merely by dissolving,
and minutely dividing, the particles of the salt, and thus diminishing
their attraction of cohesion, and consequently increasing their
chymical attraction, as I first supposed; for were this the case, ether
and alcohol, which equally dissolve, and divide, the salt, should
produce the same effect.
2. Ether and alcohol do not promote these reductions without the aid
of water; for it is evident from the experiments related, that the few
particles of reduced gold, which appear, when they are employed, depend
entirely on the quantity of water, which they leave in the silk during
their evaporation, and that attracted from the air by the solution of
gold, and by the phosphorus during its combustion, both of which have a
strong attraction for water.
3. Phosphorus does not reduce gold by giving the metallic earth
phlogiston, as the Phlogistians suppose; for were this opinion true,
a solution of gold in ether, or alcohol, should be reduced by the
phosphorus as effectually as a solution of gold in water is.
4. Phosphorus does not reduce gold, by combining with, and separating,
the oxygen of the gold, as the Antiphlogistians assert; for were
this the case, the particles of the phosphorus so attenuated by the
ether, should reduce a solution of gold in ether, or alcohol, as well
as a solution of gold in water, since the impediment opposed by the
attraction of cohesion is equally removed in both cases.
I shall conclude these remarks on the reduction of gold with the
following experiment, which often amused me.
EXP. 10. GOLD.
A small bit of silk was immersed in a solution of gold in ether, and
dried; then the solution of phosphorus was applied, which changed the
yellow colour of the silk to a brown: when the phosphorus began to
fume, I placed the silk on the palm of my hand, and breathed on it a
considerable time; a purple tinge gradually succeeded the brown, and,
in some little time after, the metallic lustre of the gold began to
appear.
The same experiment succeeds with a solution of gold in alcohol.
Another bit of silk, treated in the same manner, was placed over the
vapour of warm water for some time; the same appearances took place,
and particles of reduced gold were evident in the silk.
If the water, whence the vapour arises, be too hot; the heat retards,
and sometimes prevents, the reduction, by volatilizing the phosphorus.
EXP. 11. SILVER.
I dipped a bit of silk in a solution of fused nitrate of silver
in alcohol, and dried it in the air: then some of the solution of
phosphorus was applied, which produced a brown stain, whose margin,
after a few minutes exposure to the air, acquired a livid white
appearance, caused by a partial and imperfect reduction of the silver.
This, however, would not be taken by a person unacquainted with
experiments of this kind for reduced silver.
EXP. 12. SILVER.
A bit of silk was immersed in the solution of phosphorus; as soon as
the ether evaporated, and the phosphorus began to fume; a few drops of
the solution of silver in alcohol were applied: immediately a black
stain, intermixed with some brown, appeared: and, after some time,
obscure films of reduced silver presented themselves; these appeared
on different parts of the stain; but were so minute as to be scarce
visible. The only difference between this and the preceding experiment
is the order, in which, the solutions were applied; but even this
modifies the result in some measure.
That these imperfect reductions depended on water, deposited in the
silk, by the alcohol during its evaporation, or attracted from the air
by the phosphorus during its combustion, will appear from the following
experiment.
EXP. 13. SILVER.
A small phial was well dried in hot sand, then corked, and removed to
a cool place; after the phial cooled, it was nearly filled with ether,
and a small bit of phosphorus, which was repeatedly washed in alcohol
to free it from any aqueous moisture, that might adhere to it, was
introduced; the phial was then corked, and placed in hot sand; when the
phosphorus melted, I shook the phial, and obtained a strong solution.
Into this solution a small bit of silk, which was dipped in a solution
of silver in alcohol, and dried, was introduced: the phial was corked;
the silk instantly assumed a brown colour; but not a particle of
reduced silver could be seen, though the experiment was continued about
three months; nor did the solution of phosphorus become turbid, or
deposit any precipitate, as happened in similar experiments on gold.
At the end of this period the silk was taken out of the phial, wetted
with water, and suspended in a window; and, after a considerable time,
reduced silver was manifest on different parts of the silk.
With the solution of phosphorus, in which the silk stood during that
time, I reduced gold, and silver, with the assistance of water.
In order to compare the effects of water with those of ether and
alcohol, I made the following experiments.
EXP. 14. SILVER.
I dipped a bit of silk in a solution of nitrate of silver in water,
and dried it at the fire: the silk thus dried retained its white
colour: the solution of phosphorus was then applied, and immediately
produced a brown colour, which soon, in proportion as the phosphorus
fumed, acquired a deeper tinge, verging on black; and slight signs of
reduction appeared after a little time on the margin of the stain.
Another bit of silk, treated in the same manner, but dried much better,
exhibited still fainter signs of reduction: for the brown stain did not
appear on this piece as soon as on the former, nor was it so intense;
however, after some minutes exposure to the air, the stain became
deeper, and its margin acquired a livid white appearance, owing to a
partial reduction of the silver.
It has been often remarked, that the reduction commences first on the
margin of the stain, which the solution of phosphorus, and that of the
metal, produce in the silk: I was a long time at a loss to account
for this appearance; but the cause was accidentally discovered; for
happening to spill a few drops of the solution of phosphorus on a
table, I observed, that, as they evaporated, watery circles were formed
round the spaces, on which the drops fell; and, that all the parts
within the circles were dry.
This explains why the reduction begins on the margin of the stain.
I observed the same of alcohol; for if it be dropped on a level
surface, it leaves a watery ring behind, though not near so soon, as a
solution of phosphorus in ether does: this is the reason why alcohol
seems to promote the reduction of some metals; I say seems; for it
does not promote it, but in proportion to the quantity of water it
contains, or attracts from the air, and deposits in the silk during its
evaporation.
How essential water is to the reduction of metals will appear from the
following experiment.
EXP. 15. SILVER.
I immersed a piece of silk in the solution of phosphorus, and after
the ether evaporated, and the phosphorus began to fume, a solution
of nitrate of silver in water was applied; instantly the silver was
restored to its metallic splendour.
This experiment is very amusing, and well calculated to strike the
beholder with surprise.
The reduction is sometimes attended with spangles of a beautiful blue,
which appear chiefly where the solution of silver is most abundant.
The solution of silver is commodiously applied by a camel hair pencil.
I also tried the effects of the vapour of phosphorus on bits of silk
dipped in a solution of nitrate of silver in water, and exposed to the
vapour, in the same manner as in experiment the 9th; and the silver was
always reduced: but a solution of phosphorus in ether seems preferable
to the vapour.
A small glass tube, resembling a thermometer, with its bulb terminating
in a smaller and nearly capillary tube, I found useful, and economic,
especially in experiments on gold: by immersing the smaller end in the
metallic solution, and inspiring through the tube at the same time, the
bulb may be filled: by this means a single drop, or more, if necessary,
may be applied to the silk; and, thus, a great number of experiments
can be made on a single grain, or a much less quantity, of gold, or any
other metal.
This little instrument may be used also to apply the solution of
phosphorus to the silk; and it was by using it for this purpose,
I discovered, that phosphorus has not the power of reducing silver
without the aid of water; for blowing the solution of phosphorus from
the tube on bits of silk, which had been dipped in a solution of
silver, and dried, I was surprised to find films of reduced silver
frequently appear; whereas none appeared, when I applied the solution
of phosphorus in a different manner: this unexpected event often
occurred, before I learned the cause; at length I suspected, it might
depend on the moisture of the breath; and I was soon convinced by
moistening the silk with water, that the suspicion was well founded.
It is evident from these experiments on silver, that water is essential
to the reduction of this metal by phosphorus; and that ether, and
alcohol, do not promote it.
It is also evident, that these experiments, and those, made on the
reduction of gold, mutually illustrate each other; and confirm the
conclusions drawn from them.
EXP. 16. PLATINA.
I immersed a bit of silk in a solution of nitro-muriate of platina in
distilled water, and dried it in the air; the solution of phosphorus
was then applied to the silk; but no appearance of reduction could be
perceived.
Another bit of silk was dipped in the solution of phosphorus; when the
ether evaporated, and the phosphorus began to fume, the solution of
platina was applied to the silk; and, in some time, delicate films of
reduced platina were visible where the water was most abundant. These
films of platina commonly disappear; and nothing remains but a brown
tinge, which, however, is more intense, than what the solution of
platina alone gives the silk.
To succeed in this experiment, the silk should be replete with
phosphorus; which is easily done by applying the solution twice or
thrice, and waiting after each application, till the fumes begin to
appear. It is also necessary to keep the silk constantly wet with
water. Sometimes it requires from ten to twenty minutes to reduce
platina in this manner.
EXP. 17. MERCURY.
I dipped a bit of silk in a solution of oxygenated muriate of mercury,
and dried it in the air; then the solution of phosphorus was applied;
when the ether evaporated, and the phosphorus began to fume, a yellow
stain commenced on the margin, and gradually appeared over the whole.
To compare the effects of different degrees of moisture, I immersed a
bit of silk in the same solution of mercury, and dried it carefully at
the fire; the solution of phosphorus was then applied; the silk began
to fume; but no change, except a very slight ring of a yellow hue,
appeared. The rest of the silk retained its white colour.
Another bit of silk was immersed in the solution of phosphorus, when
the ether evaporated, and the phosphorus began to fume, the same
solution of mercury in distilled water was applied; and, in a few
seconds, a bright film of reduced mercury was visible on the margin of
the part, to which the metallic solution was applied, and after some
time appeared on the whole. The reduction was attended with the colours
of the rainbow.
After a little time, these colours vanish, and the metallic film
becomes much more obscure, according as the silk dries, and is
succeeded by a yellow stain.
EXP. 18. MERCURY.
A bit of silk was dipped in a solution of nitrate of mercury in
distilled water, and dried at the fire; then the solution of phosphorus
was applied; and, when it began to fume, a brown stain commenced at
the margin, which soon diffused itself over the whole, and gradually
acquired a faint tinge of black.
Another piece of silk, treated in the same manner, but dried in the
air, exhibited the same appearances; except that the brown tinge verged
more on black.
Another bit of silk was immersed in the solution of phosphorus, and
when it began to fume, the solution of nitrate of mercury was applied;
a brown colour instantly appeared, accompanied with a film of reduced
mercury, which was most evident where the metallic solution was most
abundant. This film soon disappeared, and was succeeded by a black
stain, in which, however, reduced mercury was visible. No colours but
black, and brown, appeared in this experiment.
It appears from these experiments on mercury, that the reduction kept
pace with the quantity of water present.
EXP. 19. COPPER.
A piece of silk was immersed in a solution of sulphate of copper, and
dried in the air: then a strong solution of phosphorus was applied; the
silk acquired a brown colour; but no other visible alteration occurred.
Another piece of silk was dipped in the same solution of copper, and
dried at the fire much better than the preceding; the solution of
phosphorus was applied; when the ether evaporated, and the phosphorus
began to fume, a brown tinge commenced on the margin of the silk, and
gradually diffused itself over the whole; but the stain was by no means
so intense as that produced in the preceding piece: so that there can
be no doubt that the difference was owing to the different degrees of
moisture in the silk.
After this piece remained in the air for some time, the brown tinge
became more intense, a proof that it attracted water from the air. This
difference in the appearances of pieces dried in the air, and at the
fire, I frequently remarked.
EXP. 20. COPPER.
A strong solution of phosphorus was applied to a piece of silk, when
the ether evaporated, and the phosphorus began to fume, a solution of
sulphate of copper was applied; a brown stain was instantly produced,
and its margins were soon covered with a _white_ metallic film, parts
of which, after some time, verged on the colour of copper, intermixed
with purple, green, and blue. If the solution of phosphorus be weak,
which is always the case, when the ether is bad, nothing appears on
the silk but the brown stain, and the _white_ metallic film. As the
silk dries most of these appearances vanish; but some of the blue tinge
survives; and the silk looks very unseemly.
A bit of silk was immersed in the same solution of copper, and exposed
to the vapour of phosphorus, as in experiment the 9th; but no change
was produced on the silk, except a few brown spots, though the heat
was such that the vapour filled the phial, and circulated through it:
the vapour corroded a brass pin, which was used to suspend the silk
in the phial. This induced me to try its effects on copper, which
was corroded by it in a remarkable manner, and changed into a black
substance resembling a mixture of charcoal and oil. It appears then
that phosphorus is ill adapted to the reduction of this metal.
EXP. 21. TIN.
A bit of silk was immersed in a solution of muriate of tin in distilled
water, and dried in the air; the solution of phosphorus was then
applied to the silk, and though it fumed considerably, no change
whatever could be perceived in the colour of the silk; nor was there
the smallest appearance of reduction.
I poured some of the solution of phosphorus on a bit of silk, and when
it began to fume, the solution of tin was applied: after a few seconds,
white metallic films appeared, first on the margin, and were gradually
diffused over that part of the silk, to which the muriate of tin was
applied: a yellow colour intermixed with red sometimes attends the
reduction. After some little time these films of reduced tin vanish,
and scarcely leave a stain behind.
I did not succeed in reducing acetite of lead, muriate of arsenic, or
sulphates of iron, and zinc, in this way.
These experiments on tin shew that water is essential to its reduction
by phosphorus, and give additional force to the preceding conclusions.
M. Sage discovered that gold, silver, &c. are precipitated from their
solutions in the metallic form, by pieces of phosphorus, which are
covered at the same time with bright coats of gold, silver, &c.
To determine if water were essential to these reductions performed by
M. Sage, I made the following experiments.
EXP. 22. GOLD.
Some solution of phosphorus in ether was poured into a china cup, and
a few drops of the ethereal solution of gold were added; instantly a
brown powder was precipitated similar to what appeared in experiment
the 6th, but no gold in its metallic form could be perceived.
EXP. 23. GOLD.
A solution of nitro-muriate of gold in water was poured into a china
cup, containing a solution of phosphorus in ether; instantly the
gold began to assume its metallic splendour, attended with a variety
of colours, as purple, blue, and red, the beauty of which cannot be
described: the quantity of the blue was gradually diminished, and what
remained, was dispersed over the surface in small films, intermixed
with spangles of reduced gold. Most of the blue films were of a
circular figure; some had a central speck of ruby red, and were fringed
with purple; some had a round central speck of a darker blue than the
surrounding parts: and some were of an irregular figure, fringed with
purple, or ruby red. I often observed these blue films assume the real
colour of gold without suffering any intermediate change of colour;
and, I think, I observed the same of one of the largest specks of ruby
red, that appeared in this experiment. All these colours disappeared,
when the reduction was completed.
The variety of colours, which those films assume, depends on the
different degrees of reduction; that is to say, on the quantity of
oxygen combined with the metal: in proportion as the metal is deprived
of the oxygen, it assumes various colours, which often succeed
each other in a regular order, showing the different stages of the
reduction: thus when gold is reduced; the first perceptible change is a
green, which soon becomes olive; this is succeeded by blue, and purple;
and sometimes by a ruby red: the purple tinge is a mixture of blue, and
red.
The various colours, which metals, and their calces, communicate to
glass, and other substances, are explicable on these principles: and
the difficulty of obtaining a ruby-coloured glass by gold is readily
understood from the facility, with which that metal parts with oxygen.
EXP. 24. GOLD.
A thread was passed by means of a needle through a small bit of
phosphorus, which was freed from any moisture, that might adhere to
it, by immersing it for some time in alcohol; it was then suspended
by means of the thread in a solution of gold in ether, contained in
a phial, which was carefully dried in hot sand: in a few minutes,
the solution became turbid, an effervescence commenced, and a brown
precipitate was formed: according as the precipitate fell, the solution
became clear, lost its yellow colour; and the whole of the gold seemed
to have been precipitated: but not a particle of reduced gold could be
seen.
Another bit of phosphorus was suspended in the same manner in a
solution of nitro-muriate of gold in water; and in a few minutes got a
splendid coat of reduced gold.
EXP. 25. SILVER.
A few drops of a solution of fused nitrate of silver in alcohol were
poured into a china cup containing a solution of phosphorus in ether:
instantly a black precipitate, with a tinge of brown, was formed; but
no silver in its metallic state could be perceived.
After some time the precipitate attracted moisture from the air; and
some films of reduced silver appeared.
The same experiment was made in a phial, which was corked, to exclude
the moisture of the air; and nothing, but the black precipitate,
appeared.
Some of the same solution of silver was diluted with water, and dropped
on a solution of phosphorus in ether; and instantly films of reduced
silver floated on the surface.
EXP. 26. SILVER.
A bit of phosphorus was suspended by a thread in some of the same
solution of silver in alcohol, contained in a phial carefully dried: a
black precipitate with a tinge of brown soon appeared; but no silver in
its metallic state could be observed; part of the precipitate adhered
to the phosphorus, and part fell to the bottom of the phial.
In another experiment made in a phial not sufficiently dried, a few
small films of reduced silver were observed on the sides of the phial;
but not a particle of silver in its metallic form could be seen on the
phosphorus.
Another bit of phosphorus was suspended in a diluted solution of
nitrate of silver in water: and in some hours, the phosphorus was
covered with reduced silver.
The case of silver, which covered the phosphorus, prevented its
spontaneous combustion in the air; the same was observed of the bit of
phosphorus coated with gold.
Hence it appears, that M. Sage’s success in reducing metals by
phosphorus depended on the water of the metallic solution.
These experiments were often repeated with nearly the same result; but
some variety often occurs, depending on various circumstances; as the
strength of the metallic solution, and that of the phosphorus; the
quantity of water present, and the purity of the materials employed.
It is difficult to obtain ether, or alcohol, with the least possible
quantity of water; and equally difficult to expel all moisture from
the surface of glass; for this reason, the bits of phosphorus in the
experiments made with alcohol and ether were suspended by threads, so
as not to touch the sides of the glass.
I shall conclude this chapter with a general view of the inferences,
which seem naturally to flow from these experiments with phosphorus.
1. Water is essential to the reduction of metals by phosphorus;
for these experiments show that the reduction is effected only in
proportion to the quantity of water present.
2. Phosphorus does not reduce the metals by giving them phlogiston.
3. Phosphorus does not reduce the metals by uniting with, and
separating, their oxygen.
How then is the reduction effected? are we not to conclude, that it is
effected by the decomposition of the water, in the following manner?
The phosphorus attracts the oxygen of the water, while the hydrogen of
the latter unites, in its nascent state, with the oxygen of the metal,
and effects the reduction.
Hence it follows, that the phosphorus is oxygenated by the oxygen of
the water, while the metal is restored to its combustible state.
Thus what could never be effected by a single, is readily performed by
a double affinity; which always takes place in preference to a single
affinity, as the experiments of Messrs. Monnet, and Kirwan, mentioned
in the preceding chapter, show.
It is well known, that phosphorus kept in water acquires an oxygenated
crust, which could not happen without a decomposition of the water:
this fact serves to confirm the explanation here offered.
And indeed the decomposition of water in these experiments must be
granted, or it must be supposed, that water itself reduces the metals,
by uniting with their earths, and constituting their phlogiston; or by
uniting with, and separating, their oxygen; suppositions repugnant to
our present knowledge of chymistry.