An essay on combustion, with a view to a new art of dying and painting

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.