As Hydrogen, or the base of inflammable air, seems to act an important part in the following experiments, and is, according to some chymists, pure phlogiston itself; I have therefore assigned the first chapter in this essay to hydrogen gas, this being the most simple form, in which hydrogen has hitherto been obtained.
But I had not the means of procuring this gas free of carbone, and other impurities, that it dissolves and elevates during its formation; or of excluding atmospheric air, which circumstances, I am sensible, must, in some measure, influence the result; as it cannot be supposed, that these extraneous bodies would remain inactive during the process of reduction. However, as such exactness is not in the power of every experimenter, I was under a necessity of using hydrogen gas, with the disadvantages here mentioned.
Though most of the experiments in this essay were made on a variety of white and coloured silks, I shall relate only those made on the former, as it exhibits the changes produced more distinctly, and contains less foreign matter to modify the result of experiment; and, for brevity’s sake, I shall use the term silk, by which white silk is always designed.
Exp. 1. Gold.
I poured a quantity of sulphuric ether on a solution of gold in nitro-muriatic acid, and, by this means, obtained a solution of gold in ether, which I separated from the acid.
In this ethereal solution of gold, I dipped a piece of silk, after it was taken out, and the ether evaporated, it was suspended in a tall glass cylinder, placed over a vessel, containing a mixture of diluted sulphuric acid, and iron filings.
The silk thus exposed to a rapid current of hydrogen gas acquired, after some time, a purple colour, and a large spangle of gold, of an irregular figure, appeared on the upper end of the silk, and looked very brilliant.
The silk was kept exposed to the gas about four months, and frequently observed, but no other remarkable change was perceived, except that the purple colour became more intense: the experiment was now discontinued; and on taking out the silk, and examining it in the light of the sun, I observed many particles of reduced gold; but they were very small, and by no means so brilliant, as that, which first appeared.
During the experiment, fresh quantities of materials for supplying hydrogen gas were occasionally added.
From the brilliant spangle of reduced gold observed in this experiment, I concluded, that there was a sufficient quantity of the metal in the fibres of the silk, could it be reduced.
This spot of reduced gold was very permanent, and adhered firmly to the silk.
Exp. 2. Gold.
In order to determine, whether a solution of gold in ether, or one in water, were best adapted to the object of these experiments; I evaporated to dryness a solution of gold in nitro-muriatic acid, and dissolved the salt in distilled water: in this solution, I immersed a piece of silk, which, after it was dried in the air, was suspended in a glass cylinder, like the former piece, and exposed to the action of hydrogen gas about two months.
The silk after some time assumed a purple colour, and five or six specks of reduced gold, of the size of pin heads, and one much larger, were observed. Examining the silk in the sun-beams, I perceived the whole of it spangled with minute particles of reduced gold.
After many experiments with these two solutions of gold, I was led to conclude, that the solution in water answered best.
Exp. 3. Silver.
Having dissolved some pure silver in diluted nitric acid, and evaporated some of the water by a gentle heat, I placed it in the dark to crystallize. The crystals were separated from the solution, and dissolved in distilled water; to one measure of this solution, which was saturated with the nitrate of silver, ten or twelve measures of distilled water were added.
In this diluted solution, a piece of silk was dipped; after it was taken out, it was dried at the fire: the silk dried in this manner, retained its white colour; whereas, were it dried gradually in the air; and especially, were the light considerable, its white colour would be changed to a reddish brown, more or less intense, according to the quantity of light present.
Some kinds of silk, on being immersed in a solution of nitrate of silver, have some of their threads immediately coloured brown: but I often got white silk, which would retain its pure white colour, if dried at the fire, or in the dark.
The piece of silk dried, as above, was suspended in the middle glass of Dr. Nooth’s machine; and into the lower glass were introduced a diluted solution of sulphuric acid, and some small iron nails.
The machine was now placed in a dark closet, to exclude the action of light; after some time, the silk, thus exposed to hydrogen gas, put on a light brown colour, which gradually became deeper, until it was changed to a disagreeable black, with some mixture of brown: then very small particles of reduced silver began to appear, which increased by degrees, in number, and brightness.
The experiment was continued four months; after which time, the silk was taken out of the machine: it had a gray metallic appearance, intermixed with a considerable tinge of brown.
This experiment was repeated on another piece of silk, every circumstance being the same, except that a quantity of water was put in the middle glass of the machine, over which the silk was suspended; the intention of interposing the water in this experiment was to purify the gas.
The appearances were much the same, as in the last experiment; except that the silk became black sooner; and that some spangles of the silver were larger, and better reduced.
The specks of reduced silver were permanent, and adhered firmly to the silk.
Exp. 4. Lead.
In a solution of acetite of lead in distilled water I dipped a piece of silk, and dried it in the air; it was then suspended over a quantity of water in Dr. Nooth’s machine, and exposed to hydrogen gas about three months.
The appearances were much the same as in the last experiment, except that the silk was not so black: the particles of reduced lead resembled silver.
Similar experiments were made in this machine on bits of silk imbued with a solution of nitro-muriate of gold in water; but the appearances being much the same as those mentioned in the first and second experiments, it is unnecessary to repeat them here.
It is much easier to imagine, than express my anxiety, to discover the cause of the brilliant specks of reduced gold and silver, with which the pieces of silk in these experiments were sometimes spangled; concluding, that were the cause ascertained, it would be a considerable step towards accomplishing the object in view.
But many and diversified were the experiments I made before the circumstance, on which these spangles depended, was perceived.
At length, I found it depended on the presence of moisture; and that the spangles of reduced metal were owing to small drops of water carried up by the elastic fluid, and deposited on the silk.
The experiments, which led to this conclusion, shall be related in their proper places. I shall now proceed to recite the remainder of the experiments in this essay, conformable to the plan laid down in the preface, premising an occurrence observed in the course of them.
I sometimes found, that the production of hydrogen gas from a mixture of acid, water, and iron nails, would unexpectedly stop, which induced me to add more acid; this not succeeding, I added more water; but still no gas was formed: the proportions of acid and water were varied without effect. Thinking the mixture of acid and water unfit for the purpose, I poured it off, and repeatedly washed and agitated the nails with more water, which was also poured off; but happening inadvertently to add some of the mixture of acid and water, which I had before poured off as unfit for use, I was surprised to find the gas produced with great rapidity.
Reflecting on the cause of this odd circumstance, I concluded that it depended on a crust of superoxygenated iron, formed on the surface of the nails, which defended them from the action of the water and acid, and that this crust was removed by the agitation and washing, which enabled the diluted acid to act again on the iron.
Exp. 5. Gold.
I immersed a bit of silk in a solution of nitro-muriate of gold in distilled water, and dried it in the air; it was then placed over a cylindrical glass vessel, containing a mixture of diluted sulphuric acid and iron nails, for about half an hour; but no reduction of the metal could be observed.
I dipped another bit of silk in the same solution of gold, and exposed it, while wet, to the same current of hydrogen gas, and instantly signs of reduction appeared; for the yellow colour, which the solution imparts to silk, began to change to a green, and very soon a film of reduced gold glittered on the surface opposed to the gas: shortly after, a beautiful blue spot, fringed with orange and purple, was formed on the middle of the silk. During the experiment, which lasted about half an hour, the silk was kept constantly wet with distilled water.
When experiments are made with this preparation of gold, it is necessary to evaporate the solution to dryness, before the salt be dissolved in the water; as an excess of acid prevents the reduction in a great measure. Solutions of gold in these experiments do not admit of being so largely diluted, as solutions of silver, and other metals do.
Exp. 6. Silver.
I immersed a piece of silk in a solution of nitrate of silver, and dried it in a dark place; it was then exposed to a current of hydrogen gas about twenty minutes; but no reduced silver appeared, the only change observable was a brown stain.
I immersed another bit of the same silk in the same solution of silver, and having exposed it, while wet, to a stream of hydrogen gas, I soon observed evident signs of reduction; the white colour of the silk was changed to a brown, which became gradually more intense; and the surface of the silk, opposed to the gas, was coated with reduced silver: various colours, as blue, purple, red, orange, and yellow, attended the reduction. These colours often change, and are succeeded by others in the progress of the reduction. The threads of the silk look like silver wire, tarnished in some parts, but of great lustre in others.
The silk was kept wet with distilled water during the experiment. When the silk happened to be too much wetted, the under surface opposed to the gas was often covered with scales of a dull blue colour: these, after the silk dries, may be brushed off, and another coat of reduced silver, which adheres firmly, but has no considerable brightness, is left behind.
These experiments on the reduction of gold, and silver, were often repeated with nearly the same result.
Exp. 7. Silver.
Thinking some other preparation of silver might answer better than a nitrate, I precipitated some of the latter with a solution of muriate of soda, and poured the whole on a filter; the precipitate was well washed with distilled water, and dissolved in ammonia. In this solution I immersed a piece of silk, and dried it in the air; and having exposed it to the action of hydrogen gas, I could perceive no signs of reduction, except a faint brown colour.
I dipped another bit of silk in the same solution of silver, and in order to determine if water had the power of promoting the reduction of the silver in this preparation, as it had in the former experiments, I exposed the silk, while wet, to the same current of hydrogen gas; and in a few seconds the metallic lustre was evident on the surface opposed to the current. After some little time, a blue speck and a faint trace of yellow appeared, but soon vanished.
This preparation of silver does not stain white silk so much as a nitrate does; the reduced silver was indeed very brilliant, but soon grew dull, and disappeared; a brown stain only remaining; so that it seems rather inferior to nitrate of silver, which also, after reduction, tarnishes, grows dull, and often disappears; but sometimes part of it remains permanently reduced.
Exp. 8. Platina.
With much difficulty I procured a small quantity of the ore of platina, and dissolved it in nitro-muriatic acid. The solution was evaporated to dryness, and the salt was then dissolved in distilled water.
A bit of silk was dipped in part of this solution, and dried in the air; it was then exposed to a brisk current of hydrogen gas about twenty minutes, but no signs of reduction appeared.
Another bit of silk was immersed in the solution of platina, and exposed, while wet, to the same current of hydrogen gas; in five or six minutes the platina was reduced, exhibiting a livid white metallic appearance on the surface of the silk opposed to the current. No colours attended the reduction. This solution imparts a yellowish brown colour to silk.
After some time, the whole of the metallic lustre disappeared, in proportion as the silk became dry.
The solution of platina requires more time, and a stronger current of hydrogen gas for its reduction, than solutions of silver and gold do.
Exp. 9. Mercury.
I immersed a bit of silk in a solution of oxygenated muriate of mercury in distilled water, and dried it in the air: it was then exposed to a stream of hydrogen gas; but underwent no visible change.
I dipped another bit of silk in the same solution of mercury, and exposed it, while wet, to the same current of gas; the metal was soon reduced in a beautiful manner, and resembled silver.
The reduction began suddenly, with scarce any appearance of previous stain; some very faint, but at the same time transparent colours attended it: the most remarkable of these were a light orange, with a fringe of blue, and a yellow verging on a faint green. These colours soon disappeared.
After the silk was turned, I observed, that its texture was, in some parts, concealed by a thin film, which, as the reduction proceeded, was perceived to dart along the threads of the silk, gilding them in a beautiful manner, and exhibiting the texture very distinctly.
After some time, the mercury seemed to disappear, so as to render it doubtful whether any of it remained in the silk; but shaking it in the sunbeams, I perceived bright atoms fly off; and rubbing the silk on a bit of blue paper, I observed shining metallic particles, which seemed to have lost their affinity of aggregation, for they did not unite.
One remarkable difference between this preparation of mercury and nitrate of silver, is, that no black or brown stain preceded, attended, or followed, the reduction of the mercury.
Mr. Scheele reduced a prussiate of mercury, dissolved in water, by adding iron filings and a small quantity of sulphuric acid to the solution[9].
Exp. 10. Copper.
A piece of silk was immersed in a solution of sulphate of copper, then taken out, and dried, and exposed for a considerable time to a brisk current of hydrogen gas; but no signs of reduction could be perceived.
Another bit of silk was dipped in the same solution of copper, and exposed, while wet, to the same rapid current of hydrogen gas; the appearances were the following.
After a minute, or two, the silk assumed a faint brown colour, and, on the surface opposed to the gas, a white metallic pellicle appeared, which vanished in proportion as the silk became dry: wetting the silk again, I perceived a similar pellicle appear, which also vanished, as soon as the silk dried. If the silk be kept constantly wet, the brown colour becomes much more intense, attended with a very slight tinge of red. The margins of the silk projecting beyond the verge of the glass cylinder, and therefore not exposed to the current of the gas, retained the blue colour, which the solution imparts.
In some of these white metallic pellicles there appeared a faint brown inclining to yellow, which reflected the light, though obscurely.
After the silk dried, nothing remained, but a brown stain.
Exp. 11. Lead.
A piece of silk was immersed in a solution of acetite of lead in distilled water; it was then dried, and exposed for some time to a stream of hydrogen gas; but underwent no perceptible change.
Another bit of silk was dipped in the same solution of lead, and exposed, while wet, to the same current of hydrogen gas; in a second, or two, the surface of the silk, opposed to the current, was coated with reduced lead, which looked like silver.
The reduction was accompanied with a brown stain, but by no means so intense as that, which attends the reduction of nitrate of silver.
The other side of the silk was opposed to the current of hydrogen gas, and soon acquired a metallic coat of the same brilliant appearance, exhibiting the texture of the silk, in a very striking manner.
It is remarkable, that lead exhibits no colour, but a light brown, during its reduction; whereas gold, silver, and mercury, display a great variety of colours, especially the two former.
After some time the lead reduced in this manner loses its metallic splendour considerably; and that in proportion as the silk dries.
Exp. 12. Tin.
I dissolved some crystals of muriate of tin in distilled water; dipped a bit of silk in the solution; and dried it in the air: it was then exposed to a stream of hydrogen gas a considerable time; but no change, or appearance of reduction, could be observed.
Another bit of silk was immersed in the same solution of tin, and exposed, while wet, to the same current of gas; after some little time, the reduction commenced, attended with a great variety of beautiful colours; as red, yellow, orange, green, and blue, variously intermixed.
The reduced tin disappears along with these colours, as the silk dries; nothing remaining but a feuille-morte colour.
The same solution of tin was also reduced by hydrogen gas, obtained from tin, and the muriatic acid.
These experiments do not succeed well with muriate of tin containing an excess of acid.
Exp. 13. Arsenic.
A muriate of arsenic, which was prepared by digesting white oxid of arsenic in muriatic acid, and continuing the heat, till most of the acid evaporated, and left behind a soft mass of the consistence of tar, was dissolved in distilled water.
In this solution a bit of silk was immersed, and dried in the air: it was exposed to a brisk stream of hydrogen gas, obtained from zinc, and muriatic acid; but no reduction took place.
Another bit of silk was dipped in the same solution, and exposed, while wet, to the same current of hydrogen gas; and instantly, the surface of the silk, opposed to the gas, was covered with a bright coat of reduced arsenic, accompanied with a yellow stain. In a short time the metallic lustre vanished; and nothing remained but the yellow stain.
M. Pelletier restored the acid of arsenic to its metallic state, by passing hydrogen gas through a solution of that acid, in twice its weight of water[10].
Exp. 14. Bismuth.
A bit of silk, which was immersed in a solution of nitrate of bismuth in distilled water, and exposed dry to hydrogen gas, obtained from zinc, and muriatic acid, underwent no visible change.
Another bit of silk was dipped in the same solution of bismuth, and placed over a languid stream of hydrogen gas; the bismuth was soon restored to its metallic form, on the surface of the silk opposed to the elastic fluid. The reduction was attended with a reddish brown stain, intermixed with a tinge of violet.
Exp. 15. Antimony.
A bit of silk was immersed in a solution of tartarite of antimony in distilled water; and dried in the air. It was then exposed to hydrogen gas, obtained from zinc, and muriatic acid; but suffered no visible alteration.
Another bit of silk, which was dipped in the same solution of antimony, was exposed wet to a weak stream of the gas; and, in a short time, the metallic lustre appeared, accompanied by a light yellow colour.
Exp. 16. Iron.
A bit of silk, which was immersed in a largely diluted solution of sulphate of iron, and dried in the air, was exposed to a strong current of hydrogen gas, obtained from iron nails, and diluted sulphuric acid; but no visible change was produced on the silk.
Another bit of silk was dipped in the same solution of iron, and placed wet over the same stream of hydrogen gas; but no reduced iron could be perceived. The silk was then immersed in a glass of clear water, and transferred a very minute metallic film to the surface of that fluid.
This experiment was repeated with a rapid current of hydrogen gas, obtained from zinc, and muriatic acid; and, in about a minute, small films of reduced iron were visible on the surface of the silk, opposed to the gas.
The silk was then immerged in water, and transferred to its surface a large metallic pellicle; parts of which were very brilliant; but other parts were dull, and much more imperfectly reduced.
Exp. 17. Zinc.
A bit of silk, which was dipped in a muriate of zinc, largely diluted with water, and dried in the air, was exposed to a rapid current of hydrogen gas, obtained from zinc, and muriatic acid; but suffered no visible alteration.
Another piece of silk was immersed in the same solution of zinc, and exposed, while wet, to the same rapid current of hydrogen gas: in about half a minute, the metal was reduced in a very evident manner, on part of the silk. The silk was then dipped in a glass of clear water, and transferred a bright metallic film to its surface.
As these reductions of iron, and zinc, by hydrogen, are contrary to M. Lavoisier’s table of the affinities of the oxygenous principle; I began to suspect, that the films, which were so evident, both on the silk, and the water, might be abraded, or torn from the zinc, by the muriatic acid; and elevated, and deposited on the silk by the gas.
In order to remove this doubt, I dipped a bit of the same silk in distilled water; and exposed it, while wet, to the same current of hydrogen gas, but nothing metallic could be seen on the silk; nor did it when immersed in water transfer a film, or the smallest appearance of a metal, to the surface of that fluid: and, therefore, there can be no doubt of the reality of these reductions.
Dr. Priestley restored iron, and lead, to their metallic state, by heating their oxids with a burning glass in hydrogen gas.
These experiments point out an error in M. Bergman’s table of elective attractions in the humid way; for he assigned the last place in that table to phlogiston, which he considered as the base of inflammable air; because he was unacquainted with any metallic reductions effected by hydrogen in the humid way[11].
Having found, that water promoted, and accelerated, these reductions in a very remarkable manner; I was curious to know, if alcohol, and ether, would produce the same effect. With this view, I evaporated a solution of gold in nitro-muriatic acid to dryness; when the vessel cooled, some alcohol was poured on to dissolve the salt; and immediately the vessel containing the salt, became so hot, that it could be scarcely endured by the hand; and diffused a fragrant smell, like that of ether, which, no doubt, was a species of that fluid.
Exp. 18. Gold.
In this solution of gold in alcohol, a bit of silk was dipped, and exposed to a stream of hydrogen gas, obtained from diluted sulphuric acid, and iron nails; and kept wet with alcohol: in about two minutes, the silk began to assume a brown colour, and white metallic films appeared on some parts of the surface opposed to the gas; some of these disappeared in a short time; and were succeeded by a few very small spangles of the proper colour of gold. These also soon vanished; and nothing remained but a disgreeable brown stain, intermixed with specks of a dull blue.
I sometimes found, on repeating this experiment, that no yellow films or spangles appeared; and am persuaded, that their appearance, and that of the white pellicles also, depends on the presence of water, contained in the alcohol, or the gas, and deposited on the silk.
Exp. 19. Gold.
A bit of silk was immersed in a solution of gold in ether, and exposed to a stream of hydrogen gas, and kept wet with ether. The silk underwent no alteration for a few minutes; at length, it began to assume a faint brown colour, but no white, or yellow films appeared.
If this experiment be continued till the silks collects a sufficient quantity of water from the gas, some films will appear.
Exp. 20. Silver.
I procured some nitrate of silver, which had been fused in order to expell as much of its water as possible; and dissolved it in alcohol. I immersed a bit of silk in this solution, and exposed it to a stream of hydrogen gas, and kept it wet with alcohol: in a few seconds, the silk assumed a brown colour, which gradually became more intense: but no reduced silver appeared for several minutes; at length, a few metallic films appeared on part of the surface opposed to the gas.
Exp. 21. Mercury.
A bit of silk was dipped in a solution of oxygenated muriate of mercury, and dried; it was then exposed to hydrogen gas about ten or fifteen minutes, and kept constantly wet with alcohol. The silk, during the first minutes, suffered no perceptible alteration: at length, a few small films were visible on the side of the silk opposed to the current.
Exp. 22. Lead.
A bit of silk, which was immersed in a solution of acetite of lead, and dried, was exposed about fifteen minutes to a stream of the gas; and kept constantly wet with alcohol; but suffered no visible change; except that a very minute film was reduced on one of its margins, which did not project beyond the verge of the glass vessel on which it was placed.
When we compare these experiments with those, in which water was used, to wet the silk, ’tis evident, that alcohol, and ether, do not promote the reduction of metals, as water does; and that the few films, which appear, when the silk is kept wet with ether or alcohol, depend entirely on water collected from the gas, or deposited by them on the silk during their evaporation.
In order to compare the effects of hydrogen gas, obtained from water, iron nails, and muriatic acid, with that, procured from the same materials, by means of the sulphuric; I made some experiments on gold, silver, mercury, and lead, in the same manner, as the preceding; and the principal difference was, that the colours produced in all the pieces of silk, except that, which was dipped in acetite of lead, were much brighter, and more beautiful, than any produced, when the sulphuric acid was used.
The reduction of the lead was accompanied with its usual brown colour.
On the upper surface of a bit of silk, which was dipped in a solution of gold, a green colour instantly appeared; and soon changed to a deep olive, in proportion as the reduction advanced: now examining the under surface, I saw it coated with a bright film of reduced gold, in the middle of which a blue spangle, mixed with purple, soon began to appear: I then moistened the upper surface of the silk with water; and in a few seconds, it also was coated with reduced gold.
The blue on the other side of the silk became much more intense: the piece was now turned; and on each colour I let fall a drop of water: the drop on the blue had a blue film, the drop on the purple, had a purple film, and the drop on the yellow, a film of reduced gold.
After some time, these drops of water evaporated, and the films came again in contact with the silk: some parts of which were left bare, as generally happens, when too much water is applied.
On the under surface of a bit of silk, which was immersed in a solution of nitrate of silver in water, a coat of reduced metal was formed, with various colours, as green, blue, orange, and yellow, the beauty and brightness of which were remarkable.
In some time a muriate of silver is formed in the fibres of the silk, which on exposure to light becomes of a bluish black colour: but the whole of the silver does not undergo this change; for part of it remains in its metallic state. The colours remain a considerable time, if the silk be removed from the gas before this muriate is formed.
Hence it appears, that hydrogen gas should not be prepared with an acid, which forms an insoluble compound with the metal to be reduced.
I also found, that hydrogen gas produces different effects not only according to the difference of the acid, but also according to the difference of the metal employed to obtain it: for this gas procured from zinc or tin, and muriatic acid, did not restore gold to its proper metallic lustre; but formed on the silk, a white metalline coat like silver.
The experiments related in this chapter indicate the following conclusions.
- Hydrogen is capable of reducing the metals in the ordinary temperature of the atmosphere.
- Water promotes, and accelerates, these reductions, in a very remarkable manner.
- Ether, and alcohol, do not promote these reductions, without the aid of water.
- A variety of colours accompanies these
reductions, similar to what appears, during
the calcination of metals by heat and air;
and depends on the same cause: viz. the
quantity of oxygen combined with the metal.
These colours have not been observed hitherto; nor indeed could they; as the metals were reduced in close vessels, and in high degrees of heat.
- These reductions often disappear.
This is commonly owing to an imperfect, and partial reduction of the metal: for the acid, and water, remaining in that part of the metallic solution, not reduced, recalcines these delicate films: sometimes the disappearance of the metallic lustre depends on the nature of the metal itself: thus arsenic, lead, silver, &c., suffer some degree of calcination by water and atmospheric air.
Messrs. Bergman and Keir relate instances, in which silver after being precipitated in its metallic state, was recalcined, and disappeared.
I first imagined, that water promoted these reductions by minutely dividing the particles of the metallic salt, and by condensing the gas, and bringing its hydrogen, and the metallic oxid, within the sphere of attraction; the hydrogen either uniting to the metallic earth and reducing it, as the Phlogistians suppose; or uniting with, and separating the oxygen of the metal, and thus restoring it to the metallic form, as the Antiphlogistians maintain.
But it is evident from the experiments related, that water does not promote these reductions solely, by minutely dividing the particles of the metallic salt: for were this the case; ether, and alcohol, should promote the reduction of the metallic salts, which they dissolve, since they divide their particles, as minutely as water can.
Since then metallic solutions in ether, and alcohol, cannot be reduced by hydrogen gas; it follows that the above supposition concerning the mode of agency of water does not account for the reduction of metals in this way.
And indeed were it true that hydrogen condensed by water reduced metals in the manner above mentioned, it would follow, that the reduction was effected by a single affinity, which cannot be admitted; 1st. because the existence of a single affinity in such cases has not been proved; 2dly, because a double affinity always takes place in preference to a single affinity, which is demonstrated by the following facts, transcribed from the works of Mr. Kirwan.
“If a solution of silver in the nitrous acid be thrown into a mixed solution of fixed alkali and common salt, the silver will be precipitated by the marine acid of the common salt, and not by the free alkali, contained in the liquor: for a luna cornea is found[12].”
“I repeated the experiment with a solution of lead, and also of mercury in the nitrous acid, and the result was similar: both lead and marine salt of mercury were formed[13].”
In these experiments of Messrs. Monnet and Kirwan, ’tis evident that a double affinity takes place in preference to a single one: for the nitrous acid of these different nitrates unites with the alkali of the common salt, while the muriatic acid of the latter seizes the silver, mercury, and lead, of the nitrates, and forms muriates of silver, mercury, and lead: the free alkali remaining passive in the mixture.
M. Lavoisier says, “There exists only in nature, as far as we can observe them, cases of double affinity, often triple, and others perhaps still more complicated[14].”
Now as water does not promote these reductions merely by dissolving, and minutely dividing, the particles of the metallic salts, and condensing the hydrogen gas; and since a double affinity takes place in preference to a single affinity; it is obvious that the water must be decomposed in these reductions in the following manner.
The hydrogen of the gas unites to the oxygen of the water, while the hydrogen of the latter unites in its nascent state to the oxygen of the metal, reduces it, and forms water.
Thus what could never be effected by a single, is readily performed by a double affinity.
Hence it follows, that the hydrogen of the gas is oxygenated by the oxygen of the water, while the metal is, at the same time, restored to its combustible state. It also follows, that the quantity of water formed is double that decomposed.