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