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direction.

The difference arises ouly from their being in one case in merely simple contact; whilst in the other there is contact in addition to chemical action which determines the formation of an oxide or a sulphuret.

The following experiment indicates the influence of chemical action in this kind of phenomena. If a piece of sulphur be burnt at one end of a copper wire which forms the coil of a galvanometer, and the other end of the wire be brought over it whilst the combustion is in full force, the current of electricity thus produced is highly energetic, and more intense than that which would be occasioned by a difference of temperature only.

We employ a tube bent into the form of a letter U, and containing a solution of the nitrate or the sulphate of copper. We immerse in the liquor in each branch a copper wire, communicating with the extremities of the wires of an apparatus like that just described. When the action has continued for an hour, the immersed wire which is connected with the negative side is covered with copper, precipitated in a metallic state. The other wire is sensibly oxidized.

Two tin wires immersed in solution of hydro-chlorate of tin, display similar results, that is to say, the wire in connection with the negative side becomes covered with crystals of tin.

Wires of zinc, of silver, and of lead, immersed in their respective solutions, exhibit similar phenomena.

Wires of platinum are without action in solutions of platinum. We here perceive the influence of the chemical action which takes place between the wires and the solutions, on the electro-chemical decomposition.

Wires of platinum, gold, and silver, immersed in solutions of lead, tin, or copper, and prepared as those above, are equally destitute of action on them, notwithstanding the intensity of the current remains the same.

When we immerse two silver wires in a solution of nitrate and sulphate of copper, the positive wire is invariably attacked by the acid; but the negative wire shows no precipitation of the metal from the solution. In this case, therefore, the oxygen and the acid appear to be more easily transported to the positive pole than the copper to the negative pole.

In a solution of the nitrate of silver, platinum wires occasion precipitation of silver as decidedly as by silver wires; but the silver wires occasion a more copious precipitation than is accomplished by the platinum. The difference in the action of these two metals is rendered very obvious by immersing in the solution at the same time, a silver wire rolled round a platinum wire.

We thus see that by feeble currents of uniform intensity, the easily reduced metals are more disposed to be precipitated upon metals of their own kind, than upon any other, in all those cases where the immersed metal itself does not occasion precipitation, in the manner that iron precipitates copper from its solution. This remarkable fact cannot be observed only by the employment of an

electrical apparatus of very feeble tension, for when the electric tension amounts to a certain degree, the metal liberated from its solution, proceeds to the negative terminal metal, of whatever kind it may be.

To what cause, under these circumstances, are we to attribute this predilection of a metal, combined with an acid, for a plate of metal of its own kind? The force of cohesion, whatever that may be, is the only influence conceivable: because that force must be supposed to act with greater energy on similar than on dissimilar molecules. In this case the force of aggregation added to that of the electric current, ought to determine the precipitation. But we must not overlook the chemical action of the solution on the positive metal, which is highly conducive to the general effect.

If it be required to obtain continuous effects with the thermoelectric apparatus, the copper loop into which the platina loop is linked, must be renewed from time to time, because the former becomes completely oxidized by a continuation of the process, and the continuity thus becomes broken, and the electro-chemical action consequently ceases.

An apparatus formed of a platinum wire and a wire of iron has no action sufficient to produce decomposition. This negative effect is undoubtedly owing to the peculiar electrical properties due to iron of which we have already spoken and now return to again.

The apparatus about to be described is destined to produce slow continuous electric actions.

We take two small glass jars, into one of them we place some nitric acid, and in the other some potash dissolved in water: and establish a communication between them by means of a bent glass tube filled with potters' clay moistened with a solution of nitrate of of potash, or of common salt. We then place in each vessel a plate of platinum to which is attached a wire of the same metal. At the free end of each platinum wire, we fix the end of the wire ou which the experiment is to be made. The plate in contact with the alkali receives the negative electricity which becomes disengaged by its reaction on the water, or the solution of the nitrate or the chloride, and the plate in the acid receives the positive electricity which is liberated during the same reaction. We have thus a permanent pile, by taking care to close the vessels so as to prevent evaporation and the action of the air on the alkali. By immersing several plates of platinum in the liquids in the jars we may put several sets of apparatus into action at the same time.

We may employ water as a substitute for the potash, and a copper wire in each vessel. Even with this arrangement we obtain chemical action, and an electric current, from the copper to the acid, of sufficient energy to produce decompositions similar to those already described.

It will not be doubted that in electro-chemical decomposition, produced by electro currents of low tension, the oxygen and acids assemble at the positive pole, as decidedly as in those energetic

currents proceeding from the action of several voltaic elements. The wire attached to the negative pole is always seen to be covered with precipitated metal: but the determination of oxygen and acid at the positive polar wire, cannot always be detected. In such cases they have formed an insoluble compound.

We have also shown above that, when two silver wires are immersed in a solution of nitrate of copper, and in connexion with the voltaic apparatus, the positive wire becomes sensibly altered, whilst the negative wire retains its metallic brilliancy, although no trace of metallic copper can be detected on its surface. We may have the choice of two modes of explanation in this circumstance. We may suppose the copper to have been arrested in the solution, as is sometimes the case when an insoluble compound is formed; and in the present case no transfer of the elements of the nitrate has taken place, although it has been decomposed; or we may suppose the deposit on the negative wire was too slight to be observed.

We may now employ two small cylindrical glass vessels, in one of which is placed a solution of the nitrate of barytes, and in the other a solution of the sulphate of copper; and form a communication between the solutions by means of a bent tube filled with potters' clay, well soaked with a solution of common salt, which will facilitate the transfer of electricity between the solutions. Into the sulphate solution we immerse a copper wire connected with the negative side of the apparatus; and in the nitrate of barytes the other wire. If now, the sulphuric acid proceeds towards the positive pole it will enter the solution of barytes, and by uniting with that base will form a precipitate.

Now, this is what actually happens. After the experiment has been continued four or five hours, the negative end is covered with copper: the solution of nitrate of barytes is not sensibly disturbed, and the positive end is oxidized. Are we to infer, from this circumstance, that nothing but the oxygen has been transferred, and that the sulphuric acid has remained in the sulphate? This question. can be answered only by an analysis of the secondary productions formed in the tube: and there is reason to believe that sulphate of barytes would be found. In general when the production is not found at one of the poles, we may be certain that it has been arrested on its way by superior affinities.

The acetates and sub-acetates of lead are also decomposed by means of leaden wires; but the acetate of copper, and the saturated solution of the same salt in ammonia resist an electric action of low tension, when copper wires are immersed in these solutions. These remarks are of some importance because these salts decompose with great facility by ordinary chemical processes.

Experiments and Observations made with the View of Ascertaining the Nature of the Gas produced by passing Electric Discharges through Water; with a Description of the Apparatus for these Experiments. By GEORGE PEARSON, M.D., F.R.S.*

IN the "Journal de Physique" for the month of November, 1789, were published the very curious and interesting experiments of Messrs. Paets Van Troostwyk, and Deiman, with the assistance of Mr. Cuthbertson, on the apparent decomposition of water by electric discharges.

The apparatus employed was a tube twelve inches in length, and its bore was one-eighth of an inch in diameter, English measure, which was hermetically sealed at one end, and while it was sealing an inch and a half of gold or platina wire was introduced within the tube, and fixed into the closed end by melting the glass around the extremity of the wire. Another wire of platina or of gold, with platina wire at its extremity, immersed in quicksilver, was introduced at the open end of the tube, which extended to within five-eighths of an inch of the upper wire, which, as was just said, was fixed into the sealed extremity.†

The tube was filled with distilled water, which had been freed from air by means of Cuthbertson's last improved air pump, of the greatest rarifying power. As the open end of the tube was immersed in a cup of quicksilver, a little common air was let up into the convex part of the curved end of the tube, with the view of preventing fracture from the electrical discharges.

The wire which passed through the sealed extremity was set in contact with a brass insulated ball; and this insulated ball was placed at a little distance from the prime conductor of the electrical machine. The wire of the lower or open extremity, immersed in quicksilver, communicated by a wire or chain with the exterior coated surface of a Leyden jar, which contained about a square foot of coating; and the ball of the jar was in contact with the prime conductor.

The electrical machine consisted of two plates of thirty-one inches in diameter, and similar to that of Teyler. It possessed the power of causing the jar to discharge itself twenty-five times in fifteen revolutions. When the brass ball and that of the prime conductor were

From Nicholson's Journal.

In another part of Mr. Van Troostwyk's memoir it is stated that the distance was an inch and a quarter from the end of the upper wire to the top of the lower wire; and that the distance between the insulated ball and the prime conductor, was at first three-fourths of an inch, but that afterwards it was increased to one inch. Although the wire fastened into the top of the tube was said to be an inch and a half in length, it is observed that when a column of three-eighths of an inch of air was collected, it was almost at the extremity of the upper wire. From these and other inaccuracies, it will be made appear that no one, from the account published, has been able to repeat the experiment.

in contact, no air or gas was disengaged from the water by the electrical discharges; but on gradually increasing their distance from one another, the position was found in which gas was disengaged, and which ascended immediately to the top of the tube. By continuing the discharges, gas continued to be disengaged and ascend, till it reached nearly to the lower extremity of the upper wire; and then a discharge occasioned the whole of the gas to disappear, a small portion excepted, and its place was consequently supplied by

water.

The residuary portion of gas being let out after each experiment, and the discharges being continued in the same water, this residuary gas was left in smaller and smaller quantity; so that after four experiments, probably made on the same day, it did not amount to more than 1-80th of the bulk of gas which had been produced. If it had been possible to pass electric sparks through this very small quantity of gas a second time, or oftener, it was supposed it would have been diminished still more. But when the tube had been left for a night only filled with water, the residuary gas was in greater quantity than after the last experiment the preceding day.*

It was concluded that the gas produced by the electrical discharges was oxygen and hydrogen gas, from decompounded water:

1. Because no other gas hitherto known instantly disappears on passing through it an electric spark.

2. The gas obtained must have been the oxygen and hydrogen of decompounded water, because they were in exactly those proportions in which by combination they reproduce water; the trifling residue being considered to be merely a portion of air which had been dissolved in the water.

3. Liquids which are not compounded of hydrogen and oxygen, as sulphuric and nitric acids, afforded gas by the electric discharges, but which did not disappear on passing through it an electric spark ; but which did disappear on adding to it nitrous gas over water. Mr. Schurer also asserts, on the authority of Mr. Van Troostwyk, that even liquid muriatic acid, which contains a very large proportion of water, affords hydrogen gas only, the oxygen being absorbed by the muriatic acid, and becoming oxy-muriatic acid.

From much experience I can safely affirm, that it is scarcely possible for the student, or even the proficient, to institute the above experiment with success from the explanation published. Hence, during the six years which have elapsed since its publication, no confirmation has been published except the experiment repeated by Mr. Cuthbertson for my satisfaction, as related in my work on the

In at least fifty experiments I have never seen the residue of gas less than 1-40th of the gas produced, although the water had been freed from air by the most effectual means. But Mr. Schurer (Annales de Chimie, tom. v, p. 276), testifies that he saw Mr. Van Troostwyk make the experiment, and that after it was repeated many times on the same parcel of water, there was no residue at all. I have very good grounds for believing that this is one of the number of inaccuracies in the account published of this subject.

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