the oxide is deposited on the positive iron wire. Many reasons lead me to believe, that iron associated with this substance, will form the most powerful voltaic element known, and I am just about to construct a pile of such couples."

[Remarks. We think that nothing more is wanting than the above statements to show, that the author was perfectly unable to determine the cause of the phenomena he had observed and that he did not know whether electric currents were produced or not: and we must add, that nothing in science is more certain than that the whole were of electric origin, nor nothing more easily discovered in researches of this kind, than the existence of electric currents in the professor's experiments.-EDIT.]

In a letter addressed to Dr. Faraday, Professor Schöenbein

states:

"From a series of experiments lately made by me with the view of ascertaining the voltaic relations of some peroxides, platina, and inactive iron to one another, I have obtained results, which, in my opinion, are such as to throw some additional light upon the cause of voltaic electricity, and to modify, to a certain degree at least, the notions we have hitherto entertained about that interesting subject. The voltaic relation of peroxide of lead to iron engaged my attention some time ago, and in Poggendorff's Annalen,' I have stated that the peroxide in question, if voltaically associated with iron, disappears by degrees when plunged into nitric acid of any strength. Now as we know that no chemical action whatever takes place under the circumstances mentioned, iron being in its peculiar condition, and having, in a voltaic point of view, all the properties of platina, I could not but be very much surprised at the disappearance of the peroxide of lead. Although I was not able to trace at the time any voltaic current, or to account for any disturbance of the electric equilibrium of the arrangement alluded to, I nevertheless suspected that the solution of the substance mentioned was effected under the influence of current electricity. Having now at my disposal a galvanometer which is provided with 2,000 coils, and made in other respects very delicate, I have taken up that subject again, and attempted first to ascertain whether there is any voltaic relation of platina to inactive iron. In contradiction to the results obtained some time ago, I have found by means of my galvanometer, that iron, being in its peculiar condition and associated with platina, gives rise to a sensible current if put into nitric acid, be the latter ever so strong or somewhat diluted with water. Making use of an acid of sp. gr. 14, the deviation of the needle (on putting the iron and platina wires in connection with the galvanometer) amounted to about 90°. I must not omit to state that the current excited under the circumstances mentioned is not a momentary but a continuous one, and at the same time quite independent of any oxidation of the iron. The direction of the current in question is such as it would be if the latter metal was attacked by the acid, that is to say, inactive

iron is positive to platina. Another fact, as curious and interesting as that just stated is the following one. Two platina wires being connected by one set of their ends with the galvanometer, and by the other set with nitric acid or an aqueous solution of sulphate of copper, excite a current, provided one of the ends (immersed in the fluid) of one of the platina wires be covered with a film of peroxide of lead. The current passes from the platina through the fluid to the peroxide: when the said film is so thin as to produce what are called 'Nobili's colours,' it disappears within a very few seconds after having been immersed in nitric acid, and the whole arrangement connected with the wire of the galvanometer. From the facts stated it appears, that platina is positive with regard to peroxide of lead, and that the disappearance of that compound is caused by a current which eliminates hydrogen at the negative peroxide, by which means the latter is reduced to protoxide of lead, and rendered soluble in nitric acid. In a similar manner I have ascertained that the voltaic relation of inactive iron to peroxide of lead is exactly the same as that of platina to the said peroxide. In using peroxide of silver instead of that of lead, voltaic effects are produced quite the same as those which were just spoken of, that is to say, a continuous current is excited, to which the peroxide acts the part of the cathode, and either of the metals in question that of the anode. As to the voltaic relation which one of the peroxides mentioned bears to the other, my experiments have shown that peroxide of silver is always negative with regard to the peroxide of lead, be the fluid made use of nitric acid or a solution of blue vitriol. Now, from all the facts above stated, I think we may be allowed to draw two important inferences: 1. That peroxide of silver, peroxide of lead, platina, and inactive iron constitute a series of substances, in which the preceding one is always negative with regard to that which follows in the list. 2. That any two of the four substances mentioned being voltaically associated with one another, and put either into nitric acid or a solution of sulphate of copper, excite a continuous current, which is not due to oxidation or any chemical change. It is hardly necessary to add, that the currents produced under the said circumstances are extremely feeble, being only indicated by most delicate galvanome

ters.

"The facts spoken of are highly important in a scientific point of view, as they seem to produce evidence in favour of that theory which asserts, that by the mere contact of heterogenous substances their electrical equilibrium can be disturbed quite independently of any chemical action taking place between them. All chemists certainly maintain, that pure nitric acid, for instance, does not chemically affect at all either platina or peroxide of lead; and inactive iron too, as we now well know, is not in the least attacked by the said acid. Now, I ask, whence does the current originate which is produced when we combine the substances in question in such a manner as to form with them a voltaic arrangement?

"I have attempted to answer this puzzling question in a paper which before long will be published in Poggendorf's Annalen,' as well as in the Biblioth. Univ.,' and in which you will find besides a detailed account of all the experiments made by me upon the subject spoken of. If my time was not so much taken up with a variety of business, I would have drawn up a memoir in English, and sent it to the editors of the Philosophical Magazine,' for insertion; but those gentlemen will, perhaps, give a translation of the paper.

"Allow me to communicate in a general manner the view which I have taken of the subject in question. In the first place I am by no means inclined to consider mere contact in any case as the cause of the excitement of even the most feeble current. I maintain, on the contrary, in accordance with the principles of the chemical theory, that any current produced in a hydro-electric voltaic circle is always due to some chemical action. But as to the idea which I attach to the term chemical action,' I go further than M. de la Rive seems to go; for I maintain, that any tendency of two different substances to unite chemically with one another, must be considered as a chemical action, be that tendency followed up by the actual combination of those substances, or be it not; and that such a tendency is capable of putting electricity into circulation.

to render this idea of mine somewhat clearer by applying it to some particular cases. Supposing a voltaic circle to be composed of platina, peroxide of lead, and nitric acid; I say that the current excited in such an arrangement is due, first, to the tendency of the acid to unite with the protoxide of lead, or, what is the same, to the tendency of one proportion of the oxygen to separate from the peroxide; secondly, to the tendency of water to combine with the same protoxide to form a hydrate; and thirdly, to the tendency of water to withdraw a proportion of oxygen from the peroxide to produce peroxide of hydrogen, which tendency, from very well known chemical reasons, is yet increased by the presence of the acid. It is true that none of the said tendencies do lead to any chemical result, for no nitrate of lead, no hydrate, no peroxide of hydrogen is actually produced; but are we allowed to infer, from the want of a practical result, that no chemical action whatever takes place when nitric acid and peroxide of lead are put in contact with one another? I ask, are we to suppose that the chemical affinities alluded to are entirely dormant, and incapable of any exertion? The results from my late experiments induce me to answer the question in the negative. Being quite of opinion, that chemical affinity and current electricity are but different forms of the same thing, I cannot help thinking that any sort of chemical action or tendency must be capable of being transformed into the shape of a current. For that current which is produced by inactive iron, being voltaically associated with platina, I likewise account by a chemical tendency on the part of the former metal. Though inactive iron be not in the least

attacked by nitric acid, its affinity for the oxygen of the latter is, on that account, by no means entirely destroyed; the metal whilst surrounded by the acid is continually tending to oxidize itself, and the current excited in such a case is nothing else but as it were the electrical translation of a chemical exertion.

"All the cases above stated, where currents are observed independently of any chemical change, can be explained by applying to them the same principles as that by means of which I have accounted for the current produced by nitric acid and peroxide of lead, &c.

"According to my experiments, peroxide of silver proves to be the most powerful means for exciting in iron its peculiar voltaic condition. It surpasses in this respect even the peroxide of lead. An iron wire, for instance, one end of which is covered with only a small particle of the first-mentioned substance, will not be attacked either by nitric acid of any degree of dilution, nor by a solution of blue vitriol. The voltaic association of one substance with the other is easily effected by connecting one end of an iron wire with the positive electrode of a pile, and by plunging for a few minutes the other end of the wire into a solution of nitrate of silver."

The next paper of Professor Schöenbein that has appeared in this country is headed "On the Polarization of certain Solid and Fluid Substances."

"I read a paper containing an account of the results of my researches on the voltaic polarization of solid and fluid bodies, before the scientific meetings which took place at Bâle and Fribourg, some few months ago.

“This memoir, I think, will soon be published in the 'Biblioth. Univ.' and in Poggendorff's Annalen,' and the scientific public thereby enabled to appreciate the facts related in it. The sort of investigations alluded to could not but lead me to make numerous experiments similar to those which were mentioned the other day in the French Academy, as performed by MM. Matteucci and Peltier, of which I have, however, up to this present moment, but a very imperfect knowledge. Having from want of time not yet been able to draw up a regular paper on the results of my most recent voltaic researches, and thinking them not quite void of scientific interest, I beg the favour of your giving in the forthcoming number of your widely circulated journal a place to the general statements, the tenor of which is as follows:

"1. A platina wire polarized either in the positive or negative way loses its peculiar condition by being heated red hot. I call positively polarized a wire which has acted for some time the part of the negative electrode in water slightly acidulated by sulphuric acid; and I term negatively polarized a wire which has in the same liquid performed the function of the positive electrode.

"2. A platina wire positively polarized loses its peculiar condition by being plunged only for a single moment into an atmosphere of chlorine.

"3. A platina wire positively polarized loses likewise its electromotive power by being placed in an atmosphere of oxygen; but in order to destroy entirely the polarity of the wire, it is necessary that it should remain for some seconds in the gas mentioned.

"4. A platina wire negatively polarized loses its peculiar condition by being put into an atmosphere of hydrogen, but in order to obtain this effect, it is required that the wire in question should remain for some seconds in the gas.

"5. A platina wire polarized either negatively or positively is not sensibly affected by being placed in an atmosphere of carbonic acid, or in one of any other gas which does not chemically act either upon hydrogen or oxygen.

"6. A platina wire (in its natural state) assumes in every respect the condition and voltaic bearings of a positively polarized wire by being plunged only for a few seconds into an atmosphere of hydro

gen.

"7. Gold and silver are not sensibly affected under the same cir

cumstances.

"8. A platina wire does not acquire any degree of electromotive power by being put into oxygen gas: the metal remains in its natural state. Neither is any degree of such power acquired by gold or silver under the same circumstances.

"9. Platina, gold, and silver, by being placed only for a few seconds in an atmosphere of chlorine, assume the voltaic state of a negatively polarized wire.

"10. Water slightly acidulated with sulphuric acid and holding some hydrogen dissolved, bears to acidulated water containing no hydrogen the same voltaic relation that zine does to copper; provided, however, both fluids be separated from each other by a membrane, and connected with the galvanometer by means of platina wires. If for the latter purpose (that is to say, for connecting the fluids with the galvanometer) gold or silver wires are made use of, the said fluids do not excite the least current.

"11. Two fluids, one being acidulated water containing some oxygen dissolved, the other being likewise acidulated water containing no oxygen, appear to be in a voltaic point of view perfectly indifferent to each other, whether they are connected with the galvanometer by platina, silver, or gold wires.

"12. Water slightly acidulated with sulphuric acid and holding some chlorine dissolved, bears to acidulated water not containing any chlorine, the same voltaic relation that copper bears to zine. In other terms, the former fluid acts under certain circumstances the electromotive part of the peroxides of silver, lead, &c.

"13. The aqueous solution of hydrogen mentioned in § 10, loses its property to excite a current by being mixed with a certain quantity of an aqueous solution of chlorine; and vice versa, the latter fluid loses its electromotive power mentioned in § 12, by being mixed with a sufficient quantity of hydrogen dissolved in water.

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