action is not called into play the very instant the circuit is completed, and that it is the rapidity in the succession of these impulses which limits the effect (see Moser, Repertorium der Physik, vol. i, Berlin, 1837, p. 281), that we cannot but hold that philosophy to be in error; and are led to think, with Jacobi, that the absence of the power once expected from these machines, arises from the countercurrents induced in the copper helices by the motion of the rotating magnets.

Experimental and Theoretical Researches in Electricity, Magnetism, &c. Seventh Memoir. By WILLIAM STURGEON, Superintendent and Lecturer of the Royal Victoria Gallery, Manchester; formerly Lecturer on Experimental Philosophy at the Hon. East India Company's Military Academy, Addiscombe; &c.

SECTION I.

On a Peculiar Class of Voltaic Phenomena.

THE great interest excited by the developement of those facts which show the various means by which modifications of chemical action on metallic bodies by acid menstrua are produced, having induced the British Association to grant pecuniary aid to Professor Schöenbein to enable him to pursue those experimental enquiries in which he had previously been so successfully engaged on this subject, it cannot be presuming too much to suppose that the Association would be desirous of becoming acquainted with every fact connected with so interesting a branch of physical science. And as I think it possible that Professor Schöenbein may not be in possession of some particular facts of this class, which were discovered several years ago, and as the theoretical views which accompanied the publication of those facts appear to me to be applicable to every phenomenon of this peculiar class hitherto made public, I now venture to introduce them to the notice of the British Association,* simply as adscititious data, independently of which any historical view of the discoveries which have been made in this class of phenomena, and of the theoretical notions which have been advanced for their explanation, must necessarily be incomplete.

347. The experiments to which I allude were published in the year 1830, in a pamphlet, a copy of which accompanies this paper; and as the experiments are clearly described, and the theoretical views which I then entertained respecting them are unequivocally stated in the original, I cannot do better in this place than to refer to them as they stand in a note commencing at page 77 of that work. This theory of the electro-chemical action of the simple metals on acid and other solutions was republished in the "Annals of Electricity,"

• The first section of this Memoir formed the substance of a paper which was read at the Glasgow Meeting of the British Association, 1840.

The reader is referred to vol. 1 of the Annals for a perusal of the theory alluded to.

&c., for October, 1836, commencing at page 11; and a more extended application of that theory commences at page 17 of the same number.

*

348. Having thus directed the attention of the Association to the character of the phenomena which I had discovered and published more than ten years ago, it will appear obvious, by comparing them with the extensive series of facts which have subsequently been developed by various experimenters, that the whole are belonging to one and the same class of phenomena: that they have an electric origin: and are particular cases of, and easily traceable to, the same general laws of electro-chemical action which I have so clearly portrayed in the pamphlet already referred to.

349. We must not, however, overlook the labours of Bergman and Keir, the latter of whom has given a long list of discoveries of this class of facts, all of which are as highly important as any that have been subsequently developed. Mr. Keir clearly describes some of those facts which have appeared as novelties within the last few years; and has shown that iron acquires that altered‡ state by the action of nitric acid, which Sir John Herschell met with in his experiments, and has called the prepared || state; and what Schöenbein and others call the peculiar, or the inactive state.

350. The fact, also, that iron in certain conditions will not precipitate copper from its sulphate and other solutions, as recently observed by M. Schöenbein, was one of the many beautiful phenomena discovered by Keir, and clearly described in the Philosophical Transactions for 1790. Keir describes a number of similar experiments on the solutions of various metallic salts, and the phenomena in every case are obviously of the same class, and easily shown to be of electrical origin.

351. I have looked very attentively to the experiments of Herschel, Schöenbein, Andrews, Noad, &c., and I have repeated and varied many of them, and instituted others to a considerable extent, in order that I might be enabled to ascertain how far those theoretical laws which I had set forth would become applicable to the phenomena by the severest test which they could present. The electrochemical phenomena developed by the action of two distinct metals, or by the action of two pieces of the same kind of metal, in acid or in alkaline solutions, are so easily traced to voltaic electricity, that no difficulty whatever is presented to their explanation. Sir Hum

• Sir J. Herschel's paper on this subject, which is next on record, is dated August 19, 1833. See Annales de Chemie, or Philosophical Magazine, for October, 1837.

+ Philosophical Transactions of the Royal Society of London, 1790, p. 353; also Hutton's Abridgment of do., vol. xvi, p. 694: and Annals of Electricity, vol. v, p. 427.

Kier calls that iron which is active in nitric acid, fresh iron; and that which has become inactive, altered iron. See Annals of Electricity, vol. v, p. 439.

|| Philosophical Magazine, for October, 1837, p. 330.

phrey Davy, in his Bakerian Lecture for 1826, has produced several interesting facts of this class, with one kind of metal only: and several others are described in my pamphlet already alluded to, and are similar to some of those which Professor Schöenbein has met with, and enquired for an explanation.*

352. It may probably appear singular that I should compare Keir's experiments on iron, in which only one metal is employed, with another in which two are made use of. I therefore wish it to be understood, that on the surfaces of those simple metals which are active in any acid solution, the particles are as decidedly in different electric conditions as any two distinct metals can possibly be, and act voltaically on the liquid accordingly. Hence in an electrical point of view, each simple metallic body presents different electric surfaces, which are equivalent to a voltaic combination of two or more distinct metallic bodies. This once admitted, the inactivity of a metal, after some minutes immersion in an acid solution, follows as a matter of course, for the very same reason that two distinct metals become inactive after being some time in an active voltaic condition. Their relative electric conditions have suffered a change, and they become inactive in that particular liquid, though they would still be active in another; and a new pair of metals, or a new piece of a single metal, would also be active in the old liquid.

353. There are several experiments described, both in the Bakerian Lecture for 1826, and in my pamphlet, in which the metals employed have changed their electrical characters, and the currents change their directions accordingly. Iron is very susceptible of these electrical mutations. A combination of two pieces of iron, as nearly alike as they can possibly be made to appearance, will sometimes exhibit several mutations of this kind before they finally cease to produce a current. In their first condition they are active, and A is positive to B; in a short time they are neutral to each other; afterwards B becomes positive to A, and becomes more and more so, till the needle indicates the maximum of action. The action again declines, and again they pass through the neutral point, and again A becomes positive to B. And after several mutations of this kind, the needle indicates that the two pieces are so nearly alike in their electrical characters that they are unable to produce an appreciable current. But agitation in the old liquid, or immersion in a new one, again brings them into a state of electrical activity.

354. Similar electro mutations, and final neutrality, take place on the surfaces of single pieces of metal.

355. There are different causes for metallic bodies changing their electrical characters by voltaic action, all of which will be found in the attachment of one or more of the constituents of the liquid employed. Hence the attachment of oxygen, nitrogen, metallic particles, &c., to metallic surfaces, will change the electrical character of them, and in many cases completely neutralize them, as regards particular li

Philosophical Magazine, for February, 1837, p. 133-4-5.

quids, though they may still be sufficiently active in other liquid bodies. Hence the voltaic energies on the surface of gold and platinum are too feeble to decompose any of the simple acid solutions, though sufficiently powerful to become active in their well-known solvent.

356. The particles of the liquids, and of their constituents, have also their electrical influence in all voltaic actions, and are electrically modified as decidedly as the surfaces of solid metallic bodies.

357. In all cases where simple metals are first active and afterwards inactive in acid solutions, it should be borne in mind that before they become inactive they are absolutely in metallic solutions, by the dissolution of a portion of their own substances. Hence in those experiments by Bergman and Keir, the cases were precisely alike, whether the iron was immersed in an already prepared metallic solution, or immersed into nitric acid only. And the more modern experiments with bismuth, &c., are of precisely the same character; and their inactivity, produced by the re-attachment (precipitation) of their own previously dissolved metallic particles, which give a new electrical character to the surface, and thus reduce the voltaic energies too low to remain any longer active on that particular liquid, though still sufficiently active to operate on a different one. Hence the cause of their brightness during their apparently inactive state: for in reality no metal is perfectly inactive when a fluid is presented to it suitable for a display of its voltaic energies.

66

358. With respect to other phenomena in the display of which only one individual piece of metal is employed, as first shown by Keir, they remain without even an attempt at explanation by any of the philosophers under whose notice they have appeared. Sir John Herschell pronounces them as of an extraordinary character;"* Professor Andrews, after giving some very satisfactory explanations of several phenomena, acknowledges that he "can offer no explanation of most of the particular facts which have been described;"† and Professor Schöenbein has not yet made public any explanation of them whatever.+

359. Under these circumstances it would be impossible to form any correct idea of the nature of the theoretical views on this subject which Professor Schöenbein will offer to the British Association at the Glasgow meeting. If, however, that philosopher should honour me with an attentive perusal of those facts and theoretical explanations to which I have already solicited the attention of the Association, it is possible I think that he will be enabled to find an easy and natural explanation to every phenomenon hitherto developed in this peculiar class, the whole of them being traceable to those laws,

• Philosophical Magazine, for October, 1837, p. 333.

+ Ibid, for April, 1838, p. 311.

An abstract of Herschel's and Schöenbein's experiments will appear in our next number.-EDIT.

which, though many years before the public, he may probably till now, never have had an opportunity of becoming acquainted with.

360. I have shown that zinc, which is the most energetic metal in dilute sulphuric acid, may have its action either partially or totally annihilated in that liquid by the contact of copper wires ;* and I have shown that amalgamated zinc is perfectly inactive in solutions of sulphuric acid, but that it is still active in solutions of nitric acid. These are cases in point, and the latter is of precisely the same character as those shown by the iron in Keir's experiments. In one liquid it is inactive, in another it is active.

361. The explanation in these and in all similar cases, is referable to the difference of voltaic action in the solid and fluid bodies employed. WILLIAM STURGEON,

Royal Victoria Gallery for the Encouragement of
Practical Science, Manchester.

September 11, 1840.

NOTE. The contents of this Memoir were reported in the volume of the "Proceedings of the British Association for the Advancement of Science, for 1840," in the following manner :

On a peculiar Class of Voltaic Phenomena, by Mr. Sturgeon."The author directed attention to some experiments published by himself in 1830, and to his theory respecting the electro-chemical action of the simplest metals on acid and other solutions. He stated that the fact of iron not precipitating copper from its sulphate and other solutions, as recently observed by Professor Schöenbein, was one of the many beautiful phenomena discovered by Keir, and published in the Philosophical Transactions for 1790."

SECTION II.

On the Theory of Voltaic Electricity.

362. Perhaps there is no individual branch of physical science that has exercised the ingenuity of philosophers to a greater extent, repecting the modus operandi whence emanates its diversified phenomena, nor has any one been more productive of diversity of opinion, as a theoretical topic, than voltaic electricity, from the first days of its discovery to the present time: and what may, perhaps, be considered still more remarkable, no theoretical discussion has been less successful in uniting the opinions of scientific men, so as to give a general sanction to any theoretical views that have hitherto been taken, from whatever quarter they may have emanated, than that which has proceeded from this subject, and which has now been continued through a long series of years, and still remains as undecided as at first.

• See my Experimental Researches, &c., experiments A and B, p. 78–79. + Ibid, p. 41-42-74-76-77.

Ibid, p. 43.