Mr. Daniell or myself: it will then be understood whether filial piety blinded me, or that I was actuated by the love of truth. Paris, July 7, 1842.

[Professor Grove has also sifted Professor Daniell's claims, in the following letter to the editors of the "Philosophical Magazine:"*-] Allow me to request your insertion of a few remarks on a letter of Professor Daniell, published in your magazine for April. sence from London and occupations of other than a scientific nature prevented my noticing it at the time; my attention has been recalled to the matter by its republication in the "Annales de Chimie.”

A few words at the conclusion of this letter refer to me: after stating that M. Becquerel has inadvertently described my experiments as anterior to Mr. Daniell's, this gentleman goes on to say, Professor Grove has never spoken of his battery but as the further application of principles which I had previously deduced."

It is perhaps of little moment to the public what principles led me to the construction of the battery in question, but it may be of some moment to me, as should I, by silence, be held to assent to certain principles, I may be accused of contradiction and inconsistency, if in any future paper I should state my adherence to others. M. Becquerel, again, in the 5th volume of his "Traité de l' Electricité," describes my battery as "pile voltaïque construite d'après les principes exposés dans les chapitres 1", &c.:" these chapters contain the papers of M. Becquerel in respect of which he claims priority to Mr. Daniell. It is obvious, that as M. Becquerel and Mr. Daniell differ in their notions as to the principles of the constant battery, I could not derive my battery from both, and I have looked over my papers on this subject to see whether I have expressly referred it to principles enounced by either of these philosophers: I cannot see that I have. I have on many occasions mentioned their experiments before my own in the history of the voltaic pile, both as acknowledging their priority and as not wishing to claim what was not my due; probably it is this which has led to a misconception on the part of Mr. Daniell; but I have distinctly stated the idea which immediately led to the construction of my battery in the paper which describes it in the "Philosophical Magazine" for May, 1839. After detailing an experiment with two strips of gold-leaf in nitric and hydrochloric acids, separated by a porous diaphragm, and showing that upon contact of the two strips, the gold in the hydrochloric acid was dissolved, and that a voltaic current was established, I say, "It now occurred to me, that as gold, platina, and two acids gave so powerful an electric current," d fortiori, "the same arrangement, with the substitution of zinc for gold, must form a combination more energetic than any yet known:" this was the simple deduction which led to my subsequent experiments. I have in most cases been con

• "Philosophical Magazine."

tent to publish experiments with no more of theory than was requisite to connect them; it is a general, and I think a just complaint, that there are already too many speculations on this subject; but in a letter published in the "Philosophical Magazine" for Feb., 1839, p. 129, previous to the discovery of my battery, I gave my own notions of the principles of voltaic batteries, notions which in some respects agree with those of Mr. Daniell, but which also suggest some new views of voltaic action. There is one experiment there detailed in which copper is reduced by copper, which had much influence on my subsequent experiments, but which is not explicable by any principles laid down by Mr. Daniell. At the conclusion of this paper I say, "if these principles be correct, very superior combinations may be discovered:" how this prediction has been fulfilled the public is the best judge.

Far be it from me to disclaim any assistance from the experiments of Mr. Daniell or of M. Becquerel; I shall ever retain a grateful recollection of the assistance rendered to my first efforts in science by the latter gentleman. I cannot at this distance of time well describe what effect their experiments had upon my mind. In the progress of science it is difficult to define the frequently unperceived effect of prior discoveries upon subsequent experimentalists, but I cannot for many reasons acquiesce in the assertion of Mr. Daniell above quoted.

Mr. Daniell was for a long time attached to the theory of the deposition of metals in the voltaic circuit being the result of a secondary action of the nascent hydrogen, a theory generally adopted until combated by Hisinger and Berzelius; thus in his papers, "Philosophical Transactions," 1836, p. 117, et seq., he proceeds to explain his constant battery as dependent upon the removal of that hydrogen by causing it to deoxidate copper: in a subsequent publication in the "Philosophical Transactions," 1839, he abandons this view, and considers the deposition of the copper as "a primary result of electrolytic action." This would altogether alter the theory of his battery and of mine. I do not think it is a matter of great consequence which theory be adopted; each has many peculiar difficulties, each tends to many similar conclusions, and either may lead to equally successful experimental results. Theory is valuable as a means, not as an end; and that theory of the voltaic battery is, in my opinion, the best which best collates the observed phenomena, and which leads to the discovery of the best voltaic combinations. But although I would hesitate, without more conclusive experiments, in ascribing this superiority to either of these theories, there is another principle of the voltaic battery enounced by Mr. Daniell, as to which, so far from agreeing with him, I must take leave (with every respect for his scientific attainments) to differ toto cœlo: it is as to the relative extent of surface to be given to the metals of voltaic combinations. Mr. Daniell has in the "Philosophical Transactions," for 1836, p. 128, and in several subsequent papers, stated that the best theoretical form for a vol

taic combination is when the generating metal is arranged with regard to the conducting one as the centre of a sphere to its periphery, and recommends a rod within a cylinder as the nearest practical approximation to such an arrangement; following the authority of Mr. Daniell, I first constructed my batteries of this form, but very soon abandoned it: see "Philosophical Magazine," for Oct., 1839, p. 288 and I am now convinced, by three years' experience, and by repeated experiments, corroborated by the experiments of others, that this is by no means the best form of arrangement, as regards economy either of space, time, or material. I believe the old arrangement of equal surfaces to be sufficient for most practical purposes; but the relative size may be considerably modified according to the nature of the electrolytes, the conducting power of the metals, and other circumstances. I cannot enter more fully on this point without writing a paper especially on this subject.

P.S.-Since the above was written I have received a paper of Mr. Daniell's, just printed in the "Philosophical Transactions," 1842, part ii, for which I have to thank the author: it contains a series of experiments on my battery, and with a voltameter of my contrivance. In this paper I see Mr. Daniell alters many of his opinions upon the relative size of the plates in voltaic combinations.

MORE FACTS.

Being now engaged in clearing up accounts, we will take the liberty of bringing before our readers a few more facts, which not only bear on some parts of the above reckoning, but are items in another perfectly distinct account.

One of the essential conditions in the performance of continuous uniform action in a voltaic battery, one of whose liquids is a solution of a salt of copper, is the reduction to the lowest possible point of the activity of the zinc on that solution, and also on the solution on which it is immersed. With respect to the solution of the sulphate of copper, the activity of the zinc is considerably abated by the intervention of the diaphragm, but never entirely subdued by the intervention of a thin membrane or paper. Amalgamation of the zinc lessens its electro-chemical energies to a considerable extent, and it is in this state that it becomes so efficient in continuing the action of voltaic batteries. This being understood, we have next to place this grand essential of "the constant battery" to the credit of those who first discovered the great diminution of electro-chemical action of zinc when amalgamated.

In the first volume of these "Annals," we have given an historical sketch of the employment of amalgamated zinc in voltaic batteries, and we have only to refer to that article to satisfy the reader on that point and with respect to the almost entire extinction of electro-chemical action of amalgamated zinc on a solution of sulphuric acid, the solution used by Mr. Daniell in his battery, a reference to page 88,

of the same volume, might be sufficient. But as Professor Grove has made a claim to the discovery of the inactivity of amalgamated zinc on diluted sulphuric acid, in a paper read in the Academy of Sciences, Paris, it may not be amiss to give, at whole length, the articles from which those extracts were taken; especially as they contain some other theoretical points in the action of voltaic batteries, which Professor Grove has also subsequently discovered. In a paper which appears in Vol. V, of these "Annals," Professor Grove states, in page 254, amongst other things, "But the most remarkable fact is, that the plate of zine which was in the acid, although much more attacked chemically than that in the alkali, always took positive electricity; i.e., it represented the copper in an ordinary voltaic combination."

We are very far from imputing to Professor Grove any improper motives for not alluding to similar discoveries, because it is probable that he might not have been aware of them at the time that he wrote, although published in the "Annals of Electricity, &c.," nearly four years previously, and originally in a pamphlet, well known in London, ten years previously to the date of Professor Grove's experiments. The pamphlet containing the following facts is dated 1830:--

*

45. Let two equal slips of sheet zinc, of any convenient size, be polished with glass paper. Let the surface of one of them be amalgamated, by spreading mercury over it with a piece of clean rag, so that it may become quite brilliant. Both pieces being furnished with connecting wires, and in proper communication with the galvanometer, let them be plunged into a weak solution of either sulphuric or muriatic acid. The amalgamated piece will operate as zinc, and of course the other piece as copper in the standard battery. But it will be observed particularly, if the combination be placed in a glass vessel, that the piece which operates as copper undergoes rapid destruction, whilst the other is scarcely affected by chemical action. Gas will copiously ascend from the former, whilst a few indolent bubbles only, will be observed on the latter, which cling to its surface without making their escape. Hence it appears from this experiment, that the most oxidizable metal in a galvanic combination, does not universally operate as zinc in the standard battery or in other words it is not always the positive metal.

Zinc may be easily amalgamated by first dipping it in a solution of sulphuric acid, and afterwards in mercury.

+ Sir H. Davy, in his Bakerian Lecture for 1826, observes that "zinc in amalgamation with mercury is positive with respect to pure zine;" but he is perfectly silent as regards the nature of the chemical action which is developed by a combination of these materials in any acid solution; though, one might have supposed that, had he made the experiment, this striking and singular phenomenon could not have escaped the attention of so penetrating an observer, nor have been permitted to pass unnoticed whilst discussing the theories of galvanism,

Sir Humphry has also stated that, "There is not any inherent and specific property in each metal which gives it the electrical character; it depends

46. I know of no experiment that operates more decidedly against the chemical theory of galvanism than the one I have last described. The electricity displayed is uniform and steady from beginning to end; and its duration is determined by the durability of the negative piece (copper in the standard battery), and not by the other, as that theory supposes. I have observed a deflection of the needle of more than 10° for two successive hours, with two pieces, each exposing about one square inch of surface to the action of the acid solution; at the end of which time, the needle was perfectly steady at that angle, although the piece which operated as copper was nearly destroyed. On examining the amalgamated piece, very slight traces only of chemical action could be observed on its surface. The same amalgamated piece was successively combined with two others, which it likewise outlasted, still operating as zinc in the standard battery; and was even then much decayed by chemical action; but had become exceedingly brittle by combining with the fluid metal.*

47. Iron and nitric acid.-When diluted nitric acid is placed in one chamber, and water in the other, the piece of iron which is immersed in the acid solution, operates as copper, and consequently the other piece which is placed in the water, displays its electricity in the character of zinc in the standard battery.

When a few drops of acid are mixed with the water, the electrical energies become very much exalted; and the needle will frequently mark an angle of 35°, particularly if the stronger portion of

upon its peculiar state-on that form of aggregation which fits it for chemical change."

From this statement of Sir Humphry's, I imagine that he has made no experiment like that described in the text; for it could never have been discovered from that experiment, nor with any other with which I am acquainted, that the amalgamation of zinc exalts its oxidability in a solution of either sulphuric or muriatic acid: the most essential "chemical change" required to satisfy the conditions of the electro-chemical theory.

Were it not on account of the brittleness and other inconveniences occasioned by the incorporation of the mercury with the zinc, amalgamation of the surfaces of zinc plates in galvanic batteries would become an important improvement; for the metal would last much longer, and remain bright for a considerable time, even for several successive hours-essential considerations in the employment of this apparatus.

Notwithstanding the inconveniences, however, the improvement afforded by amalgamating the surfaces of zinc plates becomes available in many experiments; for the violent and intense chemical action which is exercised on zinc by a solution of sulphuric or muriatic acid, with the consequent evolution of heat, and annoying liberation of hydrogen, have no place when the plates are amalgamated: the action is tranquil and uniform, and the disengagement of gas, which is trifling, occurs only when the circuit is complete, and at the surface of the copper plate. The electric powers are highly exalted, and continue in play much longer than with pure zinc: and the only care of the experimenter is, to prevent the copper, or whatever metal be substituted, from becoming amalgamated.

With a solution of nitrous acid, the electrical energies of two pieces of zinc, the one pure, and the other amalgamated, are displayed in a very superior degree; but in consequence of the amalgamated surface becoming partially