hydrogen and oxygen per minute, while with a constant battery of my construction it is easy to maintain a current equivalent to twenty cubic inches of the mixed gases in the same time. It is scarcely necessary to observe, that the difficulty of maintaining constancy of action is, of course, proportioned to the energy of the action.

It is this almost unlimited command of steady force which renders its application, either in the electrolytic or magnetic direction, possible to mechanical or manufacturing purposes: magnetic locomotive engines never could have been dreamt of without the solution of this preliminary problem.

M. E. Becquerel proceeds to say, "M. Daniell, d'après les principes exposés précédemment, a construit une pile dont nous allons donner la déscription, et qui est à présent généralement employée." (P. 442).*

Now I not only most emphatically deny that I was in any degree guided by these principles, but I assert that they were incapable of leading me to any such conclusion; as they, in fact, failed to lead M. Becquerel to the same.

In proof of this, I will briefly recapitulate the real principles of "the constant battery;" the different steps of the investigation which preceded its invention being all clearly stated in my papers in the Philosophical Transactions.

1. In the first place, I traced the origin of the decline and ultimate annihilation of the current in the common voltaic battery not to the evolution of acid and alkaline matter at the opposite plates, and the consequent establishment of a counter current by their mutual reaction, but to the deposition upon the conducting plate of a substantial coating of pure metallic zinc, the weight of which upon a platinum plate of three inches by one I have stated to be nearly twenty-nine grains. In consequence of this, zinc becomes opposed to zinc in the circuit, and all current is stopped.

2. To prevent this deposition of active metal upon the conducting metal, it occurred to me,-1st, to divide the portion of the electrolyte in contact with the generating plate from that in contact with the conducting plate by a porous diaphragm, by which the solution of zinc is prevented from reaching the copper or platinum; and secondly, to provide for the perpetual renewal of the surface of the conducting plate by the deposition of fresh inactive metal upon it, transferred by the process of electrolysis from the solution of a salt selected for the purpose and placed in the partition next to it, or precipitated by the secondary action of the hydrogen evolved upon it. By this contrivance, not only is the surface of the conducting plate perpetually renewed, but the opposing influence of the hydro

⚫ M. E. Becquerel proceeds to say, “M. Daniell, after the principles precedingly exposed, has constructed a pile of which we are now going to give a description, and which is at present generally employed."

gen during its evolution is removed, and the battery is at once rendered constant and its power greatly exalted.

As copper, from its comparative inactivity, its great conducting power, and its commercial value, is the only metal which is capable of being applied extensively for the construction of voltaic batteries upon a large scale, I constructed my cells of that metal; placing in contact with them a saturated solution of sulphate of copper in dilute sulphuric acid (eight measures of water, one oil of vitriol), separating this portion of the electrolytes from that which is in contact with the amalgamated zinc, and which is composed of the same diluted acid without the salt of copper, by a diaphragm of membrane or porous earthenware. Under this arrangement a part of the current is conveyed by the electrolysis of the sulphate of copper and a part by the dilute sulphuric acid: from the former the copper is directly deposited in that compact form which is now so well known from the formation of voltatypes, and by the latter it is thrown down in a less coherent form by the secondary action of the hydrogen; but both concur in the effects which have been previously described.

The only practical difficulty in this construction is the formation of diaphragms, capable, at once, of allowing the electrolytic action to proceed through them, and of perfectly preventing the mixture of the liquids on their opposite sides; the latter action being, it will be remembered, one of the essential principles of the batteries "pour les actions lentes," upon M. Becquerel's construction. If a portion of the solution of copper penetrates to the zinc side of the diaphragm it is decomposed, and the copper deposited upon the zinc producing strong local action and loss of the generating metal; for I have not been fortunate enough to find, with M. Becquerel, that the copper can be dissolved under such circumstances.

Such are the principles which I have derived from experiments, and which are capable of application to the construction of powerful constant batteries of different forms and materials. The form which I have preferred is that of hollow cylinders of conducting metal, with central rods of generating metal. This form is dependent upon another principle, which I also worked out from experiments upon the diffusion of the force of a small generating surface over a large conducting surface. These have also long since been published in detail in the Philosophical Transactions, but they are not alluded to in M. E. Becquerel's Notice. This cylindrical arrangement is one of great capacity, and admits of the employment of large quantities of the electrolytes which are required for energetic and longcontinued action.

But, of course, the principles of the construction are independent of form and materials, and are capable of application to flat, square and equal surfaces of the two metals, as well as to concentric arrangements. They admit also of the employment of different metals and of different electrolytes. They are not changed by placing the zine on the outside instead of the inside of the copper,

nor even by altering the name of the "constant battery" to that of the "sustaining battery."

I will embrace this opportunity of observing that M. Becquerel, in his Traité de l'Electricité (tome v, livre xiv, p. 195), has inadvertently committed an error affecting the history of "the constant battery," in giving priority to Professor Grove's experiments with the nitric acid battery over mine. He describes that gentleman's construction, and then proceeds, "Les choses en étaient là lorsque M. Daniell a repris la question, qu'il a analysé avec sagacité. Ses recherches l'ont mis à même de doter la science d'une pile construite d'après les principes précédentes, et qui est aujourd'hui généralement adoptée dans les expériences de physique.'

It is only necessary to recall the data of my first paper upon the subject in the Philosophical Transactions, viz. February 11th, 1836, and that of Professor Grove's communication to the French Academy, I believe, April 1839. Professor Grove has never spoken of his battery but as the further application of principles which I had previously deduced.

In conclusion, I cannot but express my regret that the filial piety of M. Edmond Becquerel should have betrayed him into an act of injustice by preferring a claim for his father which is totally unsupported by the facts of the case, and from which his well earned reputation can derive no permanent extension.

I remain, dear Sir, very faithfully your's, King's College, London, March, 1842.

J. F. DANIELL.

On the Sustaining Voltaic Battery: in reference to some Observations of Professor Daniell, in the April Number of the "Philosophical Magazine." By F. W. MULLINS, Esq., M.A., &c.

TO WILLIAM STURGEON, Esq.

DEAR SIR-As the conductor of a magazine, justly denominated the "Guardian of Experimental Science," I trust you will kindly make room for a few observations called forth by the following paragraph contained in the letter of Professor Daniell, "On the Constant Voltaic Battery," published in the Philosophical Magazine for March.

After setting forth the differences between the principles of the "constant battery," and M. Becquerel's voltaic combination discovered in the year 1829. Mr. Daniell adds: "But of course the

• "These particulars were there when Mr. Daniell again took took up the question, which he has analyzed with sagacity. His researches have endowed science with a pile constructed after the preceding principles, and which is generally adopted in philosophical experiments."

The preceding article is that alluded to. Professor Daniell's voltaic arrangements and experiments are fully described in vols. 1 and 3 of the Annals of Electricity, &c.-EDIT.

Gg

principles of the construction are independent of form and materials, and are capable of application to flat, square, and equal surfaces of the two metals, as well as to concentric arrangements. They admit also of the employment of different metals, and of different electrolytes. They are not changed by placing the zinc on the outside instead of the inside of the copper, nor even by altering the name of the constant battery to that of the sustaining battery."

Now, as it is quite clear that the latter part of this paragraph distinctly refers to "Mullins's Sustaining Battery," that being the distinguishing appellation applied to it by me, and borne by it alone, and as the inference to be drawn from the entire sentence is, that the principles of the "constant" and "sustaining "batteries are not only identical, but that the latter arrangement has been borrowed from the former-I cannot permit such an impression to acquire further publicity, without at once entering my protest against the correctness of such a conclusion, as well as against the mode in which it has been put forward.

I find a similar misstatement in Walker's Electrotype Manipulation, but I have not thought proper to notice it, nor should I do so on the present occasion, did I not find Professor Daniell himself using language which might be understood to sanction inuendos incapable of proof, and utterly groundless.

Sir, I formally and distinctly deny that the principles of the sustaining are the same as those of the "constant voltaic battery;" and I cannot but consider it extremely strange that Professor Daniell should hazard such an opinion in a letter written professedly for the purpose of showing (as in the case of Becquerel's battery and his own) that voltaic combinations, although constructed of exactly similar materials, with the similar design of obtaining constancy of effect, may yet have no one principle in common !!

But as facts are stubborn things, and as I like to deal with facts, and not opinions, let me first state, in Professor Daniell's own words, what are the principles of his combination, and then explain those of the other.

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First then, Mr. Daniell declares his "constant" battery to be constructed on the principle of a central disposition of the active metal, with regard to the conducting surface,' " and he carries out this principle in his battery, by the employment of a rod of cast zinc, amalgamated and suspended in the centre of a circle of copper, the said rod being, according to his detailed measurements, half an inch in diameter, and the copper cylinder surrounding it, three and a half inches; which the Professor states, "experience has proved to afford the most advantageous distance between the generating and conducting surfaces." He thus interposes, it would appear, by preference, an imperfect conductor of one and a half inches interval between the metals; this interval, of course, continually increasing See his Chemical Philosophy, page 438, sec. 737.

+ See latter part of sec. 737, in Chemical Philosophy.

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in proportion to the destruction of the central zinc, and consequently, causing additional retardation of the current. Yet he lays it down as an incontrovertible position, that such an arrangement developes more electric energy, and is more constant in its effects, than equal surfaces of similar metals in any other mode of combination. Now, in the "sustaining battery," these principles of Daniell's are directly opposed by the nature of the arrangement, in which there cannot be any such thing as central action," and in which retardation is diminished by approximating the metallic surfaces as much as possible: so that, in place of one inch and a half, as in Daniell's arrangement, they shall be no more than a quarter, or at most, half an inch asunder: a principle at variance with Daniell's; grounded on the results of careful experiments, and supported by the distinguished authority and varied investigations of Davy and Faraday, Hare, De la Rive, and many other eminent philosophers.* Secondly, Professor Daniell advocates the use of an acidulated solution in contact with the zinc, which he declares it is requisite to amalgamate, in order to avoid local action; whereas in the sustain-ing battery, no acids are used, alkaline solutions being employed as far preferable the zinc is not amalgamated, there being scarcely any local action: rolled instead of cast metal is advantageously used, and the general chemical effects are different. Again, Professor Daniell asserts another of his principles to be, "that of perfectly preventing the mixture of the liquids on the opposite sides of the diaphragm employed," such mixture "producing strong local action," &c.; whereas, in the sustaining battery, a diametrically opposite principle was from the very first brought into play, by the employment of the very thinnest membranes that could be procured; it being found that the mixture of the fluids, within a certain limit, increased considerably the effect; this mixture arising in a great degree, from the action of "endosmose;" which, according to M. Dutrochet, has most probably an electric origin, and, according to my observations, unquestionably promotes electrolysis; and this principle, the very opposite of Daniell's, was further carried out by the employment of white silk as a diaphragm, which would be superior to every other I know of, but for the disposition of the precipitated copper to collect within its interstices.

Having thus briefly, but I trust clearly, set forth the principles upon which the sustaining battery was constructed, and shown that they are altogether opposed to those claimed by Professor Daniell, I leave it to him and M. Becquerel to settle the question of originality as best they can; for my part, I make no claim to originality in regard to the principles which governed the construction of the bat

We have, for many years, employed batteries in which five pairs occupied one inch only of its length.-EDIT.

†Those membranes were abandoned solely in consequence of their liability to injury; wooden diaphragms have been substituted by me, which admit of a certain mixture of the liquids, and are extremely durable.