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an electro-negative part, and which would thus correspond to combinations of manganic and permanganic acid with the bases.

The facts I am about to make known show, I believe, in a conclusive manner, that iron can give birth to bodies which are produced in the same manner as the manganates, and which present a striking analogy with this latter class of salts.

When we heat for a considerable time to a temperature of a bright red, a mixture of potash and peroxide of iron, we obtain a brown mass which, dissolved by water, gives a solution of a very beautiful red violet, and which possesses characters hereafter to be indicated. This compound may be prepared more easily and in a few minutes, by calcining at a very high temperature a mixture of nitre, of potash, and peroxide of iron ; or still better a mixture of peroxide of potassium and peroxide of iron.

I have succeeded in reproducing this body by the humid method, by causing a current of chlorine to pass into very concentrated potash, holding in suspension the hydrate of the peroxide of iron.

This compound obtained by these different processes is of a beautiful violet colour; a great quantity of water decomposes it at length ; it becomes insoluble in very alkaline water, forming then a brown precipitate, which dissolves easily in pure water, and gives a solution of a beautiful purple colour. It appears much less stable than the manganate of potash. Under certain circumstances it is decomposed at the ordinary temperature in peroxide of iron, which becomes precipitated in pure oxygen, which disengages itself; and in potash, which becomes free: the liquor is in this case completely discoloured. A temperature of 100° makes it undergo a similar decomposition, but which is instantaneous.

All organic matters decompose it: it is consequently impossible to filtre its solution.

Such are the different facts which I have proved, and which all tend to make us admit the existence of a body more oxygenated than the peroxide of iron. I have found it impossible hitherto to isolate this compound, for when we come to treat this red solution by an acid, when the potash is saturated, there is a disengagement of oxygen and a precipitation of the peroxide of iron. If the acid is in excess it dissolves the peroxide, and forms a salt of the peroxide of iron.

In the memoir which I shall have the honour to present to the Academy, I purpose giving the analysis of these new compounds, which I found based on the complete decomposition which they undergo under the influence of a temperature of 100°, and which permits us to proportion the disengaged oxygen, and the peroxide of iron which is precipitated.

I shall discuss the different manners of considering their composition in examining whether we may admit in these bodies the existence of alkaline peroxides. I shall also make known the results which I have obtained by placing the other metallic oxides in the same circumstances.

As the bodies which form the object of my researches are of a delicate preparation, and the study of them ought to be of a prolonged nature, I have thought it my duty to take date, and to announce from to-day the first results which I have obtained.

On the Constant Voltaic Battery. By J. F. DANIELL, For. Sec. R.S.,

Prof. Chem. in King's College, London ; in a Letter addressed to R. Phillips, Esq., F.R.S., &c.*

MY DEAR SIR,- In the Annales de Chimie et de Physique for December, 1841, there is a paper by M. Edmond Becquerel, entitled “Sur les piles à Courant Constant," upon which I beg your permission to make a few observations in the Philosophical Magazine. The object of the author is thus stated :

A 'époque actuelle, où l'on cherche de toutes partes à appliquer les sciences physiques et chimiques, et par conséquent l'action des forces électriques, aux arts industriels, je pense qu'il peut être utile de présenter succinctement l'exposé de toutes les recherches qui ont été faites pour obtenir des piles dont l'action soit constante pendant un certain temps." (Ann. de Chimie, tome iii, p. 436).

In this opinion I perfectly concur; and it is for the purpose of rendering such an account more perfect that I desire to correct some misconceptions into which M. E. Becquerel has fallen, and which have the effect of greatly mystifying the origin of constant batteries. After stating the well-known defects of voltaic batteries of the common construction, in which the two metals are plunged into the liquid in the same cell; and the necessity of constructing batteries of constant action before they could be usefully employed in the arts, he proceeds to make the following comprehensive claim :

“C'est mon père qui a donné le premier les principes sur lesquels est fondée la construction de ces piles et qu'a formé les premiers piles de ce genre.” (Ann. de Chim. p. 437). I

Now as I have claimed to be the inventor of “the constant battery" (which was so named by myself), and as the Council of the Royal Society have so far sanctioned this claim as to award me the Copley Medal for my invention ; and as I have most undoubtedly worked out the principles of its construction by experiments and legitimate induction, without the slightest suspicion that M. Becquerel had preceded me in the investigation, I was naturally very anxious to examine the evidence upon which this assertion is founded.

• From the Philosophical Magazine.

+ " At the actual epoch, in which it is sought in all parts to apply the chemical and physical sciences, and consequently the action of electrical forces, to the industrial arts, I think that it may perhaps be useful to present succinctly the exposition of all the researches which have been made to obtain piles whose action should be constant during a certain time."

“ It was my father who gave the first principles on which the construction of these piles is founded, and who formed the first piles of this kind.”

Previously to stating this evidence, M. E. Becquerel makes some remarks upon the phenomenon which has been most inappropriately termed the polarization of the plates of a voltaic battery, of which his father, he observes, has given the simple explanation.

"Dans le passage d'un courant électrique à travers un liquide conducteur voici ce qui a lieu : quand le courant primitif traverse le liquide conducteur, des élémens acides sont transportés au pôle positif, et des élémens alcalins au pôle négatif; alors, en interrompant la communication entre les lames décomposantes (ou électrodes) et la pile, les deux lames se comportent vis-à-vis l'une de l'autre comme deux lames que l'on aurait plongées, l'une dans un faible dissolution alcaline, l'autre dans une faible dissolution acide : c'est-à-dire, qu'en les mettant en rélation avec un multiplicateur, il y aura production d'un courant électrique dû à la réaction des molécules acides ou se comportant comme telles, sur les molécules alcalines

par

l'intermédiaire du liquide : ce courant sera par conséquent dirigé en sens inverse du courant initial. Cet effet se manifeste toujours lorsqu'un courant traverse un liquide conducteur quelconque au moyen de deux lames métalliques. Cette polarisation des électrodes a donc lieu dans toutes les piles, lorsque les lames qui compose chaque couple plongent dans un même liquide et dans un même auge." (Pp. 437-8).*

This hypothesis, however, though it borders upon the true explanation, is not correct; for in my first paper upon “Voltaic Combinations" (Phil. Trans., 1836, p. 116), I have shown that the polarization of the plates, and the rapid decline, and final cessation, of the current in batteries of the common construction, is owing to the deposition of metallic zinc upon the conducting plates. This I at first ascribed to the deoxidating power of the hydrogen upon the oxide of zinc, but have since adduced evidence to prove it is owing to the direct electrolysis of the sulphate of zinc formed. The deposit I was able to detach from the platinum, upon which it had been precipitated, in plates of considerable thickness. This opposition of

“ In the passage of an electric current across a liquid conductor observe what takes place; when the primary current traverses the liquid conductor, the acid elements are transported to the positive pole, and the alkaline elements to the negative pole ; then, on interruping the communication between the decomposing plates (or electrodes) and the pile, the two plates act in opposition to each other, like two plates which are immersed, the one in a feeble alkaline solution, and the other in a feeble acid solution; that is to say, by putting them in connection with a multiplier, we shall have the production of an electric current due to the reaction of the acid molecules, or which act as such on the alkaline molecules by the intermediation of the water: this current will consequently be directed in an inverse direction to the initial current. This effect always manifests itself when a current traverses any liquid conductor whatever, by means of two metallic plates. This polarisation of the electrodes takes place then in all piles, when the plates which compose each pair are immersed in the same liquid and in the same trough."

zinc to zinc in the acid is sufficient to account for the result without supposing “the reaction of alkaline matter transported to the conducting plate upon acid transported in like manner to the zinc plate through the intervening fluid." It is difficult, indeed, to conceive that the latter should not rather increase the power of the direct current, by its action upon the zinc with which it must be in contact, than produce a counter current by its action upon the alkaline matter upon the distant platinum plate.

The problem of a constant battery, which M. E. Becquerel says that his father has solved, is thus stated :

“Si donc ou pouvait enlever continuellement les élémens alcalins et acides qui se déposent sur les lames, on anéantirait le courant secondaire, et la pile aurait une intensité constante, en tant cependant que les surfaces des lames resteraient à peu près aussi nettes et que l'action du liquide sur le zinc serait à peu près la même.” (P.438).*

It appears from the statement of M. E. Becquerel, that in the year 1829 his father contrived an apparatus consisting of a glass cell or rectangular vessel, the interior of which was divided into three compartments by two diaphragms of gold-beater's skin, admitting of no communication except through the membranes placed for the purpose of retarding the mixture or combination of the liquids contained in each.

The bottom of the cell was perforated only in the centre compartment by a small opening, so that upon plunging the cell into another vessel containing a conducting fluid, the liquids in the two extreme compartments would mix with great difficulty: the central aperture admitted also of being closed, and the middle compartment could then be filled with the liquid of one of the extreme compartments. A plate of zinc was immersed in one and a plate of copper in the other, and the two were placed in metallic communication by means of the wires of a galvanometer.

Under these circumstances, when all the compartments were charged with dilute sulphuric acid (36th acid), a deviation of the galvanometer needle was produced, which, as with an ordinary couple, gradually decreased. Upon consulting M. Becquerel's original memoir ( Ann. de Phys. et de Chim., tome xli, p. 21), I find the following tabular record of the results :

Time of Immersion.

O'

Deviation of Needle.

63°

15

53 46

30

• “If then we could continually remove the alkaline and acid elements which are deposited on the plates we should annihilate the secondary current, and the pile would have a constant intensity, inasmuch, however, that the surfaces of the plates would remain also almost clear, and the action of the liquid on the zinc would be almost the same."

Upon re-commencing the experiment with the addition of oth nitric acid to the dilute sulphuric acid in the copper compartment, the intensity of the current changed, but gradually diminished as in the following table :Time of Immersion.

Deriation of Needle.
O'

81°
15

73 30

65 Upon the substitution of nitrate of copper for the nitric acid, the results were sensibly the same. M. Becquerel varied these experiments in many ways, and with the aid of this apparatus arrived at the following conclusions :

“ The maximum of intensity is obtained by immersing the copper plate in a solution of nitrate of copper, and the zinc in a solution of sulphate of zinc, but there is also a diminution with time; a little less rapid however than with an ordinary couple.' The following is the table of the last results : Time of Immersion.

Deviation of Needle.
O'

84°
15

72 30

68 The next paragraph of M. E. Becquerel's Notice I will give in his own words for fear of mistakes :

“Si l'on met de l'acide nitrique étendu dans la case zinc, un peu d'eau et d'acide sulfurique dans la case cuivre, et que dans la caisse A A'on n'emploie qu'un diaphragme, ou que l'on rapproche les deux diaphragmes de telle sorte que l'acide nitrique de la case zinc puisse passer lentement dans la case cuivre, afin d'augmenter la conductibilité, alors on peut, au lieu de rendre les intensités décroissantes les rendre croissantes pendant la première demi-heur; cela dépend de la quantité d'acide nitrique versée dans la case zinc ; si l'on en met avec précaution, on peut arriver à obtenir un courant constant pendant une demi-heure ou une heure. Cette disposition du couple réalise donc pendant un certain temps le résultat que nous avous annoncé, c'est-à-dire détruit le courant secondaire ; car l'acide nitrique qui se trouve dans la case zinc s'empare constamment du cuivre de la 80lution, qui, après avoir traversé les diaphragmes, se dépose sur le zinc.

“ Ainsi ces expériences montrent la possibilité d'obtenir un courant constant en détruisant le courant secondaire.” (P. 440).*

“If we put diluted nitric acid into the zinc case, and a little water and sulphuric acid in the copper case, and that in the box A A, we only employ a diaphragm, or that we bring towards each other the two diaphragms in such a manner that the nitric acid of the zinc case may pass slowly into the copper cell, in order to augment the conductibility; then we can, in place of rendering the intensities decreasing, render them increasing during the first half-hour: this depends on the quantity of nitric acid poured into the zinc cell ; if we put the nitric acid in with precaution we may be enabled to obtain

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