OF

ELECTRICITY, MAGNETISM,

AND

CHEMISTRY;

AND

GUARDIAN OF EXPERIMENTAL SCIENCE.

SEPTEMBER, 1842.

The Study of the Phenomena which are produced by Currents discontinued and transmitted in contrary directions, when they traverse a Circuit formed of Metallic and Liquid Conductors; preceded by Preliminary Researches on the Oxidation of Pla

tinum.

(Continued from page 98.)

PART SECOND.

IN renewing the study of the phenomena which have formed the subject of my preceding memoir, I perceived that they almost all had their source in the peculiar chemical effects which the currents made use of produced by induction. These currents owed to the circumstance of their being transmitted alternately in contrary directions, the fact of bringing successively upon the metallic conductors which conveyed them into a liquid, the opposite elements which compose this liquid-oxygen and hydrogen, for example, if it is water. Now, this rapidity with which these contrary elements succeed each other on the same metallic surface, determine in them chemical effects of a remarkable order. The result is, that the relative part which the metallic and liquid conductors play in a circuit so composed, is quite different accordingly as the currents which this circuit transmits are continued, or are transmitted alternately in contrary directions. It appeared to me that I was bound to seek in what this difference really consisted, and that with these causes, I ought to commence my work it is, then, to this study that I devote this second part of my memoir, reserving to myself the task of developing at a future time its applications and consequences.

But previous to advancing directly to the particular point of the researches which I have just referred to, I shall treat on a question which is intimately connected, and the previous solution of which is of great importance to the following part of my work. I mean to speak of the property which platinum has of becoming oxidized under Ann. of Elec. Vol. IX, No. 50, September, 1842.

M

the immediate action of oxygen. I had already suspected the existence of this property from several phenomena which I have referred to in my former memoir. But I have always felt that before regarding it as completely demonstrated, and capable of being admitted as the basis of interpretation of so many results, that it ought to be supported on proofs drawn from direct experiment. This is what I have endeavoured to do, and it is the result of this work that I am about to detail in the first section of this second part of my memoir. Perhaps it will be found, at first glimpse, that this question is in some degree strange to the principal subject of my memoir; but, as will be shown in the second section, it is so little so, that the greater part of the phenomena which are described in this section are more or less completely attached to it. Besides, the subject of the oxidation of platinum itself, and the consequences which may be drawn from it in different points of view, appeared to me to present sufficient interest to justify me in supposing that, even if it was a digression, and that of some extent, it was one which I dare not forego, seeing that the question was not treated of in a manner sufficiently complete to form a memoir alone.

FIRST SECTION.

I.-Preliminary Researches on the Oxidation of Platinum.

I have attributed, in my preceding memoir, the formation of the pulverulent coating with which the surface of the platinum wires becomes covered, when they are used to transmit, during a certain time into a liquid conductor, the magneto-electric current, to the oxidation, and to the successive reduction which the surface of the metal undergoes, by the alternate disengagement of oxygen and bydrogen, which proceeds from the decomposition of the water, operated upon by these currents. I have likewise admitted the idea, that if we have not recognised sooner the faculty which platinum possesses of becoming oxidized, it is because we have not distinguished the simple superficial oxidation, which is the only one of which the metals called non-oxidable are susceptible, from the oxidation of which the oxidable metals are susceptible; an oxidation which penetrates more or less profoundly beneath their surface, as by the effect of a real cementation. I will give, in a few words, the motives which have led me to draw these consequences from the fact which I have just referred to, in order to discover the formation of the pulverulent coating.

1st. The phenomenon takes place exactly in the same manner with the metals which are well known to be oxidable, such as silver and copper; only the formation of the pulverulent coating is more rapid on these latter metals, and the disengagement of gas which takes place at the commencement ceases almost immediately, whilst that with wires of gold, and still more so that with platinum, is of considerable duration.

2nd. There is, however, a moment in which the disengagement of