Jacob Gisbert Samuel van Breda and Wilhelm Martin Logeman to Faraday   September 1854

Sir,

The experiments on electro-dynamic induction in liquids which you have published in a letter to M. de la Rive¹, have excited our lively interest, not only because the phaenomenon appeared to us to be of importance in itself, but especially because it seemed likely to throw some light upon the manner in which electricity is propagated in liquids.

Do liquids conduct exclusively by electrolysis, or do they also possess a proper conductibility, similar to that of metals? An experiment that we have made may perhaps assist in the solution of this question. It is well known that the conductibility of liquids increases with their temperature, whilst the opposite effect takes place with the metals, a fact which is easily explained if we suppose that liquids, in general oppose less resistance to decomposition in proportion as their temperature is raised. If this explanation be the true one, the next thing to be ascertained is, whether a liquid will also exhibit this increase of conductibility for a current so weak as to traverse it without producing any apparent chemical decomposition. If this were the case, it would appear probable that the decomposition nevertheless took place, and that it was by its intervention that the current passed through the liquid. We have endeavoured to solve this question by the following experiment. We passed the current of a small Daniell’s element through a column of distilled water 24 centimetres in length, contained in a glass tube of about 15 millimetres in diameter; the electrodes were of platinum wire. One of these electrodes was connected with the zinc pole of the battery, the other with one end of the helix of a galvanometer of which the wire made 1800 coils, the other end of which communicated with the copper pole. The tube was immersed in a water-bath, the temperature of which could be raised by means of a spirit-lamp. When the water was at 59˚F., the needle of the galvanometer deviated 4˚. When the lamp was lighted, this deviation was seen to increase regularly. At a temperature of 152˚.6 F., the deviation was 7˚, and at 190˚.4F. it was 11˚. The increase of the conductibility of the liquid by heat was therefore proved, even when traversed by an excessively feeble current. Had any chemical decomposition of the water taken place during this experiment? Its direct result led to the belief that such was the case, but we were also fortified in this opinion by the following circumstances. When the liquid was cooled, the communications remaining untouched, the needle of the galvanometer no longer showed any appreciable deviation. When the direction of the current in the column of water was reversed, the needle immediately deviated 8˚ and returned insensibly, but in a short time to 4˚, at which point it remained stationary. It was consequently an effect of the polarization of the electrodes that we observed in this case, a polarization which opposed the current at the first moment of its passing, without, however, being able to annul it, but which annulled it completely when it had become stronger by the passage of the stronger current through the heated liquid.

But is this polarization the peculiar effect, and consequently the irrefragable proof, of chemical action? There are many experiments which render this opinion, if not absolutely certain, at least exceedingly probable. We may mention in particular those of Schönbein, who found that the effect continues when the electrodes which have served to introduce a current into a liquid are immersed in another liquid through which no current has been passed, and also that effects exactly similar to those of the plates polarized by the current may be obtained by putting one of them only in contact with a gas (such as hydrogen or chlorine) for a very short time, and afterwards immersing them in acidulated water*. Some physicists, however, still maintain the opposite opinion. They explain polarization by an accumulation of electricity of different natures, either in the electrodes themselves, or in the adjacent portions of the liquid; these two electricities in recombining by a conductor uniting the two electrodes, after the connexion between these and the electromotor has been broken, would give rise to the current in the opposite direction to that of the latter, which is always observed in such cases.

It appeared to us that your beautiful experiment of electrodynamic induction in liquids might furnish a means of submitting this opinion to an experimental test, by trying whether the electrodes, employed in that experiment to conduct the instantaneous current of the fluid helix to the galvanometer, are or are not polarized by this current. To obtain a decisive effect it was necessary to reproduce the phaenomenon with more intensity than when, as in your experiments, the question was merely to prove the phaenomenon itself. For this purpose we made use of a tube of vulcanized Indian rubber, of about 1 centimetre in internal diameter and 13 metres in length. We twisted it round the two branches of the large electro-magnet intended for experiments in diamagnetism, which, if we are not mistaken, has the same form and the same dimensions as your own; it is covered by a coil of copper wire 3 millimetres in diameter and 180 metres long. The tube was entirely filled with a mixture of 6 parts by volumes of water and 1 part of sulphuric acid. It was terminated at both ends by glass tubes of about 4 centimetres in length; into each of these passed a platinum wire of 1 millimetre in diameter, the portion of which immersed in the liquid was about 2.5 centimetres in length. All being thus arranged, the ends of the two platinum wires were connected with the galvanometer of 1800 coils which was placed at a distance of 10 metres. We had ascertained previously that at this distance the magnet did not exercise any sensible action upon the needles. The moment the two ends of the copper-wire coil of the electro-magnet were put in connexion with the poles of a Grove’s battery of 60 large elements, arranged in a double series of 30, the needle of the galvanometer deviated suddenly about 40˚, and returned, after oscillations which occupied between 1 and 2 minutes, to 0˚. When the circuit of the pile was interrupted, the galvanometer deviated again about the same number of degrees, but in the opposite direction, returning again to 0˚ in the same manner. The needle returning in both cases to 0˚, one would be tempted, at first sight, to think that there was no polarization of the electrodes. But the strong impulsion communicated to the very astatic system of the galvanometer by the induced current, causing the needles to oscillate during a considerable period as we have just stated, the circuit remaining always complete, it appeared possible that the polarization, if it existed, had already exhausted itself before the needles had arrived at a state of repose. To get rid of this difficulty we put the two electrodes in direct communication with each other by means of a copper wire of only 10 centimetres in length, although they still remained in connection with the galvanometer. The induced current produced when the circuit of the pile was established, then passed by this wire rather than by the infinitely longer wire of the galvanometer, and the needles remained at rest. But when this wire was removed after the establishment of the communication with the pile, we saw the galvanometer deviate instantly in an opposite direction to the deviation produced by the induced current of the preceding experiment, and rest, after a few oscillations, at 10˚. By replacing the wire, then interrupting the circuit and again removing the wire, we saw the galvanometer deviate in the contrary direction, and rest, in the same manner, at about 10˚ on the other side of the divided arc. In both cases the deviation diminished regularly by little and little until it became 0˚; we did not exactly measure the time which this occupied, but it appeared to us to be about 30 or 40 seconds.

These experiments were frequently repeated, and always with the same result. We need not say that we always took the precautions pointed out by you, to prevent the effect of an induction in one of the metallic conductors.

Polarization therefore takes place in the electrodes which serve, not only to convey a current into a liquid, but to carry out the current induced in the liquid itself. It appears to us that this fact directly contradicts the theory which attributes polarization to an accumulation of the two electricities upon or around the electrodes; for in the present case not only would such an accumulation be infinitely less probable than in ordinary cases of polarization, but if it existed, it would necessarily give rise to a current not in a direction opposed to that of the principal current, but in the same direction.

May we therefore regard all polarization as an effect of electrolytic decomposition, and consequently as an irrefragable proof of the existence of this decomposition? If this be true, we shall be led to regard the opinion of those who admit the possibility of the transmission of a current, or of a portion of a current through a decomposable fluid without the occurrence of any decomposition, as resting on very slight grounds. Whenever we have passed a current, however weak, through such a liquid, we have always observed an undoubted polarization of the electrodes.

We shall take the liberty to describe one other experiment, which is still more convincing in this respect than that described at the commencement of this communication. We immersed two plates of platinum, 6 centimetres in length and 5 centimetres in breadth, at a distance of about 1 centimetre from each other, in distilled water. One of these plates communicated with the ground by a metal wire; they had previously been carefully cleaned by heating to redness, and consequently, when put in communication with the galvanometer, did not produce any sensible deviation. But as soon as a single spark from a common electrical machine had been thrown upon the plate which did not communicate directly with the ground, and the communication with the galvanometer had been established, the needle deviated from 3˚ to 4˚ in one direction, and the same distance in the opposite direction when the current of the spark was passed through the water the other way. This deviation could be brought to 15˚ or more by throwing several sparks instead of one upon one of the plates or by connecting the plate for a very short time with the conductor of the machine during the movement if its plate.

We fear that the importance of this letter will not be proportional to its length; if, however, its contents should seem to you to be worthy of attention we shall be happy to see it published in any manner you think proper.

We remain, Sir, &c., | J.G.S. Van Breda. | W.M. Logeman.

Haarlem, September 1854.

*Poggendorff’s Annalen, vol. xlvi. p.109, and vol. xlvii. p.101².