or CRAMP-FISH, has been described under the generic title RAJA; and an attempt made to explain its electrical phenomena in the article ELECTRICITY, n° 258, &c. (Both these articles are in the Encyclopedia.) From some late discoveries, however, of Volta and others, the shock given by the torpedo appears much more analogous to the shock of GALVANISM than to that of common electricity; and even the electrical organs of the fish seem to resemble the apparatus with which those discoveries in galvanism were made.
In the 63rd volume of the Philosophical Transactions, Mr Hunter describes the electric organ of the torpedo as consisting of a number of columns, varying in their length from an inch and a half to a quarter of an inch, with diameters about two-tenths of an inch. The number of columns in each organ of the torpedo which he presented to the Royal Society was about 470; but in a very large torpedo which he dissected, the number of columns in one organ was 1184. These columns were composed of films parallel to the base of each; and the distance between each partition of the columns was \( \frac{1}{3} \) th of an inch. From these facts, the reader will find the anomalies of torpedoidal electricity (supposing it the same with common electricity) accounted for in a very ingenious and philosophical manner by Mr Nicholson, at p. 358 of the fifth volume of his valuable Journal. We pass on, however, to point out the resemblance between it and the lately discovered phenomena in galvanism.
Take any number of plates of copper, or, which is better, of silver, and an equal number of tin, or, which is much better, of zinc; and a like number of discs, or pieces Torpedo pieces of card, or leather, or cloth (A), or any porous substance capable of retaining moisture. Let these last be soaked in pure water, or, which is better, salt and water, or alkaline leys. The silver or copper may be pieces of money. Build up a pile of these pieces; namely, a piece of silver, a piece of zinc, and a piece of wet card: then another piece of silver, a piece of zinc, and a piece of wet card: and so forth, in the same order (or any other order, provided the pieces succeed each other in their turn), till the whole number intended to be made use of is builded up. The instrument is then completed.
In this state it will afford a perpetual current of the galvanic influence through any conductor communicating between its upper and lower plates; and if this conductor be an animal, it will receive an electrical shock as often as the touch is made, by which the circuit is completed. Thus if one hand be applied to the lower plate, and the other to the upper, the operator will receive a shock, and that as often as he pleases to lift his finger and put it down again.
This shock resembles the weak charge of a battery of immense surface; and its intensity is so low that it cannot make its way through the dry skin. It is therefore necessary that a large surface of each hand should be well wetted, and a piece of metal be grasped in each, in order to make the touch; or else that the two extremities of the pile should communicate with separate vessels of water, in which the hands may be plunged.
The commotion is stronger the more numerous the pieces. Twenty pieces will give a shock in the arms, if the above precautions be attended to. One hundred pieces may be felt to the shoulders. The current acts on the animal system while the circuit is complete, as well as during the instant of commotion, and the action is abominably painful at any place where the skin is broken.
That this influence, whatever it may be, has a striking resemblance to the repeated shocks given by the torpedo, is obvious; but what it really is in itself must be ascertained, if it can be ascertained at all, by future experiments. Mr Nicholson indeed, from whose Journal we have taken this account of Volta's apparatus and its effects, seems confident that these effects proceed from an electrical stream or current; but this mode of operation is quite foreign from all the laws of electricity known to us. The galvanic influence in this apparatus appears to move perpetually in a circle; to which we are acquainted with no fact in electricity that is at all similar. Galvanism, too, seems capable of accumulation, even while surrounded by conducting substances, which is quite inconsistent with all that we distinctly know of electricity and its laws.
That the energy of the apparatus, however, is the effect of an electric stream or current, our ingenious author thinks proved by the condenser with which Sig. Volta ascertained the kind of the electricity, and obtained its spark. He finds the action strongest, or most pungent, on wounds on the minus side of the apparatus, or where the wounds give out electricity; a fact also observable in the common electric spark.
Suppl. Vol. II. Part II.
The theory of the learned inventor seems to be, that it is a property of such bodies as differ in their power of conducting electricity, that when they are brought into contact they will occasion a stream of the electric matter. So that if zinc and silver be made to communicate immediately by contact, there will be a place of good conducting energy; and if they be made to communicate immediately by means of water, there will be a place of inferior conducting energy: and wherever this happens, there will be a stream or current produced in the general flock of electricity. This is not deduced as the consequence of other more simple facts; but is laid down as a general or simple principle grounded on the phenomena. If so, is it not a petitio principii? That such bodies as zinc and silver, when properly disposed, produce a stream or current, or something analogous to a stream or current, in the galvanic fluid, follows indeed indubitably from the phenomena; but it by no means follows from the same phenomena that galvanism is electricity; for electricity seems subject to different laws. See Electricity and Thunder, both in this Supplement.
It must be acknowledged that the discovery of the galvanic shock and spark, and of the apparent existence of two opposite states of galvanism corresponding to positive and negative electricity, considerably increase the analogy; which, in the article Galvanism, Suppl., we have admitted to be very striking; but supposing no fallacy in any of Volta's experiments, we do not think that these discoveries amount to anything like a demonstration of the conclusions which have been drawn from them. It is by no means certain that light is essentially connected with the electric fluid; for we know that it is not essentially connected with heat; (See Thermometrical Spectrum, in this Suppl.) The flash, for example, of lightning may be merely an extrication of light, in consequence of the action of electricity upon the atmosphere in its passage, or on the bodies upon which it impinges; and there are many instances of a similar extrication, as in the collision of two pieces of flint, where neither electricity nor galvanism were ever suspected to have any share in producing the phenomenon. Why may not the progres of the galvanic fluid have a similar effect in this instance with that of electricity, though the two fluids be essentially different between themselves? But we have more to say on this subject.
Messrs Nicholson and Carlisle constructed an apparatus similar to that of Volta, which gave them a shock as before described, and a very acute sensation wherever the skin was broken. Their first research was directed to ascertain that the shock they felt was really an electrical phenomenon. For this purpose the pile was placed upon Bennett's gold leaf electrometer, and a wire was then made to communicate from the top of the pile to the metallic stand or foot of the instrument; so that the circuit of the shock would have been thro' the leaves, if they had diverged; but no signs of electricity appeared. Recourse was then had to the revolving doubler; of which the reader will find an account in our Supplementary article Electricity, n°203.
(A) Woollen or linen cloth appear to be more durable, and more speedily soaked, than card. The doubler had been previously cleared of electricity by twenty turns in connection with the earth. The negative divergence was produced in the electrometer. Repeated experiments of this kind showed that the silver end was in the minus, and the zinc end in the plus state.
Here a pile of 17 half crowns, with a like number of pieces of zinc, and of plateboard soaked in salt water, though it gave a severe shock, exhibited no symptoms of electricity till assisted by the doubler. Will it be said that this arose from want of intensity in the galvanic shock? We can only reply, that a much less intense shock of electricity would have produced a feasible divergence in the instrument without the doubler. What was the cause of this difference? We have, however, no doubt but that electricity was concerned in this phenomenon; for we have shown elsewhere (see Thunder, Suppl.), that either electricity is produced, or the equilibrium of the electrical fluid disturbed, by every chemical solution; and we shall see immediately that chemical solutions are perpetually going on in Volta's apparatus.
Very early in the course of this experiment, the contacts being made sure by placing a drop of water upon the upper plate, Mr Carlisle observed a disengagement of gas round the touching wire. This gas, though very minute in quantity, evidently seemed to have the smell afforded by hydrogen when the wire of communication was first. This, with some other facts, led Mr Nicholson to propose to break the circuit by the substitution of a tube of water between two wires. They therefore inserted a brass wire through each of two corks inserted in a glass tube of half an inch internal diameter. The tube was filled with New River water, and the distance between the points of the wires in the water was one inch and three quarters. This compound discharger was applied so that the external ends of its wire were in contact with the two extreme plates of a pile of 36 half crowns, with the correspondent pieces of zinc and plateboard. A fine stream of minute bubbles immediately began to flow from the point of the lower wire in the tube which communicated with the silver, and the opposite point of the upper wire became tarnished, first deep orange, and then black. On reversing the tube, the gas came from the other point, which was now lowest; while the upper, in its turn, became tarnished and black. Reversing the tube again, the phenomena again changed their order. In this state the whole was left for two hours and a half. The upper wire gradually emitted whitish filmy clouds, which, towards the end of the process, became of a pea-green colour, and hung in perpendicular threads from the extreme half inch of the wire, the water being rendered semi-opaque by what fell off, and in a great part lay, of a pale green, on the lower surface of the tube, which, in this disposition of the apparatus, was inclined about forty degrees to the horizon. The lower wire, of three quarters of an inch long, constantly emitted gas, except when another circuit, or complete wire, was applied to the apparatus; during which time the emission of gas was suspended. When this last mentioned wire was removed, the gas re-appeared as before, not instantly, but after the lapse of four beats of a half second clock standing in the room. The product of gas, during the whole two hours and a half, was two-thirtieths of a cubic inch. It was then mixed with an equal quantity of common air, and exploded by the application of a light waxed thread.
Mr Nicholson and Carlisle had been led, by their reasoning on the first appearance of hydrogen, to expect a decomposition of the water; but it was with no little surprise that they found the hydrogen extricated at the contact with one wire, while the oxygen fixed itself, in combination with the other wire, at the distance of almost two inches. This new fact still remains to be explained, and seems, says Mr Nicholson, to point at some general law of the agency of electricity in chemical operations. Does it not naturally suggest a suspicion that galvanism is not electricity; especially as we are informed, by Mr Cruickshank of Woolwich, that Mr Nicholson and Carlisle discovered, that "galvanism decomposes water with much greater facility than electricity, and with phenomena somewhat different?" What the particular differences are, he does not say; but we learn from Mr Nicholson himself, that from the general tenor of his experiments, it appears to be established, that the decomposition of water by galvanism is more effectual the less the distance is between the wires, but that it ceases altogether when the wires are in contact.
Mr Nicholson concludes his memoir with mentioning concisely the effects of a pile of 100 half crowns, and a chemical incident, which appears to be the most remarkable of those which he has yet observed.
The pile was set up with pieces of green woollen cloth soaked in salt water. It gave severe shocks, which were felt as high as the shoulders. The transition was much less forcible through a number of persons, but it was very perceptible through nine. The spark was frequently visible when the discharge was made in the dark, and a gleam of light was also, in some instances, seen about the middle of the column at the instant of the explosion. The assistants were of opinion that they heard the snap.
The extrication of the gases was rapid and plentiful by means of this apparatus. When copper wires were used for the broken circuit, with muriatic acid diluted with 100 parts of water in the tube, no gas, nor the least circulation of the fluid was perceived, when the distance of the wires was two inches. A short tube, with two copper wires very near each other in common water, was made part of the circuit, and showed, by the usual phenomena, that the stream of electricity was rapidly passing. The wires in the muriatic acid were then placed within the third of an inch of each other. For the sake of brevity he avoids enumerating the effects which took place during several hours, and simply states, that the minus wire gave out some hydrogen during an hour; while the plus wire was corroded, and exhibited no oxid; but a deposition of copper was formed round the minus, or lower wire, which began at its lower end: that no gas whatever appeared in this tube during two hours, though the deposition was going on, and the small tube showed the continuance of the electric stream; and that the deposition, at the end of four hours, formed a ramified metallic vegetation, nine or ten times the bulk of the wire it surrounded.
In this experiment, it appeared that the influence of electricity increasing the oxidability of the upper wire, and affording nascent hydrogen from the lower, caused Mr. Nicholson, we see, continues to call it electricity with the utmost confidence, as if it could not possibly be anything else; and yet he says that the galvanic shock is much less forcible when passed through a number of persons than when passed only through one. This, we believe, does not hold in the shocks of common electricity; and the difference probably arises from the cavity obstructing the passage of the one and not of the other. Volta himself says, that this electricity, for he too is desirous to prove it electricity, does not diffuse itself through the air. It is universally known that very dry air is no conductor of electricity, that he must mean, on this occasion, air not uncommonly dry; otherwise the non-diffusion of this electricity through air would not distinguish it, as he seems to admit it does, from common electricity. But what occasions this distinction, if the two electricities be the same?
Lieutenant-colonel Haldane, well known in the scientific world, made experiments with Volta's pillar, both in a horizontal and in a vertical position. With a large pillar, placed vertically, he obtained very weak signs of electricity. He connected the apparatus with the conductor of an electrical machine, and found the effect rather impeded than assisted by the common electric stream. He placed the plate of Bennet's electrometer in the circuit, without producing electric signs. He found that the galvanic apparatus, placed between the outside and inside of a jar, prevented its charging, and that it is also capable of conducting the charge, though not rapidly; and, on the whole, from the very minute exhibition of the attractive and repelling powers, while the causticity, the shock, and the oxidation, are so very powerful, he cannot be persuaded that electricity is the principal agent, though some might be generated, or disengaged, during the operation of the apparatus.
This is exactly our own opinion, which is strongly corroborated by the results of some very curious experiments made by Mr. Cruickshank of Woolwich. These experiments our limits permit us not to detail. They were made with a view to ascertain the nature and relative proportions of the gases obtained from water and other fluids by this influence; and the author thinks himself authorized to conclude from them:
1. That hydrogen gas, mixed with a very small proportion of oxygen and ammonia, is somehow disengaged at the wire connected with the silver extremity of the machine; and that this effect is equally produced, whatever the nature of the metallic wire may be, provided the fluid operated upon be pure water.
2. That where metallic solutions are employed instead of water, the same wire which separates the hydrogen revives the metallic calx, and deposits it at the extremity of the wire in its pure metallic state; in this case no hydrogen gas is disengaged. The wire employed for this purpose may be of any metal.
3. That of the earthy solutions, those of magnesia and argil only are decomposed by the silver wire; a circumstance which strongly favours the production of ammonia.
4. That when the wire connected with the zinc extremity of the pile consists either of gold or platinum, a quantity of oxygen gas, mixed with a little azote and nitrous acid, is disengaged; and the quantity of gas thus obtained is a little better than 1/4 of the hydrogen gas separated by the silver wire at the same time.
5. That when the wire connected with the zinc is silver, or any of the imperfect metals, a small portion of oxygenous gas is likewise given out; but the wire itself is either oxidated or dissolved, or partly oxidated and partly dissolved: indeed, the effect in this case produced upon the metal is very similar to that of the concentrated nitrous acid, where a great deal of the metal is oxidated, and but a small quantity held in solution.
6. That when the gases obtained by gold or platinum wires are collected together and exploded over mercury, the whole nearly disappears and forms water, with probably a little nitrous acid; for there was always a thick white vapour perceived for some time after the explosion. The residuary gas, in this case, appeared to be azote.
In reflecting on these experiments, it would appear that in some of them the water must be decomposed; but how this can be effected is by no means so easily explained. For example, it seems extremely mysterious how the oxygen should pass silently from the extremity of the silver wire to that of the zinc wire, and there make its appearance in the form of gas. It is to be observed, likewise, that this effect takes place whichever way the wires are placed, and whatever bends may be interposed between their extremities, provided the distance be not too great. On considering these facts more minutely, it appeared to Mr. Cruickshank that the easiest and simplest mode of explanation would be, to suppose that the galvanic influence (whatever it may be) is capable of existing in two states, that is, in an oxygenated and deoxygenated state; that when it passes from metals to fluids containing oxygen, it seizes their oxygen, and becomes oxygenated; but when it passes from the fluid to the metal again, it affuses its former state, and becomes deoxygenated. Now when water is the fluid interposed, and the influence enters it from the silver side deoxygenated (and we suppose that it always passes from the deoxygenated to the oxygenated side), it seizes the oxygen of the water, and disengages the hydrogen, which accordingly appears in the form of gas; but when the influence enters the zinc wire, it parts with the oxygen, with which it had formerly united; and this either escapes in the form of gas, unites with the metal to form an oxyd, or, combined with a certain portion of water, &c., may, according to the German chemists, form nitrous acid. When a metallic solution is the interposed fluid, the effect produced may be explained in two ways; but the simplest is to suppose that the influence, in passing from the silver wire, seizes the oxygen of the metallic calx, and afterwards deposits it on entering the zinc one. In this case no gas should appear at the silver wire; but when a perfect metal is employed, oxygen should be disengaged from the zinc wire; and this, as has been already mentioned, is exactly what takes place.
What our author considers as the strongest argument in favour of this hypothesis, and what we consider as an argument equally strong to prove that galvanism differs essentially from electricity, is, that all fluids which do not contain oxygen, are incapable of transmitting the galvanic fluid, such as alcohol, ether, the fat, and Torpedo essential oils, as he has proved by direct experiment; but on the contrary, that all those which do contain oxygen conduct it more or less readily, as all aqueous fluids, metallic solutions, and acids, more especially the concentrated sulphuric acid; which it decomposes. In this last instance, the oxygen produced can hardly be ascribed to the decomposition of water; for this acid, when properly concentrated, does not contain any sensible quantity. By this theory also we can readily explain the oxydation of the zinc plates in the machine; where the fluid in passing from the different pairs of plates appears to be alternately oxygenated and deoxygenated. Although I am not (says Mr Cruickshank) by any means entirely satisfied with this hypothesis, yet as it is the only one by which I can explain the different phenomena, it was thought advisable to throw it out merely with a view to induce others to reason upon the subject, and to incite them to make experiments, by which alone truth can be ascertained.
We approve heartily of his conduct. It is for the same reason, and not to maintain at all hazards any preconceived opinion of our own, that we have urged every objection that occurs to us against the hypothesis of the identity of galvanism and electricity. These fluids or influences appear to us to differ essentially; but still we admit that future experiments and future reasonings may remove our objections, which, however, ought never to be lost sight of till they be removed. If ingenious men, adopting implicitly the hypothesis of Volta and Mr Nicholson, shall institute a set of experiments to ascertain the laws of the galvanic influence, they will be very apt to make their experiments support their hypothesis, instead of employing them as guides to the temple of truth. Mr Nicholson says, that in all the experiments made by him and Mr Carlisle, the action of the instrument was freely transmitted through the usual conductors of electricity (meaning, we suppose, metals and watery fluids), but that it was stopped by glass and other non-conductors. We have experienced the same thing, and so far we acknowledge a striking resemblance between galvanism and electricity; but, on the other hand, we have never been able to make any accumulation of galvanism by means of coated electrics, whilst Mr Cruickshank found that the galvanic influence cannot be transmitted through alcohol, ether, or essential oils. In these instances, the difference between galvanism and electricity seems to be as striking as the resemblance is in the others. Indeed these differences between the one and the other are so many and so great, that M. Fabbroni attributes the phenomena of galvanism not to electricity, but to a chemical operation; to the transition of oxygen into a combination, and to the formation of a new compound. He had observed, in repeating the common experiment, that if he wiped his tongue as accurately as possible, the sensation of taste excited by the two metals was so diminished as to be hardly distinguished. The saliva, or some other moisture, must therefore be of some importance in this phenomenon. He afterwards instituted a set of very proper experiments; from which it appeared to him that an evident chemical action takes place in the operations of galvanism, and that it is unnecessary to seek farther for the nature of the new stimulus. Galvanism (he says) is manifestly a combustion or oxydation of the metals; and the stimulating principle may be either the caloric which is disengaged, or the oxygen which passes into new combinations; or the new metallic salt; but which of these he has not ascertained.
Without adopting or rejecting these conclusions, we recommend them to the attention of our chemical readers; for it is only by expert and scientific chemists that we expect the nature and properties of galvanism to be ascertained. In the mean time, it is proper to observe, that the pile of Volta continues in order for about three days, and scarcely three; and that on account of the corrosion of the faces of the zinc, it is necessary to renew them previous to each construction of the pile. This may be done by scraping or grinding, or by cleaning them with diluted muriatic acid.
To avoid the trouble of constantly repiling the pieces of silver and zinc, Mr Cruickshank constructed a kind of trough of baked wood, 26 inches in length, 17 inches deep, and 15 inches wide; in the sides of this trough grooves were made opposite to each other, about the tenth of an inch in depth, and sufficiently wide to admit one of the plates of zinc and silver when soldered together; three of these grooves were made in the space of one inch and three tenths, so that the whole machine contained 60 pair of plates. A plate of zinc and silver, each 1.6 inches square, well cemented together, were introduced into each of these grooves or notches, and afterwards cemented into the trough by a composition of rosin and wax, to perfectly that no water could pass from one cell to the other, nor between the plates of zinc and silver. This circumstance must be strictly attended to, else the machine will be extremely imperfect. When all the plates were thus secured in the trough, the interstices or cells formed by the different pairs of plates were filled with a solution of the muriate of ammonia, which here supplied the place of the moistened papers in the pile, but answered the purpose much better. It is hardly necessary to observe, that in fixing the zinc and silver plates, they must be placed regularly, as in the pile, viz., alternately zinc and silver, the silver plate being always on the same side. When a communication was made between the first and last cell, a strong shock was felt in the arms, but somewhat different from that given by the pile, being quicker, less tremulous, and bearing a greater resemblance to the common electrical shock. He constructed two of these machines, which contained in all 120 pair of plates; these when joined together gave a very strong shock, and the spark could be taken in the daytime at pleasure; but what surprized him not a little, was the very slender power which they possessed in decomposing water; in this respect they were certainly inferior to a pile of 30 pair, although such a pile would not give a shock of one third the strength.
This apparatus retained its power for many days, and would in all probability have retained it much longer, had not the fluid got between the dry surfaces of the metals. To remedy this defect, he soldered the zinc and silver plates together, and found that this method answers very well. The zinc plates may be cleaned at any time, by filling the different cells for a few minutes with the dilute muriatic acid. Although this apparatus may not entirely supercede the pile, especially if it should be found to decompose water, &c., but slowly, yet in other respects it will no doubt be found very convenient and portable.
If this article be thought long, and if we appear to have lost sight of our original subject, the Torpedo, we have have only to plead in excuse for our conduct, that whilst we could not avoid pointing out the resemblance between the shock given by the torpedo and that by Volta's apparatus, we felt it a kind of duty to embrace the only opportunity that we shall have of laying before our readers the additional information respecting the phenomena of Galvanism which we have received since the publication of that article. These phenomena are yet new, and they are unquestionably important; indeed so very important, that to us it appears neither impossible, nor even improbable, that to the galvanic agency of metals and minerals may be attributed volcanoes and earthquakes.