Outlines of a View of Galvanism, chiefly extracted from a Course of Lectures on the Galvanic Phænomena, read at the Theatre of the Royal Institution (1801).¹

in The Collected Works of Sir Humphry Davy, ed. John Davy (London: Smith, Elder and Co., 1839), II, 188-209.

I. HISTORICAL INTRODUCTION.

Owing its origin to the phænomenon discovered by Galvani,² the production of muscular action by the application of metals to the nerves and muscles of animals, it has derived its name from that philosopher.³

{189} Galvanism was at first limited in its application to organized bodies; but in consequence of the labours and inventive genius of experimentalists, our contemporaries, it has gradually become connected with chemistry and general physics; it has afforded powerful instruments of investigation; and its operations have been traced throughout the whole of nature. In giving an account of the progress of this science in its relation to the powers of the human mind, it will be sufficient to notice such experiments only as have derived their origin from extensive theoretical views, and such discoveries as have led to accurate generalizations of phænomena already known.

Though the history of galvanism extends only through the period of the last nine years, yet we may notice in it four epochs, each of them distinguished by the development of facts variously interesting from their novelty and the extent of their application.

2. Considering the first epoch as formed by the publication of the fundamental galvanic fact, we may derive the second from the discovery of the existence of inorganic galvanism. Till the researches of Fabroni, Dr. Ash, and Creve, had been made known, the galvanic influence was generally considered as existing only in living animal organs. But the discovery of the peculiar action of metals in contact with each other upon water, demonstrated the production of it in arrangements composed wholly of dead matter, and laid the foundation for a new class of investigations, which have intimately connected the galvanic phænomena with known physical effects.

3. The third epoch in the history of this science is perhaps the most brilliant and important. It will long be celebrated on account of the discovery of the accumulation {190} of the galvanic influence. Before this discovery was made, the world, in general, beheld nothing deeply interesting in galvanism; it had no relations to the common wants of life, and the facts that composed it were so obscure as to be with difficulty comprehended, except by long attention. The galvanic battery of Volta, not only gratified the passion for novelty by the curious effects it produced, but likewise awakened the love of investigation, by distinctly exhibiting the analogy between galvanism and common electricity.

4. The fourth and last epoch in galvanism may be considered as founded upon the knowledge of the general connexion between the excitement of galvanic electricity and chemical changes; and it chiefly owes its existence to the labours of British experimentalists.⁴ The discovery of the chemical agencies of galvanism, has led to researches which finally cannot fail to elucidate the philosophy of the imponderable or etherial fluids. The year that is past will long be distinguished in the history of science; seldom has physical investigation been pursued with greater ardour, and if new facts, by being sometimes insulated, and incapable of application to established theories, have perplexed the public mind, yet they have at the same time been useful to it, by producing a habit of rational and active scepticism which cannot fail to become at a future period the parent of truth.

II. OF THE LEAST COMPLICATED GALVANIC ARRANGEMENTS, i.e. SIMPLE CIRCLES.

The simplest galvanic arrangements require for their formation at least two bodies of the same class, and one of a different class.⁶ With regard to the form of their aggregation, they must be so disposed that the bodies of the one class may be in contact with each other, in one or more points, at the same time that they are connected in other distinct points with the body of the other class.

2. The simple galvanic circles may be divided into two general kinds.

The first is formed by two different metallic substances, or one metallic substance and charcoal, and a peculiar fluid.

The second is composed by two different fluids and one metallic substance.

Thus, if plates of zinc and of silver be made to touch in one point, and be connected together in other points by a portion of common water, or of muriatic acid, a galvanic simple circle is formed of the first order.

Or if separate portions of nitric acid and of water moistening pieces of cloth or bibulous paper be brought in contact with each other on a small surface, at the same time that other surfaces of them are connected with different parts of a plate of tin, a circle of the second kind is composed.⁷

3. All arrangements, however, of two conductors of one class with one of the other are not capable of producing galvanic effects. And even the powers of acting circles are very different in degree. It appears, from {192} all the facts, that chemical changes taking place in some of the parts of the circle, are intimately connected with its agencies. For though a momentary circulation of galvanic influence may possibly be produced by the contact of three different bodies, yet it appears most likely that the permanent excitation of it depends upon a certain exertion of their chemical affinities.

The most powerful circles of the first kind are those composed of two solids of different degrees of oxydability, and of a fluid capable of oxydating at least one of the solids.⁸ And even in the feeblest circles, it appears that some chemical action is uniformly exerted either by oxydating fluids, or solutions of alkaline sulphurets.

Thus, silver and gold do not appear to evolve galvanic influence when in contact with pure water, which is incapable of acting chemically upon either of the metals; though when they are connected with water holding in solution nitric acid, or any other fluid decomposable by silver, they form an active galvanic arrangement.⁹

And zinc and silver, which act very little with pure water, form a powerful combination with water holding in solution atmospheric air, or acids.¹⁰

The following table of some circles of the first kind, in which the different substances are arranged according to the order of their known galvanic powers, will shew how intimately chemical agencies are related to the production of galvanism.

{193}

¹¹

Thus, copper, silver, or lead, acts very powerfully when connected in the proper order with solutions of alkaline sulphurets and of nitrous acid, both of which fluids are possessed of distinct chemical agencies upon them,¹² and copper or silver acts, though with less intensity when water, or a fluid which they are incapable of decomposing, is substituted for one of the chemical agents.

{194} The following Table contains some powerful galvanic combinations of the second order, arranged according to the intensity of their action.

It appears, however, that the length and surface of the conducting series, connecting the exciting parts of the circle, are in some measure related to the quantity of action it is capable of exhibiting. This law, indeed, applies only analogically to perfect conductors; though, with regard to imperfect conductors, it is demonstrated experimentally; as in all cases, a diminution of power, in some unknown ratio, is produced by the increase of the length, or what is apparently equivalent, the diminution of the surface of the chain which they compose.

The limits of surface and of length of imperfect conductors in circles, connected with the maximum and minimum of their activity, have not yet been ascertained; and there is every reason to believe that they will be different in different imperfect conductors. Thus, portions of sulphuric acid, and of nitrous acid, will probably form better conducting series than similar portions of water; and a chain of water will perhaps act better than an equal chain of water mixed with alcohol.

From several experiments, it would appear that the powers of circles are particularly connected with the extension of the surfaces of contact between the perfect and imperfect conductors.

5. All galvanic influence in single circles is manifested, either by its efficiency, in affecting living animal organs, forming part of the arrangement, or by its power in modifying the chemical changes produced by the action of the perfect on the imperfect conductors.

A. When one part of a powerful single circle is made to touch the tongue at the same time that another fluid part is connected with some irritable surface of the {196} body, an acid taste is perceived,¹³ which becomes less distinct in proportion as the contact is longer preserved.

If the eye be made part of the galvanic circuit, a transient flash of light is produced at the moment the chain is completed,¹⁴ and when the bared cutis is employed, a faint painful sensation uniformly denotes the circulation of the galvanic influence.¹⁵

But the most distinct mode of exhibiting, by animal excitement, the existence of small quantities of galvanic power, is by connecting one part of a circle with a nerve, and another part with a muscle in a limb just separated from the body of a living animal. In this case, whenever the connexion of the arrangement is made, or broken, muscular contractions are produced.¹⁶

B. In galvanic simple circles, all primary chemical action taking place between the imperfect and perfect conductors, is apparently increased by their galvanic arrangement. Thus, zinc, which oxydates when in contact with common water alone, oxydates much more rapidly when forming a galvanic circle with it by means of gold, or other difficulty oxydable metals.¹⁷ And tin appears to dissolve faster in diluted nitric acid, when composing a circle with it by the contact of gold, than when singly immersed in it.¹⁸

C. But increase of primary chemical action is not the only inorganic effect of galvanism; for it changes the nature of this action in a very peculiar manner.

In oxydating circle with common water, no perceptible quantity of hydrogen is evolved, as in common processes, but an alkaline substance appears to be formed at the point of contact of the least oxydable {197} perfect conductor with the fluid. Thus, if zinc and silver be made to form a circle with distilled water holding in solution air, for many weeks, a considerable oxydation of the zinc is perceived, without the perceptible evolution of gas; and the water at its point of contact with the silver, becomes possessed of the power of tinging green, red-cabbage-juice, and of rendering turbid solution of muriate of magnesia.¹⁹

In the oxydating circles with acids, gas is not only evolved from the parts of the conductors undergoing chemical change, but likewise from other parts, in which no primary action apparently exists. Thus, when zinc and silver form a circle with diluted muriatic acid, gas is not only given out at the point of contact of the acid with the zinc, but likewise at the place where it is connected with the silver.²⁰ And in the circle with tin, gold, and diluted nitric acid, nitrous gas is evolved from the gold as well as from the tin.¹⁹

D. Indeed, in all the single galvanic circles, whenever an oxydating influence is exerted at one of the places of contact of the perfect and imperfect conductors a de-oxydating action appears to be produced at the other place. Thus, when iron, which oxidates rapidly when forming a circle with silver and common water, is arranged with zinc and common water, it remains perfectly unaltered whilst the zinc is rapidly acted upon.

6. The phænomena exhibited by the simple galvanic circles cannot well be theorised upon, except in the laws of their connection with the more complicated and more striking galvanic facts. And it is from the discovery made by Volta of the accumulation of galvanism only, that the instruments of investigation are derived, by means of which the nature of this influence is {198} known, and its most important agencies and relations ascertained.

III. OF COMPOUND GALVANIC CIRCLES OR GALVANIC BATTERIES.

To compose a galvanic battery, series of the conductors capable of forming simple circles are required. And they must be arranged in such a manner, that the conductors of the same class in every series, may be in contact with each other, in one or more points, at the same time that they are respectively connected with different conductors of the other class, and one of them belonging to the same series, a regular alternation being observed.

Thus the order of a compound galvanic circle is, conductor of the one class, conductor of the other class, conductor of the one class, conductor of the other class; and so on in uniform arrangement.

2. The compound galvanic circles, like the simple circles, may be divided into two general orders. The first order is composed of series containing at least two perfect conductors and one imperfect conductor. The second is formed by arrangements, consisting of not less than two imperfect conductors, and one perfect conductor.²¹

Thus if plates of zinc, and of silver, and pieces of cloth of the size of the plates, moistened in water or diluted muriatic acid, be arranged in the order of zinc, {199} silver cloth; zinc, silver cloth, and so on till twenty series are perfectly connected, a galvanic battery is formed of the first class.²²

And if plates of copper and pieces of cloth, moistened, some in water, and some in solution of sulphuret of potash, be connected in a circle, in the order of copper, cloth moistened in water, cloth moistened in solution of sulphuret of potash, and so on, a compound circle will be formed of the second class.²³

The most elegant mode however or arranging the metals of compound circles with fluids, is by means of vessels, composed of electrical non-conductors, such as glasses or boxes formed of baked wood.

Thus plates of copper and of zinc, paired, and soldered together at their edges, may be cemented into a trough composed of baked wood in regular alternation, and in such a manner as to leave a number of watertight cells, corresponding to the number of series. And this arrangement will become active, when the cells are filled with water or saline solutions, and when the extreme metals are properly connected.²⁴

Or instead of the double plates, single plates of copper, and of horn, or glass, may be used in uniform alternation; when the cells must be filled with different fluid chemical agents in the regular order so as to be connected together by pieces of moistened cloth passing over the non-conducting plates.²⁵

3. The substances most active in the single circles, are likewise most active in the compound circles. And in all cases, the relative quantities of galvanic power exhibited by equal numbers of different series, are, in some measure, proportional to the intensity of the peculiar primary chemical agencies, exerted by {200} the different conductors composing them on each other.²⁶

Thus in the battery with zinc and silver, there is no action produced when the connecting fluid is pure water, or water holding in solution hydrogen gas, which is incapable of acting on the metals.²⁷ The action is greater with water saturated with oxygen²⁸ than with water saturated with atmospheric air, and it is most intense when solution of red sulphate of iron, or of nitric acid is employed.

The tables of the single circles will indicate with the necessary change of arrangement, the relative powers of the series forming compound circles.

4. Provided those places of contact in the compound circle in which the peculiar chemical changes are produced, remain permanent, the parts of the series which do not immediately act chemically on each other, may be connected together in the same manner as in single circles, by means of conductors of their own class, without alteration of the nature of the agencies.

Thus, in the circle with copper, iron, and water, the copper and iron may be connected by means of a wire of brass.²⁹ And even the continuity of the portions of water may be broken by moist muscular fibre, and other imperfect conductors, without any other change in the effect than a diminution of its intensity.³⁰

5. The galvanic influence when highly accumulated, produces very extraordinary chemical and physical effects, and in many of its appearances, assumes the precise form of common electricity.

A. When in a powerful battery (one for instance containing two hundred series) the communication, after {201} being broken, is again rendered complete, by the contact of two perfect conductors, a flash, or spark of light is perceived, analogous to that produced by electricity.³¹ This spark, or flash, when the battery is most powerful, is capable of passing through a considerable stratum of air,³² and of inflaming mixtures of oxygen and hydrogen.³³ When the metallic substances by which it is transmitted, are of very small volume, it is possessed of the power of igniting them; and of making them enter into combustion when in contact with oxygen.³⁴

B. The galvanic influence, when highly concentrated, affects the electrometer, and is capable of communicating weak charges to the condenser and Leyden phial.³⁵ In all compound circles of the first class, the most oxydable part of the metallic plates evolves the influence, appearing as positive electricity, whilst the least oxydable part seems negatively electrified. In the second class of circles, it is, however, probably that this order is reversed.

C. Galvanism, moderately accumulated, affects the animal organs in nearly the same manner as common electricity. When the human body is made part of the circle, a shock is perceived at the moment of connection; and a subsequent numbness, and tingling sensation, denote the permanent circulation of the influence.

The fresh limbs of frogs undergo violent contractions, and soon lose their excitability, when placed in the circuit of a powerful battery.

D. The chemical actions taking place in the compound galvanic circle, present curious and most unexampled; all the primary changes taking {202} place in the different conductors being increased, and modified to a great extent.

In all batteries of the first order, when the connection is completed, changes take place which denote the evolution of influences capable of producing from common water, oxygen and hydrogen, acid and alkali, in different parts of every series.³⁶

Thus in the battery with series of zinc plates, silver wires, and common water, oxyde of zinc is formed on all the plates of zinc, whilst hydrogen is produced from the silver wires, and if the water in them be tinged with red-cabbage-juice it becomes green.³⁷

And in the battery with silver, gold, and weak nitric acid, the silver is dissolved, while the acid becomes green, and slowly evolves gas at its points of contact with the gold.

The chemical agencies exerted in the compound batteries of the first class can be best observed by the substitution of single metallic wires for some of the double plates; for in this case, the changes taking place in the series with wires will be exactly analogous to those produced in the series with plates; silver and all the more oxydable metals, oxydating in water in the usual place; and gold, and platina evolving oxygen gas.

Thus, when into two small glass tubes connected by moist animal substance, and filled with distilled water, two gold wires are introduced from a large battery, in the proper order, oxygen is produced in one quantity of water, and hydrogen in the other, nearly in the proportions in which they are required to form water by combustion.³⁸ And if the process be continued for {203} some time, the apparatus, being exposed to the atmosphere, the water in the oxygen giving tube, will become impregnated with an acid (apparently the nitrous); whilst that in the hydrogen giving tube, which in certain cases has appeared to be fixed.³⁹

From some experiments it would appear probably that the quantities of hydrogen produced in series are small, and the quantities of alkali great, in proportion as the surfaces of contact of the least oxydable metals with the water are more extended.⁴⁰

All the oxygenated solutions of bodies possessing less affinity for oxygen than nascent hydrogen, are decomposed when exposed to the action of the metal occupying the place of the least oxydable part of a series in the compound circle.

Thus sulphur may be produced from sulphuric acid; and copper and other metals precipitated in the metallic form, from their solvents.⁴¹

But little knowledge has yet been obtained concerning the chemical changes taking place in the second class of galvanic batteries. But from several experiments it would appear that they are materially different in the laws of their production from those taking place in the first class.

Thus, when single metallic wires with water, are placed as series in powerful batteries of the second order, the influence producing oxygen seems to be transmitted by the point, in the place of that part of the {204} plate which was apparently incapable of undergoing oxydation; whilst the hydrogen is evolved from that point where the oxydating part of the primary series appeared to exist.⁴²

6. The agency of the galvanic influence, which occasions chemical changes, and communicates electrical changes, is probably, in some measure, distinct from that agency which produces sparks, and the combustion of bodies.

The one appears, (all other circumstances being similar) to have little relation to surface in compound circles, but to be great in some unknown proportion, as the series increase in number. The intensity of the other seems to be as much connected with t he extension of the surfaces of the series as with their number.

Thus, though eight series composed of plates of zinc and copper about ten inches square, and of cloths of the same size moistened in diluted muriatic acid, give sparks so vivid as to burn iron wire, yet the shocks they produce are hardly sensible, and the chemical changes indistinct.⁴³ Whilst twenty-four series of similar plates and cloths about two inches square, which occasion shocks and chemical agencies more than three times as intense, produce no light whatever.

7. A measure of the intensity of power in galvanic batteries producing chemical changes, may be derived from the quantity of gas it is capable of evolving, from water, in a given time; or from the length of the fluid chain through which it can be transmitted. For the same law of diminution of activity that was applied to single circles in 4, page 200, may be likewise applied to compound circles.

{205} The general relative process of different batteries may be ascertained by connecting them in opposite orders, so as to produce a certain annihilation of power. For in all cases when the most oxydable part of one series is placed opposite to the same part of another equal series, and connected with it by means of a fluid, the galvanic agencies of both are destroyed.

IV. GENERAL OBSERVATIONS.

This fact singly, presents a very strong analogy between galvanism and the common electrical influence, and when compared with the other facts, it amounts almost to a demonstration of their identity.

On this theory, it seems most probable, that all the different galvanic phænomena owe their existence to electricity, excited in the different arrangements, in consequence of a change in the electrical capacity of such of their parts as undergo chemical action, this action being always connected with alterations in the surfaces, and conducting powers of bodies.

The circulation of electricity in galvanic circles, from {206} its different points of excitation, appears to depend, in a great measure, upon certain specific attractions for it in the different conductors inexplicable by known laws.

2. In all cases of simple galvanic action, negative and positive electricity, as respectively exhibited by their de-oxydating and oxydating influences, after being once excited, can be multiplied by a certain alternation of surface.

Thus in the circle with zinc, iron, and water, in which as was stated in page 202, the zinc oxydates, and the iron undergoes no change, if a drop of water be placed on an insulated surface of the iron, it will rapidly act upon it, and produce red oxydate, -- whereas if it be placed upon a similar surface of the zinc, it will undergo very little change.⁴⁶

This fact will, perhaps, in some measure lead to an explanation of the cause of the accumulation of galvanism in compound circles. For in those circles, all the series are so constituted, as to produce a perfect correspondence between the electricity excited by chemical action, and that produced by compensation.

3. The general chemical agency of galvanism is at present involved in obscurity. The facts relating to the separate production of oxygen and hydrogen, acid and alkali in water, are totally incommensurable with the usually received theory of chemistry; an d even supposing that the appearance of the two last of these bodies is connected with the presence of atmospheric air, it is still extremely difficult to conceive, that either oxygen or hydrogen can pass in an invisible form through fluids or organic bodies. Common physical facts present us with no analogies sufficiently distinct to enable us to reason on this subject; and the elucidation {207} of it will probably be connected with perfectly new views of corpuscular action.

4. The appearance of galvanic action in living matter, particularly in the torpedinal organ, leads to curious inquiries. Chemical changes are perpetually going on in different parts of the living body, which must be connected with alterations in their states of electricity; and organized beings contain all the substances requisite for forming species of galvanic arrangements.

These circumstances, combined with the facts of the production of muscular contraction by common galvanism, and the dependence of irritably and even life, upon the oxygenation of the blood, afford analogies which render it probably that some phænomena similar to the galvanic phænomena, may be connected with muscular action, and other processes of life. These analogies, however, at present are very indistinct, and they ought to be considered of importance only so far as they are likely to lead to the discovery of new instruments of experimental investigation.

CONCLUSION

The new galvanic facts have given an importance to the science, sufficient to render it interesting, and to ensure its progression. The spirit of inquiry is awakened in the public mind, and it is difficult to imagine the existence of causes capable of destroying it.

Galvanism may be pursued with greater facility than most of the other sciences; it requires less time and attention; it is less connected with manual labour, and the most delicate organs are the best fitted for performing and observing its operations.

The instruments required for galvanic experiments are few, and but little expensive. A battery composed of fifty plates, when arranged with chemical agents, forms a combination sufficiently powerful for common experiments. With such a combination, a few glass tubes having gold wires attached to them, and a gold-leaf electrometer, investigations may be pursued, and principles discovered, extending not alone to the laws of dead matter, but even to those of animated nature.

If to render galvanism a popular study, it were necessary to prove that it bore relations to the common wants of life, it might be stated that its agencies are likely at some period to become useful in the arts. When our galvanic instruments are rendered more perfect and more powerful, we may be readily enabled by means of them to procure the pure metals; and to form immediately from their elements, nitrous acid and alkali. The connexion of galvanism with philosophical medicine is evident. The electrical influence in its common form, as excited by machines, has been employed with advantage in the cures of diseases; in a new state of existence it may possibly be possessed of greater and of different powers.

But independent of the immediate applications of this science, much it to be hoped from the elucidations which it may bestow upon the kindred sciences. And a discovery so important as to excite out astonishment, cannot fail of becoming at some period useful to society. All the different branches of human knowledge are {209} intimately connected together, and theoretical improvements cannot well be made in them without being accompanied by practical advantages.

ROYAL INSTITUTION,
Sept. 1, 1801.

Notes.

2. The first fact relating to the action of metals on the animal organs was observed by Sulzer, who has described the sensation of taste produced by the contact of lead and silver with the tongue, in his Theorie des plaisirs, published in 1767.

3. [This discovery was made at Bologna by Galvani in 1789, and a detailed account of it given in a work expressly on the subject, entitled Aloysii Galvani de Viribus Electricitatis in Motu musculari Commentarius. Bononiae, 1791, in 4to. Volta, in his letter to Mr. Cavallo, published in the Philosophical Transactions for 1793, making mention of it, says, "Il contient une des plus belles et des plus surprenantes découvertes, et le germe de plusieurs autres."]

4. Messrs. Nicholson, Carlisle, Cruickshank, and Henry, Dr. Wollaston, and Major Haldane.

5. Volta.

6. D.

7. Ritter.

8. D.

9. Fabroni.

10. Dry nitre, caustic potash, and soda, are conductors of galvanism, when rendered fluid by a high degree of heat, but the order of their conducting powers has not yet been ascertained.

11. D.

12. Sulzer, Volta, Robinson, and other philosophers.

13. Mr. Hunter.

14. Humboldt.

15. Galvani.

16. Dr. Ash.

17. Original Experiment D.

18. Original Experiment D.

19. Dr. Wollaston.

20. D.

21. Volta.

22. D.

23. Mr. Cruickshank.

24. Count Rumford.

25. D.

26. D.

27. Major Haldane.

28. Volta.

29. Pfaff, Ritter, and D.

30. Volta.

31. Mr. Cruickshank.

32. Mr. R. Boulton.

33. Professors Tromsdorf, Bockman, Fourcroy, and Vauquelin.

34. Mr. Nicholson and Mr. Cruickshank.

35. Mr. Nicholson, Mr. Carlisle, and Mr. Cruickshank.

36. D.

37. Original experiment, D.

38. Mr. Cruickshank, the first discoverer of the galvanic production of alkali, supposes that the hydrogen wire in common water generates ammoniac. Perhaps the presence of muscular fibre is connected with the production of fixed alkali in the experiment detailed in the text.

39. Original experiment, D.

40. Mr. Nicholson, Mr. Cruickshank, and Mr. Henry, Jun.

41. D.

42. Fourcroy, Vauquelin, and Thenaud.

43. By Dr. Wollaston.

44. [Dr. Wollaston found that a solution of sulphate of copper and of corrosive sublimate was each decomposed by common electricity, in the same manner as by Voltaic; -- the metal was precipitated at the wire connected with the negative conductor: -- in the instance of water, the result was different; from the extremity of each wire the two constituent gases were disengaged. -- Vide Experiments on the Chemical Production and Agency of Electricity. By William Hyde Wollaston, M.D., F.R.S. Phil. Trans. 1801.]

45. D.