Contents Index

from "On the Powers and Properties of Matter, and the General Laws of Chemical Change,"
Division I of "On the Laws of Chemical Changes; on Decompounded Bodies, and their primary Combinations,"
from Elements of Chemical Philosophy (1812)

in The Collected Works of Sir Humphry Davy, ed. John Davy (London: Smith, Elder and Co., 1839), IV, [43]-48, 91-131.

1. Preliminary Observations.
  1. The forms and appearances of the beings and substances of the external world are almost indefinitely various, and they are in a state of continued alteration: the whole surface of the earth even undergoes modifications: acted on by moisture and air, it affords the food of plants; an immense number of vegetable productions arise from apparently the same materials; these become the substance of animals; one species of animal matter is converted into another; the most perfect and beautiful of the forms of organised life ultimately decay, and are resolved into inorganic aggregates; and the same elementary substances, differently arranged, are contained in the inert soil, or bloom and emit fragrance in the flower, or become in animals the active organs of mind and intelligence. In artificial operations, changes of the same order occur; substances having the characters of earths are converted into metals; clays and sands are united so as to become {44} porcelain; earths and alkalies are combined into glass; acrid and corrosive matters are formed from tasteless substances; -- colours are fixed upon stuffs, or changed or made to disappear; and the productions of the mineral, vegetable, and animal kingdoms are converted into new forms, and made subservient to the purposes of civilized life.

  2. To trace in detail these diversified and complicated phenomena, to arrange them and deduce general laws from their analogies, would be a labour to which even the longest life of the most industrious and sagacious individual might be devoted in vain. The student who has the advantage of referring to the knowledge accumulated by many philosophers in different times, may adopt much more simple methods of acquiring the science; -- those of recurring to its general principles, so as to ascertain the powers and properties of matter, which are the causes of the phenomena of chemistry; and of applying these principles to the actions taking place between the various substances existing in nature, or produced by art; proceeding gradually, referring to observations, experiments, and distinct analogies, so as to understand the laws by which they are governed.

II. Of the Forms of Matter.
  1. In the general views that may be taken of the properties of natural substances, certain relations appear which afford the means of arranging them in distinct classes, each of which is distinguished by certain sensible and obvious qualities.

  2. The first class consists of solids, which compose the great known part of the globe. Solid bodies, {45} when in small masses, retain whatever mechanical form is given to them: their parts are separated with difficulty, and cannot readily be made to unite after separation; some solid bodies yield to pressure, and do not recover their former figure when the compressing force is removed, and they are called non-elastic solids; others that regain this form, are called elastic bodies. Solids differ in degrees of hardness, in colour, in degrees of opacity or transparency, in density, or in the weight afforded by equal volumes; and when their forms are regular or crystallized, in the nature of these forms.

  3. The second class consists of fluids, of which there are much fewer varieties. Fluids when in small masses assume the spherical form; their parts possess freedom of motion; they differ in degrees of density and tenacity, in colour and degrees of opacity or transparency. They are usually regarded as incompressible, at least a very great mechanical force is required to make them occupy a space perceptibly smaller.

  4. Elastic fluids or gases, the third class, exist free in the atmosphere; but they may be confined by solids, or by solids and fluids, and their properties examined. Their parts are highly moveable; they are compressible and expansible, and their volumes are inversely as the weights compressing them. All known elastic fluids are transparent, and present only two or three varieties of colour; they differ materially in density.

  5. Besides these forms of matter which are easily submitted to experiment, and the parts of which may be considered as in a state of apparent rest, there are other forms of matter which are known to us only in their states of motion when acting upon our organs of sense, or upon other matter, and which are not susceptible of being confined. They have been sometimes {46} called etherial substances, which appears a more unexceptionable name than imponderable substances. It cannot be doubted that there is matter in motion in space, between the sun and the stars and our globe, though it is a subject of discussion whether successions of particles be emitted from these heavenly bodies, or motions communicated by them, to particles in their vicinity, and transmitted by successive impulses to other particles. Etherial matter differs either in its nature, or in its affections by motion; for it produces different effects; for instance, as radiant heat, and as different kinds of light.

  6. The various forms of matter, and the changes of these forms, depend upon active powers, such as gravitation, cohesion, calorific repulsion or heat, chemical attraction, and electrical attraction, the laws of which it is necessary to study with attention.

III. Gravitation.
  1. When a stone is thrown into the atmosphere it rapidly descends towards the surface of the earth. This is owing to gravitation. All the great bodies in the universe are urged towards each other by a similar force. A cannon ball sent from a piece of artillery describes a curve, and at last falls to the ground; were the impulse given to it by the gunpowder increased to a certain extent, and exerted in free space, it would continuously revolve round the earth, in consequence of the equilibrium between the two forces. The moon and the planets as Newton has demonstrated, are retained in their orbits by similar laws, and their harmonious and constant revolutions produced.

  2. Bodies mutually gravitate towards each other; {47} but the smaller body proportionally more than the larger one: hence the power of gravity is said to be directly as the mass; it is in fact the measure of the mass or quantity of matter.

  3. Gravitation acts inversely, as the square of the distance.

IV. Cohesion.
  1. When two particles of quicksilver are brought into apparent contact they may be made to unite and form one globule: when a glass tube, having a very fine bore, is introduced into a vessel containing water, the water rises in the tube to a higher level than it occupied in the vessel: both these effects are said to be owing to cohesion, or cohesive attractive. It is the same force which preserves the forms of solids, and gives globularity to fluids, and is thus a prime cause of the perman ency of the arrangements which compose the surface of the globe. It is usually said to act only at the surfaces of bodies, or by their immediate contact; but this does not seem to be the case. It certainly acts with much greater energy at small distances; but the spherical form of minute portions of fluid matter can only be produced by the attractions of all the parts of which they are composed, for each other; and most of these attractions must be exerted at sensible distances, so that for any thing we know to the contrary, gravitation and cohesion may be mere modifications of the same general power of attraction, in the one case acting at distances that can be easily measured, and in the other case, operating at distances which it is difficult to estimate.

  2. Some philosophers have attempted to account for {48} attraction in general by supposing that there is a certain unknown matter always moving through the universe in right lines, by which bodies are impelled towards each other; but though the phenomena may be explained by such a supposition, it is as yet without proofs.

VII. Of Electrical Attraction and Repulsion, and their Relations to Chemical Changes.
  1. If a piece of dry silk be briskly rubbed against a warm plate of polished flint glass, it will be found to have acquired the property of adhering to it, which it will retain for some seconds; if at the time this adhesive power exists, the silk and glass be separated from each other, they will both be found to have gained the property of attracting very light substances, such as the ashes of paper or fragments of gold leaf; and the long filaments of the silk, if there be any, will be seen to repel each other.

  2. These bodies are said to be electrically excited, and the phenomena are called electrical phenomena. The peculiar circumstances under which they occur, are best observed by the use of an instrument called the electrical machine; it consists of a cylinder of glass1 supported upon glass pillars, and which can be made to revolve, so as to press against a cushion of silk rubbed over with a little amalgam of zinc and mercury; and of two cylinders of metal, one in contact with the cushion, and the other opposite to the glass cylinder, both supported upon glass.

  3. If two gilt pith balls, suspended upon strings of silk covered with tinsel, be hung upon a wire, placed in contact with either of the metallic cylinders, and the machine be put in action, the balls will repel each other; but if one ball be attached to a wire, connected with one metallic cylinder, and the other ball be attached to a wire connected with the other, the two balls, when the machine is put into action, will attract each other; and {92} at the moment that they come in contact, sparks of light will be perceived, if the experiment be made under favourable circumstances.

    As the two balls, when in contact with the same cylinder, may be considered as receiving the same impulse of impression, they are said to be similarly electrified; but when in contact with different cylinders, they are said to be differently electrified; and electrified bodies that repel each other, are considered as in the same electrical states; those that attract each other as in different electrical states.

  4. There are probably no two bodies differing in nature, which are not capable of exhibiting electrical phenomena, either by contact, pressure, or friction; but the first substances in which the property was observed, were vitreous and resinous bodies; and hence the different states were called states of resinous and vitreous electricity; and resinous bodies bear the same relation to flint glass, as silk. The terms, negative and positive electricity, have been likewise adopted, on the idea, that the phenomena depend upon a peculiar subtile fluid, which becomes in excess in the vitreous, and deficient in the resinous bodies; and which is conceived by its motion and transfer, to produce the electrical phenomena.

  5. Flint glass and silk, silk and sulphur, sulphur and metals, resin and metals, all by friction or contact, become strongly electrical, and of course attractive, and communicate their attractive powers to small masses of matter brought in contact with them; a pith ball, or a slip of gold leaf that has been touched by flint glass, excited by silk, will be repelled by a ball or slip that has been touched by silk excited by sulphur, or by a ball or slip that has been touched by sulphur excited by {93} metals, so that the attractive and repellent states depend entirely upon the actions of the two substances, and not upon any power peculiar to and inherent in each.

  6. It is upon this circumstance, that the electrometer, which might be called the differential one, is framed; it consists of two gold leaves attached to a metallic plate, and included in a hollow cylinder of glass,2 fixed upon another metallic plate, which is connected with two pieces of tin foil, pasted upon the glass opposite to the leaves. When any electrified body is made to touch the upper plate, the gold leaves diverge; if their divergence is increased by the approac hof flint glass excited by silk, they are said to have the same state as the glass, the vitreous or the positive; if their divergence is diminished, they are said to be in the opposite state, or to possess the resinous or negative electricity.

  7. When luminous phenomena are connected with electrical excitation, the different states may be known by presenting a metallic point to the excited body; if rays of light issue from the point to the body, it is said to be negatively electrified: but if the point appears simply luminous, without sending off any rays, the electricity is said to be positive.

  8. For measuring small degrees of electricity of bodies, as compared with those of others of the same kind, the electrical balance of Coulomb is applied; it consists of a gilt pith ball, placed upon a metallic rod, on the opposite extremity of which is a thin leaf of metal; the rod is suspended horizontally, by a fine metallic wire, which passes into a glass tube, to the top of which it is attached; the glass tube is inserted into a cylinder of glass, which contains a copper ball, connected with a small bar of metal, which is carried through an aperture {94} in the glass cylinder, into the atmosphere; a very small force only is required to twist the wire, and when the two balls are brought in contact, and the bar touched by the electrified body, they gain the same kind of electricity body, they gain the same kind of electricity, and repel each other; and the degree of their repulsion may be measured by a scale of degrees, made on the circumstance of the cylinder.3

  9. Bodies receive the electrical influence in different manners. If a rod of glass be brought in contact with any excited electrical body, it will receive the electrical influence in the part where it touched the body, and will be electrical, to a little distance, round the point of contact; but its remote parts will not be affected. A rod of metal, on the contrary, suspended on a rod of glass, and brought in contact with an electrical surface, instantly becomes electrical throughout. The glass, in common philosophical language, is said to be a non-conductor of electricity, or an insulating substance; the metal a conductor. Some bodies are affected to a much greater extent than glass, but not nearly so much as metals; such are animal and vegetable substances, water, and fluids containing water; they are said to be imperfect conductors. According to the statements of Mr. Cavendish, iron conducts 400 million of times better than water, sea water 100 times better than distilled water, and water saturated with salt, 720 times better. The mineral acids are the best fluid conducting substances known, and after them, saline solutions, the powers of which appear to be nearly in proportion to the quantities of salts they contain. Charcoal and metals, and the greater number of inflammable metallic compounds are conductors. Alcohol and ether, are very imperfect conductors; and sulphur, oils, resinous substances, {95} metallic oxides and compounds of chlorine, nonconductors.

  10. There is a stone found in many parts of the world, called tourmaline, which is sometimes crystallized as a nine-sided pyramid; when this substance is gently heated, it becomes electrical, and one extremity, that terminated by the six-sided pyramid, s positive, the other is negative; to a certain extent, its electricities are exalted by increasing the temperature; when it begins to cool, it is still found electrical; but the electricities are changed, the pyramid, before positive, is now negative, and vice versa. When the stone is of considerable size, flashes of light may be seen along its surface.

    There are other gems and cystallized substances, which possess a property similar to that of the tourmaline. The luminous appearance of some diamonds, when heated, probably depends upon their electrical excitation. The substance called the Boracite, which is a cube, having its edges and angles defective, becomes electrical by heat, and in one variety presents no less than eight sides, in different states, four positive, four negative; and the opposite poles are in the direction of the axes of the crystal.

  11. It would appear, that in all cases of electrical action, the two electrical states are always coincident, either in different parts of the same body, or in two bodies; and that they are always equal, and capable of neutralizing each other. If a connection be made by a wire, between the positive and negative conductors of the electrical machine, during the time of its action, all electrical effects cease; and to produce a succession of effects, both conductors must be brought near bodies {96} connected with the ground, which gain the opposite state, in consequence of what may be called induction, and which will be explained in the next paragraph.

  12. When a non-conductor, or imperfect conductor, provided it be a thin plate of matter, placed upon a conductor, is brought in contact with an excited electrical body, the surface, opposite to that in contact, gains the opposite electricity from that of the excited body; and if the plate be removed from the conductor and the source of electricity, it is found to possess two surfaces in opposite states. If a conductor be brought into the neighbourhood of an excited body, the air, which is a non-conductor, being between them, that extremity of the conductor, which is opposite to the excited body, gains the opposite electricity, and the other extremity, if opposite to a body connected with the ground, gains the same electricity, and the middle point is not electrical at all. This is easily proved, by examining the electricity of three sets of gilt pith balls raised on wires on the different parts of the conductor, which is thus effected by induced electricity.

    If, instead of air, a plate of mica or glass be between the two conductors, the same phenomena will occur; so that it would appear that the conductor merely gains two opposite electricities, or polar electricities, of the same kind as those of the non-conductor. The phenomena of sparks, of discharges, and of accumulated electricity, depend upon this law. In the case of the common electrical spark, a stratum of air is charged in the same manner as a glass bottle, partially coated with tin-foil, is charged in the Leyden experiment;4 when the hand is held near the positive conductor of an electrical machine, the person standing on the ground, {97} the hand is rendered negative, and the states become exalted, till the polarities, as they may be called, are annihilated through the air, producing a spark, a snap, and a distinct sensation. If a number of small pith balls, placed upon a surface of metal, are caused to approach an electrified body, they are brought into the opposite state by induction, and are attracted towards the body; but when they come in contact with it, this state is destroyed, they gain the same state, and are repelled; and if they are properly placed, their alternate attractions and repulsions may be produced, as long as the machine is in action.

  13. If a number of cylinders of metal, insulated on glass, be placed in a line with each other, but not in contact, and the last be connected with the ground;5 when a powerfully electrified conductor of a machine is brought opposite to the first, they will all become electrical, and every insulated cylinder will present two poles; the negative pole of one being opposite to the positive pole of the other; and if a spark is produced by means of the last, sparks occur throughout the whole arrangement. In like manner a series of Leyden jars may be made to charge each other, the outer surface of the first rendering negative the inner surface of the second, and so on; and by connecting the surfaces that have the same kind of electricity , in the first place, and then connecting two opposite surfaces in the series, a powerful explosion6 may be produced.

  14. When a point connected with the ground is brought near an electrified substance, it rapidly gains the opposite state, and an immediate discharge takes place, which continues till the equilibrium is restored. Large surfaces are electrified by induction much more {98} slowly than small ones, and are capable of accumulating much more electricity, which renders the discharge from them much more violent. Indeed, the electrical powers seem entirely to belong to the surfaces of bodies, and not to be connected with the quantity of solid matter they contain.

  15. It is in consequence of the principle of induction, that the condensing electrometer is so much more sensible than the common electrometer; this instrument consists of two plates of polished metal,7 the surfaces of which are parallel, one connected with the plate of the electrometer, the other moveable, in connexion with the ground, and the plates are very near each other. When the body supposed to be electrical, is made to touch the top of the electrometer, and is afterwards removed, in separating the plates, the effect will be perceived.

  16. The difference in what are called the conducting powers of bodies, seems to depend entirely upon the different manner in which they receive the electrical polarities, or in which their parts become capable of communicating attractive or repellent powers, to other matter. Non-conductors appear to receive polarities, only with great difficulty, but retain them for a long while, and present probably a number of different alternations of poles, within a small space, and cannot be affected to any great distance. Imperfect conductors receive polarity with more facility, but present fewer alternations, and preserve their electricities for a shorter time. Perfect conductors are easily affected throughout, but present at most only two poles, and the powers rapidly destroy each other. The difficulty with which non-conductors receive polarity, is shewn in the phenomena {99} of charging thick and thin coated plates of glass and mica. The thin plates are capable of being charged much more highly than the thick ones, and the accumulation on the opposite surfaces is much greater.

    Rarefied air, or gaseous matter, is much more susceptible of receiving polarities, than dense air or gaseous matter; and hence, the electrical spark will pass much further through rarefied air or light gases, than through dense air or heavy gases; it passes much further, likewise in gases, than in non-conducting fluids.

  17. If a non-conducting surface, coated with two conducting surfaces, and charged so as to give a spark of an inch in length, through air, be connected by both its conducting surfaces, with a similar apparatus not charged; then both systems may be discharged together; but the spark they will give, will be only half as long as the single one would have given, if discharged alone. The quantity of the electricity in this case, is conceived not to be altered, but its intensity is said to be only half as great when it is discharged from a double surface; and these expressions of intensity and quantity, though it is not easy to attach any very definite ideas to them, are nevertheless useful, in giving more facility to the arrangement of some important electrical phenomena.

  18. When very small conducting surfaces are used for conveying very large quantities of electricity, they become ignited; and of the different conductors that have been compared, charcoal is most easily heated by electrical discharges,8 next iron, platina, gold, then {100} copper, and lastly zinc. The phenomena of electrical ignition, whether taking place in gaseous, fluid, or solid bodies, always seem to be the result of a violent exertion of the electrical attractive and repellent powers, which may be connected with motions of the particles of the substances affected. That no subtile fluid, such as the matter of heat has been imagined to be, can be discharged from these substances, in consequence of the effect of the electricity, seems probable, from the circumstance, that a wire of platina may be preserved in a state of intense ignition in vacuo, by means of the Voltaic apparatus, (an instrument which will be immediately described,) for an unlimited time; and such a wire cannot be supposed to contain an inexhaustible quantity of subtile matter.

  19. Certain changes in the forms of substances, are always connected with electrical effects. Thus when vapour is formed or condensed, the bodies in contact with the vapour, become electrical. If, for instance, a plate of metal, strongly heated, be placed upon an electrometer, and a drop of water be poured upon the plate, at the moment the water rises in vapour, the gold leaves of the electrometer diverge with negative electricity. Sulphur, when melted, becomes strongly electrical during the time of congelation; and the case seems to be analogous, with respect to non-conducting substances in general, when they change their forms.

    As electricity appears to result from the general powers or agencies of matter, it is obvious, that it must be continually exhibited in nature, and that a number of important phenomena must depend upon its operation. When aqueous vapour is condensed, the clouds formed are usually more or less electrical; and the earth below them being brought into an opposite state, {101} by induction, a discharge takes place when the clouds approach within a certain distance, constituting lightning; and the undulation of the air, produced by the discharge, is the cause of thunder, which is more or less intense, and of longer or shorter duration, according to the quantity of air acted upon, and the distance of the place, where the report is heard from the point of the discharge. It may not be uninteresting to give a further illustration of this idea: electrical effects take place in no sensible time; it has been found, that a discharge through a circuit of four miles, is instantaneous; but sound moves at the rate of about twelve miles in a minute. Now, supposing the lightning to pass through a space of some miles, the explosion will be first heard from the point of the air agitated, nearest to the spectator; it will gradually come from the more distant parts of the course of the electricity, and last of all, will be heard from the remote extremity; and the different degrees of the agitation of the air, and likewise the difference of the distance, will account for the different intensities of the sound, and its apparent reverberations and changes.

  20. In a violent thunder storm, when the sound instantly succeeds the flash, the persons who witness the circumstance, are in some danger: when the interval is a quarter of a minute, they are secure. In a thunder storm, the lowest ground is the safest place, and a horizontal posture, the least dangerous; the neighbourhood of trees, or buildings, should be avoided, particularly of trees, the living juices of which are calculated to conduct the electricity, and make part of a circuit. In a house, the celld ars are the safest places, and in a room the person should stand as far as possible from the fire. The means adopted by Franklin have however, to a {102} great extent, averted the destructive effects of atmospheric electricity; and by pointed conductors, the thunder cloud is disarmed of its terrors, and the lightning slowly discharged in harmless coruscations.

    If a school-boy's kite be mounted high in the atmosphere, by means of a string, containing filaments of metal, fastened to a conductor, fixed on a glass rod; the conductor usually gives signs of electricity, which will be greatest, when clouds are floating in the atmosphere; and it was by means of a simple apparatus of this kind, that the American Philosopher effected his grand discovery of the identity of electricity and lightning.

    The water-sprout is probably the result of the operation of a weakly electrical cloud, at an inconsiderable elevation above the sea, brought into an opposite state: and the attraction of the lower part of the cloud, for the surface of the water, may be the immediate cause of this extraordinary phenomenon.

    The coruscations of the Aurora Borealis, and Australis, precisely resemble strong artificial electricity, discharged through rare air; and as the poles are non-conductors, being coated with ice or snow, and as vapour must be constantly formed in the atmosphere above them; the idea of Franklin is not improbable, that the Auroras may arise from a discharge of electricity, accumulated in the atmosphere near the poles, into its rarer parts; through other solutions of the phenomena may be given on the idea, that the earth itself is endowed with electrical polarity; or that the motions of the atmosphere produce the effect: but all views on this subject must be hypothetical, and the light may result from other causes than electrical action.

  21. The common exhibition of electrical effects, is in {103} attractions and repulsions, in which masses of matter are concerned; but there are other effects, in which the changes that take place, operate in a manner, in small spaces of time imperceptible, and in which the effects are produced upon the chemical arrangements of bodies.

    If a piece of zinc and a piece of copper be brought in contact with each other, they will form a weak electrical combination, of which the zinc will be positive, the copper negative; this may be learnt by the use of a delicate condensing electrometer; or by pouring zinc filings through holes, in a plate of copper, upon a common electrometer; but the power of the combination may be most distinctly exhibited in the experiments, called Galvanic experiments, by connecting the two metals, which must be in contact with each other, with a nerve and muscle in the limb of an animal recently deprived of life, a frog for instance; at the moment the contact is completed, or the circuit made, one metal touching the muscle, the other the nerve, violent contractions of the limb will be occasioned. If a piece of zinc and copper, in contact with each other in one point, be placed in contact in other points with the same portion of water; the zinc will corrode and attract oxygen from the water, much more rapidly than if it had not been in contact with the copper; and if a small quantity of sulphuric acid be added to the water, it will be seen that globules of inflammable air are given off from the copper, though it is not dissolved nor acted upon.

  22. The connection of chemical effects, with the exhibition of electrical powers is, however, best witnessed in combinations, in which these powers are accumulated by alternations of different metals and {104} fluids. If plates of copper and zinc two or three inches square, and pieces of cloth of the same size soaked in a solution of salt, or sal ammoniac, or nitre, be arranged in the order of copper, zinc, moistened cloth, and so on, and made into an insulated pile, of which the series are 200;9 several remarkable phenomena will occur.

    When one hand is applied to the bottom of the pile, and the other to the top, both hands being moistened, a shock will be perceived.

    When a metallic wire, having a bit of well burned charcoal at its extremity, is made to connect the two extremities of the pile, a spark will be perceived, or the point of the charcoal will become ignited.

    A wire, connected with the top of the pile, brought in contact with a sensible electrometer, will cause the leaves to diverge; and by removing the wire and applying excited glass to the electrometer, it will be found that the electricity is positive; a wire connected with the bottom of the pile will affect it with negative electricity; a wire from the middle of the pile will have no influence on the instrument.

    If wires of platina from the extremities of the pile be introduced into water, or into two portions of water connected by moist substances, oxygen gas will separate at the wire exhibiting the positive electricity, and hydrogen gas at the wire exhibiting the negative electricity; and the proportions are such, when the proper circumstances exist, that they will produce water when exploded by the electrical spark, that is, the volume of hydrogen will be to that of oxygen as two to one.

    If the same wires be introduced into a strong solution of sulphuric or phosphoric acid, or into metallic solutions, oxygen will separate at the positive surface, the {105} inflammable or metallic matter contained in the solution at the negative surface.

    When any substance rendered fluid by heat, consisting of water, oxygen and inflammable or metallic matter, is exposed to those wires, similar phenomena occur.

    When any solution of a neutral salt containing acid, united to alkaline, earthy, or common metallic matter, is used; besides the other phenomena that take place, acid matter collects round the positively electrified surface; alkali, earth, or oxide, round the negative surface; and if two separate vessels are employed to contain the solution, connected by moist asbestos, it is found that the acid collected in the vessel containing the wire, positively electrified, will be in definite proportion to the matter collected in the other cup; that is, it will form with it a neutrosaline compound.

    If a solution of muriatic acid in water be acted on by the wires, hydrogen will separate at the negative surface, and chlorine at the positive surface.

  23. This apparatus, which exhibits in so distinct a manner the relations of electrical polarities to chemical attractions, is the grand invention of Volta, made known in the first year of this century; its electrical effects have been long known, but the phenomena of its operation in decomposing bodies, are of more recent discovery.

    Several modes of constructing it have been adopted, some of which are much superior in point of convenience, to that which has been just described.

    One mode is by soldering the plates of zinc and copper together, and by cementing them into troughs of baked wood, covered with cement, in the regular order, so as to form cells to be filled with the fluid menstruum; {106} each surface of zinc being opposite to a surface of copper; and this combination is very simple and easy of application.

    Another form is that of introducing plates of copper and of zinc, fastened together by a slip of copper, into a trough of porcelain containing a number of cells corresponding to the number of the series. The different series may be introduced separately into the troughs, and taken out without the necessity of changing the fluid, or they may be attached to a piece of baked wood and (when the number is not very large) introduced into the cells, or taken out together.10

  24. Similar polar electrical arrangements to those formed by zinc and copper, may be made by various alternations of conducting and imperfect conducting substances; but for the accumulation of the power, the series must consist of three substances or more, and one at least must be a conductor. Silver or copper, when brought in contact with a solution of a compound of sulphur and potassa, at one extremity, and in contact with water or a solution of nitric acid, at the other extremity, some saline solution being between the sulphuretted and the acid solutions, forms an element of a powerful combination, which will give shocks when fifty are put together; the order is copper, cloth of the same size moistened with solution of nitric acid, cloth moistened in solution of common salt, cloth moistened in solution of the compound of sulphur, copper, and so on; the specific gravities of the solutions should be in the order in which they are arranged, to prevent the mixture of the acid and sulphuretted solution; that is, the heaviest solution should be placed lowest.

    The tables annexed contain some series, which form {107} Voltaic electrical combinations, arranged in the order of their powers; the substance most active being named first in each column.

    The metals having the strongest attraction for oxygen, are the metals which form the positive pole, in all cases in which the fluid menstrua act chemically by affording oxygen; but when the fluid menstrua afford sulphur to the metals, the metal having the strongest attraction for sulphur under the existing circumstances, determines the positive pole; thus in a series of copper and iron, introduced into a porcelain trough, the cells of which are filled with water or with {108} acid solutions, the iron is positive, and the copper negative; but when the cells are filled with solutions of sulphur and potash, the copper is positive and the iron negative.

    In all combinations in which one metal is concerned, the surface opposite the acid is negative, that in contact with solution of alkali and sulphur, or of alkali, is positive.

  25. The energy of a combination to give repulsive or attractive powers to masses of matter or to affect the electrometer, seems to increase with the number of the series, as does the power to give shocks, and to decompose bodies; but as long as the surface of the gold leaves in the electrometer, or of the human body, or of the water acted upon, is the same, and less than that of the acting plates, increase of surface of the plates is connected with no increase of power. In the operation upon metallic substances or charcoal, or upon good imperfect conductors, the case, however, is different. Thus, though a battery composed of plates of copper and zinc a foot square, will not affect the condensing electrometer more, nor decompose more water, nor give greater shocks to the fingers, than a battery containing plates of an inch square, yet it will ignite more than 100 times as much fine platina wire, and decompose sulphuric acid, and the water in strong saline solutions with infinitely more rapidity. This has been expressed by Mr. Cavendish in the statement, that the intensity is the same in both cases; but that the quantity is in some ratio as the surface. The quantity in the small plates is as much or more than such imperfect conductors as water and the human body can carry off by a small surface: whilst better conductors can transmit the whole quantity afforded by the large plates, even when used {109} in the very thin laminae or wires. The correctness of this view may be shewn by a very simple experiment. Let two platina wires, from the extremities of a battery composed of plates of a foot square, be plunged into water, the quantity of gas disengaged from the wires will be nearly the same as from an equal number of plates of an inch square; let the fingers of each hand, moistened with water, be applied to the two extremities of the battery, a shock will be perceived nearly the same as if there had been no connection between the wires and the water. Whilst the circuit exists through the human body and through water, let a wire attached to a thin slip of charcoal be made to connect the two poles of the battery, the charcoal will become vividly ignited. The water and the animal substance discharge the electricity of a surface, probably not superior to their own surface of contact with the metals; the wires discharge all the residual electricity of the plates; and if a similar experiment be made on plates of an inch square, there will scarcely be any sensation, when the hands are made to connect the ends of the battery, a circuit being previously made through water; and no spark when charcoal is made the medium of connection, imperfect conductors having been previously applied.

    The first distinct experiment upon the igniting powers of large plates was performed by MM. Fourcroy, Vauquelin, and Thenard. But the grandest combination over constructed for exhibiting the effects of extensive surface, was made by Mr. Children: it consists of twenty double plates four feet by two; of which the whole surfaces are exposed, in a wooden trough, in cells covered with cement, to the action of diluted acids. This battery, when in full action, had no more {110} effect on water or on the human body than one containing an equal number of small plates; but when the circuit was made through metallic wires, the phenomena were of the most brilliant kind. A platina wire of one-thirtieth of an inch in thickness, and eighteen inches long, placed in the circuit between bars of copper, instantly became red hot, then white hot, the brilliancy of the light was soon insupportable to the eye, and in a few seconds the metal fell fused into globules. The other metals were easily fused or dissipated in vapour by this power. Points of charcoal ignited by it produced a light so vivid, that even the sunshine compared with it appeared feeble.

    Mr. Children has another battery in construction, the plates of which are double the size of that just described, and which are to be arranged in pairs in single troughs, and connected by means of plates of lead in regular order.11

  26. The most powerful combination that exists in which number of alternations is combined with extent of surface, is that constructed by the subscriptions of a few zealous cultivators and patrons of science, in the laboratory of the Royal Institution. It consists of two hundred instruments, connected together in regular order, each composed of ten double plates arranged in cells of porcelain, and containing in each plate thirty-two square inches; so that the whole number of double plates is 2000, and the whole surface 128,000 square inches. This battery, when the cells were filled with 60 parts of water mixed with one part of nitric acid, and one part of sulphuric acid, afforded a series of brilliant and impressive effects. When pieces of charcoal about {111} an inch long and one-sixth of an inch in diameter, were brought near each other (within the thirtieth or fortieth part of an inch,) a bright spark was produced, and more than half the volume of the charcoal became ignited to whiteness, and by withdrawing the points from each other a constant discharge took place through the heated air, in a space equal at least to four inches, producing a most brilliant ascending arch of light, broad, and conical in form in the middle.12 When any substance was introduced into this arch, it instantly became ignited; platina melted as readily in it as wax in the flame of a common candle; quartz, the sapphire, magnesia, lime, all entered into fusion; fragments of diamond, and points of charcoal and plumbago, rapidly disappeared, and seemed to evaporate in it, even when the connection was made in a receiver exhausted by the air pump; but there was no evidence of their having previously undergone fusion.

    When the communication between the points positively and negatively electrified was made in air, rarefied in the receiver of the air pump, the distance at which the discharge took place increased as the exhaustion was made, and when the atmosphere in the vessel supported only one-fourth of an inch of mercury in the barometrical gage, the sparks passed through a space of nearly half an inch; and by withdrawing the points from each other, the discharge was made through six or seven inches, producing a most beautiful coruscation of purple light, the charcoal became intensely ignited, and some platina wire attached to it, fused with brilliant scintillations, and fell in large globules upon the plate of the pump. All the phenomena of chemical decomposition were produced with intense rapidity by this {112} combination. When the points of charcoal were brought near each other in non-conducting fluids, such as oils, ether, and oxymuriatic compounds, brilliant sparks occurred, and elastic matter was rapidly generated; and such was the intensity of the electricity, that sparks were produced, even in good imperfect conductors, such as the nitric and sulphuric acids.

    When the two conductors from the ends of the combination were connected with a Leyden battery, one with the internal, the other with the external coating, the battery instantly became charged, and on removing the wires, and making the proper connections, either a shock or a spark could be perceived; and the least possible time of contact was sufficient to renew the charge to its full intensity.

  27. The general facts of the connection of the increase of the different powers of the battery with the increase of the number and surface of the series, are very distinct; but to determine the exact ratio of the connection is a problem not easy of solution.

    MM. Gay Lussac and Thenard have announced, that the power of chemical decomposition increases only as the cube root of the number of plates; but their experiments were made with parts of piles of a construction very unfavourable for gaining accurate results; and in various trials made with great care in the laboratory of the Royal Institution, the results were altogether different. The batteries employed were parts of the great combination, carefully insulated, and similarly charged; arcs of zinc and silver presenting equal surfaces, and arranged in equal glasses filled with the same kind of fluid, were likewise used; and the tubes for collecting the gases were precisely similar, and filled with the same solution of potassa.13 In these experiments ten {113} pairs of plates produced fifteen measures of gas; twenty pairs in the same time produced forty-nine: again, ten pairs produced five measures; forty pairs in the same time produced seventy-eight measures. In experiments made with arcs, and which appeared unexceptionable, four pairs produced one measure of gas; twelve pairs in the same time produced nine and 7/10 of gas; six pairs produced one measure of gas; thirty pairs, under like circumstances, produced 24.5 measures; and these quantities are nearly as the squares of the numbers.

    It would appear from the experiments of Vanmarum and Pfaff, confirmed by those of Messrs. Wilkinson, Cuthbertson, and Singer, that the increase of power of batteries, the plates of which have equal surfaces, is as the number. I found that ten double plates, each having a surface of a hundred square inches, ignited two inches of platina in wire of one-eightieth of an inch; twenty plates, five inches; forty plates, eleven inches: but the results of experiments on higher numbers were not satisfactory; for one hundred double plates of thirty-two square inches each, ignited three inches of platina wire of one-seventieth, and one thousand ignited only thirteen inches, and the charges of diluted acid were similar in both cases.

    The power of ignition for equal numbers of plates, seems to increase in a very high ratio with the increase of surface, probably higher than even the square; for twenty double plates, containing each two square feet, did not ignite one-sixteenth as much wire as twenty, containing each eight square feet, the acid employed being of the same strength in both cases.

    Numerous circumstances are opposed to the accuracy of experiments made with high numbers, or very large surfaces; the activity of combinations rapidly {114} diminishes in consequence of the decomposition of the menstruum used; and this decomposition is much more violent, the greater the number and surface of the alternations; the vapour rising likewise, when the action is intense, interferes by its conducting powers, and the gas by its want of conducting power; and when series containing above five hundred double plates are used, unless the insulation is very perfect, there is a considerable loss of electricity; thus the great battery of two thousand double plates belonging to the Royal Institution, will scarcely act by its true poles, when arranged on a floor of stone, and requires not merely the insulation of porcelain, but likewise of dry wood; and when arranged on a stone floor, it is hardly possible to walk near any of the approaching series without receiving shocks. In cases of the ignition of wire, the cooling influence of the substances in contact, and of that part of the chain not ignited, interferes most, when small quantities of wire are employed, and with feeble powers; and hence the effect is at first in a lower and then in a higher ratio than the number, when the whole range is small, as in the experiments above stated. If there is an imperfect connection in any of the series, a great diminution of power is the consequence. If one plate is corroded, or covered with more oxide than the rest, there is a general loss of effect. If copper is substituted for zinc, or zinc for copper, in a single series, the result is similar; and I find that a platina wire, introduced in the place of an arc of silver and zinc, in a series of thirty, diminished its power of producing gas so much, that it was equal only to that of four.

  28. The circumstance most important in electricity, perhaps, is its connection with the chemical powers of matter, and the manner in which it modifies, exalts, or {115} destroys these powers. Most of the substances that act distinctly upon each other electrically, are likewise such as act chemically, when their particles have freedom of motion: this is the case with the different metals, with sulphur and the metals, with acid and alkaline substances; and the relations of bodies are uniform; those that have the highest attracting powers being in the relation of positive, in arrangements in which chemical changes can go on. Thus, as is shown in the tables, page 107, zinc is positive with respect to iron, iron with respect to copper, copper with respect to silver, and so on in all combinations in which oxygen is capable of being combined with the metal; but copper is positive with respect to iron in compound menstrua containing sulphur; the electrical power being in all cases apparently connected with the power of chemical combination.

    Crystals of oxalic acid touched by dry quick-lime exhibit electrical powers; and the acid is negative, the lime positive.

    All the acid crystals, upon which I have experimented when touched by a plate of metal, render it positive. And in Voltaic combinations with single plates or arcs of metal, as is stated in page 108, the metal is negative on the side opposed to the acid, and positive on the side or pole opposed to the alkali.

    Bodies that exhibit electrical effects previous to their chemical action on each other, lose this power during combination. Thus, if a polished plate of zinc is made to touch a surface of dry mercury, and quickly separated, it is found positively electrical, and the effect is increased by heat; but if it be so heated as to amalgamate with the surface of the mercury, it no longer exhibits any marks of electricity. The case is analogous {116} with copper and sulphur; and iron acts more powerfully than zinc with quicksilver in a permanent electrical combination, as in the experiments of Colonel Haldane; apparently, because under common circumstances it is incapable of amalgamating with that metal. When any conducting substance, capable of combining with oxygen, has its positive electricity increased, it will attract oxygen with more energy from any imperfect conducting medium; and metallic bodies which in their common state have no action upon water, such as silver, attract oxygen from it easily, when connected with the positive pole in the Voltaic circuit; and bodies that act upon water, such as zinc and iron, so as to decompose it slowly, refuse to attract oxygen from it when they are negatively electrified in the Voltaic circuit.

    Acids, which are negative with respect to alkalies, metals, and earths, are separated from these bodies in the Voltaic circuit at the positive surface; and alkalies, metals, and earths, are separated from acids at the negative surface: and such are the attracting powers of these surfaces, that acids are transferred through alkaline solutions, and alkalies through acid solutions, to the surfaces where they have their points of rest. It is easy to shew this by making a combination of three agate cups,14 one containing sulphate of potassa, one weak nitric acid, and the third distilled water, and connecting them by asbestus moistened in pure water, in such a manner, that the surface of the acid is lower than the surface of the fluid in the other two cups. When two wires of platina from a powerful Voltaic apparatus are introduced into the two extreme cups, the solution of the salt being positively electrified, a decomposition will take place, and in a certain time a {117} portion of potassa will be found dissolved in the cup in contact with the negative wire, though the fluid in the middle cup will still be sensibly acid.

  29. Such are the decomposing powers of electricity, that not even insoluble compounds are capable of resisting their energy; for even glass, sulphate of baryta, flour spar, &c. when moistened and placed in contact with electrified surfaces from the Voltaic apparatus, are slowly acted upon, and the alkaline, earthy, or acid matter carried to the poles in the common order. Not even the most solid aggregates, nor the firmest compounds, are capable of resisting this mode of attack; its operation is slow, but the results are certain; and sooner or later, by means of it, bodies are resolved into simpler forms of matter.

  30. It is in consequence of the phenomena of electrical decomposition, in which metals, inflammable bodies, alkalies, earths, and oxides, are determined to the negative surface, and oxygen, chlorine, and acids, to the positive surface, that for some time it was conceived, that various substances, might be composed from pure water, by means of electricity, such as potassa, soda, and muriatic acid. A strict investigation of the circumstances under which these substances appeared, led me to discover that they were always furnished from the vessels, or from impurities in the water, and enabled me to determine the general principles of electrical decomposition, and to apply this power to the resolution of some species of matter, of unknown nature, into their elements.

  31. The connection of electrical phenomena and chemical changes is evident likewise in the general phenomena of the battery. The most powerful Voltaic combinations are formed by substances that act chemically {118} with most energy upon each other; and such substances as undergo no chemical changes in the combination, exhibit no electrical powers. Thus, zinc copper, and nitric acid form a powerful battery; whilst silver, gold, and water, which do not act chemically on each other, in series of the same number, produce no sensible effect. These circumstances led some philosophers to suppose, at an early period of the investigation of the electrical powers of metals, that they were entirely the result of chemical changes: that as heat was produced by this action, when exerted under common circumstances, so electricity resulted from it under other circumstances; and many of the phenomena were comfortable to such an idea, and some ingenious inquirers adopted it to such an extent, as to suppose electricity in all cases owing to this cause.

    This generalization, whether applied to Voltaic or to common electricity, seems, however, to be incorrect. Zinc and copper, as has been stated, different metals and oxalic acid, different metals and sulphur, or charcoal, exhibit electrical effects after mere contact, and that in cases when not the slightest chemical change can be observed; and if in these experiments chemical phenomena are produced by the action of menstrua, all electrical effect immediately cease: and it is not philosophical to assume a cause to account for an effect, when no such case can be perceived.

    It has been supposed that the action of the common electrical machine depends upon the oxidation of the amalgam; but I found by mounting a small machine in a glass vessel, in such a manner that it could be made to revolve in any species of gas, that it was active in hydrogen gas, and more active in carbonic acid gas than in the atmosphere (probably owing to its greater {119} density). The experiment has been several times repeated under different circumstances, and uniformly with the same results; and may be regarded as decisive in this important question.

  32. Electrical effects are exhibited by the same bodies, when acting as masses, which produce chemical phenomena when acting by their particles; it is not therefore improbable, that the primary cause of both may be the same, and that the same arrangements of matter, or the same attractive powers, which place bodies in the relations of positive and negative, i.e. which render them attractive of each other electrically, and capable of communicating attractive powers to other matter, may likewise render their particles attractive, and enable them to combine, when they have full freedom of motion.

    It is not a little in favour of this hypothesis, that heat, and sometimes heat and light, result from the exertion of both electrical and chemical attractive powers; and that by rendering bodies, which on contact are in the relation of positive to others, still more highly positive, as has been stated, page 116, their powers of combination are increased; whereas, when they are placed in a state corresponding to the negative electrical state, their powers of union are destroyed. That acids can be detached from alkalies, oxygen and chlorine from inflammable matter by metallic substances, or by a fluid menstruum highly positive, is likewise favourable to the supposition.

  33. This view of the possibility of the dependence of electrical and chemical action upon the same cause, has been much misrepresented. It has been supposed that the idea was entertained, that chemical changes were occasioned by electrical changes; than which {120} nothing is further from the hypothesis which I have ventured to advance. They are conceived, on the contrary, to be distinct phenomena; but produced by the same power, acting in one case on masses, in the other case on particles. The hypothesis has been attempted to be controverted by experiments which are far from satisfactory, and some of which have no connection with it. It has been said that acids rendered positive by the common machine, will still combine with alkalies, and that other contradictory results may be obtained; but a non-conducting acid, though brought in contact with a positive surface, electrified by the common machine, is not rendered positive throughout; but gains a polar electricity, which extends only to a certain depth into the crystals, and the exterior surface, if electrical at all, is negative: and if a wire, positively electrified by the common machine, be introduced into an acid solution, this solution, if at all affected, when made to act upon another solution, will be negative at its point of action; that is, it will be positive near the wire, but will be in the opposite state with regard to another surface. And common electricity is too small in quantity, in its usual form of application, to influence chemical changes; for it requires a very strong machine acting upon a very small surface, to produce any sensible polar decompositions of bodies.

  34. The power of action of the Voltaic apparatus, seems to depend upon causes similar to those which produce the accumulation in the Leyden battery, namely, the property of non-conductors and imperfect conductors to receive electrical polarities from, and to communicate them to conductors; but its permanent action is connected with the decomposition of the chemical menstrua between the plates. Each plate of {121} zinc is made positive, and each plate of copper negative, by contact; and all the plates are so arranged with respect to each other as to have their electricities exalted by induction, so that every single polar arrangement, heightens the electricity of every other polar arrangement; and the accumulation of power increases with the number of the series. When the battery is connected in a circle, the effects are demonstrated by its constant exhibition of chemical agencies, and the powers exist as long as there is any menstruum to decompose: but when it is insulated, and the extreme poles of zinc and copper are unconnected, no effects whatever are perceived to take place, no chemical changes go on, and it exhibits its influence only by communicating very weak charges to the electrometer, the end terminated by zinc communicating a positive charge, that terminated by copper, a negative charge.

    That each plate of the most oxidable metal in the apparatus, is in the relation of positive, and each plate of the least oxidable, in the relation of negative, and that every series is possessed of similar and equal polarity, is shewn by a very simple experiment; forty rods of zinc of the same size, connected with forty silver wires precisely similar, were introduced in the regular order into similar glasses filled with a solution of muriate of ammonia, rendered slightly acid by muriatic acid; as long as the extreme parts remained unconnected, no gas was disengaged from the silver, and the zinc was scarcely acted upon; when they were connected, all the plates of zinc were dissolved much more rapidly, and hydrogen gas was evolved from every silver wire. And in another experiment, in which several of these wires at equal distances were introduced {122} into small glass tubes, it was found that equal quantities of hydrogen were produced.

  35. It seems absolutely necessary for the exhibition of the powers of the Voltaic apparatus, that the fluid between the plates should be susceptible of chemical change, which appears to be connected with the property of double polarity, of being rendered positive at one surface, and negative at the other. There are substances that are imperfect conductors, which are capable of receiving only one kind of electricity, when made parts of the Voltaic circuit, and which M. Ehrman, who discovered them, has named unipolar bodies. Perfectly dry soap, and the flame of phosphorus, when connected with the two extremities of the Voltaic apparatus, and with the ground, discharge only the negative electricity. The flames of alcohol, hydrogen, wax, and oil, discharge under like circumstances only the positive electricity; but all these bodies when connected with one pole only of the pile, and with the ground, destroy the divergence of the leaves of the electrometer connected with that end. It is not difficult to exhibit these phenomena when the atmosphere is dry, by means of two hundred pair of plates carefully insulated: an insulated gold leaf electrometer having a moveable wire attached to it, should be connected with each end of the pile: when either electrometer is brought in contact with soap, the soap being connected with the ground, the slight divergence of the leaves will cease; when the soap is connected with both electrometers and with the ground, the divergence of the leaves of the electrometer connected with the end terminated by the zinc, will continue, the leaves of the other electrometer will collapse. The opposite effect {123} occurs when the flame of a taper is connected with both electrometers and with the ground.

    The unipolar conductors are incapable of being active in any part of the pile, and in this respect agree with non-conductors; many of which, it is probable, if examined in their relations to electricities of low intensity, would exhibit similar differenc es.

  36. There are no fluids known, except such as contain water, which are capable of being made the medium of connection between the metals, or metal of the Voltaic apparatus; and in cases in which Voltaic batteries have been said to be constructed by metals and paper, or metals and starch, or other like substances, the feeble effects produced are merely owing to the small quantity of water adhering to these substances, which will not act when carefully dried. The instrument, called by M. de Luc, the electrical column, formed of zinc, Dutch leaf, and paper, and which he appears to consider as a different combination from the pile of Volta, seems to be merely a feeble Voltaic apparatus, in which the quantity of electricity is not sufficiently great to produce any chemical changes, or distinct phenomena of ignition; but in which the intensity of the small quantity existing, when the combination amounts to 400 or 500, is sufficient to enable it to affect the electrometer, and to act through a plate of air.

    It is very probable that the power of water to receive double polarities, and to evolve oxygen and hydrogen, is necessary to the constant operation of the connected apparatus; and that acids, or saline bodies, increase the action, by affording elements which possess opposite electricities to each other, when mutually excited; the action of the chemical menstrua exposes continually {124} new surfaces of metal; and the electrical equilibrium may be conceived in consequence, to be alternately destroyed and restored, the changes taking place in imperceptible portions of time.

    The manner in which aqueous fluids receive and communicate electrical polarity, is shewn by a very simple experiment; let a number of fine metallic surfaces, or flattened wires (of tin for instance) be made to swim in a narrow trough containing water; and let two wires from the extermities of a Voltaic battery of 1000 double plates, be plunged into the remote ends of the trough, one into one end, the other into the other end. The metals swimming on the water will immediately acquire electrical polarity; and the positive and negative poles will be regularly opposed to each other, the pole of the metal opposite to the wire positively electrified, will be found to be negative, giving off hydrogen, the other pole will deposit oxide; the next wire to this will present the alternate order, which will be preserved in all of them; those most remote from the right line of the circuit, will be least affected. If the battery be in a highly active state, the different wires will attract each other by their opposite poles, and the circle will at length be closed with the production of brilliant sparks. The phenomena are precisely analogous to those phenomena in magnetism, presented by a number of flattened wires of soft iron, made to swim upon water, and rendered magnetic by the opposite poles of two powerful magnets; each wire has a north pole and a south pole; and in the alternation, the different poles are attractive of each other.

  37. That the decomposition of the chemical agents is connected with the energies of the pile, is evident from all the experiments that have been made; as yet no {125} sound objection has been urged against the theory that the contact of the metals destroys the electrical equilibrium, and that the chemical changes restore it; and in consequence that the action exists as long as the decompositions continue; and this conclusion is confirmed by the late researches made by MM. Gay Lussac and Thenard, on the great pile constructed by order of the French government. The manner in which chemical changes tend to restore the electrical equilibrium, is shewn by a remarkable experiment on the electrization of mercury, which I have very lately made. A few globules of mercury are placed in a vessel containing common pump water; or any water that contains a small quantity of saline impregnation; wires from a battery of 1000 double plates, not very strongly charged, are introduced into the vessel opposite to each other, so as to reach the bottom; as soon as the circle is completed, the mercury will be violently agitated, each globule will become elongated towards the positive pole, but will retain its circular outline in the part opposite to the negative pole; oxide will be given off from this part, which is positive, but no hydrogen from the part which is negative, and the oxide will pass in a rapid current from the positive towards the negative pole. As long as no hydrogen is given off, the globule is in continued agitation, and a stream of oxide flows with great rapidity from the positive to the negative surfaces; and the negative surfaces of the mercury approach rapidly towards the positive, which are at rest; if the conducting power of the water is exalted by the addition of more of the saline impregnation, or if the charge of the battery be increased, hydrogen will be given off from the negative poles; and the instant this happens the globules become {126} stationary; as if the same power which gave motion to the mercury was neutralized by, or employed in, the evolution of the hydrogen. There are many other remarkable phenomena connected with the operation of electricity on mercury, in contact with water; which may be urged in favour of the idea, that chemical and electrical attraction depend upon the same cause, and which will possibly lead to new views respecting the elements of matter; but the consideration of them properly belongs to a more advanced division of this work.

  38. The illustrious inventor of the new electrical apparatus, has given it the name of the electromotive apparatus, and has founded his theory of its operation upon the Franklinian idea of an electrical fluid, for which certain bodies have stronger attractions than others: and he conceives, that in his pile the upper plate of zinc attracts electricity from the copper, the copper from the water, the water again from the next plate of zinc, the next plate of zinc from the next plate of copper, and so on.

    This hypothesis applies very happily to most of the phenomena of the action of the insulated pile, and the pile connected by either of its extremities with the ground; but does not explain with the same facility, the powers of the apparatus connected in a circle, in which each plate of zinc must be supposed to have the same quantity of electricity as each plate of copper; for it can only receive as much as the copper can give, unless indeed the phenomena of the circular apparatus be considered as depending upon the constant and rapid circulation of the natural quantity of electricity, in the different series; which requires the proof of a constant power in a substance to attract electricity from {127} one body, at the same time that it is giving it off, to an other.

  39. Whatever may be the happiest approximation to the true theory of the Voltaic instrument, it can scarcely be doubted that the electrical organs of certain animals depend upon similar arrangements of exciting bodies. The shock of the Gymnotus Electricus, and the Torpedo, resemble the Voltaic shock: and the power resides in organs which consist of a number of similar alternations of different substances. The effects are analogous to those which a Voltaic apparatus of small surface, consisting of very numerous but not very powerful series, would produce. It has been conceived that other phenomena of living action may be connected with the operation of weak electrical powers; such as secretion; and some ingenious hints on this subject have been advanced by Dr. Wollaston and Sir Everard Home, and some experiments relating to the subject instituted by Mr. Brande. Such inquiries are worthy of further pursuit, as they may tend to elucidate some important functions of the animal economy; but they must not be confounded with certain vague speculations, that have been advanced by some authors, on the general dependence of nervous or sensitive action, and muscular or irritable action, upon electricity; such speculations are mere associations of words derived from known phenomena, and applied illogically to unknown things. The laws of dead and living nature appear to be perfectly distinct: material powers are made subservient to the purposes of life, and the elements of matter are newly arranged in living organs; but they are merely the instruments of a superior principle.

    As electrical changes are almost constantly taking {128} place in the atmosphere, and as the different substances composing the exterior of the globe, bear different electrical relations to each other, it is very probable that many of the chemical changes taking place on the surface, are influenced by the action of weak electrical powers: such as the decomposition of the surfaces of rocks, the modifications of soils, the formation of acid, and development of alkaline compounds; and the mutual agencies of the elements in the earth, the sea, and the atmosphere, may be assisted or modified by the circumstances of general electrical action.

  40. With regard to the great speculative questions, whether the electrical phenomena depend upon one fluid, in excess in the bodies positively electrified, and in deficiency in the bodies negatively electrified, or upon two different fluids, capable by their combination of producing heat and light, or whether they may be particular exertions of the general attractive powers of matter, it is perhaps impossible to decide in the present imperfect state of our knowledge. The application of electricity as an instrument of chemical decomposition, and the study of its effects, may be carried on independent of any hypothetical ideas concerning the origin of the phenomena; and these ideas are dangerous only when they are confounded with facts. Some modern writers have asserted the existence of an electrical fluid with as much confidence as they would assert the existence of water, and have even attempted to shew that it is composed of several other elements; but it is impossible in sound philosophy to adopt such hasty generalizations; Franklin, Cavendish, Epinus, and Volta, the illustrious advocates for the idea of a single electrical fluid, have advanced it only as hypothetical, as accounting in a happy way for most of the {129} phenomena; and none of the facts that have been brought forward in favour of the actual existence either of one or two fluids, can be considered as conclusive.

    From a very ingeniously contrived experiment of Mr. Cuthbertson, it appears that when a stream of electrical sparks is passed through the flame of a candle between two electrified surfaces, the surface which is negative is most heated; and it has been argued that a current must pass from the positive surface to the negative.

    But it is more probable, that this phenomenon depends upon the positive unipolar quality of the flame of wax or tallow referred to above; for supposing this flame to become positive, which would seem to be the case, it must be attracted by the negative, and not by the positive surface; and this view is confirmed by an experiment I made on an arch of flame between the two poles of the great Voltaic apparatus of 2000 plates. Platina melted with more facility in the arch at the positive than at the negative extremity, and this arch was common air intensely ignited, through which the electricity was discharged; and if any mechanical current existed from the positive pole to the negative, the maximum of heat must have been produced at the negative. When a wire of platina was made positive, and brought in contact with charcoal rendered negative, it became ignited much sooner, and fused into larger globules, than when made negative, and brought in contact with the charcoal rendered positive; and that the effect did not depend upon the greater heat of the charcoal, appears from the circumstances, that similar phenomena occurred when the experiment was made by contact with mercury. But when an imperfectly conducting fluid, such as sulphuric acid, was used, the result was reversed. The wire being negatively {130} electrified, and the acid positively, the point in contact with the surface of the acid instantly became white hot; in the opposite case a spark of blue light only was produced.

    The different appearance of the light on points positively and negatively electrified, has been urged in favour of the idea of a fluid proceeding from the positive to the negative surface. This phenomenon occurs as well in the Voltaic, as in the common discharge: for when the arch of flame passes between two points of charcoal, a vivid spot of white light is always perceived on the negative point, and rays seem to diverge from the positive point. The effect of the difference of the appearance of differently electrified points, I find, does not depend upon the nature of the elastic medium, for it takes place in hydrogen, carbonic acid, and chlorine, though it is less distinct in the heavier gases, probably from their being worse conductors; but the affections of light in passing from different parts of the circuit, can with no more propriety be urged in favour of a specific fluid, than the chemical changes produced by the different poles.

    When folds of paper are perforated by a discharge from an electrical jar, there is a burr on both sides, which may be urged as an argument against any fluid passing through; for it could penetrate in one direction only, and the experiment is favourable to the idea that electricity is an exhibition of attractive powers acting in peculiar combinations, for the substance of the paper, which was negative, may be conceived violently attracted to the positive surface, and the part which was positive, to the negative, at the moment the discharge takes place.

    It will be useless to pursue any further this recondite {131} part of the subject; whatever view is taken, active powers must be supposed to be bestowed upon species of matter, and the impulse must be ultimately derived from the same source. In the universe nothing can be said to be automatic, as nothing can be said to be without design. An imperfect parallel may be found in human inventions; springs may move springs, and wheels, indexes; but the motion and the regulation must be derived from the artist; sounds may be produced by undulations in the air, undulations of the air by vibrations of musical strings; but the impulse and the melody must arise from the master.


    1. Plate II. fig. 8.

    2. Plate II. fig. 9.

    3. Plate II. fig. 10.

    4. Plate II. fig. 11.

    5. Plate III. fig. 12.

    6. Plate III. fig. 13.

    7. Plate III. fig. 14.

    8. The conclusions are drawn from experiments made by the electricity of the Voltaic apparatus.

    9. See Plate III. fig. 14, 15.

    10. Plate III. fig. 16.

    11. [For an account of this battery and its effects, vide Phil. Trans. for 1815.]

    12. Plate III. fig. 17.

    13. Plate IV. fig. 18.

    14. Plate IV. fig. 19.