If two pieces of metal, the one of zinc, and the other of silver, or the one of zinc and the other of copper, or, what answers the purpose equally well, a penny piece and a half crown piece, be so placed that the one shall touch the upper surface of the tongue, and the other shall touch its under surface, while the edges project over the point; as often as the edges of the metals in this situation are brought into contact, a peculiar sensation is produced in the tongue; there is something like a slight shock of electricity, and there is perceived at the same time an austere, affranging, or metallic taste.

If a bit of tin-foil be placed on one of the eyes, and a bit of copper held between the teeth or touching the tongue, and a communication be formed by means of a wire between the piece of metal on the eye and that on the tongue, a flash of light is seen, and this is produced as often as the communication is completed. But, in the above experiments, if metals of the same kind be employed, no perceptible effect whatever is produced.

If a pile composed of 50 or 60 pairs of plates of zinc and silver, or zinc and copper, be arranged in a regular series, with pieces of cloth moistened in a solution of common salt placed between each pair; and if one hand previously moistened with water touch the lower pair, and the other hand, also moistened, touch the upper pair of plates, the moment the communication between the bottom and top of the pile is completed, a smart shock is felt; and if 50 or 60 pairs of plates of copper and zinc be arranged in a trough as will be afterwards described, and the spaces between the pairs be filled with water, to which about \( \frac{1}{2} \) of pretty strong nitric acid has been added, a similar shock is perceived, when the hands wetted with water touch the plates at the extremities of the trough. If a communication by means of wires and two pieces of well-prepared charcoal be made between the extremities of the trough, a very brilliant combustion is excited every time the two pieces of charcoal are brought into contact. By placing tinfoil, gold leaf, white or yellow Dutch metal or brass leaf, on a wire connected with one end of the trough, and touching the metallic leaves with a plate of copper or zinc connected with a wire from the other end of the trough, a rapid and brilliant deflagration is exhibited every time that the communication is effected.

The phenomena which are thus produced have received the name of Galvanism, from the name of Galvani, who first observed and published an account of galvanism. Some of them, and the power by which these effects are produced has been denominated the galvanic power or fluid. From its effects on animals being similar to those of the electrical fluid, it was at first called animal electricity; but then the knowledge of galvanism was limited to its effects on animals, and it was supposed to depend on something peculiar to animal life.

In the following treatise we propose to give a view of the progress and present state of galvanism; and for this purpose we shall arrange the whole under two great divisions. Under the first, we shall consider the phenomena of galvanism, or detail the facts which have been ascertained with regard to this power. The second part will be occupied in the history, progress, and theories, which have been held with regard to the nature of galvanism.

PART I. OF THE PHENOMENA OF GALVANISM.

In treating of the phenomena of galvanism, its progressive history suggests an arrangement sufficiently convenient for taking a view of the effects of the galvanic fluid. Those effects which are to be regarded as strictly chemical, were altogether unknown, till after its application to animals, and a great mass of facts relative to its effects on animal life had been accumulated. We may therefore first consider the effects produced on animals by the operation of the galvanic fluid, and in the next place those effects which are strictly chemical.

But before we proceed to this, it is necessary that the nature and construction of the apparatus, by which these effects were produced, should be understood. These topics, therefore, shall be the subjects of the three following chapters. In the first we shall treat of the construction of the apparatus by which the phenomena of galvanism are produced; the second will be employed in considering the effects of the galvanic fluid on animals; and the third will comprehend a view of its chemical effects. On the first discovery of galvanism, the apparatus for exhibiting its effects was extremely simple. It consisted merely of two pieces of different metals, such as has been described above, by which a peculiar sensation is produced on the tongue. This, it has been stated, is effected by means of a piece of zinc and a piece of copper, the one placed on the upper surface, and the other on the under surface of the tongue, while the projecting edges are brought into contact. In the same way, and with such an apparatus, a great variety of experiments, especially in cold blooded animals, were exhibited, when the knowledge of this remarkable power was first announced and investigated.

For the purpose of exhibiting some of the simpler effects of galvanism, we shall describe the following apparatus, which is of very easy construction. AB, fig. 1, is an iron wire, sharp at the point A, and fixed in the wooden stand C. If a frog prepared in the way which we shall immediately describe, be fixed on the point of the wire at A, and a gold or a silver wire (a silver tea spoon will answer the purpose) be brought into contact with the side of the wire, as at the point D; and while in contact with the wire at D, it is brought into contact with the feet of the frog at E or F, the effect of the galvanic power will be immediately perceived. The limbs of the animal will be strongly convulsed, and will exhibit as much motion by the contraction of the muscles as if it were alive, and in full vigour. But if an iron wire, similar to AB, were substituted for the gold or silver wire, no such effect would be produced.

Frogs, as they are most easily found, and as they are, perhaps, more convenient in other respects, have been oftenest the subject of galvanic experiments than any other animal. To prepare them for these experiments, various methods have been followed. Some physiologists propose to remove only the integuments, and lay bare the muscles, while others open the cavities of the thorax and abdomen, remove the viscera which are contained in these cavities, and bring into view the nerves and muscles which are there distributed. Some again, after the above previous preparation, separate all the parts between the origin of the nerve and its insertion in the muscle, so that the latter may be attached by means of the nerves only, to the trunk of the body; while others, after a similar preparation, cut off the animal's head, that the effects produced by galvanism may not be confounded with the voluntary movements of the living animal. By another mode of preparation, each of the parts is separated from the body by dislocation, after laying bare the muscles and nerves.

But in general a frog is understood to be prepared when it is divided with a pair of scissors into two portions, through the middle of the body and spine. The viscera are then removed, as well as the integuments of the inferior extremities. As the sciatic nerves of this animal rise very high upon the spine, they are distinctly seen after this treatment. When it is intended, as in some experiments, to arm the nerves, as it is called, a pair of sharp-pointed scissors is introduced beneath them, and the spine is cut through, but without dividing the nerves. A portion of the inferior part of the spine is afterwards to be separated, that room may be left for covering the nerves with a bit of tin-foil. This is what is usually understood by arming or coating the nerves. In some experiments it will be found more convenient to separate the lower extremities from the trunk, and to employ the crural nerve.

Phenomena similar to the above may be produced by placing a frog A prepared in the way described above, on a plate of zinc B, fig. 2, and on a plate of silver or copper C. If the communication between the plates A and B be completed by means of the conductor D, the muscles of the frog are immediately thrown into strong convulsions, and these motions are renewed as often as the contact is made by the conducting wire and the two metals.

The apparatus we have now described affords an example of the simplest galvanic combination, or what vanice combinations are usually denominated a single galvanic combination, binations. Here it may be observed, that this combination must consist of three different conductors. The conductors of electricity have been arranged into two principal classes: to the first belong the metallic substances and charcoal, which have been otherwise called dry and perfect conductors; the second class consists of the imperfect conductors, which are water and other oxidizing fluids, and the substances which contain these fluids. But although the conductors of electricity, for the sake of convenience, are thus arranged, they differ from each other in their conducting power, and this difference is greatest among the substances comprehended under the second class. Now, if the three conductors of the galvanic fluid be all of the first class, or all of the second, the effect is scarcely perceptible. An active, simple galvanic combination, then, must consist of three different bodies, one conductor must belong to one class, and two different conductors must be taken from the other class. In fig. 3 and 4, are exhibited examples of active simple galvanic combinations. In fig. 2, the letters AB mark the bodies belonging to the first class or perfect conductors; and a marks the bodies belonging to the second class, or imperfect conductors; and in fig. 3, A marks one body belonging to the first class, and ab two bodies belonging to the second class, or the imperfect conductors. Of the three bodies forming a galvanic combination, if two of them belong to the first class, and one to the second, this combination is said to be of the first order; but if one of the three bodies only belong to the first class, and two to the second, the combination is said to be of the second order. Fig. 3 is a galvanic combination of the first order, and fig. 4 is one of the second. This may be further illustrated by examining figs. 5, 6, 7, which consist of two bodies only, and therefore are not active combinations; and also by examining fig. 8 and 9, which consist of three bodies, but two of them are of the same kind, and therefore act as a single body. In the last five figures, the capital letters denote the bodies belonging to the first class, and the small letters those belonging to the second.

In the single active galvanic combination, or the simple galvanic circle, the two bodies of one class must be in contact with each other in one or more points, while, at the same time, they are connected together at other points. Part I.

Construction of Apparatus.

Points with the body belonging to the other clas. Thus, if a prepared frog is convulsed by the contact of the same piece of metal in two different places, the fluids of those parts which must be somewhat different from each other, are the two conductors of the second clas, and the metal constitutes the third body for the conductor of the first clas. But if two metals be employed, the fluids of the prepared animal differing little from each other, are to be considered as one body of the second clas.

Here it may be necessary to anticipate a little, by observing, that in a simple galvanic circle, the conductor or conductors of one clas must have some chemical action upon the other conductor or conductors, otherwise no galvanic action would be produced, or at least a very feeble one, from the combination of three bodies. This galvanic action, too, seems to be in proportion to the degree of chemical action, from which some have supposed, that this chemical agency is the primary cause of the phenomena.

It is found that the most active galvanic combinations, or galvanic circles belonging to the first order, are those in which two solids possessing different degrees of oxidability, are combined with a fluid which is capable of oxidating at least one of the solids. Gold, silver, and water, do not form an active galvanic combination, because water is incapable of oxidating either of these metals; but if a small quantity of nitric acid, or any other fluid which may be decomposed by the silver, be mixed with water, an active galvanic circle may thus be formed.

If zinc, silver, and water, or zinc, copper, and water, be combined together, an active galvanic circle is formed, and the water will be found to oxidate the zinc, if it hold any portion of atmospheric air in solution, and still more so, if it contain oxygen. But the combination of the same substances forms a much more powerful galvanic circle, if a little nitric acid be added to the water, because then the fluid has a strong action on the zinc, and oxidates it.

Galvanic combinations belonging to the second order are found to be most powerful, when two conductors of the second clas have different chemical actions on the conductors of the first clas, while at the same time they have an action upon each other. As an example of this, copper, silver, or lead, combined with a solution of an alkaline sulphuret, and diluted nitric acid, constitute a very active galvanic circle.

The following is a list of galvanic circles of the first order, composed of two conductors of the first clas, and one of the second.

Zinc with gold, or charcoal, or silver, or copper, or tin, or iron, or mercury; and water containing a small quantity of any of the mineral acids.

Iron, with gold, or charcoal, or silver, or copper, or tin, and a weak solution of any of the mineral acids, as above.

Tin, with gold, or silver, or charcoal, and a weak solution of any of the mineral acids, as above.

Lead, with gold, or silver, and a weak acid solution, as above.

Any of the above metallic combinations, and common water, viz. water containing atmospheric air, or especially water containing oxygen air.

Copper, with gold, or silver, and a solution of nitrate of silver and mercury; or the nitric acid; or the acetic acid.

Silver, with gold, and the nitric acid.

The following is a list of galvanic circles of the second order, consisting of one conductor of the first clas, and two of the second.

Charcoal, or Copper, or Silver, or Lead, or Tin, or Iron, or Zinc,

with water, or with a solution of any hydrogenated alkaline sulphurets, capable of acting on the first three metals only;

and a solution of nitrous acid, or oxygenated muriatic acid, &c. capable of acting upon all the metals.

But the effects of the galvanic fluid are extremely feeble, when they are limited to the operation of even the most powerful simple combinations. In the progress of the knowledge of galvanism it was soon found, that these effects might be combined and increased to almost any degree. This is done by connecting together a number of active simple combinations, which, it is to be observed, must be so disposed that they may not counteract each other. A number of simple combinations thus connected together have received the name of batteries; and these batteries are said to belong to the first or second order, according as the simple combinations of which they are formed, are composed of substances of the first or second order of conducting powers. Thus, for example, if a plate of zinc be laid upon a plate of copper, and a piece of moistened card or leather be laid upon the zinc, and a similar arrangement of three other pieces be laid upon the first, and any number of combinations of the same kind be continued, taking care that they are always arranged in the same order, the whole will form a battery of the first order. But if a plate of copper be connected with a piece of cloth moistened with water, and the latter with another piece of cloth, moistened with a solution of sulphuret of potash, and this be connected with another piece of copper, repeating the same series to any convenient number, a battery of the second order will be formed of the whole.

Batteries of the second order have been arranged by Mr Davy into the three following classes. 1. The most feeble battery is composed, when single metallic plates are so arranged that two of their surfaces or opposite extremities are in contact with different fluids, the one of which is capable, and the other is incapable, of oxidating the metal, a regular series of such combinations are formed. 2. When single combinations or elements of the series are each composed of a single plate of a metallic substance, capable of acting upon sulphurated hydrogen, or upon sulphurets dissolved in water, accompanied with portions of a solution of sulphuret of potash on one side, and water on the other. 3. The third clas is the most powerful, being formed when metallic substances oxidable in acids, and capable of acting on solutions of sulphurets, are connected as plates with oxidating fluids, and solutions of sulphuret of potash, and so arranged that the opposite sides of every plate may undergo different chemical changes, the mode of alternation being regular.

The first attempt to increase the effects of the galvanic fluid, by combining a series of simple circles, was made by Volta; to this he gave the name couronne de taffes. The following is the construction and mode of applying this apparatus.

Take any number of cups or glass tumblers A, B, C, D, E, fig. 10. Fill them about three fourths full with any of the saline solutions, which will be afterwards described, as that of common salt or sal ammoniac in water. To one extremity of a bent brass wire folder a plate of zinc of about two inches in diameter, and to the other extremity of the same wire, folder in the same manner a plate of copper of the same diameter. These connecting wires are represented in the figure by the letters a, a, a; and the plates of the different metals are marked with the letters Z and C, viz., zinc and copper. In arranging the plates in the vessels, it ought to be observed, that a plate of zinc and a plate of copper belonging to different wires, must be in the same vessel, and never two plates of the same kind. Thus in the first vessel A, there is a plate of copper; in the second B, connected by the same wire, there is a plate of zinc; in the same vessel B, there is also a plate of copper, which is connected by means of another wire to a plate of zinc in the third vessel C. The same order and arrangement are to be observed to whatever number of plates and vessels the series may extend.

Suppose now that the apparatus has been arranged in the way described above, and the vessels have been filled with a solution of common salt in water; if the number of vessels be not less than ten or twelve, a slight shock will be felt by immersing one hand in the vessel, at one extremity of the series, and the other hand in the vessel at the other extremity; as for instance, by putting the fingers of one hand in the vessel A, fig. 10, and suddenly plunging the fingers of the other hand in the vessel E. The shock will perhaps be more sensibly felt by previously wetting the palms of both hands, and taking a silver or pewter spoon in each hand, immerse the handle of the one into the vessel A, and the handle of the other into the vessel E.

The strength of this apparatus depends on the number of series of plates and vessels employed. But it is obvious that this series from the nature of the apparatus could not be greatly extended so as to afford any great increase of power. This occurred very early to the ingenious discoverer, as an insurmountable objection to the use of this apparatus. The views of this philosopher in investigating the nature of galvanism, seem at this time to have been chiefly directed to the discovery of instruments or apparatus, by means of which he might be enabled to augment its power. In the prosecution of his inquiries, therefore, he contrived another apparatus, which was afterwards known by the name of the galvanic pile, and sometimes, but more rarely by that of the voltaic pile or pile of Volta, from the name of the discoverer. This apparatus is constructed in the following manner.

A pile of moderate strength may be constructed of 60 pairs of plates of zinc and copper, each plate being about two inches diameter; it may be constructed also with similar plates of zinc and silver, or of almost any two other dissimilar metals. Such piles have been very conveniently constructed, with half crown pieces and plates of zinc of the same size, or more conveniently with penny pieces and plates of zinc of the same diameter. But of whatever different metals this kind of apparatus is to be constructed, the same order of arrangement is to be observed throughout the whole series.

Suppose the metals to be employed in the construction of the pile are zinc and copper, (and these from views of economy have been most frequently employed), an equal number of pieces of cloth, pasteboard, or leather, of the same diameter with the metallic plates, is to be prepared. The use of these pieces of cloth is to retain the moisture, by means of which the communication between the plates is formed, and the galvanic combinations are completed; and in proportion to the length of time during which the pieces of cloth or other substances retain the fluid which they have absorbed, the operation of the pile continues. The pile is formed by placing a pair of plates, one of zinc, and one of copper, upon a stand, the one immediately above the other. Upon this pair of plates is then placed a piece of cloth which has been soaked in some saline solution, as that of common salt, or sal ammoniac. Upon this piece of cloth is placed another pair of plates, arranged in the same order as the first pair. It makes no difference which of the metals is placed first in the series, only it is necessary to take care that the same order be preserved throughout the whole pile. If the series, for instance, begins with copper, it runs in the following order: copper, zinc, cloth; copper, zinc, cloth, &c., to whatever number of pairs of plates and pieces of cloth the series may extend.

But if the number of series amount to 60 pairs, it will be necessary to have rods to confine the pairs of plates, and to retain them in a perpendicular column; for without this the weight at top would be so considerable, that the least inclination to one side (and this could not well be avoided) would derange the whole apparatus. The rods which have been employed for this purpose have been sometimes made of glass, and sometimes of wood. When wood is used, it should be pretty dry, or baked, by which means its conducting power is either greatly diminished or entirely destroyed.

The pile being constructed in this manner, its effects may be observed, by applying the fingers of one hand moistened with water to the lowest pair of plates, and then touching with the fingers of the other hand moistened in the same manner, the upper pair of plates, thus completing the communication between the extremities of the pile. Every time that this communication is made, a sensation is experienced, similar to a slight shock of electricity. The intensity of this shock is in proportion to the number of the pairs of plates, the nature of the fluid employed, and the care with which the pile has been erected, or the time that it has continued in action. With a pile of 60 pairs of plates, the shock will be perceptible through the fingers, or the whole of the hand, and in some persons, when it is in full activity, it will extend as high as the elbows.

In making experiments with this kind of apparatus, it will be found that 50 or 60 pairs of plates will be a sufficient number to be erected in one pile; but to increase the power of the galvanic fluid, a number of piles may be connected together. This may be done in two ways; either by combining the separate action of the different piles employed; as, for instance, if three piles are constructed, let the pairs of plates be arranged in each exactly in the same way, and let the conducting substances, as wires, pass from the top and bottom of each to one common conductor. In this case we have the action of three different currents of the galvanic fluid; but whatever number of piles may be employed, their mutual action may be so combined, that the whole effect may be produced by one single current. Suppose the metallic plates of one pile are arranged in the following order; copper, zinc, cloth; copper, zinc, cloth, &c., then the plates of the second must be arranged in a different order, namely, zinc, copper, cloth; zinc, copper, cloth, &c., and the plates of the third in the same way as the first, viz., copper, zinc, cloth; copper, zinc, cloth, &c. The three piles being thus arranged, let a metallic conductor, as a slip of copper or zinc, be placed between the tops of the first and second pile, and a similar conductor be placed between the bottoms of the second and third piles; and when they are thus connected together, let the fingers of one hand moistened, be placed at the lowest pair of plates of the first pile, and the fingers of the other hand, also moistened, be brought in contact with the upper pair of plates of the third, a violent shock will be felt. The shock will be the same as if the whole number of pairs of plates of which the three piles are composed were formed into a single pile; for the same order of arrangement being observed from the bottom of the first pile to the top, and from the top of the second pile to the bottom, and again from the bottom of the third pile to the top, the current passes uninterruptedly through the whole series, as if it were uniformly arranged in one pile.

The effects of this apparatus may be farther observed in its chemical action. If the circle is completed, or the communication between the extremities of the apparatus by means of charcoal be formed, a spark is produced. This is done by attaching a piece of well prepared charcoal to a wire which communicates with one extremity of the apparatus, and another similar piece of charcoal to another wire communicating with the other extremity; if the two pieces of charcoal be brought into contact, thus completing the circle, a spark will be observed, and this may be repeated as long as the activity of the pile continues. The chemical effects of such an apparatus are also exhibited in the decomposition of water. The apparatus for effecting this decomposition, and the method of using it, will be afterwards described.

But it was soon found that the effects of this pile, although when it is first erected it possesses considerable energy, in a very short time it becomes extremely feeble, and at last altogether imperceptible. This is owing to the pieces of cloth or other substance which is interposed between the pairs of plates being deprived of their moisture, either by evaporation, or by being squeezed out, from the weight of the plates. The latter effect, it is obvious, must be in proportion to the height, and consequently the incumbent pressure of the upper on the lower part of the pile; and besides this, the liquid as it oozes out, trickles down the sides of the pile, so that the different pairs of plates are less perfectly insulated than they otherwise ought to be, to produce the full effect.

Various contrivances were thought of to obviate these inconveniences, and the first which was proposed was announced by the ingenious inventor of the pile himself. Volta inclosed his piles, after they were erected, with wax or pitch. By this contrivance, which he put in practice on two columns or piles, each consisting of 20 plates, he succeeded so far in preventing the inconveniences alluded to above, that their effects continued nearly undiminished for several weeks. By other contrivances the plates and pieces of cloth or pasteboard were arranged horizontally, by which means some of the inconveniences of the upright column were avoided; among these the unequal pressure was removed, but still it was found that the evaporation continued, so that it was not long before its operation began to diminish, and at last to be entirely interrupted.

As it was found that the chemical effects of the pile were greatly increased by employing plates of a larger surface, even when the number was greatly diminished, piles were erected both on the continent and in Britain, with plates from 10 to 14 inches square. Twelve or fourteen pairs of plates of the above size, arranged in the same way as those which have been already described, produced very considerable chemical effects, such as, burning phosphorus, setting fire to gunpowder, and deflagrating gold and silver leaf. The pieces of thick cloth or pasteboard moistened with water, to which a certain proportion of nitric acid was added, were usually employed in the construction of this pile; but it is unnecessary to mention that it was attended with similar inconveniences to those which accompanied the smaller pile. These inconveniences probably led to another and more effectual contrivance for exhibiting the effects of galvanism. But before we give an account of these, we shall farther illustrate the nature and construction of the pile with an explanation of fig. 11, and 12.

Fig. 11, is a representation of a pile composed of copper, zinc, and pieces of pasteboard, locked in some saline solution. The pile is erected on the stand A, and the different parts of which it is composed are retained in their perpendicular position by means of the three rods made of glass or baked wood, b, b, b. The pieces of metal are marked e, z, and the pasteboard p, in the order in which they are placed. The pile being erected from bottom to top in the same order, let a piece of wire e be inserted under the lower pair of plates, and let another wire f be kept in contact with the upper surface of the upper pair of plates; the different parts being thus disposed, if the fingers of one hand moistened be brought in contact with the wire e, and the fingers of the other hand also moistened, be brought in contact with the wire f, a shock will be felt, and thus it will be found that the energy of the pile will continue till the moisture of the pieces of pasteboard has evaporated, or the peculiar change which takes place on one of the metals during its action, and which will be taken notice of afterwards, has been effected.

Fig. 12, exhibits a view of a combination of three piles, A, B, C. In the column A the arrangement is copper, zinc, pasteboard; copper, zinc, pasteboard, &c. In the column A, this arrangement is reversed, from the bottom of the column, which is zinc, copper, pasteboard; zinc, copper, pasteboard, &c.; because it must be the same as if the column B were placed upon the top of the column A, the points A and B being brought Construction of Apparatus.

The third column C is arranged in the same manner as the column A, viz., copper, zinc, pasteboard; copper, zinc, pasteboard, &c. Thus, then, the three columns are so arranged, that the different series succeed each other from the bottom of column A to the top, from the top of column B to the bottom, and from the bottom of column C to the top, as if the whole had been disposed in one column A. A communication is then formed between the top of the column A and the top of column B, by a metallic conductor D, and between the bottom of column B, and the bottom of column C, by means of the metallic conductor E. If then the fingers of one hand moistened are brought into contact with the wire F, which communicates with the bottom of column A, and the fingers of the other hand also moistened are brought into contact with the wire G, a smart shock will be felt, from the combined action of the three columns or piles.

The inconveniences of the pile, as we have already hinted, were soon felt by those who were eager in the investigation of galvanism, and who wished their experiments to continue with undiminished energy, that they might be enabled to ascertain with precision the new and curious facts which presented themselves. These inconveniences, it is very probable, suggested the improvements in galvanic apparatus which we are now to describe.

By the invention of the trough, for which we are indebted to the ingenuity of Mr Cruikshank of Woolwich, the progress of galvanism became rapid and brilliant; for by this means philosophers were enabled not only to give a longer duration to their experiments, but to command a degree of energy in the galvanic fluid, which, before the discovery of this apparatus, was not even suspected. This apparatus, we believe, is now almost universally employed for galvanic experiments. We shall therefore give a more detailed account of the method of constructing and using it.

Troughs with plates of various sizes have been constructed, from 2 to 6, 8, and even 14 inches square; but as an example, we shall suppose the following trough to be constructed with plates of about four inches square. A wooden trough A.B, fig. 13, is to be made of baked mahogany; the length may be about 30 inches, and, as we shall suppose the number of pairs of plates to be 50, an equal number of grooves is to be cut on the sides and bottom in the inside of the trough. These grooves are to be cut at equal distances from each other, and the width of each groove is to be such, as to correspond nearly to the thickness of each pair of plates, so that the latter may slip easily into the grooves.

The plates are like those which have been already described in the construction of the pile made of zinc and copper. No difficulty has ever occurred in procuring plates of copper for this purpose; because all that is necessary is to cut them out of sheets of copper of the requisite thickness to any size that is wanted. But the case has been very different with regard to plates of zinc, especially where large plates were required. Attempts have been made to cast them in moulds of sand, such as are used for casting different utensils of other metals; but these attempts, it would appear, have been generally unsuccessful. The method which it is said has succeeded best in forming plates of any considerable size is the following. The zinc of which the plates are to be composed is to be melted in a narrow-mouthed vessel, so that a small surface of fused metal may be exposed. The reason of this is, that the metal when it reaches a certain temperature is very rapidly oxidized in consequence of the strong affinity between this metal and oxygen. The metal in this state is converted into a fine flocculent substance, known by the name of flowers of zinc. This change therefore, as it is attended with a loss of the metal, is to be as much as possible avoided. A mould of stone of the dimensions of the proposed plates (in this case four inches), and about one-eighth of an inch in thickness, is to be prepared; but one formed of brass is found to answer the purpose still better. When the metal is in perfect fusion, the plates should be cast as quickly as possible, because, as the metal cools rapidly, cavities and imperfections would appear on the surface from its flowing unequally.

The plates of zinc being prepared, plates of copper which need not exceed one-tenth of the thickness of the zinc plates are to be cut out of a sheet of copper to the requisite dimensions, viz., corresponding to the size of the zinc plates. The copper plates must be reduced by hammering to a smooth and plane surface that they may apply exactly to the surface of the zinc plates, and be in contact in as many points as possible.

The plates being thus prepared are to be soldered together; but it must be observed that it is not to be the plates through the whole extent of the plate. It is found quite sufficient to solder them about one-fourth of an inch from the edges. The folder employed for this purpose is a soft folder; and great precaution must be observed that the union at the edges be so close as to prevent any of the liquid with which the cells in the trough are to be filled from entering between the plates; for otherwise the power of its action would be greatly interrupted or perhaps entirely destroyed.

The operation of soldering was performed with considerable difficulty by many workmen; at least, it was found that in many cases the plates were either not in contact when the dimensions were large, or the joints were not perfectly secure. We are not certain in what way this operation is generally performed, but we know that this difficulty has been obviated by the following contrivance. The inside angles on the edges of the plates, that is, on the sides of the plates which are to be united together, are filed away, so that, when the plates are brought into close contact, a triangular groove all round the edge of the pair of plates remains. This groove is filled with solder, and the operation is conducted in the usual way. Plates soldered according to this contrivance have been found to answer the purpose extremely well. But this inconvenience is now rendered less embarrassing since the discovery of rendering zinc malleable and flexible was made, for plates of zinc of this description are of a much more equal thickness, are thinner and smoother, so that the copper can be brought into a closer contact. The plates which have been prepared of malleable zinc have the copper folded over the edge of the zinc plates, and in this way they are secured without difficulty, by soldering.

In whatever way the pairs of plates are to be secured, so that they may remain in close contact, they are afterwards wards to be fixed in the grooves of the box prepared for their reception; and here it is to be observed that each individual pair of plates is to be completely insulated. This is done by means of a particular kind of cement, the use of which is not only to retain the pairs of plates in their places, and to render their insulation complete, but also to defend the wood of the box against the action of the fluid which is employed to fill the cells of the trough.

The cement which is employed for this purpose is composed of rosin, bees-wax, and fine brick dust, or powdered red ochre. Different proportions of these substances, it would appear, have been recommended in the construction of galvanic troughs. According to some, five parts of rosin, four of bees-wax, and two of powdered red ochre, are found to answer this purpose extremely well. The rosin and bees-wax are melted together, that they may be completely incorporated, and the red ochre is afterwards added. According to others, four ounces of bees-wax, eight ounces of rosin, and about an ounce of fine brick dust, melted together in the same way, are also found to answer the same purpose equally well. With this cement the pairs of plates are secured in the grooves, and the intervening spaces on the inside of the bottom and sides of the trough are also covered with it, to defend the wood from the action of the fluid. It is scarcely necessary to observe, that the plates are to be arranged in the same way throughout the trough as the first pair; that is, if the copper side of the first pair of plates be towards the end of the trough at B, all the other pairs are to be so arranged as to have their copper sides towards the same point B, and the zinc sides towards the other end of the trough A. The plates being arranged in this way, the end of the trough B is called the copper end of the trough or battery, and the end A is called the zinc end.

Superior advantages are derived from arranging the plates in this way, to that of constructing them in the method described for the pile; for in this way the fluid can be applied more equally and with greater facility; the apparatus is more convenient for performing experiments; its action continues for a considerably longer time, and there is little or no trouble in cleaning the plates after the operation. It is otherwise with the pile, for, after it has been once used, the surface of the zinc plates is so much oxidated, that before they can be employed again, they must be scoured or filed, which, it is obvious, must be a troublesome and tedious process; but in the trough the oxidated surface of the plates is cleaned in every successive operation, the fluid which is employed dissolving the oxide which has collected on the surface of the zinc plates.

In treating of the construction and action of the pile, we have already observed that different saline solutions were employed, to moisten the pieces of cloth or pasteboard interposed between the pairs of plates. These solutions were muriate of soda or common salt, muriate of ammonia or sal ammoniac, and sometimes sulphate of potash. Similar solutions will answer the purpose of filling the cells of the trough, but these are found to be weaker than solutions of the acids; and, besides, as they are apt to crystallize on the plates, it becomes extremely troublesome to clean the trough. Acid solutions, therefore, which are more powerful, have been properly preferred; and the acid which seems to answer best, on different accounts, is the nitric; the proportion to be employed, it is obvious, must vary according to the strength of the acid. Of the common acid of the shops, one part with 16 of water will form a pretty active mixture; but when the acid is stronger, it may be necessary to add 20 parts of water. But this mixture is attended with the inconvenience of the evolution of nitrous gas, which, it is well known, is extremely disagreeable, and is injurious to respiration; and, on account of the high price of nitric acid, when a large quantity of this mixture is required, it becomes very expensive. Sulphuric acid mixed with water has also been employed for the same purpose, and it is found to answer very well. The use of this acid, however, is liable to many serious objections. Its action is too rapid; and, by its operation on the zinc, hydrogen gas is engendered in such quantity as to be inconvenient to the operator. So much heat is evolved during its action, that the cement which is used for securing the plates in the trough, is apt to be rendered soft and loosened. Muriatic acid also has been employed, and this is recommended by some as in different respects the most convenient. One part of muriatic acid and 16 of water form a mixture which answers the purpose extremely well. The action of this mixture is slow and uniform, and the quantity of hydrogen gas which is evolved is so small as to produce little inconvenience. The use of this acid is attended with another advantage, that the plates are kept uniformly clean.

Whatever mixture has been employed, unless the operation has been continued for a very long time, when it is emptied from the trough, it may be bottled up, and referred for future use; and if the most powerful action of the trough is not required, the same mixture may be employed several times. Here it may be worth while to notice, that the precaution of emptying the trough should be invariably observed, as soon as the experiments for which it was filled and prepared are finished; by this management there will be a considerable saving, both of the fluid and of the surface of the plates, which undergo oxidation. In filling the trough with the fluid, it should be observed that it does not rise higher than about \( \frac{1}{4} \) of an inch from the upper edge of the plates; and after the filling of the trough is completed, the upper edges of the plates, as well as the edges of the trough, should be carefully wiped dry, that there may be no communication between the fluid in the cells, but through the metallic substances.

A trough composed of 50 plates of three inches square, will be found suitable for a great variety of useful and entertaining experiments; but when it is found necessary to produce a more powerful action of the galvanic fluid, a greater number of pairs of plates, or the same number with a larger surface, according to the nature of the action required, must be employed. We have already observed, that several columns or piles may be so constructed as to have the full effect of their combined action, in the same way as if they formed a single pile. By similar management, different troughs or batteries may be so arranged as to combine together the effects of each, as if they constituted a single trough or battery. And all that is necessary to observe is, that to whatever extent the series may be carried, the surface of each of the plates must be opposed to the surface of a different plate; as, for instance, the zinc surface of one of the plates must be constantly opposite to the copper surface of the next plate in the series. The different troughs thus uniformly arranged, are to be connected together by means of metallic conductors. A slip of copper, for instance, about half the width of the trough, is inserted by its opposite extremities in the cells of the ends of two of the troughs.

When the plates are of very large size, their weight, with that of the quantity of fluid required to fill the cells, renders the trough very unmanageable. It is then necessary to fix it in a frame of sufficient strength, to support its weight by means of axles of brass or iron, fixed to the outside of the box. By this contrivance the fluid can be easily poured out into a proper vessel, placed under the trough.

We shall afterwards speak more particularly of the effects of plates of different extent of surface; here, however, it may be necessary to observe, that in combining together two or more troughs or batteries, to have the full effect of such a number of plates as may be employed, in proportion to the extent of their surfaces, the surface of the plates in each trough should be the same; otherwise, if troughs of different extent of surfaces be employed, the action of that trough which has the largest surface is diminished, and reduced to that of the action of the trough whose plates have the smallest extent of surface. This circumstance is necessary to be attended to, for, if it is overlooked in the construction or combination of different batteries, the effects will be so feeble as to produce disappointment without the cause being known.

In making experiments with the trough, the communication is to be formed between the two extremities, or the circle is to be completed in the same way as has been already directed in the management of the pile. For this purpose there is a projecting piece of wood fixed to the upper edge of each of the ends of the trough; this is perforated so as to admit a piece of wire which passes through to the fluid in the two last cells at the extremity of the trough. If then the wires are placed in this situation, and the moistened fingers of one hand touch the wire at one extremity, while the moistened fingers of the other hand are brought into contact with the wire at the other extremity of the trough, a shock will be felt; and in this way the circle is completed.

The other parts of the apparatus which are necessary to conduct experiments with a trough of this description, are so simple as scarcely to require any particular description. All that is wanted for deflagrating metals is to have a bent wire fixed at one extremity of the trough, and to have a polished plate of copper or zinc communicating with the other extremity of the trough by means of a flexible wire. The metal to be deflagrated is placed upon the bent wire, and the metallic plate is brought into contact with it.

The apparatus for the decomposition of water is the following. A glass tube, G, H, fig. 11, about three inches long, and ½ inch in diameter, is furnished with a tight cork at the upper end G, through which cork the wire i communicating with the upper part of the pile, passes. It may be also furnished with a cork at the other extremity H, but this must have grooves cut on its sides, to allow the water to escape from the tube. The wire K communicating with the bottom of the pile, passes through this cork; or without the cork at this extremity, if the tube is retained in its perpendicular position by any other contrivance, the wire K may be pulled within the tube. When this operation is to commence, the tube is to be filled with water, the cork at the upper extremity G being made air-tight, and then it is to be inverted, and the extremity H to be placed in a small cup or basin of water; after which the wire K being introduced, the circle is completed between the wires through the medium of the water in the tube, the decomposition of which will go on as long as the communication and the action of the pile are continued. This process will be observed by bubbles of air escaping from one of the wires, and rising to the top of the tube; or if the wires are of gold or of platina, bubbles of air will be seen passing from the extremity of both wires, and this air collecting at the top of the tube, forces out a quantity of water equal to the space which it occupies. The same experiment may be made by means of a still simpler apparatus. If the wires communicating with the extremities of the pile are introduced into a small glass phial filled with water, and inverted in a basin of water, the same process of decomposition will go on.

But an apparatus which is rather more complicated, but at the same time sufficiently convenient, is usually employed for this purpose. A small brass cup E, fig. 13, is supported by the wire F, which is fixed in the hole of the projecting piece of wood D, at one end of the trough; from the centre of the cup there arises a pair of brass pincers, which hold a piece of wire of gold or platina G. Over the pincers is placed a glass tube HI, which has at the upper extremity, I, a brass cap, to the inside of which is fixed another piece of wire of gold or platina. The two wires should be at a little distance from each other, as they appear in the figure. The tube is then filled with water, and is inverted over the pincers in the brass cup, which is also filled with water; and thus, by means of the water in the tube, a communication is formed between the two wires. A wire proceeding from the other extremity of the trough C, is connected with the top of the tube I, and, as soon as this communication is formed, the process of the decomposition of the water in the tube commences; for the galvanic circle, or the communication between the extremities of the trough or battery is completed. The gases, as they are disengaged from the wires in the tube, rise to the top, and the water which occupied the space now filled with air, is forced out into the cup. This process goes on as long as the communication continues, or till the surface of the water is lower than the extremity of the upper wire, when the communication is interrupted, and then the operation ceases.

With these observations we conclude what was intended to be said concerning the construction of galvanic apparatus. We shall notice what may be farther necessary to be explained, in the course of the detail which is to be given of the experiments in galvanism, or of the influence of the galvanic fluid on animals, as well as its chemical effects. We, therefore, now proceed, in the following chapter, to the consideration of some of these phenomena. It has been already observed, that the first effects of galvanism were exhibited on animals; and indeed it was supposed that these effects could only be exhibited by means of animals, and hence, from the coincidence which was observed with the properties of electricity already known, it was denominated animal electricity.

The first experiments which were made in investigating the nature and properties of the galvanic fluid, were chiefly performed on cold-blooded animals. It was indeed from observing its effects on them, as we shall find afterwards in tracing its history, that the discovery was first made. This discovery was made on the frog, and since that time the frog has been oftenest the subject of galvanic experiments than any other animal. From being found in great numbers, from being conveniently got, as well as from the irritability of the muscular fibre, as it is denominated by physiologists, continuing for a long time, it has perhaps become the devoted victim of these investigations.

We have already mentioned a simple experiment with a prepared frog, in which it forms the communication between two dissimilar metals. When the frog, as in fig. 1, is prepared, that is, skinned, and the lower extremities separated from the spine, and suspended on the iron wire AB, if the extremities of the frog be touched with a different metallic substance, such as gold or silver, while this metallic substance is in contact with the iron wire at the point D, the limbs of the frog are thrown into convulsions, and this takes place as often as the communication is formed.

Soon after the discovery of Galvani, and after the result of his experiments and opinions on the subject of this discovery was announced to the world, the attention of philosophers became much occupied in repeating and extending these experiments. Among others, Valli, an Italian physician, instituted a series of experiments, an account of which was communicated to the French philosophers, who soon after repeated them. As these experiments afford us not only a pretty full view of the effects of the galvanic fluid on animals, but also the state of galvanism at the time, we shall here detail them.

Experiment 1.—When two metallic coatings or slips of metal, the one of lead, and the other of silver, were placed on a frog, fastened to a table, the coating of lead being placed on the belly of the animal, and that of silver on the pelvis, and a communication being formed by means of a slip or wire of copper, strong convulsive motions were produced in the animal.

Exper. 2.—The coating or slip of lead which was employed in the preceding experiment, was removed, and the abdomen was left bare. The copper wire was then applied to the abdomen the same way as before; while its other extremity was in contact with the coating of silver on the pelvis, convulsive motions were still produced, but they were less sensible than in the former experiment, and sometimes did not succeed at all.

Exper. 3.—When two coatings of the same metal were employed, as, for instance, silver or gold, the effects produced by means of copper forming the communication, were found to be much fuller; and when the coatings were of similar metals, such as copper, lead, or tin, and the metal forming the communication was the same, no effect whatever was produced.

Exper. 4.—By placing the coating on the abdomen in a horizontal direction, so that the points of contact became less numerous, the effects were found to be proportionally diminished; but when the coating was brought into full contact with the surface of the abdomen, it was observed that they became equally powerful as before.

Exper. 5.—A frog was skinned and cut transversely through the middle; the nerves of the thighs were laid bare, joined together, and placed on a slip of gold, while the thighs themselves were in contact with a piece of silver. When the metallic conductor of copper was applied, flight contractions were produced. It was found also that contractions took place when both the coatings were of silver; but when coatings of tin, copper, or lead, were substituted for the silver coating which surrounded the nerves, powerful contractions took place. The gradation observed in the action of the metals, is the following. Lead produced the strongest contractions, next the tin, and lastly the copper; but in proportion as the vitality of the animal diminished, the metals were found also to lose their power of producing motion. The metals which retained this property longest were lead, tin, and zinc.

Exper. 6.—When plumbers' lead was employed on each side as a coating, and when the metal forming the communication was the same, no effect was produced; but when lead of different qualities, as, for instance, lead of the assayer and plumbers' lead, was used, and the metal forming the communication being either the one or the other, very singular effects took place.

While it was found that these two kinds of lead, by changing the different metals, were no longer susceptible of producing any effect in one of the coatings, silver, gold, bismuth, antimony, or zinc, substituted for the lead, produced very powerful contractions; and, what seemed still more singular, when the pieces of lead in the first part of this experiment were re-applied, flight convulsions took place.

Exper. 7.—After a short interruption of the experiments on the same animal, it appeared that it became susceptible of pretty strong convulsive motions, when the same experiments were repeated.

Exper. 8. When the galvanic power seemed to be nearly exhausted in the frog, it was found that the different metals, when they produced, by their contact, new convulsions, did not, when this effect could be no longer produced, leave to the animal the power of exhibiting anew any contractions with coatings of the different kinds of lead, as in experiment 6.

Exper. 9.—The following is the gradation of the diminution of effect, till it entirely ceased, when the plumbers' lead always formed one of the coatings. With the assayers' lead forming the other coating, the action became feeble, and it at last ceased. The next in order was tin, the next antimony, and so on in the order in which they are named as follows: zinc, copper, gold, silver, iron, it was observed, had lost its power of producing any effect before the antimony; but whether it was deprived of this property before lead and tin, was not ascertained. Exper. 10.—Zinc, on losing the property of exciting convulsions in a frog, on which experiments had been made for an hour, was not found susceptible of any farther action, when the communication was formed by means of lead; but it was observed as a very singular circumstance, that contractions were still produced by this metal the moment that the person engaged in the experiment removed the conductor, and interrupted the circle. This experiment was frequently repeated.

Exper. 11.—The upper part of a frog which was skinned, and divided transversely, had the crural nerves, as in the former experiments, armed with a piece of lead, and placed in a glass filled with water, while the lower part was placed in another glass, also filled with water. Strong contractions were produced when the communication was formed by means of different persons holding each other by the hand, while two of them touched the water in the glasses. One of them held in his hand a piece of metal, which was brought into contact with the coating of lead.

Exper. 12.—When any one individual of the persons who thus formed the chain of communication between the two glasses withdrew himself, so that the communication was interrupted, no effect was perceptible.

Exper. 13.—When the frog was arranged in the same way as in experiment 11, having its parts placed in two glasses, no motion was excited when a communication was established with two fingers; nor was any motion produced, when a person with one hand armed with a piece of metal, touched the body of the frog, while he brought a finger of the other hand in contact with the metallic coating of the crural nerves. But by placing one finger on the inferior part of the frog, he touched with a piece of metal the coatings of the nerves, powerful contractions were produced.

Exper. 14.—When the animal was touched with a metallic substance in an insulated state, no perceptible effect was observed; but when the metals ceased to be insulated, very considerable motions were invariably produced.

Exper. 15.—The fore leg of a rabbit was separated from the body; the brachial nerves were laid bare, and armed with a bit of sheet lead. The communication between the lead on the nerve and one of the contiguous muscles was made with a piece of silver, and strong convulsive contractions took place in the limb; but when this experiment was varied, by substituting for the metallic conductors, plumbings and affayers lead, no farther motion was produced. When one of the coatings employed was lead, and the other iron, no perceptible motion was observed. But when lead as one of the coatings, was employed with silver, gold, copper, zinc, or antimony, as the other coating, the motions and contractions of the limb were renewed. The motions were very slight, which were produced by means of a coating of bismuth, along with a coating of lead.

Exper. 16.—This experiment was instituted to ascertain the state of the electricity in the animal which was the subject of it. With this view, the animal was placed in a vessel containing one or two of Coulomb's electrometers, and it was then successively electrified, both positively and negatively; and in both of these cases the balls of the electrometer were so much influenced by the animal, as to shew, not only that its electricity was in a state of perfect rest, both before and during the time of the experiment, but also to exhibit in the system of the body on which the experiment was made, in a very distinct and striking manner, phenomena quite analogous to those of the Leyden phial.

Exper. 17.—The left crural nerve of a living frog being tied with a ligature so strongly, that the animal was deprived of the power of motion in that part of the limb below the point where the ligature was fixed; but when the nerve was armed with a metallic coating, in the way described in the former experiments, and a communication was formed between the part of the nerve above the ligature and the muscle, the motion and contraction of the limb were excited.

Exper. 18.—The ligature was afterwards placed on the left crural nerve, and brought in contact with the muscle. It was also fixed in such a way on the right crural nerve, so that part of it projected: the left part of the animal was then quite paralytic, and without motion, and the convulsive contractions which were produced when the communication was formed, were entirely limited to the right side; but when the same left crural nerve was more completely laid bare, and separated from the muscular substance which surrounded it, its conducting power was restored, and the communication being established, the convulsive motions became pretty strong. When, however, the ligature was again brought into contact with the muscle, the limb was again deprived of its power of motion.

Exper. 19.—One of the crural nerves of a frog being laid bare, was armed with a piece of sheet lead; and a communication having been formed between this nerve and the other crural nerve, which was unarmed, very strong convulsive motions were produced.

Exper. 20.—When one of the crural nerves was armed with two pieces of lead at different places in its course, and a communication formed between the two parts by a metallic conductor, violent agitations followed. It was observed, too, that the same effects took place, when the whole of the nerve was laid bare, and completely separated from the surrounding muscle.

Exper. 21.—A similar experiment was made on a hot-blooded living animal. The animal selected for this purpose was a guinea pig; but when the communication was established in the usual way, no effect followed, from which anything precise or satisfactory could be deduced.

With a view to discover during what length of time frogs, which were made the subjects of these experiments, could resist their effects, and retain the power of having motion excited in them, Valli made several experiments. At 10 o'clock at night he prepared two frogs, which on the following morning at seven o'clock he found had become extremely feeble, but not entirely deprived of the power of motion. Slight convulsions were excited in both by means of the galvanic apparatus; but an hour having elapsed, they ceased to afford any farther symptoms of vitality. No effort that could be made, succeeded in producing motion. In other cases he prepared frogs, which by the following morning were found to be quite dry, and then no symptoms of motion could be exhibited. He separated several of the muscles from the body of a frog, and after having torn them, he found it impossible to Effects of Galvanism on Animals.

To excite the irritability by any mechanical stimulus whatever; but, after previous preparation, and by means of a metallic conductor, motion was produced.

The same naturalist made a variety of experiments, to ascertain the effects of galvanism on animals which were destroyed with opium, and other narcotic substances; but the results of his experiments on animals to which opium had been exhibited internally, as well as applied externally, were found to be very different from each other. Four frogs were destroyed by means of powdered tobacco, were rendered completely insensible to any mechanical stimulus, and seemed to be in a state of total stupefaction; but by the application of the galvanic apparatus, symptoms of vitality appeared, and flight motions were produced. A number of lizards being poisoned with tobacco, exhibited, at the time of their death, convulsive motions; but they still continued to afford symptoms of vitality and motion on the application of galvanism.

Animals were destroyed in a variety of ways, with a view of ascertaining what were the effects of galvanism, after the principle of life seemed to be extinguished. A small bird, which was for some time immersed in hydrogen gas, or inflammable air, showed no symptoms of vitality or motion; but, on the application of galvanism, convulsive contractions of its limbs were produced. Two kittens were killed in azotic gas, and the fore legs were separated and prepared in the usual way. The same effects were produced as in the experiment with the bird.

Some animals were destroyed with the extract of hemlock; but it did not appear that the effects on the application of the galvanic apparatus were at all diminished by means of this poison. In frogs which were exposed to the exhalation of corrupted animal matters, perceptible motions were observed by means of galvanism; but these were very feeble.

Molcati deprived several frogs of life, by placing them in the vacuum of an air pump; and when these were subjected to experiment with the galvanic apparatus, flight motions were produced; but it was observed that these, although they followed each other in rapid succession, were excited with some difficulty. Here it was found that the blood was extravasated in the cellular membrane of the muscles, by which the flesh was tinged with a deep red colour. To this circumstance was ascribed the feeble effects produced in the above experiment, as it was supposed that the blood carried off part of the galvanic fluid, and thus prevented its action on the muscular fibres, through the medium of the nerves. This opinion was supported by another experiment, which was made on prepared frogs, in which there was no extravasation of blood; and in this case the galvanic effects did not seem to be in any degree diminished.

Before proceeding farther with an account of the experiments of the particular effects of galvanism on animals, we shall here relate two of a more general nature, the one with regard to the effects produced by the peculiar application of the metallic conductor, and the other with respect to the velocity of the galvanic fluid being increased, without increasing its intensity.

A difference, which appeared to be a very singular fact, was observed in the mode of applying the metallic conductor, to excite motion in animals by means of galvanism. It was found, that the motions produced in the animal by this means were generally more powerful, when the conductor was applied, first to the muscles, and then to the coating, than if the reverse had taken place; that is, by applying first to the coating, and afterwards to the muscles; and indeed when the galvanic power began to be nearly exhausted, no motion whatever could be excited when the application was made, first to the coating and then to the muscles, while at the same time, by the contrary mode of application, motion could be easily produced.

The other fact alluded to is, that the velocity of the galvanic fluid may be increased without increasing the degree of its intensity. This was proved by M. Valli in the following experiment. By means of a chain, without which was in contact with the nerves of a prepared frog, he completed the galvanic circle. The animal at first exhibited convulsive contractions, but afterwards remained for some time without motion. When the conductor was removed to a very small distance, motion was again excited in the animal; soon after, however, this ceased. But when an inflated conductor was brought to the muscles of the frog, the motions were immediately renewed; and when they again ceased, a communication being formed between the operator himself and the conductor, the contractions were again excited. The conclusion which he deduced from the above experiment was, that the galvanic influence is constantly the same, however various the modes of its application. The same result, however, he observes, would not be obtained, if the experiment were made on an animal in which the principle of life was in full vigour.

From a number of experiments which were made by the same physiologist, it appeared that certain intervals were necessary, in order to obtain the same intensity of action in animals subjected to the influence of the galvanic fluid. Frogs, mice, rats, and tortoises, were the subjects of these experiments; they were destroyed by means of different poisons, or by respiring some of the noxious gases. In applying the galvanic apparatus to these animals, an interval of several minutes was required, when the motions excited became feeble, or had nearly ceased; and then, after this interval had elapsed, the same effects, and almost equally powerful as before, were produced.

With regard to the conducting power of the blood-veffels, two questions were proposed to Valli, by Vicq D’Azur. 1. Whether the blood-veffels are to be considered as conductors of the galvanic fluid. And, 2. Whether, by coating the blood-veffels instead of the nerves, any motion through their medium could be excited? In the solution of these questions Valli observed, that the blood-veffels are undoubtedly to be considered as conductors of the galvanic fluid; but in whatever way this is effected, it seems to be through the nerves alone, in consequence of the way in which they are disposed, that muscular motion can be excited. The arteries and veins, he farther observes, are to be considered as less powerful conductors than the nerves; for no motion is obtained, if the veffels, without having any communication with the nerves, be distributed directly to the muscles. The tendons also, when the same communication is established, are also conductors as well as the bones, if they have not been deprived of Effects of Galvanism on Animals.

The membranes also possess this conducting power; but exhibit no motions when the communication with the nerves is interrupted.

It had been observed, that the nerves, when dry, exhibited, by means of friction, some symptoms of electricity. With a view to ascertain whether, in this dry state, the nerves were conductors of the galvanic fluid, and whether motions could be excited through this medium, Valli made several experiments; but in all these he was unsuccessful, for no motion was produced. In a series of experiments which were made on fowls, he found that ligatures applied to the nerves, did not prevent the contractions of the muscles, provided these ligatures were not applied to the nerves in immediate contact with the muscles.

In order to ascertain what would be the effects of the galvanic fluid on animals which were drowned or suffocated, Valli made a number of experiments. Several pullets were drowned, and kept too long under water, that no symptoms of life appeared. By the application of the galvanic apparatus, muscular contractions were produced in some, while others, by the same application, exhibited no motion whatever. The same experiment was repeated on six pullets, which were also drowned; and on the application of the apparatus, strong convulsive motions were produced. These continued for nearly the space of an hour. In others which were also drowned, the brain and wings were laid bare; and after this previous preparation, when the galvanic apparatus was applied, strong muscular contractions were excited: none of the animals, however, as was expected, were restored to life. Similar experiments, followed by the same result, were made on rabbits.

Several pullets were exposed to the action of different gases, as hydrogen, nitrous, and azotic gases, and did not afterwards, by any mechanical stimulus whatever that could be applied, exhibit symptoms of life. The galvanic apparatus being applied, very feeble contractions were produced; and these succeeded each other after long intervals. Similar experiments were made with the same view, on frogs, and it appeared that these animals could resist the effects of those gases better than the others. Nitrous gas, he found, was more injurious than hydrogen gas. In some of the frogs on which the experiments were made, the application of the galvanic apparatus produced violent agitations; but having repeated three or four shocks, no farther motion could be excited, not even after some interval had elapsed.

To ascertain what were the effects of different kinds of air on animals subjected to the galvanic apparatus, he separated the hinder extremities of a frog, exposed the one to the action of nitrous gas, and the other to that of atmospherical air. After being subjected for a short time to the action of these airs, the galvanic apparatus was applied. Contractions were produced in both; but those which were induced in the limb exposed to the nitrous air, were feebler than the other; and when the action of the nitrous air was continued beyond a very limited time, no motion whatever could be excited. The same experiment was made on limbs exposed to the action of hydrogen gas; and it appeared that its effects in destroying the irritability of the muscular fibre, or in diminishing its susceptibility of being acted upon by galvanism, were less powerful than the nitrous gas. Azotic gas was also found to produce effects on frogs somewhat similar. The heart was indeed observed to palpitate after the death of the animal; but, in general, the contractions which were induced by galvanism were extremely feeble.

It would lead us too much into detail to mention all the experiments which were made by this naturalist. We shall therefore only add a short account of the general results.

1. In frogs newly killed, he found, that a flugle metallic conductor was sufficient to excite convulsive contractions; and that in producing these motions, it was not found essentially necessary to apply a coating either to the muscle or nerve. Scissors, in which the steel appeared to be of a bad quality, might be successfully employed as a conductor; but gold, silver, copper, lead, and tin, in general, produced no effect.

2. The galvanic fluid was found to pass through glass and sealing wax; but it was necessary that these substances should have their temperature considerably increased.

3. Water, in which the temperature was pretty high, or when raised to the boiling point, seemed to prevent the effects of galvanism from taking place, or at least diminished them greatly.

4. Water, the temperature of which was very much reduced, seemed also to be deprived of the property of conducting the galvanic fluid.

5. It was found, that when an individual formed part of the chain in cases where the galvanic apparatus was applied to the prepared feet of rabbits, cats, and dogs, the latter were unfeeling to motion.

6. The diaphragm of a dog was immersed in a vessel of water, and so placed in the vessel, that the phrenic nerve, previously armed, projected from it; and on touching the coating with a piece of gold or silver coin, while one of the fingers of the other hand was put into the water, feeble contractions were excited in the muscle. In some other experiments on the same muscle of horses, it was found that no motion could be induced by means of galvanism, while the same power, with the same intensity, constantly excited contractions in that of dogs.

7. A metallic wire, which was entirely covered with sealing wax, produced no motion in frogs, which began to be exhausted when it was employed as a conductor. This was stated by Valli, as a proof that the galvanic fluid passes along the surface of conductors.

8. A ligature on the nerve, when placed near to the muscle, or in contact with it, interrupted or diminished the effects of galvanism: it was found also, that a ligature, applied in the same way, prevented the effects of artificial electricity.

9. A ligature was applied, at a small distance from the muscle, to the crural nerve of a frog, and another was prepared in the same way, but without any ligature; these being subjected to experiment, it appeared that galvanism produced a more perceptible action in the latter than in the former.

10. Weak shocks of artificial electricity produce motion in the muscles of that leg only where no ligature has been applied to the nerve; but in the other, muscular contractions can be excited by means of the galvanic apparatus. From this experiment, it was attempted to deduce a method of subjecting the intensity of galvanism... Galvanism.

Effect of Galvanism on Animals.

If, for example, it is found that the effects of artificial electricity are considered as amounting to five, six, or seven degrees, and this power is insufficient to excite contractions, while they are produced by means of galvanism, it may be said that the latter is five, six, or seven degrees stronger than the former.

11. Valli did not succeed in effecting the muscular contraction of the heart by means of galvanism; nor did he succeed in similar experiments made on the stomach, intestines, or bladder, although he armed or applied metallic coatings to the nerves of all these organs.

12. To produce contractions in the wing of a fowl, the nerves of which were coated and previously steeped in oil, very powerful shocks of artificial electricity were found requisite; but the effects of the galvanic fluid did not, by this process, seem to be at all diminished: it retained its whole energy.

Fontana, in his experiments and investigations on this subject, found that he could accelerate the motions of the heart, when these motions were going on; and when the motions had ceased, could bring it to produce contractions. By placing the heart between two pieces of metal, zinc and antimony, so that it shall be in contact with both, and then forming a communication by means of a metallic conductor between the two metals, its motions are excited, even after it is separated from the body and cut in pieces. According to the experiments of Marigliani, part of the heart of a fowl, placed on a piece of charcoal, and another portion put on a piece of pasteboard, covered with tinfoil, gave repeated contractions, and was strongly convulsed.

M. Delametherie made a variety of experiments, at a very early period, on this subject. The following are some of the general results of these experiments.

1. He found that the effects of galvanism in a prepared frog were feeble.

2. That it possesses the greatest intensity at the time when the animal has been just deprived of life; from this he infers, that the intensity of the effect must be greater in the living animal; from which he thinks it follows, that it is only by means of good conductors that the galvanic fluid can be conveyed from the nerves to the muscles of a frog; and it is by means of the metals, which may vary in the degree of their conducting power, that this communication is established.

3. Plumbago and charcoal were found to be inferior in their conducting power to metallic substances; but by their means the galvanic fluid could be conveyed from the nerves to the muscles of a frog.

4. He did not find from his experiments that this effect could be produced by forming the communications by means of animal substances; for when a person touched at the same time the nerves and muscles of a frog which had been laid bare, the same effect did not follow.

Volta, whose name has been already mentioned as the inventor and improver of the apparatus by means of which the galvanic power could be greatly increased, was, at the same time, one of the most zealous and the most indefatigable inquirers into its nature and properties. The views which this philosopher entertained with regard to the nature of this fluid, were different from those of Galvani. They are distinguished for their originality, exhibit a train of careful investigation, and have served as an excellent foundation on which the future structure of galvanism was quickly raised. We shall therefore give a pretty full detail of the experiments and reasonings of this philosopher; and from the importance of his views, which we have stated above, it will not be less acceptable to the reader, if this detail be given, as we propose to do, in his own words. In this, indeed, something of what belongs to the second part of this treatise, will be unavoidably anticipated; but the sacrifice of strict method to perspicuity, will, we are persuaded, be readily admitted as a sufficient apology for this deviation.

To understand clearly the peculiar views which Volta has embraced in the observations which we have now referred to, it will be necessary to anticipate a little farther, by stating, that, according to Galvani, the fluid which bears his name is a peculiar kind of electricity, which resides in the organs of the animal, and is essentially and inseparably connected with them. But, according to the theory of Volta, the whole phenomena of the galvanic fluid depend entirely on artificial electricity, which is excited into action, or put in motion, when conductors of a different nature are brought into contact; and these, he thinks, are to be considered as the primary exciters. The motion of this fluid is induced in three different ways, that is, by means of three conductors at least, which are of a different nature, being so arranged as to form the communication or circle. In the first way, two metals or conductors of the first class, of a dissimilar nature, are employed. These are brought directly into contact by one of their extremities; but the communication between the other extremities is established by means of moist conductors, or conductors belonging to the second class. This fluid is put in motion in another way, by a single metallic conductor of the first class, placed between two moist conductors of a dissimilar nature, between the latter of which a communication is established. In the third way of exciting the action of this fluid, or putting it in motion, a communication is formed among three conductors, each of which is of a different nature. To illustrate the variety of action observed in these conducting substances, the following account of the experiments of this naturalist, with his views and reasonings, was communicated by him in letters to Gren.

"If a tin basin, says he, be filled with soap-suds, lime-water, or a strong ley, which is still better, and if you then lay hold of the basin with both your hands, having first moistened them with pure water, and apply the tip of your tongue to the fluid in the basin, you will immediately be sensible of an acid taste upon your tongue, which is in contact with the alkaline liquor. This taste is very perceptible, and, for the moment, pretty strong; but it is changed afterwards into a different one, less acid, but more saline and pungent, until it at last becomes alkaline and sharp in proportion as the fluid acts more upon the tongue, and as the activity of its peculiar taste and its chemical power, more called forth, produce a greater effect in regard to the sensation of acidity occasioned by the stream of the electric fluid, which, by a continued circulation, passes from the tin to the alkaline liquor, thence to the tongue, then through the person to the water, and thence to the..." I explain the phenomenon in this manner, according to my principles; and indeed it cannot be explained in any other, as everything tends to confirm my attention, and to prove it in various ways. The contact of different conductors, particularly the metallic, including pyrites and other minerals as well as charcoal, which I call dry conductors, or of the first class, with moist conductors, or conductors of the second class, agitates or disturbs the electric fluid, or gives it a certain impulse. Do not ask in what manner; it is enough that it is a principle, and a general principle. This impulse, whether produced by attraction or any other force, is different or unlike, both in regard to the different metals and to the different moist conductors, so that the direction, or at least the power with which the electric fluid is impelled or excited, is different when the conductor A is applied to the conductor B, and to another, C. In a perfect circle of conductors, where either one of the second class is placed between two different from each other of the first class, or, contrariwise, one of the first class is placed between two of the second class different from each other, an electric stream is occasioned by the predominating force either to the right or to the left; a circulation of this fluid, which ceases only when the circle is broken, and which is renewed when the circle is again rendered complete. This method of connecting the different conductors will be more readily comprehended by turning to the figures, where the capital letters denote the different conductors or exciters (moteurs) of the first class, and the small letters those of the second class. Fig. 3. and 4. express the two cases abovementioned.

I consider it as almost superfluous to observe, that when the circle consists merely of two kinds of conductors, however different or however numerous the pieces may be of which each consists, two equal powers are opposed to each other; that is, the electric fluid is impelled with equal force in two different directions, and consequently no stream can be formed from right to left, or, contrariwise, capable of exciting convulsive movements.

There are other cases, however, and other modes of combination, where the powers are equally in equilibrium, and where no current of the electric fluid can take place; or, at least, none of such a force as to make an impression on the tenderest nerves, or to excite any convulsive movement in the best prepared frog that may be placed in the circle, notwithstanding the intervention of two or more different kinds of metals. This is the case when each of these metals is placed between two moist conductors, or of the second class, and which are very nearly of the same kind; or when, in a circle of three pieces, two of them of the same metal, and one of a different metal, are so connected, that the latter is immediately between the other two.

When one of the ends of a piece of metal, which is a conductor of the first class, is immediately applied to another of the same class, but, instead of immediately touching with the other end, the other piece touches an intermediate conductor of the second class, either great or small, either a drop of water, a piece of raw or boiled flesh, or of sponge not moist, pate of meal, jelly, soap, cheese, or the white of an egg boiled to hardness; in this new combination, where a conductor of the second class is between two of the first class, the powers are no longer opposed to each other; and this is sufficient to determine an electric stream. When, therefore, a prepared frog is placed as the conductor of the second class, it will always be violently agitated as often as this circle is made complete.

It may be readily perceived that the two last experiments coincide with those announced by M. Humboldt, where a drop of water, a small bit of fresh meat, or a very thin stratum of any fluid, performs the whole wonder. When another drop of water, or any other aqueous conductor, is applied between the other end of the first conductor and the other corresponding piece, each piece of metal is insulated, as I shall express it, between two aqueous conductors; but then the powers from right to left, and from left to right, are again completely opposed to each other; consequently the electric stream is impeded, and the frog remains without any movement. It is, therefore, absolutely necessary that two different metals or conductors of the first class, should be in immediate contact with each other, on the one side, while with their opposite ends they touch conductors of the second class.

We might consider this mutual contact of two different metals as the immediate cause which puts the electric fluid in motion, instead of ascribing that power to the contact of the two metals with the moist conductors. Thus, for example, in fig. 3, instead of admitting two different actions, at least, in regard to the magnitude of the power, one where B comes in contact with a, and another where A comes in contact with a also, by which an electric current arises in the direction from A to B, we might suppose only one action at the point where B comes in contact with A, which impels the fluid in that direction. In both suppositions the result, as may easily be seen, is the same. But though I have reasons for adopting the first as true rather than the second, yet the latter represents the proposition with more simplicity, and it may be convenient to adhere to it in the explanation, as it affords a readier view of it. We may then say, that in the cases above stated, no effect will be produced, because here there is no mutual contact of different metals; the effect also will be null, when a conductor of the first class, on two opposite sides, is in contact with two others of the same class; for the actions therefore are in equilibrium; and, lastly, that an electric current will be occasioned by the action which arises from the contact of conductors of the first class, and which is counteracted by no other contact of the like kind.

Having seen the result of employing three pieces of metal, or conductors of the first class, viz. two of one kind and one of a different, when combined sometimes in one way and sometimes in another, with conductors of the second class, we shall now try what will be the result, according to my principles, with four pieces of metal, two of which are of one kind, for example, zinc, when connected with moist conductors of different kinds.

I shall first observe, that when they are connected in a circle, the powers which endeavour to put the electric fluid in a streaming movement, will be opposed to each other, and in perfect equilibrium, and that consequently no movement can take place in the frog, here supposed to be the moist conductor a, or a part of it, however irritable and well prepared it may be; Effects of Galvanism on Animals

be; and if the experiment be made with accuracy and the necessary precaution, so that the metals, in particular, be very clean and dry at the points of contact, it will perfectly confirm what I have above said; the frog will experience no agitation, no convulsive movement.

"The movements, on the other hand, took place, as might be foreseen from my principles, as often as I omitted one of the middle pieces, or changed the order.

"The conductors of the second clasps, which, in all the figures, are denoted by small letters, may be cups with water, in which the ends of the pieces of metal denoted by the large letters are immersed; or sponges or other bodies which have imbibed aqueous moisture. They may be either large or small, and may consist of one or more pieces, provided they be in proper contact; they may also be persons, if their skin be moistened at the places of contact, &c. By the last method the experiments will be very beautiful and instructive, when the circle consists of three or more persons (I have formed it frequently of ten, and even more), of two or more frogs properly prepared, and of four pieces of metal, two of silver and two of iron, tin, and particularly zinc. The change of effect, when you change the connection, is striking.

"Let the position be as represented in fig. 14, where g is the prepared frog, which the two persons p, p, hold in their hands, one on the one side by the feet, and the other on the opposite by the rump. Z, Z, are two plates of zinc, which are held also by these persons, and A, A two pieces of silver, which are held by a third person, denoted also by p. It must not be forgotten that the hands should be very moist, as the dry skin is not a conductor sufficiently strong. As in this chain the actions of the electric exciters are opposed to each other, and in exact equilibrium, as may be readily perceived, no convulsion or agitation in the frog will take place.

"Now, let one of the metallic pieces A, Z, which stand between the two persons p, p, or between any other moist conductors, be left in combination as it is; and let the position of the two other metallic pieces A, Z, be reversed, by converting fig. 14 into fig. 15, (so that the actions, instead of being contrary, will act together to impel the electric fluid to one side or to produce the same current); or introduce between A and Z another person, or any other conductor of the second clasps, so that the chain be formed as in fig. 16; or take away one of the pieces A, Z, in fig. 14, and make the chain like those of fig. 17, and 19; or, in the last place, remove the whole two pieces A, Z, either in the one or the other side, as represented fig. 19. (by which means it will correspond with fig. 17, as the whole chain p, g, p, p, may be considered as a single moist conductor of the second clasps.) In all these combinations, which are represented by fig. 15, 16, 17, 18, and 19, the actions arising from the metallic contacts are no longer contrary to each other, or in equilibrium, as they were in fig. 14; consequently an electric stream is produced, and the frog g, which I suppose to be properly prepared, and which forms a part of the chain, will be violently agitated as often as the circle, when broken at any one place, particularly between metal and metal, is again restored.

"In regard to the experiment where a moist conductor, or one of the second clasps, is to be introduced between the two pieces A, Z (fig. 16,) that is, between two different metals, a drop of water, or a small bit of moistened sponge, or a thin stratum of any fluid, soap, or any other viscid matter, will be quite sufficient, as has been already observed. This surprising experiment I generally make in such a manner, that, instead of the piece of the metal, I employ a cup or spoon filled with water, and then cause the person who holds the perfectly dry and pure stick of tin, to touch with that stick sometimes the perfectly dry sides of the spoon or cup, and sometimes the water contained in them. It is wonderful to see, that, as by the latter method, the violent agitation of the frog never ceases, the first method, which corresponds with fig. 14, does not produce the least irritation; unless by accident there be a small drop of water, or a thin stratum of moisture, at the place of contact, by which the case represented fig. 16, would be restored. This may serve to show with what care and attention the experiment must be made, in order to guard against error or deception, which might so easily arise, and everywhere exhibit anomalies.

"When I introduce water or any other moist body, great or small, not merely between one pair of metallic pieces, A, Z, as fig. 16, but between two pairs, as represented fig. 20, each piece of metal is between like moist conductors, and by these means all the actions are again rendered contrary, or brought into equilibrium; or, according to the other mode of viewing the matter, there is no longer any action, for want of the mutual contact of two different metals, which, as we have seen, is certainly necessary to excite an electric current; and it is always found that the frog experiences no agitation.

"I shall not enlarge farther on these combinations, which may be varied ad infinitum with a greater number of metallic pieces, and by which one may be enabled to foretell the phenomena which, according to my principles, will always be found to take place. It will be sufficient, for the present, to draw this conclusion, that in a circle consisting merely of two conductors, however different they may be, their mutual contact can produce no electric stream sufficient to excite sensibility, or muscular movement; and that, on the contrary, this effect infallibly follows as often as the chain is formed of three conductors, one of one class, and two different from each other of another class, which come into mutual contact with each other, and that this effect will be stronger, the greater the difference is between the latter; that in other cases, where there are more than three different conductors, the effect either is not produced, or will be produced in different degrees, according as the forces called forth by the different combinations, which will be expanded at each heterogeneous contact, and which are often in opposition, and endeavour to impel the electric fluid in opposite directions, are perfectly in equilibrium with each other (which must be a very rare case), or when the sum of those which exert themselves in one direction is more or less exceeded by the sum of those which act in another direction.

"I shall here, however, leave the two complex combinations, and return to the simple cases, those with three different conductors, represented by fig. 3, which are more demonstrative; or, in other words, those with Effects of two different metals or conductors of the first class, which are in contact with each other, and are applied on the other side to moist conductors, or conductors of the second class. This method has been commonly employed since Galvani's discovery, and is in exact proportion with the diversity of metals, on which I consider the whole phenomena to depend.

"The other method of combination, which is expressed by fig. 4, or that of a metal placed between two different moist conductors, for example, between water on the one side, and an aqueous, saponaceous, or saline fluid on the other, I discovered in the autumn of 1794; and though since that period I have repeated the much varied experiments of different persons, both foreigners and others, among which was that of Humboldt, and though I wrote to several correspondents respecting it, that light has not yet been thrown on this new phenomenon which it seems to deserve.

"The singular circumstance before mentioned, in regard to the acid taste when the tongue is brought into contact with an alkaline liquid, belongs, as you may perceive, to this second method of exciting the electric fluid, and putting it in circulation (if the tin vessel be touched on the outside by the hand moistened with water, and on the inside by the alkaline liquor), and shows that this current is no less strong and active than that excited by the first method, viz. by employing two sufficiently well-chosen metals, such as lead and copper, iron and silver, zinc and tin, I must here observe, that though with tin alone, placed between water and an alkaline liquor, you obtain nearly the effect which is produced by two of the most different metals, as silver and zinc, combined with any conductor whatever of the second class; you can obtain the same, and even in a higher degree, with iron alone or silver alone, when the iron is introduced between water on the one side and nitrous acid on the other, or when the silver is applied between water and a solution of sulphur of potash.

"If you take a frog, the head of which has been cut off, and which has been deprived of all life by thrusting a needle into the spinal marrow, and immerse it, without skinning it, taking out the bowels, or any other preparation, into two glasses of water, the rump into one, and the leg into the other as usual, it will be strongly agitated and violently convulsed when you connect the water in both glasses by a bow formed of two very different metals, such as silver and tin or lead, or, what is better, silver and zinc; but this will by no means be the case when the two metals are less different in regard to their powers, such as gold and silver, silver and copper, copper and iron, tin and lead. But what is more, the effect will be fully produced on this so little prepared frog when you immerse in one of the two glasses the end of a bow merely of tin or zinc, and into the other glass the other end of this bow, which has been rubbed over with a little alkali. You may perform the experiment still better with an iron bow, one end of which has been covered with a drop or thin coating of nitrous acid; and beyond all expectation, when you take a silver bow having a little sulphur of potash adhering to the end of it.

"Fig. 21. represents the form of this experiment, where g is the frog, a, a, the two glasses with water, A the bow formed of one single metal, and m the drop or a thin stratum of a mucous, saline, &c. fluid, with which the bow has been rubbed over, and which on this side is between the metal and the water.

"The very considerable difference in regard to the quantity of effect in the before-mentioned experiments already shows, that if the electric stream excited by contact is strongest towards a certain metal, when that metal is placed between a certain fluid on the one side, and another fluid on the other, there are other fluids which produce a greater effect with another kind of metal; so that it will be necessary to discover by experiment the particular arrangement of conductors suited to each metal, in which the fluids or conductors of the second class must be disposed according to their activity. I have paid great attention to this circumstance, and have formed several tables, which I shall publish as soon as I have brought them to perfection.

"I shall here, however, only observe, that in order to clasps, in some manner, the innumerable different moist conductors of this kind, I distinguish them into aqueous, spirinuous, mucous, and gelatinous, saccharine, saponaceous, saline, acid, alkaline, and fulphurous (livers of sulphur) liquids; that I make subdivisions in the acids down to the best known simple mineral acids, (as I find in this respect great difference between the nitrous and the muriatic acids,) comprehending the principal vegetable acids and the acid of galls; and do the same in regard to the saline fluids, according as they are solutions of neutral salts, earthy salts, and particularly metallic salts.

"When it can be determined in what order all these kinds of fluids follow each other, in regard to the power in question, for the metal A, and another for the metal B, &c. we shall then be in a condition to determine what place must be assigned to a great number of other heterogeneous fluids, whether mineral, vegetable, or animal, which belong to several of the above classes. In general, the order for the greater part of the metals hitherto observed is as follows: 1st, pure water; 2nd, water mixed with clay or chalk (which shows a pretty different effect when the before-mentioned experiment is made with two glasses, a bow of tin or zinc, and a properly prepared frog, which has a sufficient degree of vitality); 3rd, a solution of sugar; 4th, alcohol; 5th, milk; 6th, mucilaginous fluids; 7th, animal gelatinous fluids; 8th, wine; 9th, vinegar, and other vegetable juices and acids; 10th, saliva; 11th, mucous of the nose; 12th, blood; 13th, brains; 14th, solution of fats; 15th, soap-fuds; 16th, chalk-water; 17th, concentrated mineral acids; 18th, strong alkaline leys; 19th, alkaline fluids; 20th, livers of sulphur. With some metals there is, however, a considerable deviation from this order, in regard to livers of sulphur, alkaline fluids, and the nitrous and saline acids.

"As to the metals, which in their position between these different fluids are more or less proper for the electric effect in question, I have found in general, that tin exceeds all others, and that silver is the worst; except when one of the fluids between which the silver is placed is water, or any other aqueous conductor, and the other liver of sulphur; in this case silver far exceeds zinc, and even tin. Iron also produces a much greater effect than any other metal, when it is in contact, on the one side, with mere water or an aqueous conductor, Part I.

Effects of conductor, and on the other with the nitrous acid, were it even only a drop. The excitement occasioned in both cases is wonderful; since it exceeds, as I have already remarked, that produced, according to the usual method, by means of a double metallic bow, even of different metals, as zinc and silver, applied to conductors of the second class of the same kind. It is sufficiently strong and powerful to produce convulsive movements in a half-prepared frog, the bowels of which have not been taken out, when one of the two moist conductors is a concentrated alkaline solution, and the metal placed between them is zinc, or rather tin. With other metals and other fluids you can seldom produce convulsions in a frog, if it be not perfectly prepared, or at least embowelled.

The reader will readily perceive, that when a bow of one and the same metal touches with both its ends the same kind of saline water, the same acid, the same alkaline fluid, &c., an electric stream will not take place, as happens also when it touches on each side merely water: in that case two opposite actions are opposed to each other, and keep each other in equilibrium. That these contrary powers, however, may be in perfect equilibrium, it is necessary that the fluids applied to both ends of the homogeneous metallic bow be exactly of the same kind and of the same strength. For this reason the most careful attention and a certain dexterity are required, in order to ensure success to the experiment, which I have often performed to the great astonishment of the spectators, and which any one may repeat as was done by my friend Humboldt. That philosopher has already published some of the most striking and decisive of these experiments in his second letter; and I shall here give a more particular account of them.

Having placed a completely or only half-prepared frog as usual in two glasses of water, take a very clean bow of silver (it will be best when it has been washed with water from the glasses), and immerse both ends of it at once, or the one after the other, in the glasses; no agitation of the frog will be occasioned. Repeat the experiment, after you have daubed over one end of the bow with the white of an egg, liquid glue, saliva, mucus, blood, a solution of tartar, or any other fluid or conducting substance sufficiently different from pure water. First, immerse the pure end, or that moistened merely with water, in the water of one of the glasses; and afterwards the other end, daubed over with the above substances, in the water of the other glass; you will then infallibly produce a convulsive movement in the frog, and several times in succession, if you draw out the bow and again immerse it until nothing more of the above substances is left adhering to the metal, or until the metal, with its ends in both the glasses, touches only pure, or nearly pure, water. Daub both the above substances uniformly over both ends of the bow, and immerse them at the same time in both the glasses of water, and no convulsions will arise. They will often be produced in newly prepared and highly irritable frogs, when the saline fluid, or in general, the substance with which the two ends of the bow are daubed over, is not perfectly the same, or when the substance at the one end is more diluted than at the other, &c. Wash and clean carefully the one end of the bow, daub over the other more or less, and convulsions will be again produced as soon as the circle is made complete by the double immersion of the bow. Clean both ends completely, and no agitation will arise, as in the first experiment.

For comparative experiments of this kind, I would recommend viscous fluids or substances rather than saline, because the latter are too soon dissolved in the water. It oft-times happens that the convulsions of the frog, when it is completely prepared and highly irritable, take place, though both ends of the metallic bow are daubed over with the same kind of saline fluid. The cause of this is, that when one end is immersed in the water after the other (and it may be easily seen that it is impossible to do so in a moment with sufficient accuracy), the one end of the bow loses a portion of its saline substance sooner than the other, or at least the adhering part is more diluted by the water, so that the fluid with which both ends have been daubed over is no longer the same.

For these experiments I would also recommend silver, as a metal that is less liable than others to be attacked and changed by saline and other liquids. Tin, lead, copper, and in particular iron, are more susceptible of lasting variations; so that bows of these metals, and of iron above all, retain for a long time the power of producing convulsions in a newly prepared and highly irritable frog, even when both the ends of the bow are immersed in two glasses of water, although the places of the metal, attacked by any of the saline fluids, have been carefully washed and cleaned. A superficial alteration in the metal is sufficient to produce this change, as may be easily seen. These variations often show themselves to the eye by a yellow blackish spot, &c., which it is difficult to remove. I do not here speak of lasting variations, that proceed to a greater depth, which can be produced in the end of the metallic bow, and particularly in iron, when its hardness is changed; a process by which such a bow can be rendered capable of producing not only convulsions in frogs, but also a particular sensation on the tongue, and light before the eyes, if both its ends, made perfectly clean, are only brought into contact with pure water. These, and many other experiments of the like kind, form the chief subject of my first letter to the abbe Vaffalli, professor of natural philosophy at Turin, written in the beginning of the year 1794, and afterwards published with the other in Brugnatelli's Journal.

If silver be less exposed to be attacked by saline and other fluids (except by liver of sulphur, which instantaneously renders it black); if it be less susceptible of considerable and lasting variations, and has therefore this advantage over other metals, that it is liable to fewer irregularities; tin, on account of its greater activity, that is, the strength of the effects which it produces by being brought into contact with almost all moist conductors, as I have already observed, is to be preferred to silver, and in a certain degree to all other metals. The experiment I have already described with a tin basin filled with an alkaline fluid, and held in the hands moistened with water, by which an acid sensation is excited on the tongue when brought into contact with the above fluid, is a proof of it; for it would be vain to expect a like effect from a basin of lead, iron, or copper, and much more so from one of silver. With the latter it would be obtained only when it contained The electric fluid is excited also with the greatest strength and activity, when the metal is tin, between water and a saline fluid; but it will be excited with still greater energy to produce an acid sensation on the tongue when the tin is between water and an insipid mucilaginous fluid; or when the experiment is made with a tin basin filled with a solution of gum, liquid glue, white of an egg, &c. The other metals, in like circumstances, produce some effect, but much weaker; silver produces the weakest, except with liver of sulphur, as I have already observed.

A like experiment, which I made three years ago, and exhibited to various persons, not with two different fluids and one metal, as in that above described, but contrariwise, with two metals of a different kind and a fluid, is already known. I took a basin of tin (one of zinc is better), placed it on a silver stand, and filled it with water. When any of the persons in company applied the tip of his tongue to the water, he found it perfectly tasteless as long as he did not touch the silver stand; but as soon as he laid hold of the stand, and grasped it in his hands well moistened, he experienced on the tongue a very perceptible and pretty strong acid taste. This experiment will succeed, though the effect is proportionally weaker, with a chain of several persons who hold each other's hands, after they have been moistened with water, while the first applies the tip of his tongue to the water in the basin, and the last lays hold with his hands of the silver stand.

If these experiments, in regard to the taste excited on the tongue by the action of two different metals, are striking, the others, in regard to the taste excited, modified and changed by one metal between two different fluids, are no less so, and they are also newer. They are still interesting, on this account, that they discover to us the cause of that taste often perceived in water and other liquids, which is more or less considerable or various when drunk from vessels of metal, and particularly of tin. When the outer extremity of the vessel is applied to the under lip, rendered moist by the saliva, and the tongue is extended so as to be in contact with the water, beer, wine, &c., in the vessel, or when the tongue is bent as is done in drinking, is there not then a complete circle, and is not the metal between two more or less different liquids, that is, between the saliva of the under lip and the liquor in the cup or vessel? A stronger or weaker electric stream must thereby be occasioned, according as the fluids are different—a stream which will not fail in its way to affect the sensible organs of the tongue in the said circle.

Besides the two methods already considered, of producing an electric current, that is, by means of one or more moist conductors, or conductors of the second class, placed between two different metals or conductors of the first class; or contrariwise by means of a conductor of the first class placed between two of the second class, also different; there is still a third method of exciting the electric fluid, though in a degree so much weaker, that it is scarcely capable of causing convulsions in a perfectly prepared frog, in which there is still a strong degree of vitality. This new method consists in forming the circle of three different conductors, all of the second class, without the intervention of one of the first or a metal one. Some think they find in this method a strong objection against my principle.

Fig. 22. represents this third method compared with the other two. In the experiments of Professor Valli, respecting which so much noise has been made without any reason, t represents the leg of the frog, and particularly the hard tendinous part of the musculus gastrocnemius; m the rump, or the muscles of the back, or the sciatic nerves, to which the said tendinous parts are applied; and a the blood, or the viscid saponaceous or saline fluid, applied to the point of contact.

I have fully described this new method, where no metal is used, in my third and fourth letter to Professor Vassalli, written in the autumn and winter of the year 1795. I have there shewn, that these new facts, far from altering my ideas and principles, serve rather to establish them; and that they render more general the principle that the conductors, by heterogeneous contact, that is, of two different from each other, become exciters of electricity, and confirm the beautiful law arising from it, that to produce an electric stream, the circle must necessarily be formed of three different conductors. You now see in what the whole secret, the whole magic consists; and that it depends not merely on metals, as might have been believed, but on all the different conductors. As long as we adhere to these principles, it will be easy to explain all the before-mentioned experiments without being reduced to the necessity of having recourse to any imaginary principle, or any peculiar and active electricity of the organs. By their assistance you will be enabled to invent new experiments, and to foretell the result of them, as I have several times done, and still do daily. If you, however, abandon these principles, you will find nothing but uncertainty and contradiction, and the whole will be an inexplicable problem.

Some new facts, he observes in a farther communication, lately discovered, seem to show that the immediate cause which excites the electric fluid, and puts it in motion, whether it be an attractive or a repulsive power, is to be ascribed much rather to the mutual contact of two different metals, than to their contact with moist conductors. But, though it cannot be denied, that in the latter case there exists an action, it is proved that it exerts itself in a far more considerable degree when the two metals mutually touch each other. There arises by the mutual contact, for example, of silver and tin, an action or power by which the former communicates the electric fluid, and the latter receives it; or the silver suffers it to escape, and the tin attracts it. This produces, when the circle is rendered complete by moist conductors, a stream, or continual circulation of the fluid. When the circle is complete, there is an accumulation in the tin at the expense of the silver; which indeed is very small, and far under the point necessary to enable it to announce itself by the most delicate electrometer. I have however been able, by the affluence of my conductor, constructed on a new plan, and still better by Nicholson's doubler, to render it very perceptible: I shall here communicate the result obtained by my experiments, which I made some time ago with great satisfaction.

Experiment I. The three plates of the doubler are of brass. I took two strong wires, one of silver and the Effect of the other of tin, and brought the former into contact with the moveable plates, and the other with one of the fixed plates; while they both rested on the table, or, what is better, on moist pasteboard, or any other moist conductor, so as to be in communication by the intervention of one or more conductors of the second class. I suffered the apparatus to remain some hours in this state, then removed the two wires, and put the machine in motion. After 20, 30, or 40 revolutions (or more when the atmosphere was not dry, or the insulation imperfect), I brought one of my straw electrometers into contact with the moveable plate, and observed indications of positive electricity (+E), which arose to 4, 6, 10 degrees, and more. If I suffered it to touch the fixed plates, I had the corresponding indications of the opposite kind of electricity (−E).

"The silver, therefore, poured the elastic fluid into the brass plate, when it had been some time in contact with it; and the tin attracted it from the other plate, which was also of brass, while in contact with it. This was confirmed by the following experiment, which is a real experimentum crucis.

"II. I reversed the experiment, so that the silver was in contact with one of the fixed plates, and the tin with the moveable one. The electricity which I obtained from the latter, after the apparatus had remained a sufficient time in that position, was negative (−E); while that of the fixed plate was positive (+E).

"III. I applied only the tin wire to the moveable plate, and insulated the two fixed ones, or brought them into communication with the table or any other moist conductors with which the tin wire was in contact. This simple contact of the tin with the brass of which the moveable plate consists, is sufficient to excite in it a very small degree of negative electricity; only a longer time is required.

"Those acquainted with the action of electric atmospheres, and the construction of the doubler, will need no farther explanation, to enable them to comprehend the mode of action of this very ingenious instrument; how the electricity, once obtained from the moveable plate, must occasion an opposite kind in the fixed plate, and vice versa; how the opposite kinds of electricity are increased by each revolution of the machine, &c. In the present experiment, therefore, when the moveable plate is −E, the fixed plate must be +E.

"IV. This is the reverse of the former. The piece of tin was applied to one of the fixed plates, and the metallic one was insulated from all metallic contact. The result was now reversed; that is, the fixed plates were electrified negatively, and the moveable one had positive electricity.

"All these experiments succeed much better, and in a shorter time, if, during the mutual contact of the different metals, the moveable plate be opposite to either of the other two that are fixed; but still better when a piece of thick paper, such as a card, not moist, and of a thickness equal to the intermediate space, is placed between the two plates that stand opposite to each other. It is of advantage to leave the card some time in its place, and not to remove it till the moment when the metals in contact are removed and the machine put in motion. To render the insulation complete, and make the contact of the metals immediate, without the least moisture, which would be highly prejudicial, it will be proper to place the apparatus in the sun. Half an hour, and often less, will then be sufficient to obtain the required electricity, &c.; whereas, in other cases, several hours are necessary before the desired result can be obtained. This experiment is represented in figs. 23, 24, 25, and 26. LLL (fig. 22. and 23.) are the three brass plates of the doubler; A the piece of silver which is in contact with one of these plates; E the piece of tin applied to the other plate, which is opposite to the former; a a, the moist conductor, or chain of moist conductors which form a communication with the pieces of metal. When the silver, as in fig. 23, is in contact with the anterior moveable plate, it gives up to it a little of the electric fluid, and the latter accumulates as much of it as possible; consequently the electricity of the plate becomes positive, as the sign + of the plate shows: whereas the tin attracts the electric fluid from the corresponding fixed plate, which by these means has negative electricity, as the sign (−) of the plate indicates; and it even communicates this electricity to the other fixed plate, which therefore has the sign (−) also.

"In fig. 24. every thing is reversed; the moveable plate is negatively electrified (−E), while the two fixed plates become positive (+E).

"Lastly, in the 25th and 26th figure, it is seen that the tin abstracts the electric fluid from the brass plate with which it is in contact. This plate is therefore negatively electrified, or has −E; and by the action of its atmosphere occasions positive electricity (+E) in the other plate standing opposite, which is in communication, either with the third plate, as fig. 25, or, what is still better, with other conductors, as fig. 26. These opposite electricities increase afterwards with each revolution of the machine; the action of which, according to the theory of electric atmospheres, produces this effect to the degree mentioned, and justifies the appellation of doubler of electricity, which has been given to this instrument.

"I now come to the experiments, which show that we are to seek for the cause which calls forth the action of the electric fluid; which excites it, of whatever kind it be; determines its transition, &c., much rather in the mutual contact of the metals, than in the contact of the moist conductors with these metals. Though, according to every circumstance, we must admit some action of this kind in the latter contact, it cannot be denied that the former is certainly the most effectual. At present I shall only mention the two following experiments, which I contrived in such a manner that they may serve to explain a question of this kind.

"V. I left the two fixed plates of brass without making any alteration; took off the third moveable plate, and supplied its place by one of tin; and arranged the machine in such a manner, that the latter stood opposite to one of the other two plates. I then applied to this tin plate a bit of brass, and to the opposite fixed plate of brass a piece of tin. After a convenient time, (for example an hour, when the weather was perfectly dry), I took away the two pieces of metal, or only that of brass, and made the moveable plate of tin, which... Effects of which was in contact with the piece of brass, to revolve Galvanism about 30 times. It then gave me very perceptible marks of positive electricity.

VI. I reversed the former experiment, and made the piece of brass touch the brass plate, and the piece of tin the plate of the same metal. I, however, obtained nothing, or almost nothing; even when the apparatus was left a much longer time in that situation, and when the machine had made twice or three times as many revolutions.

These two experiments are represented by fig. 27. and 28.; where L is the piece of brass, E that of tin, and a a the moist conductors which connect the two different pieces of metal.

In the arrangement of fig. 28. the same contact of different metals, viz. brass on the one side, and tin on the other, with the same kind of moist conductor, takes place, as well as in the preceding experiment of fig. 27. The addition of the electric fluid in the one, and the abstraction of it in the other, ought therefore equally to take place, though in an inverted order, when the action on the fluid calls forth the moving power, by this contact of the two metals L, E, with the moist conductor between them; and yet this is not the case, as no signs of electricity are obtained even after a long time, and when the machine has been caused to make twice or three times as many revolutions. The condition essentially necessary to obtain electricity is, that the different metals must be in contact with each other, which is the case in fig. 27. but not in fig. 28.

When the machine has been repeatedly turned, something may be obtained. This arises either from small remains of old electricity, which could not be destroyed or dissipated in the time during which the arrangement of fig. 26. was continued; or even from fresh electricity, which the moveable plate may have obtained from the atmosphere or vapours during the pretty considerable time of the machine being in a state of revolution; or some accidental difference, either between the two tin or the two brass pieces, may be the cause of some action on the electric fluid, or of some derangement in regard to the equilibrium. In the last place, the contact of the moist conductor with the tin on the one side, or with the brass on the other, may have a different action, which, in my opinion, must be very small, but yet is not entirely without effect.

As it is now proved that, according to the arrangement of the sixth experiment, nothing, or almost nothing, is obtained by 40, 60, and even 80 revolutions of the doubler, while a great deal is obtained by that of the fifth with 20 or 30, we must therefore conclude that the contact of two metals of a different kind with moist conductors, without the mutual contact of these metals themselves (which is wanting in the sixth experiment, where brass is in contact with brass, and tin with tin), produces nothing, or almost nothing; and that, on the contrary, the mutual contact of the two metals of a different kind, which takes place in the fifth experiment, produces the whole, or almost the whole, effect.

Dr. Fowler instituted an elaborate series of experiments on this subject, in which he confirmed and extended many of the results which had been already obtained in the experiments and investigations of other naturalists. He found that metallic substances were the best agents or conductors, and he concluded that the contact of two dissimilar metals is an essential condition in the production of the phenomena of galvanism. It did not indeed escape his observation, that in some cases a single metal produced muscular contraction, but this he ascribed to mechanical stimulus, which excited a painful sensation in the animal, not quite dead, or to the impurity of the metal, containing some portion of alloy, or folder. Future observation, however, proved, that these motions could be produced without any metal whatever. He found that the most powerful effects were produced by employing zinc, in combination with gold or silver. By means of these metals he produced contractions twenty-four hours after they had ceased. In the experiment by which this was established, the nerve was coated with tin, and a different metal was employed to complete the circle between the coating and the muscle. The same philosopher also found that the effects were increased in proportion to the bulk of the metals employed, and the extent of surface brought into contact; that a communication might be formed between the metals in contact, and the nerves of the animal which were exposed, by means of water; and that the temperature of the season and the nature of the animal's death seemed to have considerable influence on the duration of the phenomena. In many cases he was able to produce contractions in a frog, after three days had elapsed from the time that the head had been separated from the body. He seems to have directed his attention particularly to the conducting power of the substances employed in galvanic apparatus, and in tracing the analogy between this property and electricity. Although metals were found to be good conductors, this was not the case with the metallic oxides, or with the salts which have these oxides, for their basis.

An earthworm placed on a circular piece of zinc, exhibited contractions similar to those produced in living frogs, when a piece of silver was brought in contact to complete the circle. Worms of the same kind, suspended across a silver rod, and the head and tail being at the same time brought in contact with a piece of zinc, sustained a shock which seemed to pass through the whole body. A similar experiment, followed by the same result, was made on leeches. If an earthworm or leech be placed on a piece of silver, resting on a plate of zinc, the animal experiences a painful sensation, when any part of its body comes in contact with the zinc. It seems to have the same disagreeable sensation when it is placed on the zinc, and any part of the body is brought into contact with the silver.

The inquiries of the same philosopher were also directed to ascertain whether the nerves in general are all equally subject to the galvanic influence, or whether its effects are limited to those which are subject to the power of the will. With this view the heart of a cow was separated from the body, soon after the animal was killed, and prepared in the way which has been already described, in the preparation of frogs; and while the contractions of the auricles still continued, the intercostal nerve being coated, and the apparatus arranged, the metals were brought into contact, but seemed to have no effect whatever on the contractions while they continued, and after they had ceased, had not the power of renewing them. He failed in many similar attempts on hot- hot-blooded animals, but succeeded in producing muscular contractions in part of a frog, after an hour had elapsed from the time that the natural motions had ceased. He made a similar experiment on the heart of a cat which had been drowned in warm water, and he found that in this case the motion of the heart could be excited by means of galvanism; but when the animal was drowned in cold water, no effect could be produced.

It was another object of his investigations, to ascertain the effects of galvanism on the organs of the senses. The disagreeable taste which remains on the tongue, when two dissimilar metals, the one placed on the upper surface, and the other touching the under surface, are brought into contact, has been already taken notice of, and the method of applying the metals particularly described. The stronger impression, it was observed, was produced, when gold and zinc were employed. He introduced a metallic substance of a different kind into each ear, and having formed a communication between them, he experienced a shock in the head when these two metals were brought into contact. A bit of tin foil was placed on the point of the tongue; the rounded end of a silver pencil case was applied to the internal angle of the eye; and when the other extremity of the pencil case and the tin foil on the tongue were brought into contact, he perceived a flash of pale light, as well as the metallic taste in the tongue which is produced in a preceding experiment. The flash seemed most vivid when gold and zinc were employed. A similar effect is produced by introducing one of the metals between the upper lip and the gum, and the other between the under lip and the gum, and retaining them in this position to bring the edges in contact; or, by inserting one of the metals into the nose, and placing the other on the tongue, to form the communication between them.

Similar experiments were made by the late Professor Robison of Edinburgh. He particularly observed, that the effects of the galvanic fluid were more sensibly felt when one of the conducting metals was placed on a wound, or on the nerve of a carious tooth. From the peculiar impression on the tongue on the application of gold or silver trinkets, he could ascertain whether any folder was employed about them.

In another experiment the same philosopher seemed to think that he had proved that the effect was produced even before the metallic conductors were brought into direct contact. A piece of zinc was introduced between the gums and cheek on one side of the head, and a piece of silver was placed in the same way on the other side of the head. A rod of zinc was then applied to the zinc piece, and a rod of silver to the silver piece on the different sides of the head; the extremities of these rods which projected from the mouth were then cautiously brought into contact; and, as soon as this was completed, a strong sensation was produced in the gums. But before the direct contact was made between the extremities of the rods, he perceived a flash of light which was repeated when the rods were again separated to a small distance from each other. It is scarcely necessary to add, that when the arrangement of the rods was reversed, the effects ceased; that is, when the zinc rod was substituted for the silver rod, and the silver one for that of zinc.

To the account of the experiments on animals now given, which were chiefly made on cold-blooded animals, we shall now add those of Aldini, the nephew of Galvani, which were made on the body of a man executed in London for murder. This man who was experimented on the 17th January 1803, was 26 years of age, and seemed to have been of a strong, vigorous constitution. The body was exposed for an hour to a temperature two degrees below the freezing point Fahrenheit, at the end of which it was conveyed to a house not far distant, where the apparatus for the experiments had been arranged. The following is the account of these experiments in the author's own words.

"Experiment 1.—One arc being applied to the mouth, and another to the ear, wetted with a solution of muriate of soda (common salt), galvanism was communicated by means of three troughs combined together, each of which contained 40 plates of zinc, and as many of copper. On the first application of the arcs the jaw began to quiver, the adjoining muscles were horribly contorted, and the left eye actually opened.

"Exper. 2.—On applying the arc to both ears, a motion of the head was manifested, and a convulsive action of all the muscles of the face; the lips and eyelids were also evidently affected, but the action seemed much increased by making one extremity of the arc to communicate with the nostrils, the other continuing in one ear.

"Exper. 3.—The conductors being applied to the ear, and to the rectum, excited in the muscles contractions much stronger than in the preceding experiments. The action even of those muscles further distant from the points of contact with the arc was so much increased as almost to give an appearance of re-animation.

"Exper. 4.—In this state, wishing to try the power of ordinary stimulants, I applied volatile alkali to the nostrils and to the mouth, but without the least sensible action; on applying galvanism great action was constantly produced. I then administered the galvanic stimulus and volatile alkali together; the convulsions appeared to be much increased by this combination, and extended from the muscles of the head, face, and neck, as far as the deltoid. The effect in this case surpassed our most sanguine expectations, and vitality might, perhaps, have been restored, if many circumstances had not rendered it impossible.

"Exper. 5.—I next extended the arc from one ear to the biceps flexor cubiti, the fibres of which had been laid bare by dissection. This produced violent convulsions of all the muscles of the arm, and especially in the biceps and the coraco-brachialis, even without the intervention of salt-water.

"Exper. 6.—An incision having been made in the wrist, among the small filaments of the nerves and cellular membrane, on bringing the arc into contact with this part, a very strong action of the muscles of the fore-arm and hand was immediately perceived. In this, as in the last experiment, the animal moisture was sufficient to conduct the galvanic stimulus without the intervention of salt water.

"Exper. 7.—The short muscles of the thumb were..." Effects of Galvanism on Animals

"Exper. 8.—The effects of galvanism in this experiment were compared with those of other stimulants. For this purpose, the point of the scalpel was applied to the fibres, and even introduced into the substance of the biceps flexor cubiti without producing the slightest motion. The same result was obtained from the use of caustic volatile alkali and concentrated sulphuric acid. The latter even corroded the muscle, without inducing it to action.

"Exper. 9.—Having opened the thorax and the pericardium, exposing the heart in situ, I endeavoured to excite action in the ventricles, but without success. The arc was first applied upon the surface, then in the substance of the fibres, to the carnea columnae, to the septum ventriculorum, and lastly, in the course of the nerves by the coronary arteries, even with salt water interposed, but without the slightest visible action being induced.

"Exper. 10.—In this experiment the arc was conveyed to the right auricle, and produced a considerable contraction, without the intervention of salt water, but especially in that part called the appendix auricularis; in the left auricle scarcely any action was exhibited.

"Exper. 11.—Conductors being applied from the spinal marrow to the fibres of the biceps flexor cubiti, the gluteus maximus, and the gastrocnemius, separately, no considerable action in the muscles of the arm and leg was produced.

"Exper. 12.—The sciatic nerve being exposed between the great trochanter of the femur and the tuberosity of the ilium, and the arc being established from the spinal marrow to the nerve divested of its sheath, we observed, to our astonishment, that no contraction whatever ensued in the muscles, although salt water was used at both extremities of the arc. But the conductor being made to communicate with the fibres of the muscles and the cellular membrane, as strong an action as before was manifested.

"Exper. 13.—By making the arc to communicate with the sciatic nerve and the gastrocnemius muscle, a very feeble action was produced in the latter.

"Exper. 14.—Conductors being applied from the sciatic to the peroneal nerve, scarcely any motion was excited in the muscles.

"Exper. 15.—The sciatic nerve being divided about the middle of the thigh, on applying the conductors from the biceps flexor cruris to the gastrocnemius, there ensued a powerful contraction of both. I must here observe that the muscles continued excitable for seven hours and a half after the execution. The troughs were frequently renewed, yet towards the close they were very much exhausted. No doubt, with a stronger apparatus we might have observed muscular action much longer; for, after the experiments had been continued for three or four hours, the power of a single trough was not sufficient to excite the action of the muscles: the affluence of a more powerful apparatus was required. This shows that such a long series of experiments could not have been performed by the simple application of metallic coatings. I am of opinion that, in general, these coatings, invented in the first instance by Galvani, are passive. They serve merely to conduct the fluid pre-existent in the animal system; whereas, with the galvanic batteries of Volta, the muscles are excited to action by the influence of the apparatus itself.

"From the above experiments there is reason to conclude:

"1. That galvanism, considered by itself, exerts a considerable power over the nervous and muscular systems, and operates universally on the whole of the animal economy.

"2. That the power of galvanism, as a stimulant, is stronger than any mechanical action whatever.

"3. That the effects of galvanism on the human frame differ from those produced by electricity communicated with common electrical machines.

"4. That galvanism, whether administered by means of troughs, or piles, differs in its effects from those produced by the simple metallic coatings employed by Galvani.

"5. That when the surfaces of the nerves and muscles are armed with metallic coatings, the influence of the galvanic batteries is conveyed to a greater number of points, and acts with considerably more force in producing contractions of the muscular fibre.

"6. That the action of galvanism on the heart is different from that on other muscles. For, when the heart is no longer susceptible of the galvanic influence, the other muscles remain still excitable for a certain time. It is also remarkable that the action produced by galvanism on the auricles is different from that produced on the ventricles of the heart, as is demonstrated in experiment the tenth.

"7. That galvanism affords very powerful means of resuscitation in cases of suspended animation under common circumstances. The remedies already adopted in asphyxia, drowning, &c., when combined with the influence of galvanism, will produce much greater effect than either of them separately."

Excepting the experiments of Aldini which we have just detailed, the greater number of those of which an account has been given, it has been already observed, were made on cold-blooded animals, and besides, the apparatus usually employed, was a single galvanic combination. After the construction of the pile was known, and still more so after batteries in the form of troughs were invented and employed, very different effects were exhibited on the animal body, both in the dead and living state.

With batteries composed of 200, 300, or 400 pairs of plates arranged in troughs, very powerful shocks will be felt when the circle is completed between the extremities of the battery by means of the two hands of any person, so that the fluid shall pass through the body. This experiment may be performed by touching with one hand wetted, a wire connected with one extremity of the battery, and with the other hand also moistened a wire proceeding from the other end of the battery. Every time that the contact is made a shock is felt. The effect will be more powerful if round balls of brass having brass rods attached to them after being well wetted, be placed in the palms of the hands also well wetted, and a communication be established between the ends of the battery. The same effect is produced when the circle is completed by means of a number of persons joining hands together; but it must be observed, that each person must take care to have Effects of the hands well moistened, otherwise the intensity of the Galvanism shock will be greatly diminished, or its effect entirely obliterated. No experiments have been made, so far as we recollect, to ascertain with any degree of precision, how far the intensity of the shock is diminished by increasing the number of persons composing the circle of communication, or whether indeed, when the experiment is made with the requisite degree of caution and attention, it suffers any diminution.

It has been observed by some, (and so far as we can judge from our own feelings in numerous experiments made with a pile composed of 60 pairs of plates, or with a trough of 50 pairs, and sometimes with two and four troughs of 50 pairs each combined, the observation which we have made coincides with that of others), that the shock from the galvanic battery polled some peculiarity, by which the sensation it excited was much more disagreeable than a shock of artificial electricity which seemed to be of no greater intensity. But it must be allowed, that in the comparison of experiments of such delicacy, the result of which depends on the feelings, great ambiguity must prevail; and therefore, when the comparison is unavoidably so inaccurate, it can afford no precise conclusion.

The sensation is extremely unpleasant when the shock of galvanism, even when it is very slight, passes through the fingers, if they have been scratched or wounded.

A slight shock directed through the head between the temples, produces the sensation of a flash of light before the eyes, and an irresistible contraction of the muscles of the upper eyelids, so that the person who is the subject of the experiment involuntarily winks every time that the circle is completed. This experiment, which should be repeated with caution, is performed in the following manner: Place a bit of tin foil which will adhere by wetting with water to the part to which it is applied, on each temple. Then having formed the communication between one end of the trough and one temple by means of a metallic conductor, flat like a small button, in that part which touches the tin-foil; this is retained in contact with the tin-foil by an assistant; and by means of another assistant, another similar conductor is applied to the tin-foil on the other temple. Things being thus arranged, the wire connected with the latter, is by the operator brought into contact with the other extremity of the battery, or with that part of it to which the extent or intensity of the shock is to be limited. Every time that this contact is repeated, the sensation of the flash of light, and the other effects, are produced. It has been hinted above, that this experiment should be performed with caution. Not more than from 12 to 20 pairs of plates should be employed, at least on those on whom the effects of a small number have not been previously tried; and perhaps with that number, at least in the experiments of this kind which we have seen made, there are not many persons who would choose to have them repeated on themselves. But these effects, it may be added, will be more or less powerful in proportion to the period that the battery has continued in action with the same fluid.

A battery composed of 200 pairs of plates will produce strong contractions in the limbs of a fowl or rabbit, which has been recently killed. These effects may be conveniently exhibited by introducing one of the conducting wires, by means of a hook, into the mouth, or fixing it about the back part of the head of the animal, and fixing a similar hook from another wire connected with the other end of the battery near the rump, so that the current of galvanic fluid shall pass through the body. When the communication between the extremities of the battery is formed, the convulsive motions of the limbs of the animal take place, and are repeated as often as the circle is completed. Similar effects are produced on a dog or sheep; but to induce strong convulsions in the larger animals, a more powerful apparatus must be employed. It will be necessary to put in action a battery consisting of at least 300 or 400 pairs of plates arranged in troughs.

With a battery of such extent and power, the convulsive motions produced on the limbs of horses that were subjected to its action, were so strong that they could scarcely be resisted by the strength of two persons.

The head of an ox, soon after it was separated from the body, and while it was yet warm, was acted on by six batteries, amounting to about 300 pairs of plates. Strong convulsive motions were produced; the eyes opened, and the pupils were greatly dilated; the ears were also put in motion; and the tongue drawn out and fixed to the table with an iron skewer which entered the wood above half an inch, was retracted with such force as to detach itself from the skewer which was thrown to some height into the air.

It has been said that the motions thus induced on the limbs of animals by means of galvanism, resemble the convulsive motions of epilepsy. Perhaps the motions of animals during the struggles of death may be considered as nearly similar. Whether this be so or not, we have observed that the convulsive contractions of animals subjected to galvanism, greatly resemble the peculiar motions of each animal in the struggles of death. This observation however only extends to what has happened to fowls, rabbits, and sheep; but so far as it goes, it has been allowed by those to whom we have remarked the circumstance to be pretty correct.

With these observations we conclude this long detail of the effects of galvanism on animals. This seems to be necessary in order to give the reader a distinct view of what may be considered as the dawn of this department of science; for as we have already hinted, the experiments and investigations of naturalists were at first limited to its effects on animals; and from their labours an immense body of facts was accumulated before its chemical effects were much known or distinctly ascertained. We now therefore proceed to the consideration of the chemical effects of galvanism. These shall be the subject of the next chapter.

CHAP. III. Of the Chemical Effects of Galvanism.

In the account we propose to lay before our readers, of those effects of the galvanic fluid which are to be considered as more strictly chemical, we shall first state more generally some of the experiments by means of which these effects are illustrated, and describe the method of performing them, and then enter into a more particular detail of the experiments of different philosophers. We shall limit the account of the experiments first alluded to above to the combustion of charcoal, the deflagration and combustion of metallic substances, the decomposition of water and some other fluids, and the precipitation of metals from their solution in acids.

**Exper. 1.**—With a battery composed of 50 pairs of plates, of three or four inches square, with proper management, a brilliant light may be produced from the combustion of charcoal. The charcoal for this experiment should be well prepared, from some of the harder woods, such as beech or boxwood. It has been said that it could only be properly prepared by exposing it to a degree of heat equal to that of a glass-house furnace; but we know from experience that so high a temperature is by no means absolutely necessary. We have prepared charcoal which was found to answer the purpose of the present experiment, with such a heat as can be easily commanded in a small chemical furnace. The wood which is to be converted into charcoal is divided into slips of about one-fourth of an inch square; it is then put into a crucible, which is filled up with sand, and may be covered with another crucible inverted, so as still more effectually to prevent the access of air. The crucible is then placed in the middle of the furnace, which is to be filled up with charcoal, and a strong heat maintained for eight or ten hours. After this the charcoal will be found sufficiently prepared, and this is of some consequence to be attended to, because on the complete conversion of the wood into this state much of the success of the experiment depends.

Slips of charcoal reduced to a fine point are attached to wires, which communicate with the extremities of the battery. The charcoal may be fixed to the conducting wires by means of a bit of thread, or fine iron or brass wire, or they may be fixed in pincers, or an instrument similar to that which is used for holding crayons or blacklead pencils; but in whatever way this part of the apparatus is contrived, when the two pieces of charcoal connected by means of metallic conductors with the extremities of the battery are brought into contact, combustion immediately takes place. The rapidity or brilliancy of this combustion is proportioned to the strength and activity of the battery. The light produced by such a battery as that we have described above, will be at times pretty vivid; but with two such batteries, whose action is combined, it is still more brilliant. When four batteries, consisting each of 50 pairs of plates of eight inches square, are employed for this experiment, nothing perhaps can exceed the brilliancy of the light which is given out during the combustion of the charcoal. With the smaller battery, the process is occasionally interrupted; but with the larger apparatus the combustion goes on for a short time, giving out a continued and uniform brilliant light. When this is the case, the rays seem to proceed from the point where the combustion is going on, and exhibit all the variety of the prismatic colours. When the pieces of charcoal are immersed in water, and brought into contact under its surface, the combustion also goes on with considerable rapidity.

**Exper. 2.**—The deflagration and combustion of many metallic substances may be also effected with a battery composed of 50 pairs of three inch plates, and this may be done with a very simple apparatus. A bent wire, such as we have already described, is inserted into the perforated, projecting piece of wood, at the extremity of the battery. The wire is to be bent at a right angle to that part of it which is fixed perpendicularly into the extremity of the trough, and on the horizontal part of it is placed the metallic substance to be deflagrated. A plate of copper, which must be perfectly clean and free from oxide, is to be connected with the other end of the battery by means of a conducting wire. When the apparatus is thus arranged, if the copper plate be brought into contact with gold or silver leaf, for instance, the combustion of these substances will take place, and this combustion, it is scarcely necessary to add, will be in proportion to the power of the battery and its energy. In the same way tin-foil, white and yellow Dutch metal, as it is called, may be subjected to experiment, and with a battery of moderate power, a brilliant combustion may be produced.

When a battery of greater power is employed, a very brilliant and rapid combustion of steel wire can be effected. This experiment is made by stretching a piece of wire, such as that which is used for the smaller strings of musical instruments, between the two metallic conductors connected with the opposite extremities of the battery; and thus completing the circle, the combustion takes place. When the experiment succeeds, several inches of the wire are almost instantaneously reduced to the state of oxide. In this way the energy of the battery may be in some measure ascertained, as it must be in proportion to the length of the wire which is burnt. When a very powerful battery is in action, 10 or 12 inches of such wire may be completely burnt; that is, not merely made red hot, but having undergone the process of combustion, and having passed from the metallic state to that of oxide.

**Exper. 3.**—We have already described the apparatus for the decomposition of water. To exhibit this experiment, it is only necessary to fill some of the tubes which have been mentioned for this purpose with water, and to complete the circle of communication between the extremities of the battery, the water in the tube to be decomposed forming part of this circle. If the conducting wires terminating in the tube consist of metals which do not readily undergo oxidation, such as gold or platinum, the gases which are the constituent parts of water are separated from the wires, the oxygen gas from the one, and the hydrogen gas from the other, and are seen rising in bubbles to the top of the tube, displacing a quantity of water equal to the space occupied by the gases evolved. This process goes on till the surface of the water falls below the conducting wire passing through the top of the tube; and the circle being then interrupted, the process stops. When this is the case, if the two conducting wires within the tube can by any contrivance be brought into contact, a spark is produced, by which the gases are set fire to, and are again converted into the state of water. This combustion is attended with an explosion. Or if the tube be carefully taken from the apparatus under water, while the finger is placed upon the open end, and then inverted, the gas collected will rise through the water; it may then be let fire to by means of a burning body, a similar combustion will take place, attended with an explosion. But if the wires terminating in the tube be of brass or iron, or any metal which is easily oxidated, only one of the gases is collected in the tube; the other (the oxygen) combines with the metal, forming an oxide, which collects on the point of the wire.

By a very simple contrivance the gases may be collected separately. With this view two tubes in which the conducting wires terminate, are employed. These tubes being filled with water, must be inverted in the same basin of water, the latter of which forms the communication between the extremities of the battery.

Other fluids, as oil, alcohol, ether, and ammonia in solution, may be also decomposed by a similar process. For the decomposition of oil, alcohol, and ether, the pieces of charcoal may be immersed in vessels containing these liquids; and, when they are brought into contact, the decomposition is effected, with the formation and evolution of carbonic acid gas, which is seen rising in bubbles to the surface.

Exper. 4.—By means of galvanism, and with a battery of moderate power, metals may be precipitated from their solutions in acids. The apparatus to be employed for this purpose is similar to that for the decomposition of water, and the tube is filled with a solution of the metallic salt. The communication being then established, the metal is precipitated, and appears in an arboreal form on the point of the wire. In this way the acetate of lead, or sugar of lead, the nitrate of silver, and many other metallic salts, may be revived.

Many other curious and amusing experiments might have been related, but what we have now given will enable the reader to have a distinct notion of the chemical effects of galvanism. Many other of the chemical effects of the galvanic fluid are closely connected with the peculiar views and theories of those who have discovered and observed them; that we shall not enter into any detail of them till we come to consider that part of the subject. In the mean time we shall occupy the remaining part of the present chapter with an account of some of the experiments on the chemical effects of galvanism which were observed by philosophers in the earlier part of its progress.

Mr Cruickshank, the inventor of the galvanic trough, very early directed his attention to this inquiry, and prosecuted it with great ardour and success. In one of his early communications on this subject we have a comprehensive view of some of the chemical phenomena of galvanism. We shall, therefore, give it in his own words.

"I shall not, says he, give any particular account of the apparatus employed, being a pile, and not differing materially from that in use. I shall only just observe, that it consisted of plates of zinc and silver, of about 1.6 inches square, and that the number of each employed in the following experiments varied from 40 to 100, according to the power required.

"I found that a solution of the muriate of ammonia answered better for moistening the interleaved papers than common water.

"When the machine was in full action, sparks which were perfectly visible in the daytime, could be taken at pleasure, by making a communication in the usual way between the extremities of the pile, and a small report or snap could be heard; the shock given at that time was very strong, and a gold-leaf electrometer, placed in the circle of communication, was very sensibly affected: these circumstances, some of which, I believe, have been already ascertained by Messrs. Nicholson and Carlisle, shew the strong resemblance of this influence to electricity. These gentlemen have likewise discovered that galvanism decomposes water with much greater facility than electricity, but with phenomena somewhat different.

"Exper. 1.—A quantity of common water was introduced into a glass tube, being confined at each end by corks, but perfectly at one by a cement of rosin and beeswax: pieces of silver wire were passed through the corks, and brought within an inch of each other in the fluid, their other extremities being at the same time connected with those of the machine or pile, one with the lower zinc plate, and the other with the upper silver plate. In future, to avoid circumlocution, I shall call the wire attached to the silver plate, the silver wire, and the other the zinc wire. The tube was then placed upright in a cup containing water, with the uncemented end downwards. As soon as the communication was made between the extremities of the pile by the wires, a quantity of small air bubbles began to ascend from the end of the wire connected with the silver, as observed by Messrs. Nicholson and Carlisle; but a white cloud at the same time made its appearance at the one, proceeding from the zinc, or the zinc wire. This cloud gradually increased, and assumed a darker colour, and at last became purple, or even black. A very few air bubbles were likewise collected upon and ascended from this wire, but when the machine was in full force, a considerable stream could be observed.

"The gas was collected, and found to be a mixture of hydrogen and oxygen, in the proportion of three parts of the former to one of the latter. No great dependence, however, was placed upon this in point of accuracy. The zinc wire was found to be much corroded, and looked as if a considerable portion of it had been dissolved. As the cloud which was formed around this wire became purple on exposure to the light, I suspected it might be lunar cornea, or muriate of silver proceeding from the silver, which had been somehow dissolved, and afterwards precipitated in this state, by the muriatic salts in the common water. This led to the following experiments:

"Exper. 2.—The glass tube was now filled with distilled water, to which a little tincture of litmus was added; when the communication was made by the wires as in the former experiment, a quantity of gas arose from both wires, but in the greatest quantity from that connected with the silver. In a few minutes a fine red line, extending some way upwards, was perceived at the extremity of the zinc wire; this increased, and in a short time the whole fluid below the point of this wire became red; the fluid however, above the silver wire, looked of a deeper blue than before, the slight tinge of purple being destroyed.

"Exper. 3.—I next filled the tube with distilled water, tinged with the tincture of Brazil wood; it was no sooner placed in the circle of communication, than the fluid surrounding the silver wire, particularly towards its extremity, became purple, and this tinge increased so fast, that the whole fluid surrounding this wire, and occupying the upper part of the tube, soon assumed as deep a colour, as could be produced by ammonia.

"The portion of the fluid in contact with the zinc wire..." Chemical wire became very pale, and almost colourless, nor could the purple tinge extend below its upper extremity. From these experiments it would appear, that an acid, probably the nitrous, is produced at the wire proceeding from the zinc, and an alkali, probably ammonia, at that in contact with the silver. These facts sufficiently explain the action upon the silver wire, and the nature of the whitish cloud proceeding from it, and afterwards becoming purple. When lime water was employed instead of common or distilled water, the wire was likewise acted upon, but in a less degree, and the cloud had at first an olive colour, exactly resembling the precipitate of silver by lime-water.

"The quantity of silver dissolved or corroded, if I may use the expression, in these experiments, was very considerable, and where common or distilled water had been employed, a small portion of it remained in solution, which was discovered by the addition of the muriatic acid. Indeed a much larger quantity would probably have been suspended, had it not been for the alkali generated at the same time, and which manifestly produced a precipitate at, or near, the upper extremity of the zinc wire, where, after a certain time, a dark zone or stratum was always formed.

"Exper. 4.—It is a well known fact, that hydrogen gas when heated, or in its nascent state, reduces the calces of the metals; I expected, therefore, that by filling the glass tube with a metallic solution, I might be enabled to separate the hydrogen from the oxygen gas, and thus procure the latter in its simple or pure state. With this view the tube was filled with a solution of the acetate of lead, to which an excess of acid was added, to counteract the effects of the alkali. When the communication was made in the usual way, no gas could be perceived, but after a minute or two, some fine metallic needles were perceived at the extremity of the wire connected with the silver. These soon increased, and assumed the form of a feather, or rather that of the crystals of the muriate of ammonia. The lead thus precipitated was perfectly in its metallic state, and very brilliant; a little gas escaped from the wire connected with the zinc, and it was considerably corroded as usual.

"A solution of the sulphate of copper was next employed, and with the same result, the copper being precipitated in its metallic form by the wire connected with the silver. In this instance the metal did not crystallize, but formed a kind of button at the end of the wire, which adhered completely to the silver, that it was found impossible to separate it.

"The most beautiful precipitate, however, was that of silver from its solution in the nitrous acid. In this case, the metal shot into fine needle-like crystals, articulated, or joined to each other, as in the Arbor Diance.

"What became of the oxygen gas usually produced in these experiments?

"Exper. 5.—A quantity of pure water mixed with distilled vinegar was introduced into the tube, and placed in the circle of communication; some gas was disengaged from the silver wire, but no cloud appeared at the extremity of the zinc. After some time, however, a quantity of metallic silver was precipitated by the silver wire, and this precipitate at last became very copious; a perfectly similar effect was produced, when the tube was filled with very dilute sulphuric acid; in these cases the precipitated silver had the appearance of shining scales, like that thrown down by copper in the usual way. It may be proper to observe, that in all these precipitations and reductions, nothing but wires of pure silver were employed. The results in this last experiment were exactly what was expected; the vinegar prevented the alkali from precipitating the silver, dissolved by the generated acid; in consequence of which, when a sufficient quantity of the metal was taken up, it was again thrown down by the silver wire in its metallic form.

"Exper. 6.—A solution of the muriate of ammonia being introduced into the tube, and exposed to this influence, a little gas was disengaged from the silver wire, while the zinc one was incrusted with a substance which soon became black, and was found to be luna cornea. The liquor which remained in the tube after the operation had been finished, was highly alkaline, and smelled strongly of ammonia; common salt was decomposed in a similar manner. This experiment accounts for the decomposition of the muriate of soda and ammonia, which always takes place when the papers in the pile are moistened with a solution of these salts.

"A solution of the nitrate of magnesia appeared to be likewise decomposed by this process; for after some time, a white powder resembling magnesia, was precipitated on the surface of the silver wire, very little gas was disengaged.

"Exper. 7.—In order to ascertain how far this influence might be carried, provided the circle of communication was complete, two tubes were employed, and connected by a silver wire passing through corks; the tubes were filled with water and secured by corks; two other wires being then passed through these corks, the arc was connected with the silver, and the other with the zinc, at the extremity of the pile. A quantity of gas as usual was disengaged at the extremity of the silver wire, and the portion of the connecting wire in the same tube was partly dissolved, and as mentioned in experiment 1st; but the other portion of the same wire in the other tube gave out gas, while the communicating zinc wire was corroded. And I make no doubt that a similar effect would be produced, if any number of tubes were connected in a similar manner, by which means a large quantity of gas might be procured in a short time.

"Besides silver wires, I likewise employed those of copper or iron, and it did not appear that they were more corroded or acted upon than the silver; indeed, in some of the above experiments, not less than half, or three-quarters of an inch of the wire was entirely consumed. The copper wire connected with the zinc gives out a greenish blue substance resembling the nitrate of copper with excess of the metal, or when part of the acid has been expelled by heat, &c. In examining the gas which was procured at different times, I always found it mixed with a little oxygen gas, but sometimes this did not exceed one-eighth of the whole, in bulk; however, I paid but little attention to this part of the process, for as my wires were always corroded, no conclusion with regard to the composition of water could be drawn from it."

We might have here detailed a greater variety of experiments, vol. iv. PART II. OF THE HISTORY AND PROGRESS OF GALVANISM.

IN the first part of this treatise we have given a pretty full view of the method of constructing apparatus for the purpose of exhibiting the phenomena of galvanism, and we have entered at considerable length into a detail of the experiments which have been made, to ascertain the effects of the galvanic fluid on animals, as well as those experiments by which its chemical effects are illustrated, with some of the theoretical views and opinions of those who have been engaged in researches concerning the properties of this fluid. It is now proposed, in the second part, first, to consider the progressive history of galvanism, with the theories by which philosophers have attempted to account for its effects; secondly, we shall endeavour to trace the analogy between artificial electricity and galvanism; and lastly, give an account of the experiments and inquiries which have been made concerning the formation of muriatic acid and soda by means of this power. These will form the subjects of the three following chapters.

CHAP. I. History of the Discovery and Progress of Galvanism.

The first hint which is usually quoted as connected with the phenomena of galvanism, is extracted from a book entitled the General Theory of Pleasures, by Sulzer, which was published in the year 1767. In this work the author particularly describes the experiment with two dissimilar pieces of metal which we have related at the beginning of this treatise, and by which we have endeavoured to illustrate what is understood by galvanism, in its effects on the living body. The experiment alluded to is that in which a piece of zinc and a piece of silver being placed, the one in contact with the upper, and the other with the under surface of the tongue, and their projecting edges being brought into contact, a taste is produced, which the author observes, resembles vitriol of iron. This sensation is ascribed to a vibration of the particles of the metals affecting the nerves of the tongue.

Other hints and experiments have been quoted, which seem to be connected with the phenomena of galvanism; but as they were not prosecuted, and as no conclusion, with the view of establishing any particular point, was deduced from them, it would be unnecessary to give an account of them, excepting those of Vassalli, member of the royal academy of Turin, who published in 1789, a theory on this subject, supported by a series of experiments which he had instituted. Here he throws out a conjecture, that a provision has been made by nature in the system of a living animal, by which the electricity accumulated in any particular part of the body is preserved and retained for some necessary purpose of its existence. It had indeed been supposed by some, that the animation of the blood depended on the electric fluid, but according to others, this fluid and the nervous fluid were to be considered as one and the same.

This subject was particularly investigated and illustrated, when in the year 1791 a remarkable discovery was made by Dr Galvani, professor of anatomy in the university of Bologna in Italy, was announced to the world. This discovery, like most others, was accidental. Some frogs deprived of the skin were placed upon a table near which the professor happened to be engaged in experiments with an electrifying machine. The crural nerve of one of the frogs was touched by a person present, with the point of a scalpel during the time that the machine was working. The whole animal was thrown into convulsions. The same experiments were afterwards repeated with the same success. Every time that the scalpel was applied to the nerve, while the machine was in motion, violent convulsions were produced. But when the machine ceased to move, on the application of the scalpel to the nerve no effect followed. To this accidental discovery this branch of science owed its origin, and from the name of the discoverer was called Galvanism.

Since the period of this discovery, a great many experiments have been made, and many curious phenomena have been observed, which have excited much interest and attention among philosophers. We shall now present our readers with a historical sketch of the progress of these discoveries.

The experiment which has been mentioned was repeated by Galvani in every possible way he could think of. He varied it both by means of artificial and atmospheric electricity, and the result of all these experiments he found to be uniform and consistent. When Galvani first began his researches, he supposed that the phenomena depended on common electricity, passing through the animals on which the experiments were made. He had observed that the same effects were produced, but in a smaller degree, in living frogs and in other animals, as in those which had been newly deprived of life. In the course of some experiments which he made on atmospheric electricity, he suspended some frogs, by means of metallic hooks fixed in the spine, from iron palisades; and he observed that the muscles of these animals were frequently and involuntarily contracted, as if they had received a shock of electricity. At first he ascribed these convulsions to the changes in the state of the electricity in the atmosphere; but after a repetition of the experiments he found that he was mistaken. He discovered, however, at last, after many ingenious experiments, that he could at pleasure produce the convulsions, by touching two different parts of the animal, each with a piece of metal, and then bringing these pieces of metal into contact. The experiment may be made in the following manner.

Let the crural nerve of a frog be laid bare to about an inch in extent; let a piece of zinc be placed in contact with the nerve, and let a piece of silver be placed on the muscles with which the nerve communicates. Then bring the zinc and silver into contact, and the whole limb will be instantly thrown into convulsions.

After Galvani had published his experiments, the convulsions thus excited were ascribed to the action of some unknown fluid to which the name Galvanism was given, or Animal Electricity. According to Galvani, a fluid is secreted in the brain, the same with the nervous fluid; but being analogous to common electricity, might with more propriety be termed animal electricity. The conductors of this fluid are the nerves. It is carried off by them as it is secreted, and deposited on the interior surface of the muscular fibres, which being non-conductors of the fluid, do not permit it to pass through them. The state of the muscular fibres exactly resembled that of a charged Leyden jar. Their inner surface is electrified positively, and the outer surface is electrified negatively. The communication between the exterior and interior surfaces of the muscular fibres is formed by the nerves. They convey the redundant electricity from the internal to the external surface, and, like the effect of the electrical stimulus, every discharge is attended with a muscular contraction.

On the other hand Volta, another philosopher who carried his researches far into this subject, and of whose experiments and views we have given a long detail, adopted a different opinion. He thought that the convulsions occasioned by the galvanic apparatus were entirely independent of the action of the nervous fluid, and were to be ascribed to common electricity excited by the metallic conductors which are employed. These different opinions were supported with much ingenuity in a controversy which commenced between Galvani and Volta. The writers on galvanism divided themselves into two parties. While one party maintained with Volta, that the phenomena were owing to the action of common electricity on the muscular fibres, another party thought that they were entirely dependent upon something peculiar to animal matter. By many this seemed to have been considered as the nervous fluid, which was supposed to be the same with, or analogous to, common electricity.

It had been long asserted, that porter, and some other liquors, drank out of a pewter pot, had a different taste from what it has when drunk out of glass or earthenware. Pure mercury, it has been observed, retains its metallic splendour for a long time; but when amalgamated with any other metal, it is soon tarnished or oxidized. The Etruscan inscriptions on pure lead are in good preservation to this day; whereas some medals of lead and tin, of no great antiquity, are much corroded; and works of metal, whose parts are soldered together by the interposition of other metals, soon tarnish about the places where the different metals are joined. When the copper sheeting of ships is fastened on by means of iron nails, the nails, but particularly the copper, are readily corroded about the place of contact. A piece of zinc placed in water for a considerable time scarcely undergoes any change; but if a piece of silver happen to touch the zinc whilst it is in the water, it is soon corroded or oxidated.

In the course of a very few years after the publication of Galvani's discovery, a great number of writers appeared, and presented to the world a great body of facts which they had ascertained by experiments and observations. The following are among the most important:

1. When a piece of metal is placed on the muscle of an animal just dead, and still moist, and another piece of a different metal is placed on the nerve which leads to the muscle, or on another part of the muscle, and if the two pieces of metal be brought into contact, a contraction or convulsion of the muscle takes place.

2. A single piece of metal, or two pieces of the same metal, have no effect in exciting contraction of the muscle. It is necessary to have two perfect conductors of electricity in contact, before any convulsion can be produced.

3. The muscle must be moist. The effect is not prevented by a ligature on a nerve; but the susceptibility of a muscle to be thrown into convulsions is diminished, and at last destroyed by the application of opium, which destroys its irritability. The same change takes place if the muscle be allowed to remain for some time after death.

4. The different muscles of the body are differently affected by the galvanic influence. They are not equally susceptible of the same degree of convulsive effect.

5. If a plate of zinc be placed on the upper surface of the tongue, and a plate of silver or copper be applied to its under surface; and if the two pieces of metal thus placed be brought into contact, a strong metallic taste is immediately perceived. An acid taste is perceived, when the tongue is dipped into an alkaline solution contained in a tin or zinc cup held in the moist hand.

6. If a piece of metal, as a silver spoon, be placed on the ball of the eye, and another piece of a different metal, as a piece of zinc, be placed on the tongue, and if the two pieces of metal be brought into contact, a flash of fire is instantly perceived; and it is perceived, both when the metals are brought into contact, and when they are separated.

7. Another fact, which was ascertained by Aldini, who performed a great many experiments in galvanism during his visit to this country, is, that convulsions may be excited merely by forming a proper chain of muscles and nerves. This is proved by the following experiment. He took a prepared frog, and held it suspended in one hand by the foot. The fleshy nerves were brought into contact with the tongue of an ox, the head of which had been recently separated from the body. He then introduced the other hand moistened with a solution of common salt in water into the ear of the animal, thus completing the circle. Every time that the communication was formed, the muscles of the frog were thrown into convulsions.

Most of the facts which we have now related, were ascertained by the different philosophers, whose researches were directed to the subject of galvanism, between the years 1791 and 1794. Hitherto the connection between galvanism and animal bodies was considered by Part II.

History. Most writers, so close and intimate, that they supposed the one could not exist independent of the other. Some facts, however, which were established by Fabroni and others, seemed to favour the opinion of those who considered galvanism as the action of a peculiar fluid on the animal fibre. This fluid is developed by the mutual action of the metals employed as exciting causes, and it exists in other bodies as well as in those which are endowed with life. We have already mentioned that two pieces of different metals put into water produce changes on the water which neither of them separately could effect. This was observed by Fabroni, from which he concluded that a chemical change was effected by the metals on each other. To this change he supposed part at least of the phenomena of galvanism was owing. Thus he explained the necessity of two different metals and of moisture in the production of these phenomena. Those metals, he also observed, which occasioned the most rapid changes on each other in water, were most powerful in exciting galvanic convulsions.

Metals and charcoal, it was ascertained by Volta, being good conductors of electricity, attract and repel that fluid with different forces. When two different metals in their natural state of electricity are brought into contact, electric matter passes from the one to the other; the one becomes electrified positively, and the other negatively. From this he concluded, that the electricity which occasioned the galvanic phenomena did not reside in the animal fibres, but in the metals employed as exciters, and that the convulsions were produced by the electric matter passing through these fibres.

The seeming inconsistency which appeared in the opinions of Volta and Fabroni was removed by succeeding discoveries, which demonstrated that both electricity and chemistry were concerned in the galvanic phenomena. Galvanism was now no longer considered as something connected with living matter, which was totally inexplicable, but as something developed by the mutual action of inorganic substances on each other, the effect or energy of which might be estimated and measured by its action on the muscular fibres. The discovery of the galvanic pile by Volta put it in the power of philosophers to increase the power or energy of the galvanic influence at pleasure. This pile, and the method of constructing it, have been already described.

A description has also been given of a different apparatus, the invention of Mr Cruickshank of Woolwich, which has been employed in place of Volta's pile. This is called the galvanic trough, and it consists of a number of square plates of different metals as in the other, which are soldered together in pairs, and fixed by means of cement in a box of baked wood, at a small distance from each other.

A striking analogy was at once observed between this apparatus and charged electrics. A great deal of discussion took place on the subject; much investigation followed; and philosophers held different opinions concerning the phenomena of galvanism, whether it was to be considered as the same with common electricity, or as something specifically different.

It was at last ascertained by Nicholson and Carlisle that the zinc end of the pile was in the state of positive electricity, and the silver or copper end in the negative state. The zinc end of the pile, then, according to the commonly received theory of electricity, gives out the electric fluid, which enters at the silver or copper end. And if the circle be completed by means of metallic wires or charcoal, when the pile is sufficiently powerful, sparks similar to what take place by the discharge of common electricity may be perceived. Electric batteries have been charged by means of the pile; metallic wires, tin-foil, gold leaf are burnt; and mixtures of hydrogen and oxygen gas are exploded in the same way as happens when electric discharges are made to pass through them. From the whole of the phenomena, there seems now to be little doubt of the identity of the two fluids.

Chemistry, however, has a very considerable share in the phenomena of galvanism. The action of the pile is most powerful in oxygen gas: it ceases entirely in the vacuum of an air-pump, or in azotic gas. The electrical machine also, it has been ascertained, cannot be excited in any gas unless it contain oxygen; and it seems probable, that the effect of the amalgam, which is employed in exciting the electrical machine, bears a proportion to the facility or rapidity of its oxidation. But we shall discuss this point more fully in the second chapter.

When the action of the pile has continued for some time, it gradually becomes weaker, till at last its energy is entirely lost. This power can only be renewed by cleaning the plates, the surfaces of which have been very much changed. It was observed that the time in which the action of the pile ceased, was in proportion to the energy which it originally possessed. When it was strongest, the duration of its action was shortest. It was observed also, that one of each pair of plates was covered with a coat of oxide; and when this process of oxidation was finished, and the surface of the plate was entirely covered, the action ceased. Of the two metals employed in the construction of the pile, that which is most easily oxidated, always undergoes this process. When zinc and silver, or zinc and copper, are used, the zinc is always oxidated; and unless this oxidation take place, there is no action of the pile. Its action or energy is proportional to the oxidation of the metal; and thus it appears that this oxidation is essentially necessary to the action of the pile. For, unless the liquid which is employed to moisten the pieces of card or cloth between the pairs of plates, or that which fills the cells in the trough, be capable of oxidating the zinc, no action follows. There is no action at all with silver and zinc, and perfectly pure water. In vacuo the action of the pile soon ceases, even with common water; for the oxygen which is held in solution by the water soon combines with the zinc, and then the process stops. The action is increased by oxygen gas, because the oxidation of the zinc is facilitated. Its action is also increased, and goes on even in vacuo, when nitric acid, which supplies oxygen for the process of oxidation, is substituted for the water. Thus, by estimating the proportion between the oxidation of the metals and the action of the pile, it may be determined what metals are proper for forming piles, and with what liquids they may be employed. In the choice of the different metals, it must be observed, that one of them must always be more easily oxidated than the other. Two perfect conductors which are unequally oxidable, with an im- perfect conductor which is capable of oxidating the most oxidable of the perfect conductors, constitute the elements of the galvanic battery.

But some of the most important phenomena of galvanism are exhibited in its chemical effects. Most of these were first observed by the chemical philosophers of this country. We have already detailed many of the experiments by which these effects are illustrated; and we shall here only, for the sake of giving a connected view of the subject, merely recapitulate some of them.

When water forms part of the circle between the extremities of the battery, and the conducting wires are brought within a small distance of each other, being immersed in a glass of water, the water is decomposed, and it will be recollected that the phenomena are different according to the nature of the wires employed. When the wires are of gold or platinum, they undergo no change; oxygen gas is evolved in small bubbles from the positive wire, and hydrogen gas from the negative wire; and if the gases be collected separately by the apparatus formerly described, they are found to be in the proportions of the component parts of water. If one of the wires be immersed into one glass, and another into a separate glass, by completing the circle with a finger plunged into each glass, the process goes on, and the hydrogen gas is extracted in the one vessel, while the oxygen is given out from the wire in the other. This fact was first discovered by Mr Davy.

When spring water is used, or water having azotic gas in solution, an acid is formed at the extremity of the positive wire, and an alkali at the extremity of the negative wire. The acid was found to be nitric, and the alkali ammonia. If the wires be plunged in different glasses, and the connexion be formed by means of an animal body, the positive wire produces in the water tinged with an infusion of litmus, a red colour, while the negative wire also reddens an infusion of brasil wood.

If other wires beside those of gold or platinum be used, it is found that the positive wire undergoes oxidation, but little or no gas is separated from it; while the negative wire, as in the former case, gives out hydrogen gas. When the wires are immersed into metallic solutions, as acetate of lead, nitrate of silver, &c., the silver or lead is revived, and deposited on the negative wire; and if solutions which contain sulphuric, nitric, or oxymuriatic acids, are used for the immersion of the conducting wires, the acids are decomposed, oxygen gas is evolved from the positive wire, and sulphur or hydrogen gas makes its appearance at the negative wire. The decomposition of ammonia has already been mentioned. This was discovered by Mr Henry. The hydrogen is given out by the negative wire, while the azotic gas is evolved by the positive wire. When plumbago or charcoal are employed as conductors in place of metals, it is found that carbonic acid is evolved from the positive end, and hydrogen gas from the negative.

It may be necessary here to describe a galvanic battery, constructed by Mr Davy, on principles somewhat different from that of Volta. In the Voltaic pile there are two perfect conductors, and one imperfect conductor; but this consists of two imperfect, and one perfect conductor: the two imperfect conductors are nitrous acid and liquid sulphuret of potash. A trough is divided into cells with slips of horn and plates of zinc, arranged alternately; nitrous acid is poured into the first cell, and sulphuret of potash into the second; the two liquids being separated by the slip of horn, a communication is formed between them by means of a moist piece of cloth laid over the horn, and in the same way the rest of the cells are filled. In this case the liquids are the imperfect conductors, and the zinc is the perfect one; and the action of the battery continues till the oxidation of one of the surfaces of the zinc takes place, the other surface remaining unchanged.

Having finished the short view which we proposed to give of the history and progress of galvanism, we should next proceed to detail some of the later experiments and discoveries which have been made on this subject. What we here chiefly allude to, is the discovery of the formation of muriatic acid and soda by means of the galvanic fluid. But this is proposed to be the subject of a separate chapter. We shall therefore proceed in the next chapter to consider the hypothesis by means of which the phenomena of galvanism have been explained, and to point out the analogy between electricity and galvanism.

**CHAP. II. Of the Theory of Galvanism, and the Analogy between the Galvanic Fluid and Electricity.**

We have already observed, that the philosophers who were occupied in researches on galvanism, early divided themselves into two parties. According to one party, with Volta at their head, the phenomena of galvanism, were ascribed to the action of common electricity on the muscular fibres; while another party maintained the opinion that they depended entirely on something peculiar to animal matter. This was the opinion of Galvani himself, the original discoverer, and it was supported by his nephew Aldini, with certain modifications. The greater number of philosophers have now adopted the opinion of Volta, as being more consistent with the phenomena. We shall therefore now give a more particular account of the hypotheses which has been more generally followed in explaining these phenomena on the principles of electricity.

According to the received principles of electricity, there is a subtle fluid which exists in all bodies; but electricity, the existence of this fluid can only be recognized when the proportion which a body contains is greater or less than the quantity which is natural to it. When the quantity is greater than usual, the body is said to be electrified positively or plus; and when the quantity is less than usual, the body is said to be electrified negatively or minus. The electric fluid penetrates certain bodies, and passes through them with facility, and these bodies are called conductors of electricity; but there are other bodies which it cannot pass through without difficulty, these bodies are called non-conductors or electrics. Of conductors there are two kinds; one of which is denominated perfect, because the electric fluid passes through them with ease; the other is called imperfect conductors, because the fluid passes through them with difficulty. The perfect conductors are solid bodies which are susceptible of oxidation; and when they enter into combination with oxygen, they lose their properties as perfect conductors. The metals and charcoal are are the only perfect conductors which are known. The imperfect conductors are those bodies which contain oxygen, and when they are deprived of it, they lose the properties of imperfect conductors. They are all liquid bodies, and usually contain water as one of their component parts. See Electricity.

There is an affinity between the perfect conductors and the electric fluid, in consequence of which this fluid remains in combination with the perfect conductor, till it is attracted by some body, for which it has a stronger affinity, or is expelled by some body combining with the conductor, for which the conductor has a stronger affinity than it has for the electric fluid. Perfect conductors possess different forces or degrees of affinity for the electric fluid. Thus, if two perfect conductors be brought into contact, the proportion of electric matter in each of them changes. That conductor which has the strongest affinity for the fluid, is electrified positively, or plus; and the conductor which has the weaker affinity is electrified negatively, or minus.

If a plate of zinc and one of copper, each of which possesses its natural proportion of electric fluid, be brought into contact, the zinc is electrified plus, and the copper minus; or, if iron and silver be brought into contact, the iron is electrified plus, and the silver minus; and if no other circumstances operate to change the state of the electricity, these two states will be permanent.

But, when a perfect conductor in the positive state of electricity, enters into combination with oxygen, it parts with the excess of electric fluid which it contained, and the discharge is made towards that side of the conductor which is combined with oxygen. The affinity of imperfect conductors for the electric fluid is weaker than that of the perfect conductors, so that, if a perfect and imperfect conductor be brought into contact, the perfect conductor becomes plus, and the imperfect, minus; and this state is not changed, if the imperfect conductor cannot communicate oxygen to the perfect one.

Between the electric fluid and hydrogen there is also an affinity, so that the electric fluid combines with hydrogen, provided this latter be present when the fluid is separated from a perfect conductor. The electric fluid is differently conducted through the bodies which are called perfect and imperfect conductors. The fluid passes through the perfect conductors, in its simple and uncombined state; but unless the fluid be combined with hydrogen, it cannot pass through the imperfect conductors, and this compound of electricity and hydrogen is capable of passing invisibly through liquid conductors.

Let us now suppose a plate of copper and another of zinc, to be brought into contact, the zinc is immediately electrified plus, and the copper minus; but let us suppose also, that the surface of the zinc farthest from the copper, is brought into contact with a liquid which can communicate oxygen to that surface, so that it becomes oxidated, such, for instance, is water impregnated with common air, or with an acid. As soon, then, as the oxygen of the imperfect conductor combines with the zinc, the excess of its electricity is separated, and passes towards the imperfect conductor; but the zinc is oxidated by the decomposition of the water, the oxygen of which combines with the metal, while the hydrogen is set free. The electricity of the perfect conductor enters into combination with the hydrogen, and in this state it can pass through the imperfect conductor. If then the imperfect conductor be in contact on the other side with a perfect conductor, such as a plate of copper, which cannot, in this case, be oxidated, the electric fluid leaves the imperfect conductor, and enters the perfect one; but it cannot combine with a perfect conductor while it is in union with hydrogen; the hydrogen, therefore, is left behind, and accordingly, when the electric fluid passes from the perfect to the imperfect conductor, a portion of hydrogen gas is given out at the surface of the perfect conductor; or, if that surface has undergone any degree of oxidation, the hydrogen combines with the oxygen, and thus leaves the conductor in the metallic state. But, farther, if a plate of zinc be in contact with a plate of copper, the fluid having a greater affinity for the zinc, will enter it; and if the zinc be again followed by another imperfect conductor, its surface is oxidated, the electricity is disengaged; it combines with hydrogen, and passes through the imperfect conductor as in the former case. Whatever the number of these sets of bodies may be, if they are arranged in the same order, the same phenomena will be exhibited.

Let us now suppose, that a battery is constructed, either in the form of a pile or trough, of any given number of pairs of plates; and suppose, if this battery is in the form of a pile, that the uppermost plate is zinc, the lowest is therefore of copper; the zinc is electrified plus, and the copper minus. If, then, a communication is established between the upper and lower plates of the pile, by means of conductors, according to the laws of electricity, the excess at the top of the pile immediately passes to the bottom. A current of electricity, therefore, will pass through the pile, and will continue till the surfaces of the zinc next the imperfect conductors are completely oxidated, when the action ceases, because the double decompositions on which this action depends, can no longer take place.

The number of repeated charges which pass through the pile, must be in proportion to the number of plates, effects from so that the intensity of the pile increases with the number of plates of which it is composed. Hence it is, that the effects of galvanism on animals is found to be in proportion to the number of plates employed in the battery; but this depends upon its intensity, or the number of discharges followed by intervals, which pass through the body in a given time.

But, on the other hand, the effect of the galvanic fluid on metallic substances depends on the absolute quantity which passes through the metal in a given time. But the absolute quantity of fluid discharged from a single pair of plates, must be proportional to the surface of these places; and hence it is, that the quantity of electricity discharged from a pile in a given time, depends upon the surface of the plates. When a battery is discharged, the small charge contained in each pair of plates, passes through the discharger; but there must be an interval between each of those separate charges, for they cannot be supposed to pass instantaneously, although the interval being too small to be perceptible, the discharge of the battery seems to be instantaneous. As then the number of small discharges which are apparently instantaneous, when a battery is discharged, is in proportion to the number of plates, Theory. the intensity of each little discharge is proportional to the places which the pair of plates occupies in the battery; and hence it is, that the block is increased by the number of plates more rapidly than the effect of the battery on metals is increased; but, on the contrary, the surface of the plates being increased, the effect on metals is also increased, because the quantity discharged at once from the upper pair is increased; and it seems to be in this way that the effect on metallic substances is produced.

In the same way the chemical changes which are effected by means of galvanism may be explained. Let it be supposed, that a gold wire, connected with the upper plate of the battery, terminates in a glass of water, and another gold wire from the lower plate of the battery, terminates in the same water. The circle is then completed by the gold wire, which is a perfect conductor. The current of electricity passes through the wire which is connected with the uppermost plate to the base of the battery, and it would pass uninterruptedly, if there were no interval between the wires. This interval is supplied with water, and, when the electric fluid reaches the extremity of the wire, it must pass through the water, but it can only pass through an imperfect conductor when it is in combination with hydrogen. It therefore combines with the hydrogen of the water, which is accordingly decomposed at the point of the wire. The oxygen is disengaged, and the hydrogen in combination with the electricity passes through the water till it reach the point of the other wire; and the affinity between this wire and the electric fluid being greater than the affinity of the latter for water, the electric fluid enters the wire, and passes on to the other end of the battery; but the hydrogen is previously separated from the extremity of this second wire, in the form of gas, because the fluid cannot enter the wire in combination with hydrogen.

If the wires are immersed in ammonia, the hydrogen is derived from that substance of which it forms one of the component parts; the azotic gas, the base of which is its other constituent, is evolved at the extremity of the first wire, and hydrogen gas at the extremity of the second. But, if the wires are plunged in the water which contains common air, and consequently a certain portion of azote, as oxygen gas combines with azote in its nascent state, or at the moment of its evolution, the compound resulting from this combination is nitric acid. Hydrogen gas also, in its nascent state, will combine with azote, and ammonia is the result of this combination. Hence it is, that in some experiments nitric acid is found at the point of the positive wire, and ammonia at the point of the negative wire, when common water is employed.

When liquids holding in solution a metallic salt, the base of which is an oxide of the metal, are employed; as hydrogen gas possesses the property of reducing or reviving metals, if in its nascent state it comes in contact with their oxides, the metallic salts are in this case decomposed, and the metal is revived. It is found deposited on the negative wire. When copper or iron wires are employed to complete the circle, instead of wires of gold or platinum, as oxygen has the property of combining with these metals, at the moment of its disengagement, it is deposited on the positive wire, and in this case none is separated from it; but if the circle be completed by means of charcoal or plumbago, and the interval between these conducting substances be water, carbonic acid gas is separated from the positive conductor, because the oxygen in its nascent state is susceptible of combination with carbure; and the hydrogen in the same state combining with carbure, carburetted hydrogen is given out by the negative conductor.

Such is the hypothetical explanation which has been given of the action of galvanism, and the phenomena which it exhibits. A fuller view of the analogy between galvanism and electricity has been given by Dr Wollaston.

"Notwithstanding, he observes, the power of Mr Volta's electric pile is now known to be proportional to the deposition of one of the metals to be oxidated by the fluid interposed, a doubt has been entertained by many persons, whether this power arises from the chemical action of the fluid on the metal, or, on the contrary, whether the oxidation itself may not be occasioned by electricity, yet in motion by the contact of metals that have different conducting powers.

"That the oxidation of the metal is the primary cause of the electric phenomena observed, is, I think, to be inferred from the following experiments, which exhibit the galvanic process reduced to its most simple state.

"Exper. 1.—If a piece of zinc and a piece of silver have each one extremity immersed in the same vessel, containing sulphuric or muriatic acid diluted with a large quantity of water, the zinc is dissolved, and yields hydrogen gas, by decomposition of the water; the silver, not being acted upon, has no power of decomposing water; but, whenever the zinc and silver are made to touch, or any metallic communication is made between them, hydrogen gas is also formed at the surface of the silver.

"Any other metal besides zinc, which by assistance of the acid employed is capable of decomposing water, will succeed equally, if the other wire consists of a metal on which the acid has no effect.

"Exper. 2.—If zinc, iron or copper, is employed with gold in diluted nitric acid, nitrous gas is formed, in the same manner, and under the same circumstances, as the hydrogen gas in the former experiment.

"Exper. 3.—Experiments analogous to the former, and equally simple, may also be made with many metallic solutions. If, for instance, the solution contains copper, it will be precipitated by a piece of iron, and appear on its surface. Upon silver merely immersed in the same solution, no such effect is produced; but as soon as the two metals are brought into contact, the silver receives a coating of copper.

"In the explanation of these experiments, it is necessary to advert to a point established by means of the electric pile.

"We know that when water is placed in a circuit of conductors of electricity, between the two extremities of a pile, if the power is sufficient to oxidate one of the wires of communication, the wire connected with the opposite extremity affords hydrogen gas.

"Since the extrication of hydrogen, in this instance, is seen to depend on electricity, it is probable, that in other instances, electricity may be also requisite for its conversion into gas. It would appear, therefore, that in the solution of a metal, electricity is evolved during the..." the action of the acid upon it; and that the formation of hydrogen gas, even in that case, depends on a transmutation of electricity between the fluid and the metal.

"We see, moreover, in the first experiment, that the zinc, without contact of any other metal, has the power of decomposing water; and we can have no reason to suppose that the contact of the silver produces any new power, but that it serves merely as a conductor of electricity, and thereby occasions the formation of hydrogen gas.

"In the third experiment also, the iron by itself has the power of precipitating copper, by means, I presume, of electricity evolved during its solution; and here likewise the silver, by conducting that electricity, acquires the power of precipitating the copper in its metallic state.

"The explanation here given receives additional confirmation from comparative experiments which I have made with common electricity; for it will be seen, that the same transfer of chemical power, and the same apparent reversion of the usual order of chemical affinities in the precipitation of copper by silver, may be effected by a common electrical machine.

"The machine with which the following experiments were conducted, consists of a cylinder seven inches in diameter, with a conductor on each side, 16 inches long, and three and a half inches diameter, each furnished with a sliding electrometer, to regulate the strength of the spark received from them.

"Exper. 4.—Having a wire of fine silver \( \frac{1}{2} \) of an inch in diameter, I coated the middle of it for two or three inches, with sealing wax, and by cutting through the middle of the wax, exposed a section of the wire. The two coated extremities of the wire, thus divided, were immersed in a solution of sulphate of copper, placed in an electric circuit between the two conductors; and sparks, taken at \( \frac{1}{2} \) of an inch distance, were palled by means of them through the solution. After 100 turns of the machine, the wire which communicated with (what is called) the negative conductor, had a precipitate formed on its surface, which, upon being polished, was evidently copper; but the opposite wire had no such coating.

"Upon reversing the direction of the current of electricity, the order of the phenomena was of course reversed; the copper being shortly re-dissolved by assistance of the oxidizing power of positive electricity, and a similar precipitate formed on the opposite wire.

"Exper. 5.—A similar experiment made with gold wires \( \frac{1}{2} \) of an inch diameter, in a solution of corrosive sublimate, had the same success.

"The chemical agency, therefore, of common electricity, is thus proved to be the same with the power excited by chemical means; but, since a difference has been observed in the comparative facility with which the pile of Volta decomposes water, and produces other effects of oxidation and de-oxidation of bodies exposed to its action, I have been at some pains to remove this difficulty, and can at least produce a very close imitation of the galvanic phenomena, by common electricity.

"It has been thought necessary to employ powerful machines, and large Leyden jars, for the decomposition of water; but when I considered that the decomposition must depend on duly proportioning the strength of the charge of electricity to the quantity of water, and that the quantity exposed to its action at the surface of communication depends on the extent of that surface, I hoped that, by reducing the surface of communication, the decomposition of water might be effected by smaller machines, and with less powerful excitation, than have hitherto been used for that purpose; and, in this hope, I have not been disappointed.

"Exper. 6.—Having procured a small wire of fine gold, and given it as fine a point as I could, I inserted it into a capillary glass tube; and after heating the tube, so as to make it adhere to the point and cover it in every part, I gradually ground it down, till, with a pocket lens, I could discern that the point of the gold was exposed.

"The success of this method exceeding my expectations, I coated several wires in the same manner, and found, that when sparks from the conductors before-mentioned were made to pass through water, by means of a point so guarded, a spark palling to the distance of one-eighth of an inch would decompose water, when the point exposed did not exceed \( \frac{1}{2} \) of an inch in diameter. With another point, which I estimated at \( \frac{1}{2} \), a succession of sparks \( \frac{1}{2} \) of an inch in length, afforded a current of small bubbles of air.

"I have since found, that the same apparatus will decompose water, with a wire \( \frac{1}{2} \) of an inch diameter, coated in the manner before described, if the spark from the prime conductor passes to the distance of \( \frac{1}{2} \) of an inch of air.

"Exper. 7.—In order to try how far the strength of the electric spark might be reduced by proportional diminution of the extremity of the wire, I palled a solution of gold in aqua regia through a capillary tube, and, by heating the tube, expelled the acid. There remained a thin film of gold, lining the inner surface of the tube, which, by melting the tube, was converted into a very fine thread of gold, through the sublimate of the glass.

"When the extremity of this thread was made the medium of communication through water, I found that the mere current of electricity would occasion a stream of very small bubbles to rise from the extremity of the gold, although the wire, by which it communicated with the positive or negative conductor, was placed in absolute contact with them. Hence it appears, that decomposition of water may take place by common electricity, as well as by the electric pile, although no discernible sparks are produced.

"The appearance of two currents of air may also be imitated, by occasioning the electricity to pass by fine points of communication on both sides of the water; but, in fact, the resemblance is not complete; for, in every way in which I have tried it, I observed that each wire gave both oxygen and hydrogen gas, instead of their being formed separately, as by the electric pile.

"I am inclined to attribute the difference in this respect to the greater intensity with which it is necessary to employ common electricity; for, that positive and negative electricity, so excited, have each the same chemical power as they are observed to have in the electric pile, may be ascertained by other means.

"In the precipitation of copper by silver, an instance of de-oxidation (or phlogistication) by negative electricity has been mentioned; the oxidating power of po- Galvanism.

Theory.

Fitive electricity may be also proved, by its effects on vegetable blue colours.

"Exper. 8.—Having coloured a card with a strong infusion of limes, I palled a current of electric sparks along it, by means of two fine gold points, touching it at the distance of an inch from each other. The effect, as in other cases, depending on the smallness of the quantity of water, was most discernible when the card was nearly dry. In this state a very few turns of the machine were sufficient to occasion a redness at the positive wire, very manifest to the naked eye. The negative wire, being afterwards placed on the same spot, soon restored it to its original blue colour.

"By Mr Volta's apparatus the same effects are produced in a much less time.

"Besides the similarity which has thus been traced between the effects of electricity excited by the common machine, and those observed from the electric pile, I think it appears also probable, that they originate from the same source.

"With regard to the latter, its power is known to depend on oxidation; so also does the excitement in the former appear very much to depend on the same process; for,

"Exper. 9.—I have found that, by using an amalgam of silver or of platina, which are not liable to be oxidized, I could obtain no electricity. An amalgam of tin, on the contrary, affords a good degree of excitement. Zinc acts still better; but the best amalgam is made with both tin and zinc, a mixture which is more easily oxidated than either metal separately.

"Exper. 10.—But, as a farther trial whether oxidation assists in the production of electricity, I mounted a small cylinder, with its cushion and conductor, in a vessel so contrived, that I could at pleasure change the contained air.

"After trying the degree of excitement in common air, I substituted carbonic acid gas, and found that the excitement was immediately destroyed, but that it returned upon re-admission of atmospheric air.

"In conformity to this hypothesis, we find that the metal oxidated is, in each case, in a similar state of electricity; for the cushion of the machine, by oxidation of the amalgam adhering to it, becomes negative; and in the same manner, zinc, oxidated by the accumulated power of an electric pile, or simply by action of an acid, is also negative.

"This similarity in the means by which both electricity and galvanism appear to be excited, in addition to the resemblance that has been traced between their effects, shews that they are both essentially the same, and confirms an opinion that has already been advanced by others, that all the differences discoverable in the effects of the latter, may be owing to its being less intense, but produced in much larger quantity."

This analogy was still further established by the experiments of Van Marum, in which he succeeded in charging an electrical battery, consisting of 137 square feet, by means of the galvanic pile. On examining the power of the shocks which were given by the battery charged with the pile, it was found that the shock from 100 pairs of plates was about equal to a shock from the battery, when it was charged by means of 200. A pile of 200 pairs of plates seemed to have six times the power of an electrical machine, having a plate of 31 inches diameter.

The following experiments made by Mr Cuthbertson, distinguishing with galvanic batteries, are supposed by him to afford proof of a distinguishing property between the galvanic and electric fluids. 1. Charcoal was delagrated and ignited for above an inch in length. 2. Iron wire 1/16 of an inch diameter was melted into a ball of 1/4 inch diameter. 3. Platina wire 1/16 inch diameter, was melted into a ball 1/4 inch diameter. 4. Brass wire 1/16 inch diameter, three-fourths of an inch in length was ignited. 5. Brass wire 1/16 inch diameter was red hot at the end. 6. Iron wire 1/16 inch diameter was red hot for 16 inches in length. 7. Iron wire, 1/2 inches in length was deflagrated. 8. Iron wire five inches in length was deflagrated. 9. Iron wire eight inches in length was ignited.

The first seven experiments above were made with two troughs, each containing 30 pairs of plates, five inches square, but in the last two experiments, one of these troughs only was used. The conclusion drawn from the four last experiments is, that double quantities of galvanic fluid only burn double lengths of wire, and not the square, as electrical discharges do.

To discover what quantity of coated glass would be required to take a charge sufficient to ignite the same lengths of wire, the two last experiments were compared with common electrical discharges. Two jars, each containing about 170 square inches of coating, were set to the conductor of a 24-inch single-plate electrical machine, with the author's universal electrometer, loaded with 31 grains. Eight inches of the same kind of wire were laid in the circuit, and with 57 revolutions of the plate the electrometer discharged the jars, and the wire was ignited as perfectly as in experiment 9th. Afterwards five inches of the wire being laid in the circuit, a discharge was produced with the same number of revolutions of the machine, and the wire was deflagrated, and fused into balls, in the same manner as in the 8th experiment. Hence he concluded, that 340 square inches of coated glass, properly constructed, are sufficient to bear a charge equal to a galvanic battery of 180 square inches of surface. On comparing the above experiments with some others made some time before, the author finds it necessary to modify the conclusion which he had deduced from them. With a pile of 16 pairs of plates, of 10 inches diameter, eight of which were laid upon each other in the usual manner, and cloths moistened with diluted muriatic acid interposed, he burnt half an inch of wire of 1/16 inch diameter; and when the other eight pairs were added, he burnt four inches of the same wire. This was repeated with the eight in pairs with the same result, with respect to the burning of metals, but it gave strong and loud sparks from metal to metal, which might be heard at the distance of 300 yards. This result, he observes, had not been attained from troughs, to be heard at any distance. In the last experiment the cloths were moistened with a strong solution of muriate of ammonia. Comparing this effect of the pile and the trough, Mr Cuthbertson thinks, there is some defect in the arrangement or construction of the latter.

In many experiments which Volta made on piles composed of a single metal, and a single wet stratum, which which of themselves are inactive, it was found that they became more or less active, after affording a passage for a longer or shorter time to an electric current, which was set in motion by an active pile. According to Ritter, the active pile or common electrometer transmits a real charge to the pile, which is itself inactive, and this he calls the charged pile. Volta, however, is of opinion, that no charge is transmitted but by means of the ordinary chemical action; for the electrical current being continued, changes the single wet stratum interposed between two pieces of gold, for example, into two different fluids; one acid, by which the electric current issues out of the metal, and the other alkaline, by which it enters, thus constituting a pile of the second order, composed of one metal, and two fluids of different natures. The action of this pile, however, soon ceases, because the fluids soon mix together.

**CHAP. III. Of the Formation of Muriatic Acid and Soda, by means of Galvanism.**

Some of the most curious phenomena which have yet been exhibited in galvanism, relate to the formation of muriatic acid by means of this power. In the account which has been given of Mr Cruickshank's experiments, it will be recollected that he made the discovery of the formation of an acid and alkali, during the action of the galvanic battery. This acid, he concluded, was the nitric, and the alkali ammonia. The theory of the production of these substances in the galvanic pile has been already mentioned, and it corresponds with the explanation of the principles which have been adopted for explaining the phenomena of galvanism; later researches, however, have been conducted with more accurate observation, or have opened a wider field of discovery. The truth of this remark will be fully confirmed, if it be at last finally ascertained, that common salt, the component parts of which are muriatic acid and soda, is produced by the action of galvanism.

The first hint of this discovery was given by Mr Peel of Cambridge, in a letter dated April 1805, addressed to the editor of the Philosophical Magazine, of which the following account is given in his own words.

"I took (says he), about a pint of distilled water, and decomposed one half of it by means of galvanism; the other half I evaporated, and I found to remain at the bottom of the glass a small quantity of salt, which upon examination I found to be muriate of soda, or common salt.—What induced me to try the experiment was this; I knew that when water was decomposed by means of galvanism, the water near one of the wires had alkaline, while that near the other had acid properties. This being the case, I inferred, that if an alkali and an acid were really produced, I should, by decomposing a large quantity of water, obtain a small quantity of some kind of neutral salt: as was actually the case on trying the experiment. The salt could not have been contained in the water before I made the experiment, because I used every precaution to have it free from impurities. I even took the trouble to repeat the experiment, though a tedious one, and I again obtained the same result." He adds, that a similar experiment being repeated by a friend of his, afforded a similar result.

It having been suggested to Mr Peel, that it might be worth while to vary the experiment, by employing water formed of its elements, he gives the following account of the result of this process, in another letter, dated June 1805.

"Having proceeded, he observes, to the formation of water from its elements, with which to repeat my former experiment, I found when the oxygen and hydrogen gases were quite pure, and exactly in due proportion, that no residuum of air was left, and that the water formed was not in the slightest degree acidulous. When the process was not conducted with great accuracy, or any precaution to have it accurate was omitted, I then found the water acidulous, and the acid that caused this acidity to be the nitric acid.

"The acidulous water thus obtained I neutralized with lime, from which I distilled the water, and this water I decomposed by the galvanic process, as in the experiment detailed in my former letter.

"I did not imagine the using water so obtained could make the least difference on the result of the experiment; but as a wish was expressed to have the trial made, I again undertook that interesting but very tedious labour.

"When I came to examine the residuum, to my great astonishment I found that not muriate of soda, but muriate of potash, was produced. I must own I feel myself entirely at a loss how to account for this, nor shall I attempt it; all I can say is, that this, as well as my former experiment, was conducted with the greatest care and accuracy that I could bestow."

About the same time a discovery of a similar nature was made by Professor Pacchioni of Pisa. This discovery, which relates to the composition of muriatic acid, was first announced in this country in the number of the Edinburgh Medical and Surgical Journal, published the 1st July 1805. The following is an account of his experiments, and the conclusions which he deduces from them in his own words. "The simplicity of the apparatus, (he says), and of the means adopted to attain my views, the care with which I endeavoured to avoid every source of error, have, I hope, sufficiently secured me against those illusions which frequently deceive young men ardent in the pursuit of science, and even those practised in the art of extorting from nature her secrets. Want of time prevents me from relating the series of experiments by which I arrived at the discovery I have mentioned; but you may see it by perusing the manuscript of my memoir, which will be immediately published, to submit my researches and their results to the judgment of the learned. For the present, I shall select from the experiments and facts therein described those whose which are decisive, and which establish, in an evident manner, the following truths:

"I. Muriatic acid is an oxide of hydrogen, and consequently composed of hydrogen and oxygen.

"II. In the oxygenated muriatic acid, and therefore, a fortiori, in muriatic acid, there is a much less proportion of oxygen than in water.

"III. Hydrogen is susceptible of very many and different degrees of oxidation, contrary to what is universally believed by pneumatic chemists, who assert that hydrogen is susceptible only of one invariable degree of oxidation, that in which it forms water.

"Having at first examined the phenomenon of the decomposition of water by the galvanic pile, and having, by accurate experiments, ascertained the true theory," Formation theory, I readily discovered a very simple and exact apparatus of Muriatic acid, in which I could distinctly perceive the changes which happen to water, which, from the continued action of the galvanic pile, is continually losing its oxygen at the surface of a wire of very pure gold immersed in it.

"I therefore proceeded to examine these gradual changes of water thus losing its oxygen; and I at last observed a very singular fact, which unequivocally indicated the formation of an acid. In other antecedent experiments I had examined the nature of the air obtained before arriving at this remarkable point, and I always found, by means of the eudiometer of Giobert, that it was very pure oxygen, as the residuum scarcely amounted to one-fiftieth.

"Having thus examined the nature of the air formed in various experiments, from the first moment of decomposition, until there were evident indications of the formation of an acid, I began to endeavour to determine, in a more positive manner, the existence and nature of this acid.

"When the water, or, to speak more accurately, the residual fluid, occupied about half the capacity of the receiver, which at first contained the water, this residual fluid presented the following characters:

"Its colour was an orange yellow, more or less deep, according as the bulk of the residual liquor was greater or less, and it resembled in appearance a true solution of gold.

"From the inferior orifice of the vessel, which was closed with a piece of taffety, and then with double bladder, there escaped a smell which was easily recognized to be that of oxygenated muriatic acid.

"The gold wire had in part lost its metallic lustre, and its surface appeared as if corroded by a solvent.

"The bit of taffety which had been in contact with the coloured fluid, in consequence of its action, was easily torn, as is usual with similar bodies when half burnt (femi-combustio).

"Around the edges of the vessel, on the bladder, there was formed a deep purple ring, which surrounded a circular space rendered entirely colourless, or white.

"A drop of this fluid tinged the skin of the hand, after some hours, with a beautiful rose colour.

"Having obtained, in various successive experiments, the same liquid, possessing constantly the same properties, I chose that obtained in the last experiment to subject it to chemical examination. The very able chemist of this university, Signior Giuseppe Branchi, had the goodness to enter zealously into my views; and in his laboratory we easily proved,

"1. The existence of a volatile acid, by the white vapours which were formed by ammonia placed near it.

"2. That this acid was certainly oxygenated muriatic acid, since it formed in nitrate of silver a curdy precipitate, the luna cornea of the ancients, or the muriate of silver of the moderns. From these facts we may draw the following positive and undeniable results:

"1. Muriatic acid is an oxide of hydrogen, and is therefore composed of hydrogen and oxygen.

"2. Oxygenated muriatic acid, and of course muriatic acid, contains less oxygen than water does.

"3. Hydrogen has not one degree of oxygenation, but many. One of these constitutes water, another below it oxygenated muriatic acid, and, below this, there is another which constitutes muriatic acid."

Mr Henry of Manchester, in an account of his investigations on this subject, observes that there is a considerable point of difference between the English Henry's and the Italian chemist. The result of Mr Peel's experiment was found to be muriate of soda; but in Professor Pacchioni's, in which an interrupted gold wire was employed, it appeared to be muriate of gold. This ingenious chemist, with the same view, made the following experiment. He took a glass tube 4½ inches long, .35 inches diameter, in which were secured with corks, two slips of platinum, having their extremities at a proper distance to effect the decomposition of the water. The quantity of water, at the beginning of the experiment, amounted to two drams. After being exposed to the galvanic action for five days, it was so far diminished, that ¼ inch of the tube was unfilled. The water which was employed was carefully purified, by being first distilled, and then, after adding nitrate of silver, by a second distillation. After the experiment was finished, with the addition of nitrate of silver, it became opalescent in a few seconds, and being exposed to the light, exhibited those changes which indicate the presence of muriatic acid. It did not appear that muriate of platinum had been produced, for muriate of ammonia being added to one portion, and carbonate of soda to another, produced no precipitation.

In making this experiment, Mr Henry suggests a very useful precaution. The water employed, he observes, should never, on any account, come into contact with the fingers, because there is a constant excretion of muriate of soda from the skin, and in this way the purest water is very soon contaminated. He recommends also, that glass stoppers should be employed in place of corks, for transmitting the conducting wires*.

In another communication by Mr Peel on the same subject, he relates the following experiments, which were undertaken, he says,

"1st. To determine whether the difference in the result of the before-mentioned experiments was owing to any degree to my having employed lime to neutralize the water employed in my second experiment, before it was distilled.

"2nd. To ascertain whether the salts found in the residual water, or any component part of them, came from the galvanic battery by means of the wires.

"To determine the first point, I varied my experiment by employing for decomposition water distilled under different circumstances.

"Exper. 1.—The water employed in this experiment was distilled from water containing lime. A portion of it was decomposed in the manner that has before been stated. The remaining water yielded muriate of potash.

"Exper. 2.—Water distilled from water containing magnesia was decomposed in the same manner. The result was muriate of soda.

"Exper. 3.—In this experiment double distilled snow water was employed. The result was muriate of soda.

"Ibid. 183." Exper. 4.—Water distilled from barytes was now used. The result was still muriate of soda.

The water which I used in the experiment detailed in my first letter was distilled from pump water (the pump is on the premises where I live), which I have not myself analyzed, but a friend has been so good as to take upon him that trouble. He has not been able to detect in it the minutest portion of magnesia. In one of the above experiments, having used water distilled from magnesia, I obtained muriate of soda; but, having obtained the same result from distilled snow water, and from water distilled from barytes, I conclude that the production of the soda has nothing to do with the presence of magnesia.

But, in the production of potash, the presence of lime seems to be essential, and, as you hinted, a portion of lime must have been carried over with the distilled water; a fact which few would suspect, and which probably may often be the cause of differences in the results of chemical investigations, conducted, to all appearance, in a similar manner.

To determine the second point which I had in view, namely, whether the salts found in the residual water, or any component part of them, came from the galvanic battery by means of the conducting wires, I made similar experiments to those before stated, employing for the decomposition of the distilled water a powerful electrical machine instead of a galvanic battery, but without obtaining results different from what have been already stated.*

It is stated in the same number of the Philosophical Magazine, that the following result was obtained in an experiment on the same subject. By continuing to pass the galvanic fluid from a trough composed of 40 pairs of square inch plates, through distilled water, contained in a glass tube, the tube being furnished at one end with a wire of gold, and at the other with a wire of platinum, it was found that a coating of oxide of gold was deposited on the gold wire, from which it is concluded, that oxymuriatic acid was found in the process†.

A more particular account was afterwards given by the author of this experiment, and of the precautions he observed in repeating it. He took a clean glass tube, which was bent as in the former experiment; but, instead of the gold wire, he employed one of platinum, so that both wires were of the same metal. One of the wires was only introduced a short way into the tube containing the distilled water; the other wire introduced at the other extremity, passed nearly through its whole length, till it reached beyond the point at which the short wire terminated. After the apparatus had stood for three days, with the zinc end of the trough connected with the short platinum wire, the latter assumed the colour of gold, and the long one became black from the lower end to the height of the short wire, and continued so for the space of three weeks. The water being diminished one-third, the short wire was connected with the copper end of the trough, and in one day's time the long wire became bright, and the short one black. After two days had elapsed, that part of the long wire which reached to the height of the short one, assumed a yellowish golden tinge. Both the wires remained so for three days, when they were placed in their first situation. The black powder then left the short wire, and the long one became black. A slip of blue test paper being immersed in the remaining water, its colour was changed, which indicates the production of an acid.

Pacchiani, the discoverer, in another letter on this subject addressed to Fabroni, seems to think that those who have failed in obtaining the same results in the decomposition of water, have either been influenced in conducting their experiments by preconceived opinions, or have deviated from the process which he followed. But far an account of his views and reasons, see An. de Chim. tom. lvi. or Phil. Mag. xxiv. 176. We shall only observe, that he still considers himself warranted to draw the same conclusion with regard to the formation of the acid, by the action of galvanism.

Mr Sylvester of Sheffield made the following experiment on this subject. The water which he employed was not changed by adding nitrate of silver. This water was introduced into a tube which was secured at one end with a bit of bladder. At the other end was a cork, through which a wire of platinum was passed, nearly to the bottom of the tube. The tube was then set in a wine glass, containing also pure water, and into this was also introduced another wire of platinum, the extremity of which came under the end of the tube, and as near as possible to the bladder. The wire within the tube was connected with the zinc end of the trough, and the wire in the glass, which was in contact with the bladder, proceeded from the copper end. After the process had continued for an hour, the liquid in the tube was put to the test of nitrate of silver, and when a sufficient precipitate was obtained, to ascertain the presence of muriatic acid, the liquid in the glass contained an alkali, which the author suspected was ammonia.

Brugnatelli observes, that, after having galvanized several times, both negatively and positively, a certain quantity of pure water with golden wires, inserted in separate tubes, till he found, by the usual tests, that acid was produced on the one part, and alkali on the other, when the two liquids were mixed to perfect saturation, and evaporated in the air, he always obtained muriate of soda crystallized in cubes. He has therefore no doubt, that water negatively and positively galvanized, by means of gold wires, produces or disengages muriatic acid in the one case, and soda in the other.

Such are the authorities for this curious phenomenon which we have hitherto had an opportunity of consulting; but although in general it would appear that the experiments made with the view of ascertaining the truth of the discovery announced by Pacchiani, have most generally succeeded, some other experiments, made with the same view, have failed. For this purpose a series of experiments was instituted by the Galvanic Society of Paris, whose attention was directed to endeavour, as well by means of electricity as of galvanism, to confirm this important discovery; but although they employed a very simple apparatus, and one which seemed least susceptible of any foreign influence, they do not think it possible to produce anything by the action of the galvanic pile, except the decomposition of a greater or less proportion of the water submitted to its action. The water remaining in the tube being carefully examined, produced no effect on the tinctures of turpentine or brazil wood, or the solution of nitrate of silver. Formation silver. Hence it is concluded that neither muriatic acid nor soda was formed in this experiment.

Some other experiments made with the same view have also failed; but according to De Buch, certain precautions seem to be necessary in conducting this experiment, which, if overlooked, it cannot be expected, he thinks, to be followed with success. For the particulars of these, see Phil. Mag. xxiv. 244. For an account of the analogy between the peculiarity of structure of the torpedo, by which it is enabled to give electric shocks, and the galvanic battery, see TORPEDO; and for the medical effects of galvanism, see Materia Medica.

The following facts, which seem to extend the analogy of galvanism with electricity on the one hand, and with magnetism on the other, were omitted in the preceding treatise.

Ritter, one of the most indefatigable philosophers, in prosecuting experiments and inquiries on this subject, has succeeded in charging a piece of money with the galvanic fluid, and with this some of the phenomena of galvanism can be exhibited. To effect this, he places a louis d'or between two pieces of pasteboard, thoroughly wetted, and keeps it for five or eight minutes in the chain of circulation connected with the pile. In this way the louis becomes charged, without being immediately in contact with the conducting wires. If this louis be afterwards applied to the crural nerves of a frog, recently prepared, the usual contractions will be produced. It is found that the charge is retained, in proportion to the time that the piece has remained in the circuit of the pile. Some have retained it for five minutes. Ritter has also discovered, that the piece of Formation gold thus galvanised, exerts at once the action of two of muriatic Acid, &c.

If the facts which the above experiments seem to prove, should be fully ascertained, there is an obvious analogy, not only between electricity and galvanism, but also between the latter and magnetism.

A galvanic pile has been constructed by Dr Baronio of Milan, entirely of vegetable matters. For this purpose he cut discs of horse-radish and beet-root, of two inches in diameter. He then prepared equal discs of walnut-tree wood; the latter discs were raised at their edges, to contain a little solution of acidulous tartarate of potash in vinegar, in which they had been previously boiled to free the wood from rosin. Sixty pairs of discs were employed in the following order; viz. horse-radish, beet-root, discs of wood, in each of which the solution was put. The spinal marrow of a prepared frog was connected with the pile, by means of a leaf of cochlearia; the muscles of the frog were connected with the top of the pile by means of a double band of gray paper wetted with vinegar, and as often as this circuit was completed, contractions were excited in the animal.