4

Apparatus at first simple.

Plate CCXXIX. fig. 1.

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 zinc wire, sharp at the point A, and fixed in the wooden stand C. If the 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 immediate ly 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 a zinc wire, similar to AB, were substituted for the gold or silver wire, no such effect would be produced. Methods of Frogs, as they are most easily found, and as they preparing are, perhaps, more convenient in other respects, have frogs for been oftener the subject of galvanic experiments than experiany other animal. To prepare them for these experiments. ments, 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 dissection, 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 scissars 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 scissars is introduced beneath

them, and the spine is cut through, but without divid- Construcing the nerves. A portion of the inferior part of the tion of spine is afterwards to be separated, that room may be Apparatus. 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 Fig. 2. 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 Single galexample of the simplest galvanic combination, or what vauie comis 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 oxidating fluids, and the substances which contain these fluids. But although the conductors of electricity, for the sake of conveniency, 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 dif ferent 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 Fig. 3. of active simple galvanic combinations. In fig. 3. the and 4letters AB mark the bodies belonging to the first class or perfect conductors; and a marks the body belonging to the second class, or imperfect conductors; and in fig. 4. 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 fig. 5, 6, 7, which Fig. 5, 6, 7, consist of two bodies only, and therefore are not active 8, 9. 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

Construc- points with the body belonging to the other class. Thus, tionof if a prepared frog is convulsed by the contact of the Apparatus. same piece of metal in two different places, the fluids

Action of

accompanied by

of those parts, which must be somewhat different from each other, are the two conductors of the second class, and the metal constitutes the third body for the conductor of the first class. 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 class.

may

Here it be necessary to anticipate a little, by obgalvanism serving, that in a simple galvanic circle, the conductor or conductors of one class must have some chemical action upon the other conductor or conductors, otherchemical wise 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.

action.

Galranio

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 atmospherical 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 class have different chemical actions on the conductors of the first class, 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 eircles of order, composed of two conductors of the first class, and one of the second.

the first

order.

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 80lution 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 atmospherical 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 ace- Construe

tous acid.

Silver, with gold, and the nitric acid.

tion of Apparatus.

10

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 com- Batteries. binations thus connected together have received the name of batteries; and these batteries are said to belong to the first and 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 class 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 alteration being regular.

The first attempt to increase the effects of the gal- Couronne vanic fluid, by combining a series of simple circles, was de tasseo.. made by Volta; to this he gave the name couronne de

tasses..

Fig. 10.

ter.

Construe tasses. The following is the construction and mode of tion of applying this apparatus. 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 waTo one extremity of a bent brass wire solder a plate of zinc of about two inches in diameter, and to the other extremity of the same wire, solder 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, 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.

12

Pile of Volta.

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 ar

Suppose the metals to be employed in the construc- Apparatus, tion 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 observed 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

was announced by the ingenious inventor of the pile Construchimself. Volta inclosed his piles, after they were erected, tion of with wax or pitch. By this contrivance which he put Apparatus. 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.

Construc- in each exactly in the same way, and let the conducttion of ing substances, as wires, pass from the top and bottom Apparatus. 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 bottom 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 pro. duce the full effect.

Various contrivances were thought of to obviate these inconveniences, and the first which was proposed

As it was found that the chemical effects of the pile were greatly increased by employing plates of a largersurface, 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 Fig. 11. copper, zinc, and pieces of pasteboard, soaked 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 c, %, 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 Fig. 12. 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

into

Construc- into contact, only having a piece of pasteboard intertion of posed. The third column C is arranged in the same Apparatus. 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 in to 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.

13 Galvanic trough.

Fig. 13.

14

Casting of

the zinc plates.

The inconveniences of the pile, as we have already binted, 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 AB, 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 of 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 3

which it is said has succeeded best in forming plates of Construeany considerable size is the following. The zinc of tion of which the plates are to be composed is to be melted Apparatus. 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 oxidated 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.

15

The plates being thus prepared are to be soldered Soldering 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 solder employed for this, purpose is soft solder; 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