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iving out hydrogen gas, on the contact f. made, the metal in solution became reduced. Thus, when iron and silver were placed in a solution of copper, the iron immediately began to reduce the copper in solution, while the silver had not the slightest action. Upon bringing the two metals in contact, however, the silver became coated with copper. Dr. Wallaston attributes the curious phenomon, above described, to a change of states in the electricity of the metals; and in order to confirm this idea, he attempted the same by means of common electricity, in which he succeeded to his utmost satisfaction. He supposes, that the chemical affinities are so altered by the presence or absence of electricity, as to induce the anomalous appearances, which took place in the above experiments. The silver wire became coated with copper, and at the same time appeared to have the power of decomposing water. The only mystery we observe in these experiments is the liberation of the hydrogen, in a situation where no oxygen is manifested, either in the form of gas, or in any other state. Nor does the new doctrine, lately advanced by Mr. Davy, throw much light on this subject. The zinc, in this experiment, is said to be positively electrified, and the copper or silver to be negative. That the zinc, on that account, attracts the oxygen of the water, and the silver the hydrogen. That the constituent parts of water are by the same law made to appear in situations where the decomposition did not take place, is very evident; hence it would appear that the hydrogen is carried by some means from the zinc to the silver; or that the oxygen passes from the silver to the zinc; or, according to Mr. Davy's hypothesis, the decomposition of the watertakes place between the metals, the oxygen passing inevitably to the zinc, and the hydrogen in a similar way to the silver. To the latter there are several objections, which will appear from the following experiments. Let a tube of three feet in length be filled with dilute muriatic acid, and corked at both ends, having a wire of zinc inserted in one end, and one of silver or platina in the other. The zinc will immediately begin to give out hydrogen, but no effect will be observed at the silwer wire. Let a communication be established between the wires on the outside of the tube. The silver does not immediately give out bubbles, as was the case in the experiments of Dr. Wollaston, nor

does that effect take place till a few se

conds after the contact of the metals. Can we for a moment suppose that the slight negative and positive electricity produced by the contact of two small wires, which would not affect the most delicate electrometer, can have the power, the one of attracting oxygen, and the other hydrogen, at the distance of eighteen inches, reckoning from the middle of the tube 2 If the same tube be bent in the middle to an acute angle, like the letter V, according to Mr. Davy's hypothesis, the appearance of the hydrogen at the silver wire ought to take place as soon after the contact, as with the straight tube; but what is very singular, it will not take place at all. This experiment would seem to prove, that one of the constituents of the water is carried through the whole length of the tube ; and that by some law which differs from those of electricity, since the angle of the tube appeared to interrupt its passage. The interruption is still greater, even with a shorter tube, when the tube is bent in different places, forming a sort of zig-zag. The idea that hydrogen is carried from the zinc to the copper-wire, is strongly favoured by another experiment. Take the glass tube A B, fig. 2, filled with dilute muriatic acid, having a cork at B, through which the wires, z and c are passed, z being a wire of zinc, and c a wire of platina, silver, or copper. So long as the wires remain unconnected at z, the platina-wire appears unchanged ; but as soon as the contact is formed, bubbles of hydrogen are first seen at do they then very slowly begin to appear in the lower parts of the wire; but what is singular, the moment they begin to appear at f, they are also seen at s, and some seconds are elapsed before any bubbles are seen at g. If the hydrogen in the last experiment were attracted by the negative state of the platina-wire, since the metal is the best conductor, it would seem, that the points would be the last part to have parted with its electricity; and, of

course, the bubbles of hydrogenought to.

have appeared the last at that point, whicn is contrary to fact. It therefore appears more likely, that the hydrogen has been held in combination by the electricity, the latter of which is taken by the nearest metallic conducter in the circuit, leaving the hydrogen in its gaseous form: the law, however, by which it moves along the liquid, does not appear to agree with any known properties of electricity, since the hydrogen is some seconds in reaching the point g.

It will appear from the above experiments, that the galvanic F. are essentially promoted, by having two metallic surfaces so situated that one shall be oxydated, and that the other shall be situated as near it as possible, for the urpose of receiving its electricity. We ave shewn, that the current is not only interrupted by distance, but that it ; essential the passage should be a direct line. In Dr. Wollaston’s experiments, when the wires were placed in a metallic solution, such as that of copper and silver, and the contact formed between the zinc and silver wires, no hydrogen was evolved by the latter, the contrary of which was the case with the dilute acid; but the metal in solution became reduced upon the silver. There does not appear anything mysterious in the reduction of the metal, since the hydrogen does not appear, being employed in the deoxydation of the metal. A further proof that this is the case is, that no other metals can be reduced in this way but such as do not decompose water. This singular process enables us to account for several facts which have hitherto appeared anomalous. If a glass plate be smeared over with a solution of nitrate of silver, and a common pin be laid in the middle of the plate, beautiful ramifications of metallic silver will soon appear, as if vegetating from the pin. If the process be examined by a magnifying glass, the ramifications of silver may be fairly seen to grow from their ends. Though the more oxydable metal, the pin, may, in the first instance, have reduced a portion of silver, it does not account for the vegetative appearance which is afterwards observed. The pin cannot reduce the silver at so great a distance from itself, which is sometimes more than an inch. In order to prove, that the agency of the oxydable metal was not essential to the reduction of the metal, the writer of this article covered one half of the plate with liquid nitrate of silver, and the other half with dilute muriatic acid, suffering the liquids to touch each other; a wire of zinc was laid in the dilute acid, and one of platina in the nitrate of silver. As soon as the opposite ends of the wires were brought in contact, beautiful ramifications of silver soon began to appear from the platina wire, but no gas was observed. If a solution of gold be used, instead of that of silver, the platina becomes speedily gilt. The experiment producing

what is called the lead-tree cannot be accounted for in any other way : it consists in filling a bottle with a solution of acetate of lead, in the upper part of which is suspended a piece of metallic zinc: in the course of a day or two, metallic lead is observed in shining filaments, suspended from the piece of zinc. The same difficulty occurs in this as in the last experiment: the filaments of lead constantly grow from the ends at a distance of many inches from the zinc. In order to prove that this experiment is similar to the last, that is, that the lead is reduced by the hydrogen, take a tube, A B, fig. 3, at one end of which tie a piece of bladder so tight that the tube may hold water; let a cork be inserted at A, through which the platina wire, P p, is passed ; the tube being set upright in the zinc cup, D, containing dilute muriatic acid, and a connection formed at P, the platina soon becomes covered with brilliant crystals of metallic lead; hence it would appear, that the platina had the power of reducing the lead into its metallic state, or that some substance had been transmitted through the bladder adequate to that effect. If, instead of the acetate of lead, the tube be filled with dilute acid, upon the connection being formed at P, the platina becomes covered with bubbles of hydrogen: need we, therefore, hesitate in concluding, that the lead owes its reduction to the hydrogen The method of whitening brass and copper, by boiling them with cream of tartar and tin, is a process of this kind; the cream of tartar, and the metallic tin, answering the purpose of the zinc and acetate of lead in the last experiment: a portion of the tin in solution is reduced upon the copper or brass, rendering it white by the hydrogen which is produced during the galvanic contact of the copper or brass with the tin. In all the experiments, the zinc wire is, during its contact with that of the platina, silver, &c. undergoing an increased oxydation, which is proportionate to the quantity of hydrogen evolved at the platina wire; since the oxygen of that and hydrogen, both of which are derived from the water, are disposed of in the oxydation of the zinc. The hydrogen passes from the zinc to the opposite wire, with the greatest facility, through a direct liquid communication, the shorter the better. It becomes much interrupted by having to turn sharp angles, or in passing through small apertures. It passes with more or less freedom through solid bodies, when moistened with water, but does not pass at all, except when moisture is present. Having given an account of the effects resulting from a single galvanic combination, we will next give some account of the constructions of that compound apparatus, termed Galvanic, or, more properly, the Voltaic battery.

The pile of Volta, of which we have already given a slight description, is at present so little used, that we shall direct our attention more particularly to the trough, as being more convenient for experiments than the pile, and at the same time less liable to be out of order.

The wood of which the trough is formed should be the oldest and hardest mahogany, being less liable to warp than other kinds of wood. The sides of the trough must be dove-tailed together, and the bottom ought to be grooved into the sides, and fitted in with turpentine; perpendicular grooves must be made in the sides of the trough, for the reception of the plates, correspondent to which there must be grooves in the bottom. When the length of a trough is more than two feet, it becomes unwieldly; it should not even be that length, when the size of the plates would render it too heavy to be handed about. The distance between the plates should be about three-eighths of an inch; if they are nearer together, the acid employed is too soon exhausted, and, consequently, the power of the battery less lasting. The plates should be of copper and zinc. Though silver is stronger than copper, it is not so in proportion to the price. The zinc plates are best cut out of sheets of malleable zinc, as being cheaper, less liable to break, and may be used "much thinner. The copper may be employed so thin as six ounces to the square foot. The plates of copper, being made a little larger than the zinc, may be lapped over the edges of the latter, by which means they fit much closer to the zinc plate, without the labour of hammering the copper plates previously flat. The copper plates only require to be soldered to the upper edge of the zinc plate, since the other three edges are so secured with cement in the grooves as to preclude the vecessity of sołdering. The lapping over of the copper is sufficient to keep it close to the zinc plate till the plate is fastened in the trough. Previously to inserting the plates in the trough, the in

side must be lined with a cement, formed of resin and bees-wax, or, what is cheaper, of six parts of resin and one of lime and oil. The plates, being previously warmed, are to be pressed down into the grooves before the cement becomes quite cold. After the plates have been inserted, in such order that all the zinc surfaces shall face one way and the copper the other, the cement must be more evenly adjusted with a hot iron which will reach to the bottom of the cells; the trough being laid first on one side and then on the other for that purpose. When the cementing process is finished, and the whole sufficiently cold, the trough must be dressed off, and varnished with copal varnish, where it can be had; but in lieu of that with common spirit varnish. When the varnish is dry, it must be polished with rotten-stone and water. In the above construction it is manifest that two of the surfaces are lost by being laid and soldered together. About two years ago the writer of this article had conceived the possibility of making use of both the surfaces of the copper and zinc plates at the same time. Accordingly he cemented into a trough, in the groove made for the plates of metal, plates of glass. The metal plates were formed by soldering together a plate of each, of copper and zinc, and then bending them till the plates became parallel to each other, leaving a space between the two surfaces a little wider than the thickness of the glass plates. The cells between the glass plates being filled with the proper liquid, each of the above compound plates were made to bestride one p the glass plates, in such order that a zinc and copper plate of two different compound plates, in succession to each other, may occupy each of the cells. All the surfaces are by this contrivance exposed to the action of the liquid, and might be considered double the power of a common trough, having the same number of plates. Little or no advantage was gained by this method. Though there are two surfaces of each metal in each of the cells, it will be evident, from several minor experiments already given, that two of the surfaces are so completely disconnected as to produce little or no effect. One of the zinc surfaces in this trough is facing the glass on one side the cell, and one of the copper surfaces is similarly situated on the other side. The trough, therefore, which is represented in figure 1, and which has been

particularly described, is, for general use, the, most convenient, and in other respects, the best battery yet introduced. The next thing to be considered, is the management of the galvanic battery. First, all of the cells of the trough must be filled, within about half an inch of the top, with a liquid, composed of water, with about one twenty-fifth part of the muriatic or the nitric acid. The plates of the trough are shorter than the depth of the trough by about three-fourths of an inch ; so that the trough may be leaned on one side in the filling, for the purpose of letting the liquid run equally into all the cells. If a number of troughs are to be connected together, the communication must be made by arcs of metal, which are inserted into the liquid of one cell of each trough, as represented in fig. 1, at C. In making the connection, it is to be observed, that the zinc surface of one trough must correspond with the copper one of another, and the zinc of the latter with copper of a third, and so on. This arrangement may be better conceived by placing them in the same order, and to end in such a way, that all the zinc surfaces may face one way, and the copper ones the other. After all the troughs are connected together, let the two unconnected ends, at which the experiments are to be made, be as near together as possible. A connection being now formed between the two ends, one of which we shall term the zinc end, and the other the copper end, the united energy of the whole will be transmitted through the connecting medium.

ExPERIMENTs.

The most striking and the most common experiments are those which consist in the galvanic energy upon the organs of animals. If two metallic rods, or, what is equally convenient, two silver spoons, be grasped, one in each hand, the skin of the part being previously moistened with a solution of salt, and one of the spoons be brought in contact with one end of the battery, the moment the other comes in contact with the other end of the battery the shock is perceived. Fifty compound lates will give a shock which will be felt in the elbows. One of a hundred will be felt in the shoulders. A greater number of plates give so forcible a shock to the muscles, as to be dreaded a second time. WOL. V.

The shock appears to depend upon the number of plates. The stun, or first impression, is much the same, whatever may be the size of the plates; at least, from the size of two inches square to that of ten; the surfaces being as four to one hundred. The effect upon the muscles, as well as upon the cuticle itself, is very different from large plates, when the series is the same. It appears that the shock, or first impression, is as the series, which is also as the intensity of the electricity. If the shock be received from the same number of large plates, the same species of commotion is produced, in the first instance, as with the small plates; but if the contact be still kept up, a continuation of the effect is perceived, which is felt through the whole arms, producing a vast tremor, attended with a sensation of warmth. If the plates be from eight to twelve inches square, this effect may be perpetually kept, while the acid in the cells is expended. Though small plates have been recommended for medical purposes, we think large ones will be found more likely to have a good effect. If the medical advantage is to be derived from the stimulus of galvanism, the effect of a perpetual and regular current of that stimulus must certainly be preferable to the rapid transmission of a small quantity. The galvanic shock may also be conveniently given, by immersing the hands or the feet into vessels containing a solution of salt, and bringing wires from each end of the battery into the liquid. If any other part of the body is intended to be operated upon, a sponge, moistened with salt water, fastened to a metal plate connected with one end of the battery, may be applied to the part, and the hand or foot put into a vessel of the same liquid, connected by a wire with the other end of the battery. Small bits of sponge or bits of leather may be fastened to the end of the connecting wires, and made more or less moist, as the delicacy of the part may require. This contrivance is very useful in operating upon the eyes or eats. When galvanism is used medically, it should first be applied very feebly, and the effect gradually increased, as the susceptibility of the part will admit. If the part has, from disease, become so languid and insusceptible, as not to be sensible of the effect, it should be scarified, or by other means have the cuticle removed. This is sometimes the case with languid tumours, and some cases of paralysis— Ll

Though we had no great opinion of the medical agency of galvanism, we have lately heard of several very successful cases, one of which in particular was the cure of perfect loss of speech. If the naked metal of the wire from a powerful battery be applied to the skin, it becomes cauterized and blistered. If the plate, covered with a moistened sponge, connected with one end of the battery, be applied to the back of the head, at the same time that the moisttened fingers of one hand are slightly applied to the other end, a smarting sensation will be felt in the part, and a taste at the same time will be felt in the mouth, similar, but in a greater degree, to that occasioned by the piece of zinc and the shilling when laid upon the tongue. This experiment succeeds the best with a small number of large plates, as much as ten inches square.

Decomposition of Water and other Bodies.

The most simple way of performing this experiment is, to bring, the wires coming from each end of the battery into a vessel of water. A profusion of bubbles of gas will appear to be given out from each wire, as far as they are immersed in the liquid. The nearer the wires are brought together, so as not to touch, the more rapidly the decomposition goes on. The gas produced from the wire coming from the zinc end of the battery, if the wire be of gold or platina, is found to be oxygen gas ; but if the wire be of any more oxydable metal, no gas will appear, but the wire becomes oxydated. The gas furnished by the wire from the copper end of the battery, or whatever kind of metal the wire may be, is pure hydrogen. If the immersed part of this, however, be previously oxy dated, no gas will be observed for some time, the hydrogen being employed in reducing the oxide upon the surface.

Both the gases are furnished from the decomposition of the water.

An apparatus more convenient for this experiment, and at the same time fitted for collecting the gases, is shown in fig. 4; c g, is a cup of glass capable of receiving the glass tube, h; Ec, and f z, are two wires of platina, fitted into two holes perforated in the bottom of the glass cup; the tube, h, which is close at the top, is first filled with the water or other liquid, and the cup invered upon it; the whole are then sud

denly returned into their erect position. This apparatus is then placed in the frame, fig. 5; A B C D are four pieces of brass, united together by the pieces of glass, F and G, and supported by four legs, through which also the brass rods, H and K, are passed. It is plain, the two sides of this frame are insulated with respect to each other, at least as much as is necessary for any galvanic experiment. The part f, in fig. 4, being introduced into any of the holes, such as n m, the opposite end, F, is made to rest on the opposite brass rod, K. If the wires from the battery be now connected with the frame at H and K, the gass will instantly begin to rise from the wires, c and z, up into the tube, while the liquid descends and occupies the cup. A number of the apparatus, such as fig. 4, may be employed at the same time; and if the different tubes are filled with different liquids, such as the various solutions of salts, and the communication of cach occasionally cut off, by placing some non-conductor at E, their relative conducting powers may be ascertained. - e If two tubes of smaller size be placed, one over the wire, z, and the other over that of c, the gases may be collected separately. If the tube contains a metallic solution, such as silver, lead, or copper, the wire from the copper end of the battery will afford no gas; but the metal of the solution will be reduced. Let the glass vessel A, fig. 6, have the two tubes, z and c, ground into its two necks. At the ends, z and c, of the tubes, are tied bits of bladder, so that any liquid in the tubes may have no tendency to enter the vessel A. The vessel being previously filled with some liquid, the tubes are so inserted that no air may exist between the ends of the tubes; the tubes are also provided with two small caps of ivory or wood, through which the platina wires, pp. are passed, reaching the bottom so near as not to pierce the bladders. The tubes being filled with water, and the wire from the zinc end of the battery connected with the wire of tube z, while that of the copper is attached to that of tube c, the decomposition of water will speedily commence, the wire in zaffording oxygen gas, while that of c affords hydrogen gas. In a very short time, the liquid of the tube z will be found to contain muriatic acid : or, rather, the oxymuriatic ; and the tube, c, will at the same time be found to con

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