Part 13

The two plates are commonly soldered, not through their whole extent, but about one fourth of an inch from the edge; so that at the edge their union may be complete.

Care must be taken that all the plates be cemented to the trough in the same direction; so as to have the copper side of every plate opposite to the zinc side of the next.

The liquid employed to fill up the cells between the plates, is formed by diluting muriatic acid with water, in the proportion of one ounce of the former to a pint of the latter. When the trough is not in use, it should be emptied of this solution (which may be preserved for subsequent experiments, unless saturated with the metals) and then rinsed clean with fresh water.

This construction is preferable to the Voltaic pile, for experiments in which it is necessary to have the Galvanic action for a length of time. But for occasional experiments the pile is more convenient; as the trough, if suffered to remain long without the fluid, is apt to crack and separate the cement from the plates, which renders it necessary to cement them again.

When several batteries are required, they should be disposed in the same order as if they all constituted one trough, (observing through the whole series to keep the zinc surfaces constantly opposed to the copper ones,) and connected together by some metallic substance, such as a piece of sheet lead, or tin-foil, about half the width of the trough. Batteries combined in this way should all be, as nearly as possible, of the same power. For if a bad battery be united to five good ones, each of the same number of plates, the effect of the whole will be equal only to six times that of the bad one—as in electrical batteries, if three jars of different sizes be charged together, the whole charge will be equal to only three times that of the smallest jar.

CHAP. IV. _The Method of performing Galvanic Experiments with Frogs; with some conclusions drawn from them._

Every sensible heart must be shocked with the idea of torturing defenceless animals, merely to gratify an idle curiosity. The chapter which we shall now lay before the reader is founded entirely on the assertions of other writers upon this subject; to which, however, we have not the least doubt that the fullest credit is due. But we have not chosen to prove the veracity of their statements by our own experiments, believing that any small additional knowledge we might possibly have obtained in this way, would have been purchased at too great a price—the sacrifice of feeling and humanity.

Take a living frog, and after amputating the hind legs, (for they are the best, on account of the number of joints) let the largest nerve, called the _crural nerve_, be laid bare, and surrounded with a slip of tin-foil, or a piece of sheet lead—then lay a piece of zinc, or other metal different from that on the nerve, in contact with the neighbouring muscles; form a communication by another piece of zinc, or other good conductor, between the metal in contact with the muscle and the _armed_ part of the nerve, and violent contractions will be produced in the limb.

There is another method of producing these convulsions, which has been preferred on account of its simplicity.—It is by forming a communication between a nerve, armed as above, and an adjoining muscle, by a piece of zinc, without the assistance of a communicator.—This was one of the first methods of Galvanizing frogs, before the invention of the pile and trough. But since these discoveries, frogs have been made to show more violent convulsions.

We now proceed to relate some of the conclusions which have been drawn from the experiments on frogs.

1. The contractions produced in the limb of a frog are stronger the farther the metal is placed from the origin of the nerve.

2. When the metal has remained for some time on a particular part of the nerve the motion will cease; but it may be renewed by changing the position of the metal, and carrying it lower on the nerve.

3. Contractions may be produced in the prepared limb of a frog, by putting it in water, and then bringing two metals in contact with each other, at a short distance from the limb.

4. Only those muscles to which the nerves lead suffer contraction from the Galvanic influence.

5. When a contraction has taken place in any muscle, no other will follow while the metals remain in contact.—In order to renew the motions, therefore, the metals must be separated and joined again.

6. Galvanic excitement, instead of destroying the irritability of a muscle, gives it an additional support. Dr. Valli, an Italian physician, has fully confirmed this principle by the following experiment. “Having prepared the wing of a fowl, or the paw of a cat or dog, I subjected it to the customary trial. At the expiration of half an hour, I armed the other wing of the fowl, or the other paw of the cat or dog, and had recourse to my exciting arc.—The latter wing or paw, however, did not give any sign of electricity, (for he conceived the motion to be occasioned by electricity,) while the parts which had been subjected in the first instance to the experiment, still continued in a convulsed and agitated state.”

7. Galvanic experiments do not succeed so well in a room crowded with persons, as when only two or three individuals are present.

8. Galvanic contractions are more powerful the instant the animal is deprived of life, than some time after; and therefore more violent agitations can be produced in the living animal.

9. Volta concluded that Galvanism was generated by the metal, and not by the animal upon which he operated.

These are the principal remarks which we think worth noticing. If they do not content the reader, we must refer him to Wilkinson on Galvanism; where he will find a detail of almost every thing that happened in the Galvanic world till the time he wrote.

CHAP. V. _Various Experiments with the Galvanic Pile._

The first experiments which we shall mention were performed by Mr. Cruickshank, with the Galvanic pile. He employed plates of zinc and silver, 1.6 inches square, and the number of plates of both metals varied from forty to a hundred, according to the power required. The lower end of the pile we shall denominate the _silver_ end, because the plate at the bottom is of silver, and the upper end the _zinc_ end, because the uppermost plate is of zinc. The first experiment of Mr. Cruickshank with the Galvanic pile, was upon water and silver wires. These wires were passed through corks, fitted into a glass tube filled with water, and projected about one third of the way, on both sides, into the tube; so that the space between the inner ends of the wires was one third of the length of the tube. One of the corks was made perfectly tight by cement. The tube was then placed upright in a tumbler of water, with the uncemented end downwards.

As soon as a communication was made between the extremities of the pile by the wires, small air bubbles began to ascend from the wire connected with the silver end, and a white cloud made its appearance at the wire proceeding from the zinc end.—The cloud gradually increased, assuming a darker colour, and at last it became purple, and even black. A few air bubbles were likewise observed upon this wire, which ascended from it; but when the pile acted well, a considerable stream of air could be perceived.—When this gas was examined, it was 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 reliance, however, can be placed on the accuracy of this analysis. The wire proceeding from the zinc end, was found much corroded, and looked as if a portion of it had been dissolved.

Mr. Cruickshank supposed the cloud formed round the wire of the zinc end to be the muriate of silver, proceeding from the silver wire which had been somehow dissolved, and afterwards precipitated in this state, by the muriatic salts contained in the common water.

The next experiment was with distilled water, a tincture of litmus, and silver wires, as before. The apparatus being adjusted in the manner above described, and one wire connected with one end of the pile, while the other touched the other end, gas immediately arose from both wires, but in greater quantity from the one connected with the silver plate. In a short time the whole fluid below the point of the wire from the zinc plate, became red, and the fluid below the wire from the silver plate, looked of a deeper blue. Distilled water tinged with Brazil wood, soon became of as deep a purple as could be produced by ammonia.—From the two last experiments, Mr. Cruickshank was led to suppose, that an _acid_, probably the nitrous, is produced at the wire connected with the zinc plate, and an _alkali_, probably ammonia, at the one connected with the silver end of the pile.

As hydrogen gas, whether heated or in its natural state, reduces metallic oxyds, Mr. Cruickshank resolved to subject solutions of metallic oxyds to the hydrogen gas which was produced by the pile.—The result answered his expectation, for in a minute or two after the communication was formed, fine metallic needles or crystals, something resembling a feather, were perceived round the wire connected with the silver plate.—The oxygen too which escaped from the metal, and that generated from the fluid used in the solution, was commonly pure, when an excess of acid was added to take up the alkali.—The acetite of lead and the sulphate of copper, were among the oxyds experimented upon, but whatever the metal was, the results coincided. These experiments were made in a tube like the preceding ones.—A number of experiments were made by the same gentleman upon the _earths_, but we shall not detail them; we must content ourselves with some conclusions drawn from his observations.

1. Hydrogen gas, mixed with a small portion of oxygen and ammonia, is somehow disengaged at the wire communicating with the silver extremity of the pile; and this effect is equally produced, whatever the nature of the metallic wire may be, provided the fluid operated upon be _water_.

2. When metallic solutions are used, the same wire which separates the hydrogen gas, revives the metallic calx, and deposits it at its extremity, in its pure metallic state; in this case no hydrogen is disengaged. The wire employed for this purpose may be of any metal.

3. Of the earthy solutions, only those of magnesia and argill are decomposed by the wire: a circumstance which strongly favours the production of ammonia.

CHAP. VI. _Experiments on the deflagration of Metals by the Galvanic Pile._

The pile with which these experiments were made consisted of thirty-six plates of silver, and an equal number of zinc ones, between which were interposed disks of flannel, moistened with a solution of the muriate of ammonia.—Each plate had a diameter of ten inches, or contained 78.58 square inches;—consequently the whole surface of silver in the pile, reckoning only one side, was 2828.57 square inches, and that of zinc the same.

With this instrument, in December 1801, gold, silver, copper, tin, lead and zinc were deflagrated with surprising facility. The gold burned with a vivid white light, inclining a little to blue, and deposited an oxyd of a deep purplish-brown colour.—The silver gave a vivid flame of a greenish hue, and extremely brilliant. Its oxyd was of a blackish colour. The copper presented phenomena similar to those which attended the gold.—Lead gave a very vivid light, of a dilute bluish purple.—The tin afforded a light similar to that of the gold, but burnt with much less energy; probably because the leaves were thicker. The zinc gave a blueish white flame, which was edged, at the moment of contact, with red. It was more difficult to inflame than any of the preceding metals, but the leaves were likewise much thicker. The oxyds of the four last metals were not examined.

Water was poured upon the upper plate of the pile, so as to form a _standing pool_; and several pieces of the same kind of metals with those before experimented upon, were presented to the plate through this aqueous medium, and were deflagrated. They afforded a flame of the same colour as when they were brought to the bare plate.—A vapour was sometimes perceptible immediately after the deflagration, and was supposed to arise from a portion of water converted into steam by the intense heat.

It is very remarkable that the shocks taken from this pile, which produced such astonishing effects upon metals, could be received with but very trifling inconvenience, through the human body.

Besides these experiments, which were made by a society of gentlemen, a variety of others were performed, from which nearly the same conclusions were deduced.—Two other facts, however, deserve notice.

1. When metallic leaves are deflagrated in carbonic-acid gas, the flame is weak: but when in oxygen gas, the communication between the upper and under plates of the pile is no sooner formed, than the metallic leaves are destroyed with one sudden flash.

2. When metals are subjected to Galvanism in an exhausted receiver, they emit light but are not oxydated.

CHAP. VII. _Further Galvanic Experiments on Metals, and on other Substances._

It is hardly necessary to mention, that every experiment made by means of the Galvanic pile may be performed, with equal success, with the trough. The experiments related in this chapter may be effected by the pile, but they cannot be done with the same convenience as when troughs are used. The battery[19] employed in these experiments consisted of sixty pieces of silver, and a like number of zinc, each two and a quarter inches square. The shock produced by this trough, by means of two metallic conductors, was distinctly felt in the shoulders, and the contraction or spasm was so violent, as to render the operator unable to hold the conductors, when in contact with the plates by which the trough terminated each way.—A sensation resembling that produced by hot water, was at the same time felt in the wrists and fore-arm.

A small steel wire, which was used for the conductor to form the communication, upon its contact with the plates, produced a vivid spark and bright scintillations.—When a piece of phosphorus was placed upon the end of this wire, and made a part of the circuit, it was instantly inflamed.

Another battery of the same size being connected with the one above described, gun-powder was fired, and gold leaf deflagrated without any perceptible residuum—being probably volatilised by the heat occasioned by the experiment.

Mr. Davy, secretary of the Royal Society, placed a small piece of pure potash (which had previously been exposed to the atmosphere, so as to render it a conductor of the Galvanic fluid,) upon an insulated plate of platina, connected with the negative[20] end of a battery, of the power of two hundred and fifty plates, six inches by four, in a state of intense activity.—A wire communicating with the positive end, was brought in contact with the upper surface of the alkali. The whole apparatus was in the open air. Under these circumstances a vivid action was soon perceived.—The potash began to fuse at both points where the fluid acted upon it.—There was a violent effervescence at the upper surface:—at the lower or negative surface there was no liberation of elastic fluid, but there appeared small metallic globules, very much resembling quick-silver. Some of these globules burned with an explosion and a bright flame, as soon as they were formed, while others remained which were merely tarnished; and finally a white film was formed over their surfaces, which was afterwards found to be pure potash.

Soda was acted upon in the same manner as potash, and exhibited the same results; but its decomposition required a stronger action of the battery, or it was necessary that the soda should be in smaller pieces than the potash.

The metallic globules produced from the potash remained fluids in the open air, at the time of their production; but those from soda, though fluid at the time of their formation, upon cooling, became solid, having much the lustre of silver. The alkalies could be made to produce metallic results in vacuo.

Since Mr. Davy’s first experiments on this subject, several others have been made, much in the same manner, upon the earths. Messrs. Pontin and Berzelius, two Swedish chemists, have succeeded in obtaining metallic amalgams from lime, magnesia, strontites and barytes; but they could produce no such effect on alumine and silex. Mr. Davy however effected this, by a battery of 36000 square inches.—He also improved upon their other discoveries. He, by distillation, drove off the mercury from the amalgamated metals which they obtained from the earths, and procured a pure metal.

Ammonia was also found to contain a metal. This discovery inclines one to believe, that the air we breathe contains metal in a gaseous state, as azote, which is a component part of ammonia, forms a large portion of our atmosphere.

When compounds, soluble in water, were put into water contained in agate cups, and subjected to the action of Galvanism, their decomposition was rapid.—A solution of the sulphate of potash, being put into two cups and Galvanised by fifty pair of plates, for four hours, the acid was found by itself in the cup connected with the positive end of the battery, and the alkaline basis in the cup communicating with the negative end. Similar phenomena took place in solutions of sulphate of soda, nitrate of potash, nitrate of barytes, phosphate of soda, sulphate, succinates, oxalate and benzoate of ammonia; also with alum. When muriatic salts were used, they afforded oxymuriatic acid. When metallic solutions were employed, metallic crystals and an oxyd were deposited on the negative wire, and a great excess of acid was found in the positive cup.—Strong solutions afforded signs of decomposition quicker than weaker ones.

We could enumerate a variety of similar experiments, but the limits of our work forbid it.

CHAP. VIII. _Experiments which may be performed without the assistance of the Battery._

_To shew the Galvanic light._

Place a piece of zinc upon your tongue, and a piece of silver between your cheek and upper jaw; then move your tongue so as to bring the two metals in contact with each other, and you will perceive a very curious sensation upon your tongue, accompanied by a cool sub-acid taste,[21] and at the same time you will see a _flash of light_, whether your eyes be open or closed. The sub-acid taste resembles, in a degree, that produced by electricity.[22]

_To affect the Taste by means of Water._

Place a tin or pewter bason filled with clean water upon a silver mug: with both your hands, which must previously be wet with a solution of salt in water, grasp the silver vessel, and put your tongue into the water, taking care not to touch the tin or pewter vessel with any part of your body; you will now perceive an acid taste; which will be more sensible, if you withdraw your hands from the silver vessel while your tongue remains in the water, and then replace them.

_To prove that Earth-Worms have a nervous system._

Place an earth-worm upon a plate of zinc, resting on a larger plate of silver.—The animal, as soon as it approaches the silver, seems to be repulsed by a painful sensation, and at last becomes fatigued by its repeated and fruitless exertions to make its escape, which nothing apparently prevents.

This evidently proves that the animal is provided with a nervous system, as experiments have proved that Galvanic irritation is excited only in the nerves.

CHAP. IX. _Some common Effects which are supposed to be occasioned by Galvanism._

We have already remarked, that a sub-acid taste is perceptible when two different metals are applied to the tongue and fauces: it has also been found that Galvanism affects the taste, when two different _fluids_ and a single metal are in contact with the tongue. Upon this principle a variety of known facts have been accounted for.—For example—It has long been observed that beer, cyder, &c. when drunk from a tin or silver vessel, were more palatable than when received from a vessel of glass, or any other substance not metallic. The supposed explanation of this, is as follows.—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 liquid contained in the vessel, a Galvanic arc is formed, which produces the brisk and lively taste.

It has been supposed, by persons fond of this theory, that snuff, when taken from a metallic box, excites a more agreeable sensation than when taken from a box of tortoise shell, or leather.

The fact that a silver spoon becomes discoloured by being used for eating eggs, is familiar to every one. This, also, is attributed to the Galvanic action. By experiment, sulphur has been discovered in both the albumen and yolk of an egg.—The Galvanic combination is between the sulphur of the egg, the silver spoon, and the saliva; for no tarnish is produced on the spoon when it is immersed in either the albumen or yolk; and that part of the spoon which enters the mouth is most discoloured. In every Galvanic experiment, water is decomposed into its constituent parts, hydrogen and oxygen gases. These things being premised, the fact is easily accounted for.—The hydrogen, which before the operation is nascent in the water, (which holds the sulphur in solution) now readily unites with the sulphur, and forms sulphurated hydrogen gas, which produces the tarnish on the silver.[23]

We shall mention a few other common appearances, and leave the solution to the ingenuity of the reader.

When copper sheathing is fastened on a ship with iron nails, the nails, and particularly the copper, are found to be corroded about the places of contact.

Works of metal, the parts of which are joined by a solder of a different metal, are observed to tarnish about the places where the different metals meet. A seam which has been soldered so accurately that it cannot be perceived by the eye, may be discovered by passing the tongue over it.

CHAP. X. _The Effects of Galvanism on Vegetables._

This part of Galvanism has been particularly attended to by Humboldt, a German. He first observed the irritability of the vegetable fibre.

Remarking the great similarity of appearance between the substance of mushrooms and the muscular fibre, he wished to ascertain whether they possessed a similar power of contraction. He accordingly made a considerable number of experiments, from which he concluded that the different kinds of mushrooms, which in becoming putrid emit an animal insipid cadaverous smell, are as perfect conductors in the Galvanic chain as the organs of animals. His experiments likewise proved that they possessed irritability.

Mr. Humboldt afterwards directed his inquiries to the _manner_ in which Galvanism acted upon the irritable fibre, which, as we have already mentioned, he first observed. These experiments, however, were unsuccessful. We shall not therefore relate them.

The effects of Galvanism on vegetation are supposed to be deleterious, as will appear from the following extract from the “Monthly Magazine.”