to the galvanic effects, is evident from the fact of the constant restoration of the powers of a pile after they had ceased to appear in the hydrogen, nitrogen, &c. by momentary immersion in water saturated with atmospheric air. In these experiments the piles were plunged into the water confining the gases, and again immediately elevated into the gas without being exposed to the atmosphere and the phenomenon could be owing to no other cause than the impregnation of the water with atmospheric air, because when piles were plunged into water saturated with nitrous oxide*, their powers were not restored.-d. I have proved by many experiments that water, deprived of air, is capable of attracting it from the spirit of turpentine when the last is in contact with the atmosphere. The galvanic pile acts in spirits of turpentine for a great length of time, and nearly as well as in the atmosphere, the water between its plates being constantly supplied with air from the spirits. It acts but for a short time in spirits of wine, on account of the combination of this fluid with its water.-e. After a pile had ceased to act in hydrogen, its powers were uniformly restored by a momentary immersion in very diluted marine acid. They were likewise restored, and rendered more intense than in the atmosphere by momentary immersion of the pile in diluted nitrous acid, though they continued to be exerted for a short time only, i.e. till the acid was decomposed or saturated. 6. The Power of Action of the Pile of Volta appears to be in a great measure proportional to the Power of the conducting fluid Substance between the double Plates to oxidate the Zinc.

This seems sufficiently proved from the facts in the following sections. The zinc oxidates less rapidly in nitrous gas than in atmospheric air, and less rapidly in atmospheric air than in oxygen; and the power of action of the pile as known by its evolving gas from water is greater in oxygen than in atmospheric air, and greater in atmospheric air than in nitrous gas. The power of the pile to decompose water, and to give the shock is wonderfully increased after it has been dipped in marine acid, and still more increased after it has been dipped in weak nitrous acid; and these bodies only enable the zinc to oxydate itself more rapidly. A series of plates in which the oxydating conducting fluid was strong nitrous acid, acted, as will be seen hereafter, infinitely more powerfully than any other combination; so that it would seem that the power of a pile is not much connected with the evolution of hydrogen from water.

7. Conclusions.

Of two phenomena, or of two series of phenomena, we can only affirm that the one is the cause of the other when it uniformly precedes it, and when their modifications are connected. But it appears from all the foregoing facts, that the galvanic pile of Volta acts only when the conducting substance between the plates is capa

This gas expels much common air from water.

ble of oxidating the zinc; and that in proportion as a greater quantity of oxygen enters into combination with the zine in a given time, so in proportion is the power of the pile to decompose water, and to give the shock greater. It seems therefore reasonable to conclude, though with our present quantity of facts we are unable to explain the exact mode of operation, that the oxidation of the zinc in the pile and the chemical changes connected with it are some how the cause of the electrical effects it produces.

8. Of a new Mode of constructing a Pile.

Assuming the truth of this conclusion it was easy to conceive, that a pile much more powerful than any hitherto constructed might be made, particularly supposing that the decomposition of water was not essential to the process, plates of zinc and silver, 12 inches square, were fastened in pairs by resinous cement; eighteen of these pairs were connected to each other by cement, and so inclosed by it as to leave water-tight partitions open at one side only between each pair of plates. When muriatic acid was poured between the partitions of this machine, the plates being perpendicular, it acted very powerfully; its capability of decomposing water and giving the shock, being at least equal to that of a common pile of seventy plates. Diluted nitrous acid made it act still more powerfully. When the partitions were filled with water, its action was barely perceptible. Concentrated nitrous acid was poured into them. In this case the first shock was so powerful as to benumb my fingers for some seconds, and I did not dare to take another. I was almost immediately obliged to throw the pile into water to prevent it from being destroyed, so that there was no time to ascertain its power of decomposing water.

In a second experiment, with strong nitrous acid, I used only five pairs of plates, when the shock was full as powerful as from the common pile of thirty plates.

Three pairs of plates, with nitrous acid, gave a very sensible shock. I have procured (on account of the loss of the silver when this substance is part of the pile with nitrous acid) a number of plates of copper, iron, and zinc. They have not yet been disposed in the apparatus; but I expect by means of nitrous acid, to produce effects from them, equal to those of the strongest electrical battery.

An Account of some Additional Experiments and Observations on the Galvanic Phenomena. By Mr. Davy, Superintendent of the Pneumatic Institution.

I.

Additional Experiments on the Causes of the Galvanic Phenomena.

1. Sulphuric acid, when highly concentrated, is possessed of but little power of action upon zinc, though when diluted it dissolves it with the greatest rapidity. Assuming then the truth of the principles advanced in my last paper, namely, that the powers of the

pile of Volta, are primarily excited by the oxidation of the zinc, it follows, that diluted sulphuric acid, when made the medium of connection between the pairs of plates, ought to produce much greater effects than concentrated sulphuric acid.

This I have found is actually the case. When the cells of a series of twenty pairs of plates of silver and zinc, constructed with waxen cement, in the mode described in 8, of my last paper, were filled with sulphuric acid, nearly of specific gravity 1.9, no galvanic action, except the production of a slight caustic taste, was perceptible by the usual methods of trial; though when diluted sulphuric acid was used, the ends of the series gave shocks to the moistened fingers, and wires connected with them effected the usual changes

in water.

That concentrated sulphuric acid is not of that order of more perfect galvanic conductors which, when interposed between the plates, destroy their electrical effects, is evident from the following experiment the cells of ten pairs of plates of copper and zinc, constructed with waxen cement, were filled with concentrated sulphuric acid; but not the slightest galvanic power was produced. A small drop of water was then poured upon the acid in each of the cells. The action of the series was immediately shewn by its producing the usual appearances on wires in water.

When the

2. The galvanic conducting powers of liquid sulphurets are at least equal to those of water. I found that when the fingers were plunged into glasses, containing solution of sulphuret of strontian connected with the ends of a pile, the shock was full as sensible as if the communication had been made through water. galvanic current was made to act on solution of sulphurets of strontian by means of silver wires, the zinc wire became blackened, and gas was given out round the silver wire. But solutions of sulphurets are incapable of giving oxygen to zine; they, consequently, ought to produce no galvanic effects when made the media of connexion of the double plates in the pile of Volta. Twenty-five pairs of silver and zinc, erected with cloths moistened in solution of sulphuret of strontian, produced no sensible galvanic action, though the moment the sides of the pile were moistened with a little nitrous acid, the ends gave shocks as powerful as those of a similar common pile.

3. No phenomenon is more constant than the cessation of the action of the common galvanic pile in a vacuum, when the gage is below one-tenth. Supposing the expulsion of atmospheric air from the water preventing it from oxidating the zinc, the sole cause of this cessation, it follows, that a pile ought to act in vacuo when nitrous acid, or diluted sulphuric acid, is the medium of connexion between the plates. Into each of the cells of a series of twelve pairs of silver and zinc plates, which had just been moistened with a little water, a large drop of nitric acid was introduced: when the wires connected with the ends immediately began to produce the usual appearances in water. The series was introduced under the receiver

of an air pump, and the silver wire from its zinc end connected with a vessel of water that had been long boiled. The wire from its silver end was so fastened by resinous cement, to a sliding brass wire passing through the top of the receiver, that it could be plunged at pleasure into the water when the vacuum was made. The receiver was exhausted till the gage stood at six-tenths of an inch, when the communication was effected. The zinc wire immediately began to oxidate, and gas was given out round the silver wire. The process went on for many minutes, and when it had ceased, was not sensibly revived by the admission of the atmosphere. In another experiment the same phenomena were observed. Gas appeared to be given out more rapidly from the silver wire than in the atmosphere; but this was from the diminution of pressure. The oxidation was certainly less which may be easily accounted for, when we consider, that no nitrous acid could be recomposed in vacuo, as in the atmosphere from the nitrous gas disengaged between the plates, and that, in consequence of the diminished pressure, some of the acid must probably have assumed the aëriform state.

A drop of sulphuric acid, poured into each of the moistened cells of twelve pairs of plates, enabled the wires from the ends to effect the usual changes in pure water for rather more than half an hour in vacuo, the gage being at six-tenths. The oxidation went on nearly as vividly as in the atmosphere, and what is rather remarkable, some gas was given out from the oxidating wire, though very little was produced from the silver wire.

4. The results of the last experiment are interesting not only from their coincidence with the other facts, but likewise because they afford proofs that the presence of oxygen in that loosely combined or peculiar state in which, when absorbed by combustible bodies, it produces inflammation, and in which, in my infant chemical speculations, I supposed it to be combined with the matter of light, is not essential to the galvanic effects. Whether water is absolutely essential, we shall find some difficulty in determining, as it exists in larger or smaller quantities in all the non-metallic fluid galvanic conductors that have been yet experimented upon. The following fact is in favour of its essentiality. The compound of concentrated sulphuric acid and oxygenated muriatic acid (which may be formed by introducing oxygenated muriate of potash into sulphuric acid, or by passing oxygenated muriatic acid gas through it), slowly oxidates both zinc and silver, the oxygenated marine acid being decomposed. I expected that it would produce strong galvanic effects when made the communicating medium of the cells of a pile; but in this I was disappointed; a series of twenty pairs connected by it produced hardly any sensible action.

5. If any person wishes to repeat the experiments in vacuo just

• I accidentally discovered this combination in July, 1799. Some of its properties are very peculiar. More interesting enquiries have hitherto prevented me from minutely examining them.

detailed, great caution must be observed with regard to the quantities of acids introduced into the cells. Two or three drops in each will be sufficient, particularly if it has been previously a little moistened. When larger portions are employed, the effervescence highly increased by the removal of atmospheric pressure will be often sufficient to moisten the edges of the cells, and to make a communication between them. In consequence of the use of too much acid, I have many unsuccessful experiments.

The water used in vacuo for connecting the wires should be always previously deprived of loose air by long ebullition, or otherwise the disengagement of that substance from it will much disturb the results.

II.

Observations gained from minute Inspection of Galvanic Processes. 1. Whenever the galvanic circuit, passing through the pile with wires, is broken by means of water, oxygen is uniformly produced at the zinc metallic point, and hydrogen at the silver metallic point. This is shewn from many experiments in Mr. Nicholson's "Philosophical Journal." Considering analogies, an interesting question occurs. Do not the same phenomena take place in every part of the series? i. e., is not oxygen fixed on every plate of zinc, and hydrogen produced on every plate of silver, at the points of their contact with the water of the cloths? With the hope of gaining a solution of this question, I constructed a series of twenty glasses with spring water, containing plates of silver and zinc connected by brass wire, in the mode pointed out by Volta. This series gave feeble shocks, and a silver wire connected with it produced the usual appearances in water. Oxygen was fixed upon that part of the wire in the glass containing the last silver plate, and hydrogen was liberated from that part of it in the glass containing the last zinc plate.

The series was made analogous in all its parts, the end glasses being connected by a pair of plates, so that every glass contained a silver plate and a zinc plate. On minutely inspecting the glasses immediately after, no particular phenomena could be perceived. But after occasional attention to the process for many hours, I observed the zinc plates beginning to oxidate in many of their points, though no gas was produced upon them. No gas had formed upon the silver plates, but the surface of the water in contact with them became covered with an opaque white pellicle.

2. The silver plates used in this experiment were not perfectly polished. This might have influenced the results; and some gas might have escaped my observation. That the operation might go on in closed vessels, I cut off the bottoms of some bottles with a file, so that they could be easily joined again by cement. Into one of these bottles I introduced a plate of polished zinc,* and into another

• Of 1-2 inches square, the size used in all the former experiments.