2. Reasoning from the common phenomena of the action of redhot charcoal on water, and on the analogous galvanic facts, it was reasonable to conclude that the gas evolved from the charcoal on the silver side of the apparatus was hydrocarbonate; and that carbonic acid had been produced on the zinc side, which had been chiefly absorbed by the water. To ascertain if this conclusion was true, two small open tubes, about one-fourth of an inch in diameter, and three inches long, were provided. Into one end of each of them a thin piece of hard and polished charcoal was introduced, and fastened by cement. They were then filled with distilled water, and inverted in a glass containing that fluid; the tops of the pieces of charcoal being made to communicate with the ends of a pile. The process was carried on for more than fourteen hours; at the end of which time the quantity of gas produced from the charcoal on the silver side was at least fifty times greater than that produced on the zinc side. The tube from the zinc side, with its water and gas, was introduced into a vessel of lime water. On agitation the water became clouded, but the gas was not perceptibly diminished: mingled with twice its bulk of nitrous gas, it gave such an absorption, as denoted that it contained nearly the same quantity of oxygen as common air. The gas produced from the silver side of the pile did not at all diminish with nitrous gas; twelve measures of it, mingled with eight measures of oxygen, in a detonating tube, and acted on by the electric spark, inflamed and left a residuum equal to rather more than three measures. Lime water introduced to these became a little clouded, and a slight absorption took place. After this absorption, at least two measures and a quarter of gas remained, which, mingled with nitrous gas, gave red fumes and a diminution. Hence they evidently contained oxygen. 3. Surprised at these results, from which it appeared that the gas from the silver side of the apparatus held very little charcoal in solution, and required nearly the same quantity of oxygen to destroy it as the inflammable air from the metals, I repeated the experiment, making use of water that had been long boiled, and was yet warm. In this case no gas was given out from the zinc side during the whole of the process, and more than half an hour elapsed before any was produced from the silver side. What was produced, however, gave nearly the same diminution, when fired with oxygen, as common inflammable air, and the residuum produced but a slight precipitate admitted to lime water. It was easy to account for the deficiency of gas on the zinc side in this process, by supposing that the gas produced in the former experiment was air previously dissolved by the distilled water, and liberated in consequence of the stronger attraction of carbonic acid for that fluid; but as I had before found that in the common galvanic process with the metals, the hydrogen was immediately evolved, even in boiled water, it was difficult to conceive why such a length of time was required for the production of the inflammable gas. When I introduced charcoal connected with the zinc side, and silver wire connected with the silver side, into boiled water, gas was almost immediately given out from the wire; though when I connected silver with the zinc side, and charcoal with the silver side, no gas was liberated for many minutes. 4. A slip of charcoal was connected with the zinc end, and a silver wire with the silver end, and both plunged into a vessel of lime water. Gas was immediately given out from the silver wire; a few globules only formed round the charcoal: they were apparently covered with a white crust. As the process advanced, white clouds fell from the charcoal and diffused themselves through the fluid. 5. Two pieces of charcoal were connected with the ends of the pile, and plunged into a strong solution of caustic potash. During two hours no gas was given out from either of the pieces, and no change of colour was perceived in the fluid, though the communication was perfect. When a silver wire was connected with the zinc, and charcoal with the silver, gas was produced from the wire, but none from the charcoal. When charcoal was connected with the zinc, and silver wire with the silver, gas was very rapidly produced round the point of the wire; but not an atom formed round the charcoal. 6. When the slips of charcoal connected with the pile were introduced into solution of ammoniac, gas was given out from the zinc charcoal; but none from the silver charcoal. When silver wire was connected with the silver side, the charcoal being still connected with the zinc side, gas was given out from both, but most rapidly from the wire. These gases were caught and examined. That from the charcoal gave no diminution with nitrous gas. An accident prevented me from examining it by other tests; the gas from the silver equalled twenty times the volume of the other gas, and appeared to be pure hydrogen. I shall, at present, offer no theoretical conjectures concerning these experiments. The two last will probably lead to interesting conclusions. I am, at this moment, engaged in examining small quantities of solution of potash and ammoniac which have been long galvanised in contact with charcoal: the result of this examination, if at all important, I shall take the liberty of communicating to you at some future time. I remain, Sir, very respectfully, yours, &c. To Mr. NICHOLSON, Notice of some Observations on the. Causes of the Galvanic Phenomena, and on certain Modes of increasing the Powers of the Galvanic Pile of Volta. By MR. DAVY, Superintendent of the Pneumatic Institution. The nature of this communication is incompatible with a detail of the opinions prevailing amongst philosophers, respecting the causes of the galvanic phenomena; they have been generally supposed to depend on the different powers of bodies to conduct electric fluid; Fabroni was the first who systematically attempted to prove that they were chemical effects. Immediately after I had perused an interesting observation of Lieutenant-Colonel Haldane on the non-excitement of galvanism in the vacuum of an air pump, I began an investigation with the view of ascertaining precisely the influence of the atmosphere on the phenomena. In carrying on this investigation, I have met with some new facts which are capable of arrangement, and which will probably lead to a complete explanation of the galvanic effects. The piles that I employed for ascertaining the influence of factitious airs on the galvanic phenomena, were erected horizontally in the usual mode; but to prevent the plates from separating when in an oblique position, their sides were joined together by resinous cement at two or three points, sufficient interstices being preserved to admit of a free circulation of air. The gases, when any where produced, were received in small tubes filled with distilled water, containing wires covered externally with wax, and communicating with the ends of the pile. The piles were introduced into the airs through water, and elevated above the water by a metallic plate cemented to their lower extremities. 1. Zinc, whether connected with Silver in single Galvanic Circles, or constituting the Plates of the Galvanic Pile, seems to undergo no Oxidation at common Temperatures, as long as the Water in contact with it is pure. By pure water, is more immediately meant water holding in solution no oxygen gas, no nitrous gas, and no acids. It has long been known that certain metallic bodies, which oxidate slowly in water exposed to the atmosphere, effect no change in pure water: this I have observed is particularly the case with regard to zinc. zinc, when in contact with silver in the atmosphere, and forming with it a circuit by means of water, becomes oxidated much more rapidly than when simply in contact with water, was observed by Dr. Ash. That Supposing the more rapid oxidation to be the effect of a peculiar electrical influence produced by the contact of the metals, it would be reasonable to conclude, that zinc in single circles with silver and pure water, or at least in the galvanic pile erected with cloths moistened in pure water, would undergo oxidation. Fabroni, however, has advanced that single galvanic circles do not oxidate in water, unless it be exposed to the atmosphere. That the zinc of the galvanic pile does not oxidate in contact with pure water, will appear from the following observations: • Before these experiments were made, I had found, by numerous trials, that a pile acted in the atmosphere immediately after its immersion in water without being wiped, though more feebly than before: I had likewise found that after the first immersion, the powers were not diminished by subsequent ones. a. A small pile of silver and zinc, having its pasteboards moistened with water, that had been just boiled, was introduced into a vessel of water that had been long boiled, and was yet warm. Resinous cement was poured upon the surface of the water, and fastened to the glasses as it cooled, to preserve it effectually from the contact of air. The apparatus, after remaining for two days, was examined the zinc plates were scarcely at all tarnished; no oxide was deposited in the water, and no gas had been evolved through it. A similar pile, exposed for nearly the same time to water in contact with the atmosphere had deposited much white oxide, and given out some gas, and the zinc plates were whitened both internally and externally.+ : b. No influence can be communicated from an elastic atmosphere, enabling the zinc of the galvanic pile to decompose pure water; for piles were introduced into hydrogen, nitrogen, nitrous oxide, and hydro-carbonate, and suffered to remain in them for different lengths of time; but in none of these gases was the zinc more oxidated than if the pile had been immersed in pure water. c. A galvanic pile was suffered to remain in vacuo for fourteen hours, the gauge being about, the zinc plates were slightly tarnished, but no white oxide had formed upon them. 2. The Oxidation of the Zinc Plates of the Galvanic Pile takes place whenever the Water in contact with them holds Atmospheric Air, or Oxygen, or Nitrous Gas, or Nitrous Acid, or Marine Acid, &c. in Solution. a. The oxidation of the zinc of the pile in the atmosphere, and the protusion of carbonate of soda, has been accurately described by Messrs. Nicholson and Carlisle. I have found that the phenomena of oxidation takes place much more rapidly in pure oxygen than in the atmosphere. I have likewise found that it takes place more slowly in nitrous gas than in the atmosphere. That zinc is oxidated in solutions of nitrous and marine acids, is a well known fact. 3. When the Zinc in contact with Water holding in Solution Substances containing loose Oxygen, or Acids, is oxidated, these Substances are altered, or they exert some Chemical Affinities. a. A small galvanic pile, exposed to about twenty-one cubic inches of oxygen gas for six hours, effected a diminution of it which might have equalled one-fourth. b. A similar pile, exposed to an equal quantity of atmospheric air Oil of turpentine and even common oil, as will be seen hereafter, is ineffectual for this purpose. The temperature in these experiments was from 54° to 61°. It is impossible to free water of all its dissolved air by boiling; it is likewise impossible to prevent a few globules of air from passing through the cement whilst it is cooling; the very slight tarnish of zinc kept in boiling water may be owing to the minute quantities of common air existing in the water from both these causes. for two days, diminished it one-sixth; the residuum being. suffered to pass into the atmosphere, gave a smell which strongly resembled that of ammoniac; and the pile held over marine acid produced dense white clouds. In another experiment, an equal quantity of air, exposed to the pile for three days, gave but a very slight diminution with nitrous gas, and could not be inflamed with atmospheric air. c. I have noticed, Res. Chem. & Phil. that wetted zinc, placed in contact with nitrous gas over mercury, slowly converts it into nitrous oxide and ammoniac. A small pile, exposed to about twentytwo cubic inches of nitrous gas for three days, diminished it onefourth, and some of the gas was rendered absorbable by water. d. The formation of nitrous gas, nitrous oxide, and ammoniac, when very weak solutions of nitrous acid are made to oxidate zinc, demonstrate both the decomposition of the acid and the water. e. The oxidation of zinc in solutions of marine and sulphuric acids in water, appears to be owing to the affinity which has been called predisposing. 4. The Galvanic Pile of Signor Volta seems incapable of acting when the Water between the Pairs of Plates is Pure. The word pure is here used in the same sense as in 1. a. I have found, by numerous experiments, that the galvanic pile introduced into hydrogen, through common water, ceases to evolve gas in the tube, and to act in about five or six minutes, i. e. in about the time required to consume the atmospheric air dissolved in the common water between its plates. The phenomenon is exactly the same in nitrogen, nitrous oxyde, and hydro-carbonate. The action of a pile, as known by its powers of evolving gases from water, is diminished immediately on its introduction into those gases. It ceases in them nearly in the same time, and cannot be restored by admitting fresh gases of the same kind, though, as will be seen in the next section, it is immediately restored by immersing the pile for a moment in water saturated with atmospheric air. b. I have found, by numerous experiments, made with the assistance of my friend, Mr. King, that the galvanic pile ceases to act in vacuo when the guage is at about one-tenth of an inch, even though the poles are connected by wires with the atmosphere, and the water it is made to act upon in contact with the atmosphere. 5. The Pile acts when the Water between the double Plates holds in Solution Atmospheric Air, or Oxygen, or Nitrous Gas, or Nitrous Acid, or Marine Acid. This fact I have proved by numerous experiments.-a. A pile acted in atmospheric air, included in a glass cylinder over water for two days till nearly all the oxygen of the air was consumed.-b. A pile decomposed water much more rapidily in oxygen than in common air, and less rapidly in nitrous gas than in common air.-c. That the influence of an elastic oxygenated atmosphere is not essential |