tors, in different electricial states, are made to act on each other. contact or paration. Sect. III. It is an established fact, that from the contact Experiment to and separation of dissimilar, and insulated metals there show whether electricity be is produced such a change in the electrical state of each produced by metal, that, after the separation the one is found to be positive, the other negative in relation to surrounding bodies; but it appeared to me, (not having in mind the experiments of Wilke and pinus,) a matter of some doubt, whether the alteration in electrical state is the effect of contact, or of separation. To determine this point, in place of the small plate which usually renrains on my electrometer, I adapted a copper plate about 5 inches in diameter. It is evident, that when this apparatus is placed on a common table, the cop per plate will be connected with the wire and gold leaves, but will in every other respect be perfectly insulated; and, consequently, that, whenever a state, different from that of surrounding bodies, is produced in the copper plate, it will be indicated by a divergence of the gold leaves. The apparatus, above described, being so circumstanced, that the tin foil of the electrometer was connected with the Earth, while the copper plate, the wire, and the gold leaves were insulated, I brought, by means of an insulating handle, a zinc plate, also about 5 inches in diameter, into contact with the ropper plate on the electrometer; but although they remained some time in contact; there was no visible divergence of the gold leaves. On separating the metals, the gold leaves immediately diverged; on again bringing them into contact, if the charge of the zinc plate had not been removed, the leaves returned to their natural position; on again separating the plates the divergence took place as before, and similar phenomena appeared, as often as the experiment was repeated. If the charge of the zinc plate had been removed after the separation, the succeeding contact did not reduce the gold leaves to their natural state; but left a slight divergence in them; and when the plates were again separated they diverged in a greater degree, than after the preceding separation. Thus, by repeating the experi ment, and discharging the zinc plate after each separation, the divergence was eonsiderably increased; not however be yond Electrical states of bodies rendered dif I yond certain limits, which apparently varied according to the state of the atmosphere as to moisture: and it is worthy of remark, that the manner in which the plates are se parated materially effects the result of the separation. If one be slid along the other, neither will evince signs of electricity. The contact and separation of two copper plates produced no sensible effect on the gold leaves. From these, and the experiments of Wilke and pinus, I feel myself warranted in concluding, that the electrical states ferent by their of dissimilar metals, and other dissimilar bodies, are separation. This applica- not rendered different by the contact of these bodies with ble to minute one another, but by their separation after contact*. particles. would also, from analogy, extend my conclusion to the mis nute particles of dissimilar kinds of matter; and would say, that when in contact, as in composition, they possess their natural, or, as I have endeavoured to show, in similar elec trical states; but that on their separation, as in decomposition, they acquire electrical states different from what they had while in contact, and consequently different from their natural electrical states; and that from such change in the electrical states of the constituents of a compound, in cont sequence of separation, analogous to what takes place in respect to the voltaic plates, the one set of particles becomes relatively to the Earth and surrounding bodies positive, the other set negative. Supposition ! The experiments, to which I have just alluded, appear to that the metale me perfectly sufficient to point out the fallacy of the exin the galvanic pile are in dif. planation, which is very generally received, of the excitement ferent states, of the galvanic pile; the whole of which rests on the assump eironeons, tion, that dissimilar metals, while in contact, are in different electrical states, the one being relatively positive, the other negative; which has been shown to be perfectly untenable. The following also I consider as additional and weighty ob jections to the hypothesis. 1. The voltaic plates only act when applied to each other by extensive surfaces. In the present most improved galvanic troughs, the metals are con nected together by comparatively few points, and the contrivance has not only rendered the apparatus more conve nient for use, but also more powerful, 2. Volta's plates act An account of the experiments of Wi'ke and of Œpinus will be found in Dr. Priestley's History of Electricity. only only when the polish of their surface is preserved; the cop per and zinc plates of a galvanic battery are always very much tarnished. 3. The galvanie apparatus can only be excited by a decomposable fluid, and this fluid is always decomposed, when the apparatus is excited. From these considerations, I am inclined to conclude, that the princi ples, on which decomposable fluids act in producing their peculiar effects on the galvanic battery, have not yet been accurately determined. - It will be a general, and I think perfectly correct state. ment of the facts, relative to the decomposition of bodies by The difference galvanism, to say, that hidrogen, the alkalis, the metals, or state is ow. and certain metallic oxides are, immediately after their se position hav ing to decom paration by galvanism from oxigen, and from acids, found ing taken at the negative wire; and that oxigen and acids, after their separation from the first class of substances, appear at the positive wire. I trust, however, that the experiments and reasonings, which I have adduced, are sufficient to prove, that the particles of dissimilar kinds of matter do not exist in different electrical states while in composition, but that they acquire a difference of electrical state in the act of decomposition: this difference of electrical state is, there fore, not the cause, but the effect of decomposition. • It yet remains to be determined, on what principle the opposite wires of a galvanic battery act, when their action How is decomoccasions the separation of the constituents of compounded by galvanposition effectbodies. To do this, I by no means conceive it necessary to ism? enter into an investigation of the remote cause of electrical phenomena; on the contrary, I think the question may be decided by a reference to well known and undoubted facts. If two conducting bodies, in different electrical states, be brought near to each other, the difference will be By a repulsive destroyed; and if the difference between the electrical states of the conducting bodies be considerable, while the caloric. operation is going on by which it is removed, the conducting bodies will frequently be fused. This happens not only to bodies easily fused, but also to very refractory sub stances; as the alkalis, the earths, the metals. The fact dis vested of all hypothesis is, that the action of differently' electrified conductors occasions a repulsive force to be ex erted force analo gous to that of erted between the particles of the conductors, and is, in this respect, precisely analogous to that power, which in the language of modern chemistry is denominated caloric. Mode in which It has been long known, that calòric, aided by the affinity this is effected of a substance for one of the elements of a compound, is in the case of caloric, sufficient to effect the decomposition of the compound: and this fact is particularly observable in the reduction of mee tallic oxides, by heating them with inflammables, or metalsą By these means the French chemists have lately succeeded in their attempts to decompose the fixed alkalis, and have obtained, in an uncombined state, their constituent 'ele= ments, which appear to be oxigen, and a metallic base. The rationale of these décompositions is sufficiently obvious. The repulsive force of caloric separates the constituent par ticles of the compound; at the same time, by diminishing the cohesion of the inflammable, or uncombined metal, it renders its attraction for oxigen efficient; and hence the separation of oxigen from the oxide, and its combination with the uncombined metal, or with the inflammable. {Thé? oxigen, entering into a new combination, is removed fromi the sphere of chemical action, and thus its reunion with the metal, from which it had been separated, is prevented h and in that of galvanism. The decompositions by galvanism will, I think, admit of explanation on similar principles. The action of the two wires of the galvanic battery occasions such a repulsion, at a certain number of points, as separates the constituents of the compound, which is made a part of the circuit, and which must possess a degree of conducting power The ses paration of the particles of dissimilar kinds of matter, which had been in contact, produces different electrical states: in them: the one set of particles is, consequently, attracted with greatest force by the positive wire, the other set of pari ticles; is attracted with greatest force by the negative wire; the separated particles are thus placed beyond the sphere of chemical action, and their reunion does not take place. Having, then, considered at some length the question pro posed by Mr. Davy, I am satisfied, that we cannot admit the hypothesis, which refers chemical phenomena to the elec trical energies of the particles of matter. I am willing to, allow, that it is highly ingenious, and that at first sight it has really really the appearance of a simple generalization of factsi but I think it has been shown, that the assumption on which it rests is contrary to experiment and analogy; that the assumption is incapable of explaining the phenomena on account of which it was taken up; and that these phenomena can be explained on principles unconnected with any hypothesis, and which are the result of experiment and observa tion. " III. Observations on the Igniting, or Wire-melting, Power of the Voltaic Battery, as proportioned to the number of Plates employed; with an Account of some Experiments on this Subject, made in conjunction with Mr. JOHN CUTHBERTSON; by Mr. GEORGE JOHN SINGER, Lecturer on Chemistry . and Natural Philosophy. Communicated by Mr. SINGER.. IN a lecture recently delivered at the Royal Institution, Inquiry cou tio of the pow number of Dr. Davy detailed some experiments of the French Philo- cerning the ra. Sophers, made with the intention of ascertaining the pro- er of igniting portion, in which water is decomposed by different Voltaic wires to the combinations, the number of plates being subjected to va plates by Mr. riation. After some observations on the probable source of Davy, inaccuracy in these experiments, he proceeded nearly as follows: "There is still another very interesting subject of inquiry, which has not yet been touched on; I mean thể "proportion the igniting power of the battery bears to the "number of plates employed." The Dr. then proceeded to exhibit some experiments on this subject; they were made with a new apparatus fitted up in troughs of Wedgwood ware; the size of the plates 11 inches, by 4 inches. The result of these experiments was very equivoca!, two Anomalies in Batteries ignited four times the length of wire ignited by the experi one battery; but six batteries ignited little more than twice the length that three could ignite. Dr. Davy supposed that the rate of ignition might vary in higher numbers, obeying a different law to that which obtains when a few plates ments. |
