Experiments of identification, continuity and effects of DC-circuit phenomena in the Pile circuit

Identification

The identification of a new phenomenon, an electric current, was based on its effect-phenomena on material bodies, animals and humans. For example, having done the first experiments with the Pile, Volta reported “contractions and spasms in the muscles”,

“convulsions in the limbs” and sensations of “taste, sight, hearing and feeling” (Volta 1800, 302). Contraction and convulsion phenomena were quite commonly known already in connection with electric discharges. However, the more varied sensations such as taste and hearing became typical only during the phase of studies addressing DC-circuit phenomena.

The Leyden jar and different electrometers were used to identify that the effects produced by the Pile were of electrical origin. Previously, when conceptions of the nature of electricity had been developed, electricity was associated with sparks (shocks) seen in Leyden jars when discharged, and the sparks obtained (electrical shocks received) were identified as electrical. Now the same kind of electrical shocks were received also from the Pile by touching it, and the similarity between the effects was understood as evidence for a similarity between these two areas of phenomena (Volta 1800, 289-290). The similar bases of these two areas of phenomena were also confirmed through other experiments: 1) The Pile was reported to be capable of charging a condenser by contact enabling the condenser to emit sparks. 2) The effects of the Leyden jar were imitated by the Pile by frequently opening and closing the circuit of the Pile by a human body. (Volta 1800, 292) 3) An electrometer was charged by connecting the Pile by a wire to the electrometer. In these experiments the separation between the leaves of the electrometer were taken as evidence of the similarity between static electricity phenomena and DC-circuit phenomena (Nicholson 1800, 182).

Continuity

Continuity of the DC-circuit phenomena was an important difference between the two areas of phenomena of electrostatics and direct current. This feature of the electric current was so essential that it was addressed already in the first page of Volta’s original letter to Banks (Volta 1800, 289). Actually, the continuity was a crucial cause and motive to study this new phenomenon in greater detail. Without continuity there would have been nothing essentially new, but only a new source of electricity – Volta’s Pile.

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By using the Pile, Volta carried out many experiments based on sensory experiences and sensations. The motive of these numerous experiments was Volta's natural eagerness to vary, generalize and augment the experimental situations and to explore more thoroughly the area of DC-circuit phenomena. On the other hand, his ultimate goal was to find evidence for continuity, which he had identified already in his experiments with the bi-metallic pair, and thus to show the epochal significance of his discovery. In Volta’s text the continuity of the DC-circuit phenomenon was described as follows:

The transition of the electric fluid…is not momentary, as a discharge would be, but is permanent, and continues…as long as the communication between the two coatings subsists.

Walker 1937, 112 The sensory experiences and the sensation reported by Volta in his experiments with the Pile were numerous and for example he demonstrated that delicate parts of skin, like the forehead, eye-lid or tip of the nose, could feel “a blow and a prick” if connected to a circuit (Volta 1800, 303). In addition the current of electric fluid could be “tasted”

because it irritated the sense of taste (Volta 1800, 305). There also were experiments done on the sense of hearing. To do these experiments Volta connected himself to the circuit of the Pile as follows:

I introduced, a considerable way into both ears, two probes or metallic rods with their ends rounded, and I made them to communicate immediately with both extremities of the apparatus.

Volta 1800, 308 In these hearing experiments, it was observed that an electrical shock was received at the moment the circuit was closed, and after that was heard a continual sound, “a kind of crackling with shocks” (Volta 1800, 308). This was an entirely different observation than in case of experiments done with Leyden jars, where shocks were instantaneous and no signs of any continuous or persistent effects of electricity were detected. These experiments of Volta clearly focused on the continuity of the DC-circuit phenomena. It was extremely important that the sensations were observed to continue or in some cases even to increase in force until the circuit was opened. This strongly supported the view that the electric current phenomenon itself, behind these effect-phenomena, was also continuous. The same kind of shocks in context of opening and closing the circuit were taken as further evidence of the continuous nature of the phenomenon. (Volta 1800, 303) Chemical phenomena and the directedness of the electric current

A new branch of experimentality based on the Pile was rapidly established after the publication of the Pile. For example the Englishmen William Nicholson and Anthony Carlisle studied the observed effects of the electric current in a circuit of the Pile by replacing a common conducting material, a metal, with different kinds of liquids. This

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replacement was quite natural, because in many experiments it had been for practical reasons necessary to replace part of a metal conductor with water.

These water experiments revealed a new electric-current phenomenon, ”a disengagement of gas round the touching wire” (Nicholson 1800, 182). This new phenomenon was observed and studied with the following equipment:

On the 2d of May we, therefore, inserted a brass wire through each of two corks inserted in a glass tube of half an inch internal diameter. The tube was filled with New river water, and the distance between the points of the wires in the water was one inch and three quarters. This compound discharger was applied so that the external ends of its wire were in contact with the two extreme plates of a pile of thirty-fix half crowns with the correspondent pieces of zinc and pasteboard.

Nicholson 1800, 182 The above-depicted equipment of Nicholson and Carlisle was described also in Volta’s drawing. In Figure 20 there are two Piles connected in series instead of one Pile depicted in a quotation.

Figure 20 The Pile and chemical phenomena (VO, II: 329). In this circuit of two Piles (D and E) ABC is the tube of water, A and C are wires of platinum.

The phenomenon observed in a tube of water was depicted so that “a fine stream of minute bubbles immediately began to flow from the point of the lower wire in the tube”

(Nicholson 1800, 182). The new phenomena were identified as a decomposition of water and the formation of a gas (Nicholson 1800, 185). Actually the same chemical reactions were observed to happen also inside the Pile:

It appears that the same process of decomposition of water is carried on between each pair of plates

Nicholson 1800, 183.

Also the connection to electricity was clear already from the very beginning:

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…a discovery (the Pile) which must for ever remove the doubt whether Galvanism be an electrical phenomenon. But I cannot here look back without some surprise, and observe that the chemical phenomena of Galvanism…

Nicholson 1800, 181 Thus these observations expanded the phenomenal area of direct current to the area of chemical reactions. Alongside the chemical actions of the electric current there was also observed an other characteristic of the phenomena of the electric current namely the direction of these phenomena:

A fine stream of minute bubbles immediately began to flow from the point of the lower wire in the tube, which communicated with the silver, and the opposite point of the upper wire became tarnished, first deep orange, and then black. On reverting the tube, the gas came from the other point, which was now lowest, while the upper in its turn became tarnished and black. Reverting the tube again, the phenomena again changed their order.

Nicholson 1800, 182