Mr Nicholson had suggested the opinion, that the elec tricity of the pile differs from that of the machine, in con sequence, of the latter being in a state of higher intensity, but in less quantity ; the former of course being in greater quantity, but of low intensity. Dr Wollaston coincided in this idea, and supposed that it might explain the difference between the operation of the two instruments. It had been long known that water might be decomposed by the electric shock, but the effect differs from that of the pile, the two gases being separated promiscuously from both ends of the wire, not as when the pile is employed, the oxy gen from one end, and the hydrogen from the other. But Dr Wollaston succeeded in producing the galvanic effect on water by common electricity, so as to keep the gases separate. This he accomplished by coating two silver wires, so that the ends of them only were exposed. He then connected these wires with the two conductors of the electrical machine, and passed the spark, from one to the other, through a solution of a salt of copper ; the negative wire was found to be covered with a metallic coating, as if it had been connected with the copper or silver end of the pile. See Phil. Trans. 1801, p. 427.
Professor Trommsdorff, about this time, discovered that the pile possesses a very powerful effect in burning metal lic leaves. He formed an instrument of large plates of zinc and copper, and fixed gold leaf to the zinc end ; then, by bringing it in contact with the silver end, the leaf was ra pidly consumed, the process being attended by a beautiful emission of coloured light. Silver, tin, and copper leaves were burned in the same manner, each giving out a brilliant flame tinged by its appropriate colour. (Nicholson's Jour nal, vol. v. p. 238.) The repetition of these experiments on the combustion of metals, led Fourcroy to a curious discovery, that the energy of the shock is not increased by the size of the plates, but by the number of the repetitions ; while the same extent of surface, arranged in the form of a few large plates, readily consumed the metallic leaves, but had only a comparatively small effect on the sensations. (Ann. de Chim. xxxix. 103.) As the action of the pile was generally admitted to depend upon electricity, various at tempts were made, by different experimentalists, to change the Leyden phial, and Mr Cruickshanks at length accom plished it. It was now also generally agreed, that the ex tremity of the pile which gave out oxygen, was in the state of positive electricity, and the end which disengaged hydro gen in the negative state.
It became a curious subject of investigation to ascertain what was the precise difference between the electric fluid, as generated by the pile, and as disengaged by the common machine; and Dr Van Marum entered upon a series of ex periments, in which the action of the pile was compared with that of the great Teylerian machine at Haarlem. He succeeded in charging, not only single jars, but whole bat teries, by the pile ; and they were always charged to the same degree of intensity with that which the pile itself in dicated to an electrometer placed upon it. He found that the zinc end of the pile communicated positive electricity to the side of the jar or battery with which it was in con tact, and the copper end the reverse. No perceptible dif ference could be experienced between shocks of the same intensity given by a jar or by the battery ; whether they were charged by the pile or* by the machine. He found
that the intensity of the pile was always the same from the same number of plates, whatever was their size ; but he perceived Fourcroy's observation to be correct, that it was necessary to employ large plates to burn the metals. He formed a pile of large plates of zinc and copper, and suc ceeded in fusing iron wires of considerable thickness ; he at last even fused a wire of platina. He found that a battery, consisting of 137A square feet of coated glass, was charged by a galvanic apparatus to an intensity equal to itself, in 1-20th of a second ; a circumstance which proves the ama zing velocity of the fluid. He conceived that the energy of the pile was much augmented when it vas kept in an insu lated state, and likewise when a solution of the muriate of ammonia was interposed between the copper and zinc plates. See Ann. de Chim. xl. 289.
'We have already noticed the discovery of Mr Cruick shanks, that the pile acted more powerfully in oxygen gas than in the air of the atmosphere ; and an observation, the converse of this, was made by Biot and Cuvier, which con firmed the relation between the action of the apparatus and the chemical state of the fluid in which it is immersed. When the pile was inclosed in a limited quantity of air, they found that, after some time, the was sensibly de oxidated. See Ann. de China. xxxix. 242.
The discoveries that were made with the galvanic pile, especially by the Englilih chemists, completely established some of the most important points which had previously been subjects of doubt or controversy. Animal electricity, as produced in the original experiments of Galvani, and af tcrwards in those of Valli, Fowler, Volta, and others, was now admitted to depend upon nothing inherent in, or at tached to, the animal body, but upon an agent, called into action by external causes, and manifesting itself in conse quence of the delicate sensibility of the nervous and muscu lar systems. This agent was now generally recognized as being identical with electricity, conducted by the same sub stances, possessing the same properties, and, in short, sub ject to the same physical laws. It was conjectured, that the apparent difference between electricity, as excited by the machine and by the pile, depended upon the different states of intensity in which they exist, the electricity of the machine being in a much higher state than that of the pile, although this latter is generally disengaged in greater quan tity. This may be regarded as the state of the science in 1801 ; from this time, until the grand discovery of Sir H. Davy, which we have marked out as the third era, the at tention of the different experimentalists, who devoted them selves to this department of natural philosophy, was partly directed to improving or modifying the apparatus, and partly to hypothetical discussions, respecting the nature of the action, and its connexion with chemical affinity. This latter topic, in conformity with the plan which we laid down, will be treated more at length in the Second Part of the Ar ticle. A number of new facts were, however, from time to time, discovered, which we shall proceed to detail ; and in order to preserve the historical order, we shall also brief ly touch upon those points of theory that arc to be consi dered more fully hereafter.