[72] 537.
It was in his “Seventh Series,” that he finally established a principle of definite measurement of the amount of electrolytical action, and described an instrument which he termed[73] a volta-electrometer. In this instrument the amount of action was measured by the quantity of water decomposed: and it was necessary, in order to give validity to the mensuration, to show (as Faraday did show) that neither the size of the electrodes, nor the intensity of the current, nor the strength of the acid solution which acted on the plates of the pile, disturbed the accuracy of this measure. He proved, by experiments upon a great variety of substances, of the most different kinds, that the electro-chemical action is definite in amount according to the measurement of the new instrument.[74] He had already, at an earlier period,[75] asserted, that the chemical power of a current of electricity is in direct proportion to the absolute quantity of electricity which passes; but the volta-electrometer enabled him to fix with more precision the meaning of this general proposition, as well as to place it beyond doubt.
[73] 739.
[74] Arts. 758, 814.
[75] 377.
The vast importance of this step in chemistry soon came into view. By the use of the volta-electrometer, Faraday obtained, for each elementary substance, a number which represented the relative amount of its decomposition, and which might properly[76] be called its “electro-chemical equivalent.” And the question naturally occurs, whether these numbers bore any relation to any previously established chemical measures. The answer is remarkable. They were no other than the atomic weights of the Daltonian theory, which formed the climax of the previous ascent of chemistry; and thus here, as everywhere in [300] the progress of science, the generalizations of one generation are absorbed in the wider generalizations of the next.
[76] 792.
But in order to reach securely this wider generalization, Faraday combined the two branches of the subject which we have already noticed;—the theory of electrical decomposition with the theory of the pile. For his researches on the origin of activity of the voltaic circuit (his Eighth Series), led him to see more clearly than any one before him, what, as we have said, the most sagacious of preceding philosophers had maintained, that the current in the pile was due to the mutual chemical action of its elements. He was led to consider the processes which go on in the exciting-cell and in the decomposing place as of the same kind, but opposite in direction. The chemical composition of the fluid with the zinc, in the common apparatus, produces, when the circuit is completed, a current of electric influence in the wire; and this current, if it pass through an electrolyte, manifests itself by decomposition, overcoming the chemical affinity which there resists it. An electrolyte cannot conduct without being decomposed. The forces at the point of composition and the point of decomposition are of the same kind, and are opposed to each other by means of the conducting-wire; the wire may properly be spoken of[77] as conducting chemical affinity: it allows two forces of the same kind to oppose one another;[78] electricity is only another mode of the exertion of chemical forces;[79] and we might express all the circumstances of the voltaic pile without using any other term than chemical affinity, though that of electricity may be very convenient.[80] Bodies are held together by a definite power, which, when it ceases to discharge that office, may be thrown into the condition of an electric current.[81]
[77] Researches Art. 918.
[78] 910.