722.  From the foregoing and many other experiments, it results that variation in the size of the electrodes causes no variation in the chemical action of a given quantity of electricity upon water.

723.  The next point in regard to which the principle of constant electro-chemical action was tested, was variation of intensity.  In the first place, the preceding experiments were repeated, using batteries of an equal number of plates, strongly and weakly charged; but the results were alike.  They were then repeated, using batteries sometimes containing forty, and at other times only five pairs of plates; but the results were still the same. Variations therefore in the intensity, caused by difference in the strength of charge, or in the number of alternations used, produced no difference as to the equal action of large and small electrodes.

724.  Still these results did not prove that variation in the intensity of the current was not accompanied by a corresponding variation in the electro-chemical effects, since the actions at all the surfaces might have increased or diminished together.  The deficiency in the evidence is, however, completely supplied by the former experiments on different-sized electrodes; for with variation in the size of these, a variation in the intensity must have occurred.  The intensity of an electric current traversing conductors alike in their nature, quality, and length, is probably as the quantity of electricity passing through a given sectional area perpendicular to the current, divided by the time (360. note); and therefore when large plates were contrasted with wires separated by an equal length of the same decomposing conductor (714.), whilst one current of electricity passed through both arrangements, that electricity must have been in a very different state, as to tension, between the plates and between the wires; yet the chemical results were the same.

725.  The difference in intensity, under the circumstances described, may be easily shown practically, by arranging two decomposing apparatus as in fig. 67, where the same fluid is subjected to the decomposing power of the same current of electricity, passing in the vessel A. between large platina plates, and in the vessel B. between small wires.  If a third decomposing apparatus, such as that delineated fig. 66. (711.), be connected with the wires at ab, fig. 67, it will serve sufficiently well, by the degree of decomposition occurring in it, to indicate the relative state of the two plates as to intensity; and if it then be applied in the same way, as a test of the state of the wires at a’b’, it will, by the increase of decomposition within, show how much greater the intensity is there than at the former points.  The connexions of P and N with the voltaic battery are of course to be continued during the whole time.