The effect of superposed alternating current on the polarisable primary cell zinc-sulphuric acid-carbon. Part I.—Low frequency current

Under the title “Chemical Action that is Stimulated by Alternating Currents,” some interesting experiments were published a few years back by Brown. Briefly, he found that if an alternating current of suitable strength and of either 100 or 12,000 periods per second were passed through a primary cell of the type Zinc/Dilute Sulphuric Acid/Carbon, itself fitted up so as to discharge through a circuit of low resistance, the polarisation of the cell was destroyed and its current output materially increased. No further details are given on the experiments with 100-cycle current. Using the high frequency, however, the conclusion was come to that the increased current output was essentially the result of a changed state of affairs at the not at the carbon, electrode. Thus, when the current densities at the two electrodes were varied by altering their relative areas immersed in the electrolyte, it was found that a high alternating current density at the zinc electrode had a far greater effect in increasing the direct current output of the cell than when the high current density was employed at the carbon electrode.I In other words, a given alternating current produced a greater effect if the cell had a small zinc and a large carbon electrode than if it had a large zinc and a small carbon electrode. More conclusive was the observation that, using a small zinc and a large carbon electrode, the same effect was observed when the carbon electrode was already fully depolarised by immersion in strong nitric acid. Brown concluded that, whilst the surface of the carbon electrode only affects the results in so far as it determines the resistance of the cell, the alternating current in some manner increases the velocity of the sulphations in the neighbourhood of and towards the zinc anode, the latter being more rapidly dissolved, particularly with a small electrode and a consequently high current density.