Further observations on voltaic combinations; in a letter addressed to Michael Faraday, Esq., D. C. L. F. R. S., Fullerian Professor of Chemistry in the Royal Institution, &c. &c. By John Frederick Daniell, Esq., F. R. S., Professor of Chemistry in King's College, London
In the course of an inquiry on the effects of changes of temperature upon voltaic action, the author was led to observe some curious disturbances and divisions of the electric current produced by the battery, arising from secondary combinations; the results of which observations form the subject of the present paper. He found that the resistance to the passage of the current was diminished by dissolving the sulphate of copper which was in contact with the copper in the standard sulphuric acid, instead of water. The increased effect of the current, as measured by the voltameter, was farther augmented by the heat evolved during the mixture; and wishing to study the influence of temperature in modifying these effects, the author placed the cells of the battery in a tub, filled with hot water. On charging the cells with a solution of muriate of ammonia in the interior, and aqueous solution of sulphate of copper in the exterior compartment, he observed that a portion of the current is discharged by the water in which the apparatus was immersed; its passage being indicated by the disengagement of gas betwixt the adjacent cells, in which case, one of the zinc rods is thrown out of action, and the copper of that cell acts merely as an electrode to the antecedent zinc. A saturated solution of common salt was next placed in contact with the zinc, while the exterior compartments of the cells were filled with a saturated aqueous solution of sulphate of copper; but the effects were much diminished. It thus appeared that the substitution of solutions of the muriates for dilute sulphuric acid was in every way disadvantageous; and it was moreover found that, when the circuit was broken, the copper became seriously injured by their action, and by the formation of a submuriate of that metal.