Page:Proceedings of the Royal Society of London Vol 4.djvu/178

Rh to a stout glass tube bent into the form of the letter U, and firmly- fixed on a wooden post. The current transmitted by this double cell is more retarded than when passing through the single cell, on account of the greater distance of the electrodes ; but it answers its intended purpose of stopping the transfer of the liquid even in the case of saline solutions, and there is still sufficient conducting power to render it powerfully effective. Experiments were then made to ascertain whether in the electrolysis of the dilute sulphuric acid any transfer of the acid takes place ; from which the author concludes that during the electrolysis of an equivalent of water, a portion of acid passes over from the platinode to the zincode ; and possibly an equal portion of water also passes over from the zincode to the plati- node. These experiments appear to confirm the results previously obtained ; namely, that one fourth of an equivalent of sulphuric acid passes from the platinode to the zincode for every single equiva- lent of a compound which has been electrolyzed by the current.

The author then proceeds to examine the following question, viz. : does the acid during its transfer, in the case of the mixed acid and water, or do the acid and the- alkali, in the case of the saline solution, con- vey any portion of the current which effects the simultaneous de- composition of the water in both instances } He next investigates the action of the voltaic cuiTent on the aqueous solution of the chlo- rides, as the simpler constitution of this class of salts promised to throw some light on the nature of the electrolysis of secondary com- pounds.

The results of all these experiments tend to the establishment of the fundamental principle, that the force which is measured by its definite action at any one point of a circuit cannot perform more than an equivalent proportion of work at any other point of the same circuit ; and that the current, which is measured by its electrolysis of an equivalent of simple chloride of lead, cannot at the same time be sufficient to electrolyze an equivalent of chloride of sodium, and an equivalent of water, at the same electrodes. The sum of the forces which held together any number of ions, in a compound elec- trolyte, could, moreover, only have been equal to the force which held together the elements of a simple electrolyte, electrolyzed at the same moment in one circuit.

In applying these principles to the electrolysis of the solution of sulphate of soda, water seems to be electrolyzed, and at the same time the acid and alkali of the salt appear in equivalent proportions with the oxygen and hydrogen, at their respective electrodes. It cannot be admitted, that after the decomposition of the water there is any excess of force applicable to the decomposition of the salt; but it must be concluded that the only electrolyte which yields is the sulphate of soda, the ions of which, however, are not the acid and alkali of the salt, but an anion, composed of an equivalent of sulphur, and four equivalents of oxygen and the metallic cathion, sodium. From the former, sulphuric acid is formed, at the anode, by secondary action, and the evolution of one equivalent of oxygen ; and from the latter, soda at the cathode, by the secondary action of