A system for controlling electrical and chemical parameters in the Faraday constant determination by dissolution of silver

The development of an electrochemical system for the Faraday constant determination has been undertaken at I.N.RI.M. In this system a new two-electrode cell for processing silver dissolution has been set up. The parts of this cell have been carefully designed to avoid sources of undue influence. New elements for monitoring the Ag+ ion concentration in the two half-cells have been introduced and the operations necessary to keep the electrochemical reactions under strict control have been identified and tested. The solution stability, the residue recovery, the O2 prevention and the solution filtering process without its transfer to other containers are other merits. The electrical charge measurement equipment has been assembled and integrated with the one for monitoring the reaction parameters. A control apparatus displaying when some specific operations in the two half-cells are required has been added. The measurements showed that by employing the setup assembled with some proper precautions an uncertainty of about 1–2 parts in 105 can be reached, mainly limited by the silver purity, and the evolution toward a measurement system at a metrological level (parts in 106 or better) is attainable.