Determination of the value of the faraday with a silver-perchloric acid coulometer

Abstract

An accurate value of the faraday has been determined by the electrolytic dissolution of metallic silver in aqueous solutions of perchloric acid. Standards of electric current mass, and time as maintained by the National Bureau of Standards were utilized in the determinations. The electric current was measured in terms of the standards of electro-motive force and electrical resistance. Silver of high purity, freed from oxygen, was used. The value of the faraday was found to be faraday=96516.5±2.4 coulombs gram-equivalent-1 (physical scale), faraday=96490.0±2.4 coulombs gram-equivalent-1 (chemical scale). These values were obtained using 107.9028±0.0013 and 107.8731±0.0013 for the atomic weight of silver on the physical and chemical scales, respectively. The electrochemical equivalent of silver was found to be electrochemical equivalent of silver=1.117972 ± 0.000019 milligram coulomb-1. This value may be used in an alternate method of defining the ampere in absolute value, namely, that steady current which will dissolve 1.117972 milligrams of silver per second and depends only on the standards of mass and time. The indicated uncertainties are overall limits of error based on 95 percent confidence limits for the mean and allowances for the effects of known sources of possible systematic error.