Abstract
The cathode polarisation potential of silver in aqueons silver nitrate solutions under varying conditions of concentration; current density; and agitation has been studied. It has been shown that, for the system under consideration, the half-cell method leads to the most reproducible results. Various types of addition agent (organic and inorganic) have been examined, both with regard to their effect on the polarisation, and also on the nature of the deposit. These addition agents my be divided into two classes, on a basis of their effect on the deposit. The first class, which ) consisted of glucose; thiourea; thioglycollic acid; the wetting agents; and the inorganic cations, had practically no effect on the deposit, while the second class (citric, tartartic and aminoacetic acids and gelatine) all caused a marked decrease in the grain size of the deposit. As a developement of this, bright deposits of silver were obtained from solutions of silver nitrate by the addition of large quantities of aminoacetic acid, and traces of other addition agents, under carefully controlled experimental conditions. An investigation has been made of the effect of different planes of a silver single crystal on the polarisation and nature of the deposit, when only one crystal plane was available for deposition. The deposits obtained have been examined by X-ray diffraction methods, and it has bean shown that there are no significant structural differences between smooth and bright deposits. Finally, it has been shown that the adsorption theory of electrodeposition provides the most comprehensive qualitative explanation of the observed experimental results. It is considered that the quantitative treatment of polarisation phenomena will not be possible until a more detailed knowledge of the adsorption processes occurring at metal/solution interfaces is available.