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Colloidal solutions of lead and silver were mixed under the exclusion of air. The equilibration of the Fermi levels in the two different types of metal particles took place over a few days at room temperature. The equilibration took place by the transfer of lead atoms from lead to silver particles until the latter carried a lead mantle of one to two monolayers. This could be concluded from the observed changes in the optical spectrum of the silver particles. The results are discussed in terms of two mechanisms 1 Pb atom transfer following heterocoagulation of the lead and silver particles and 2 electron transfer during Brownian encounters, followed by Pb2 desorption from the lead particles and subsequent Pb2 reduction on the silver particles carrying the transferred electrons. Traces of methylviologen, MV2 , in the solution drastically increase the rate of equilibration; this is explained by a relay mechanism in which electrons in the lead particles are first picked up by MV2 and are then transferred from MV to the silver particles
Henglein et al. (Thu,) studied this question.