### The transference of electricity by colloidal particles

Frank Powis
1916 Transactions of the Faraday Society
On applying an e.m.f. to electrodes immersed in a colloidal solution the particles usually travel towards either the anode or cathode, and therefore behave as if they carried an electric charge. The formula 6qrzi e = -H wheree = mean charge carried by the particles ; q = viscosity of medium ; r = mean radius of the particles ; u = velocity of the particles ; H = potential gradient ; has been used : k to calculate the mean charge carried by the particles in a colloidal solution. Another method
more » ... n. Another method of calculating the value of e, however, appears possible. For if we know the number of particles present in unit volume and their velocity under unit potential gradient, we can calculate what amount they would contribute to the conductivity of the solution if they carried a charge equal to IZ times that on a univalent ion. Conversely, if we knew what part of the conductivity was due to the transference of electricity by the colloidal particles we could calculate the mean charge carried by them. The difficulty is, of course, in determining this. But in the case of colloidal solutions of the noble metals prepared by *sparking, the amount of foreign electrolyte present is exceedingly small, none being intqntionally added to the conductivity water used. We might therefore reasonably attribute any increase in conductivity that occurs on making such a solution to the transference of electricity by the colloidal particles, and from this calculate the mean charge carried by them. The number of cases in which the necessary measurements for such a calculation have been made seems to be extremely small, the only one I have found being by Burton,t for a coarse silver sol.