There are several experimental techniques for the determination of transport numbers.
Hittorf method This method was developed by German physicist
Johann Wilhelm Hittorf in 1853, The exact relationship depends on the nature of the reactions at the two electrodes. For the electrolysis of aqueous
copper(II) sulfate () as an example, with and ions, the cathode reaction is the reduction and the anode reaction is the corresponding oxidation of Cu to . At the cathode, the passage of coulombs of electricity leads to the reduction of moles of , where is the
Faraday constant. Since the ions carry a fraction t_+ of the current, the quantity of flowing into the cathode compartment is t_+(Q/2F) moles, so there is a net decrease of in the cathode compartment equal to (1-t_+)(Q/2F) = t_-(Q/2F).
Moving boundary method This method was developed by British physicists
Oliver Lodge in 1886 and
William Cecil Dampier in 1893. The boundary tends to remain sharp since the
leading solution HCl has a higher conductivity than the
indicator solution , and therefore a lower electric field to carry the same current. If a more mobile ion diffuses into the solution, it will rapidly be accelerated back to the boundary by the higher electric field; if a less mobile ion diffuses into the HCl solution it will decelerate in the lower electric field and return to the solution. Also the apparatus is constructed with the anode below the cathode, so that the denser solution forms at the bottom. ==See also==