Abstract: An apparatus and process for adding electrolytically dissolved tin to the electrolyte solution of a tin plating cell is described. The tin plating process cell has an insoluble anode. In conventional plating processes, this requires the addition of tin salts to the process cell electrolyte. The tin salts represent a substantial cost, both in term of materials and waste removal. The present plating apparatus includes a secondary cell, separate from the main process plating cell, which has a dedicated rectifier, and in which a soluble tin anode and a cathode are separated by a perm-selective ion exchange membrane. The anode compartment of the secondary cell is hydraulically connected to the process cell and serves to continuously add tin to the plating process, as needed.