THE MAIN MERCURY CIRCULATION SYSTEM THROUGH AN ELECTROLYTIC CELL, A DENUDING DEVICE, AND A MERCURY PUMP IN A MERCURY-PROCESS ELECTROLYTIC APPARATUS IS FULLY SEALED AND ISOLATED FROM THE ATMOSPHERE DURING OPERATION AND IS PROVIDED WITH A SEPARATION DEVICE OUTSIDE OF THE SYSTEM FOR REMOVING CONTAMINATES FROM THE MERCURY AMALGAM CONDUCTED FROM THE ELECTROLYTIC CELL TO THE DENUDING DEVICE, A DEVICE FOR PREVENTING BACKFLOW OF MERCURY WHEN THE MERCURY PUMP STOPS, AND A BYPASS DEVICE FOR CIRCULATING CONTAMINATES WITHIN DENUDED MERCURY, TOGETHER WITH A PART OF THIS MERCURY AND WASH WATER, BACK TO THE DENUDING TOWER.