Abstract: A furnace for treating granular activated carbon comprises a single vertical column having a pair of electrodes arranged at vertically spaced locations within the column. The electrodes extend across the column and are so constructed that the particulate material can pass with ease through the electrodes. Suitable connectors connect the electrodes to a source of rectified three phase electric power. Pointed prongs are provided below the upper electrode. A valve controls the outlet from the column so that the furnace can operate continuously. A central cone is provided above the outlet to control the flow of granular carbon down the column.