Abstract: Activated carbon is made by pre-treating a fibrous cellulose material with a Lewis acid comprising one or more selected halides, drying and softening the treated material, suspending the material from a frame in a tensionless manner, heating the suspended material in a furnace to effect carbonization of the cellulosic material in an environment which is substantially non-reactive towards that material, activating the suspended carbonized material at an elevated temperature in an atmosphere comprising an activating gas until the desired degree of activation has been produced, and thereafter cooling the furnace, the furnace having at least one heating element at its base and at least one heating element arranged on or in a side wall, each heating element being spaced apart from the suspended material.