Abstract:
A sphere of carbon which encloses an empty space and has pores formed in the shell thereof so as to provide free passage between the interior and the exterior of the sphere is obtained by coating a spherical core with a layer of finely divided coal and subjecting the coated sphere to a heat treatment at a temperature higher than the decomposition temperature of the substance of which the core is formed. The heat treatment causes the core to be thermally decomposed and evacuated from the coat which, by this time, has been hardened to a shell. A lightweight hollow sphere of activated carbon which has been activated not merely on the outer surface of the sphere but equally on the inner surface defining the empty space is produced by calcining for activation the said sphere of finely divided coal, with the said fine pores retained intact.