239,694. Sauer, J. N. A. Sept. 3, 1924. Carbon. - Activated carbon for purifying and sterilizing liquids and gases is prepared from fibrous carbonized material of vegetable origin, preferably of low ash content and without inorganic admixtures, by heating it in an activating gas wherein it is maintained in a state of flotation, suspension, or movement by mechanical means or by a blast of gas, activation being continued until the product is of an apparent specific gravity of 0.15 or less and a true specific gravity of 2 or more. The carbon is made from light porous wood such as pine, willow, or lime if for use with liquids, or from denser material such as oak, birch, cocoa-nut shell or fruit-pips for gasadsorption. These materials are dry distilled at a temperature up to 500‹ C., and then carbonized at a temperature up to 800‹ C., carbon dioxide or monoxide, hydrogen, or retort or generator gas being preferably passed over the material during distillation and carbonization. The material is granulated either before distillation or after carbonization, care being taken not to destroy the fibrous structure. The carbon is then activated by heating to about 800‹ C. in superheated steam, carbon dioxide, air, generator gas, chlorine, or volatilized chlorides, but preferably in steam and chlorine, either separate or mixed. Activation is effected in a retort, preferably heated both externally and internally, and provided with baffles comprising rows of rods arranged in staggered relation to facilitate rapid heating of the carbon. The carbon is introduced near the bottom into an upwardly-moving stream of hot gas and removed at the top, or is dropped as a shower through the gas. Alternatively, the carbon may be passed in a thin layer over heated surfaces. Internal heating of the retort may be obtained by introducing hot combustible gases with air or oxygen, or crude oil, petrol, or other liquid fuel, these gases serving, if desired, as activating gases. The carbon is then purified by treating it with alkali and acid, caustic soda or sodium carbonate, and hydrochloric or acetic acid being specified; or by heating with exclusion of air to a high temperature. Some acid, preferably hydrochloric, or chlorine is left in the carbon to act as a sterilizer if the carbon is to be used in a filter. Specifications 155,610, 166,229, 198,328, 206,862. 213,935, and 234,149, [Class 46, Filtering &c.]. are referred to. Reference has been directed by the Comptroller Specifications 225,891, 228,582, 228,812, and 228,954.