A series of fast acting activated carbons is made having high surface areas and at the same time very small pore size. The method of manufacturing them, which specifies certain carbonaceous starting materials and pulverizing, agglomerating, crushing and oxidizing steps, determines or controls the pore sizes and surface areas. My activated carbon has highly uniform, very small pore sizes and at the same time a large surface area per unit of weight and a large macropore volume. New methods of separating mixtures of compounds, such as mixtures of hydrocarbons, are disclosed employing my new molecular sieve activated carbon. In my fast-adsorbing molecular sieve, molecules of generally lower molecular weight are adsorbed by the carbon rather than the usual case for activated carbon, which is that the carbon tends to adsorb generally larger molecules in preference to smaller ones.