Such materials are also called adsorbates. Adsorption is distinct from absorption in that it is the process of adhesion of the molecules of the substance to the surface of the adsorbent. The common adsorbents are activated carbon, or activated clays, alumina, magnesium silicate, or silica gel. The noncarbonaceous adsorbents are used for decolorizing vegetable, animal, or mineral oils, but activated carbon may also be used in conjunction with clays to adsorb color bodies not removed by the clay. Granular adsorbents are employed as Hlter beds, but powdered adsorbents are stirred into the liquid and are usually more effective. Adsorption from a gas is usually done with activated carbon. Silica gel is usually employed for removing trace quantities of water from water- insoluble liquids, while activated carbon is used for removing trace quantities of oils or chemicals from water. Adsorbents are normally recovered and are regenerated for reuse by heating, steaming, or burning off the adsorbed material.

Adsorbents are also used to separate chemicals of different molecular diameters without regard to their boiling points. A double hydrated aluminum calcium silicate marketed by the Union Carbide Corp. as a zeolite will pass chemicals with molecular diameters less than 5 angstroms and retain larger ones by selective adsorption. Such adsorptives are called
molecular sieves. However, a material used in the separation of liquid mixtures whose components boil too close together for simple fractional distillation is called an azeotrope. It is a solvent added to the mixture to increase the relative volatility of one of the components so that it can be separated. The solvent may be alcohols, glycols, or nitrobenzene.The adsorbents used in vacuum tubes to adsorb or combine with residual gases are called getters. Flash getters are pellets or strips of barium or barium alloy used to shorten the exhaust period. The getter is
evaporated by induction heating during tube exhaust, and condenses on the tube walls, adsorbing the gas residues. Later, at operating temperatures of 300 to 400°F (150 to 204°C), the getter formed on the tube wall traps gases liberated during tube life. Bulk getters are sheets or wires of zirconium, tantalum, or columbium mounted on the hot electrode to trap gases at temperatures of 900 to 2200°F (482 to 1204°C). Thorium or thorium-misch metal may be used as getters for high temperatures by a coating sintered on the tube anode.