The adsorption and desorption branches of H1 are almost vertical and nearly parallel over an appreciable range of gas uptake. The adsorption and desorption branches of H4 are almost horizontal and nearly parallel over a wide range of relative pressure. The shapes of hysteresis loops are associated with specific pore structures.For example, porous materials which consist of wellaligned, spheres and briquettes can produce an H1 type loop line, and materials of this type tend to have relatively narrow distributions of pore size. For the H2 type loops, the hysteresis loop is wide, and the desorption curve is more precipitous than the adsorption curve. This situation usually occurs when the distributions of pore size radii are wide. The presence of slit-shaped pores and/or panel-shaped particles generates the H3 and H4 curves. However, the exhibition of H4 loops indicates the existence of the micropore