PURPOSE: To prevent powder from rising during mixing operation and to perform a uniform dispersion of water to mixed material at a moisture rate controlled at mixture material by a method wherein water is added to active carbon powder to humidify the powder, the powder is mixed with water retension material, salt water is added to the mixture and metallic powder is mixed with the material.

CONSTITUTION: Water is added to active coal powder to humidify the powder and preferably the material is left for 24 hours or more. Water retention material is mixed with the humidified active carbon powder. As the water retension material, there may be applied vermiculite, high water-absorptive resin, wood powder, fibrous powder, pearlite and silicagel and the like. The mixtures are formed into a sandwich by dividing each of powder components in more than two times and added and they are mixed by a mixing machine. Then, salt water is added to the got powder mixtures and lastly they are mixed with metallic powder such as iron powder, aluminum powder and the like and they are sealed within a bag. In this way, it is possible to restrict stirring up of powder when the powder substances are mixed to each other.