Mitsui Minings & Melting Co., Ltd.

Tokyo Kokyu Rozai Co., Ltd.

Hiroshi Uchiyama

Junshiro Hayakawa

Kazunobu Kakimoto

Shigeru Yamagishi

Yoshio Fujiwara

A filter medium which permits an increased amount of filtration. The filter medium can be prepared by blending 100 parts by weight of aggregate particles, 5-18 parts by weight of an inorganic bonding material having a chemical composition of about 10-50% by weight of SiO.sub.2 and about 5-20% by weight of B.sub.2 O.sub.3 and containing at least 70% by weight of a non-vitreous substance such as talc or boric acid, and about 3-15 parts by weight of a combustible substance such as wheat flour, kneading the mixture with a caking material and water, molding the kneaded mixture, drying it, and then calcining the dried mixture at a temperature not lower than about 1100.degree.C. The size and number of the air-permeable pores in the filter medium can be controlled by adjusting the amounts of the bonding material and combustible substance.

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Hachiouji, Japan

Hiroshi Uchiyama