The viscosity of molten SiO 2 -CaO-MgO-TiO 2 slag was measured using a rotating cylinder method at the concentration of Graduate Student, Osaka University (2-1 Yamadaoka, Suita, Osaka 565-0871, Japan) **大阪大学学生 現:三宝伸銅工業㈱ (〒590-0906 堺市三宝町 8-374) Student, Osaka University, now with Sambo Copper Alloy Co.,