This review article deals with a new element ‘nipponium’ reported by Masataka Ogawa in 1908, and with its scientific and science historical background. Ogawa positioned nipponium between molybdenum and ruthenium in the periodic table. From a modern chemical viewpoint, however, nipponium is ascribable to the element with Z=75, namely rhenium, which was unknown in 1908. The reasons for this corrected assignment of nipponium are (1) its optical spectra, (2) its atomic weight when corrected, (3) its relative abundance in molybdenite, the same being true with rhenium. Recently some important evidence was found among the Ogawa’s personal collection preserved by his family. Deciphering the X-ray spectra revealed that the measured spectra of the nipponium sample that Ogawa brought from University College, London clearly showed the presence of the element 75 (rhenium). Thus was resolved the mysterious story of nipponium, which had continued for almost a century. It is concluded that nipponium was identical to rhenium.

(Communicated by Toshimitsu YAMAZAKI, M.J.A.)