 Frank <unk> , celebrated for his development of the ion @-@ exchange technology that revolutionized the rare earth industry in the mid @-@ 1950s , once related the story of how he was lecturing on the rare <unk> in the 1930s when an elderly gentleman approached him with an offer of a gift of several pounds of europium oxide . This was an unheard @-@ of quantity at the time , and <unk> did not take the man seriously . However , a package duly arrived in the mail , containing several pounds of genuine europium oxide . The elderly gentleman had turned out to be Herbert <unk> McCoy who had developed a famous method of europium purification involving <unk> chemistry . 
