Praseodymium was first identified in 1885 by Austrian scientist Carl Auer von Welsbach. It was discovered in didymium, a substance incorrectly said by Carl Mosander to be a new element in 1841. Welsbach reacted didymium to form nitrate salts, which he then fractionally crystallised from nitric acid to yield greenish-brown praseodymium and pink neodymium salts. The fractional crystallisation experiments were very time consuming, involving more than one hundred crystallisation operations, each lasting up to 48 hours. Praseodymium was named using the Greek words prasios didymos meaning ‘green twin,’ reflecting its green salts and the close association with neodymium. Pure metallic praseodymium was first produced in 1931.