by train, to St. Petersburg for the academy meetings and guidance of research. In the period 1911–1915, Walden published 14 articles in the "Proceedings of the Academy of Sciences" on electrochemistry of nonaqueous solutions. In particular, in 1914 he synthesized the first room-temperature ionic liquid, namely ethylammonium nitrate ()· with the melting point of 12 °C. After 1915, due to the difficulties caused by the World War I, political unrest in Russia and then October Revolution, Walden had reduced his research activity and focused on teaching and administrative work, taking numerous leading positions in science. Due to the political unrest in Latvia, Walden had immigrated to Germany together. He was appointed as professor of inorganic chemistry at the University of Rostock where he worked until retirement in 1934. In 1924 he was invited back to Riga, where he gave a series of lectures. He was offered leading positions in chemistry in Riga and in St. Petersburg, but declined. Despite his emigration, Walden retained his popularity in Russia, and in 1927 he was appointed as a foreign member of the Russian Academy of Sciences. Later, he also became a member of the Swedish (1928) and Finnish (1932) Academies. Personal life Walden's daughter, Antonina Anna Walden (1899–1983), was a music teacher who married Finnish translator and essayist Juho August Hollo. Their son was the Finnish poet and translator Anselm Hollo. Late years In his late years, Walden focused on history of chemistry and collected a unique library of over 10,000 volumes. The library and his house were destroyed during the British bombing of Rostock in 1942. Walden moved to Berlin and then to Frankfurt am Main where he became a visiting professor of the history of chemistry at the local university. He met the end of World War II in the French Occupation Zone, cut off the Rostock University, which was located in the Soviet Zone, and thus left without any source of income. He survived on a modest pension arranged by German chemists, giving occasional lectures in Tübingen and writing memoirs. In 1949, he published his most well known book on "History of Chemistry". He died in Gammertingen in 1957 at the age of 93. His memoirs were published only in 1974. References Further reading 1863 births 1957 deaths People from Cēsis Municipality People from Kreis Wolmar Baltic-German people Latvian scientists Chemists from the Russian Empire Latvian chemists 20th-century German chemists