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'Karl Ernst Claus' (Dorpat, Russian Empire, [now Tartu, Estonia ] 22 January 1796 – 24 March 1864) was a Russian chemist of Baltic German origin, professor at Kazan State University, and discoverer of ruthenium.
'Karl Claus' was the Prof. of Biology in Vienna under whom Sigmund Freud started his studies on the yet unsolved Eel life history [1]
[2] [3]
Claus discovered the element Ruthenium, which is a trasition elemnt now listed in the periodic table